Synthesis and Reactivity of Nickel an Palladium Fluoride Complexes with PCP Pincer Ligands. A NMR-Based Assessment of Electron-Donating Properties of Fluoride and Other Monoanionic Ligands

1 Synthesis and Reactivity of Nickel an Palladium Fluoride Complexes with PCP Pincer Ligands. A NMR- Based Assessment of Electron-Donating Properties of Fluoride and Other Monoanionic Ligands. Luis Miguel Martínez-Prieto,† Cristóbal Melero,† Diego del Río,‡ Pilar Palma,† Juan Cámpora*,† and Eleuterio Álvarez.† †: Instituto de Investigaciones Químicas, CSIC - Universidad de Sevilla. c/ Américo Vespucio, 49, 41092, Sevilla, Spain. ‡: SRI International. 333 Ravenswood Avenue, Menlo Park, CA, 94025, USA. Abstract: A series of complexes of the type [(iPrPCP)M-L] (IM = Ni, Pd), containing the 2,6- bis(diisopropylphosphiomethyl)phenyl (PrPCP) pincer ligand and simple monoanionic ligands L (F, Cl, Br, H, Me, Ph, NO3 and OTf) have been synthesized and characterized. The fluoride derivatives [(iPrPCP)M-F] were prepared from the halides [(iPrPCP)M-X] (M = Ni, X = Br; M= Pd, X = Cl) by exchange reactions with AgF or, alternatively, by protonolysis of the methyl complexes [(iPrPCP)M-Me] with Et3N·3HF (TREAT-HF). A survey of the 13C NMR data for the new complexes and previously reported ones with L = OH, OMe and NH2 revealed significant trends that can be directly related to the electronic properties of the anionic ligands L coordinated to Ni(II) and Pd(II) centers. The chemical shift of the 13C resonance of the metal-bound (ipso) is very sensitive to the  -donating capacity of L, which increases in the order L = OTf > NO3 > F > OAc > OMe > Cl > OH ≈ Br > I > NH2 > Ph > Me > H. In addition, the reactivity of [(iPrPCP)M-F] complexes was investigated. These readily undergo fluoride exchange with LiOMe, affording the corresponding methoxides [(iPrPCP)M-OMe] and LiF. They also react with n-C12H13I to cleanly yield [(iPrPCP)M-I] and n-C12H13F. Comparison of the rates of the latter reactions and analogous ones involving bromide or chloride complexes showed that the fluorides are significantly more nucleophilic, particularly the palladium derivative. This property was applied in a palladium-catalyzed reaction for the synthesis of alkyl fluorides using AgF as the fluoride source. Introduction In the last two decades, late transition metal complexes containing covalently bound hard monoanionic ligands, L, such as amides, alkoxides or fluorides have been subject of sustained interest.1,2 This class of compounds is involved in many catalytic reactions, such as hydrogen transfer hydrogenations, aerobic oxidations or carbon-heteroatom couplings.3 The ability to catalyze these processes is connected to the unique reactivity of the M-L linkage, which combines high nucleophilicity and basicity and the ability to undergo many typical organometallic reactions, e. g. insertion reactions, -hydrogen elimination or C-heteroatom reductive couplings.4 Although the chemistry of late transition metal complexes containing terminal (non-bridging) M-N, M-O or M-F bonds has lately experienced a considerable development, their synthesis is still challenging. This is due to a number of reasons, such as the tendency of terminal ligands to bridge other metal centers, thermal instability or hydrolytic sensitivity. A useful strategy for minimizing such problems is using rigid PCP pincer chelates to stabilize the metal-containing moiety. We have previously prepared and studied several monomeric hydroxo, alkoxo or 2 amido complexes of Ni and Pd containing the strongly donor and relatively bulky 2,6-bis(iisopropylphosphinomethyl)phenyl ligand (iPrPCP) which imparts a balance between stability and reactivity to such complexes.5 Late transition metal fluoride complexes have been recently the object of much attention, particularly in the context of C-F bond activation6 and formation,1b,7 as well as in relation with their use as sources of the hypernucleophilic (and elusive) “naked fluoride” anion.8 In addition, fluoride complexes can be valuable starting materials in organometallic synthesis. For example, we have showed before that the fluoride ligand is cleanly displaced from the precursor complex [(dippe)Ni(Me)(F)] by lithium alkoxides and amides, providing a versatile route to monomeric methyl-alkoxo and methyl-amides that would have been difficult to prepare by a different method.9 Although number of monomeric nickel and palladium fluorides stabilized by monodentate or bidentate ligands have been reported in the literature, but only a couple of examples contain pincer-type ligands.10 These would be interesting candidates to participate in the generation of new C-F bonds, since many pincer complexes have found interesting applications as catalysts for coupling reactions.11 Herein we report the synthesis of new Ni(II) and Pd(II) fluoride complexes, the pincer derivatives [(iPrPCP)Ni-F] and [(iPrPCP)Pd-F]. We also investigate the use of Ni and Pd pincer as starting materials for the synthesis of organometallic alkoxides and their ability to catalyze fluoride exchange between AgF and alkyl halides. One of the most striking questions regarding the bonding and reactivity of late transition metal complexes with strongly -electron donor ligands such as OR, NR2 or F is to which extent these metal-ligand linkages are destabilized by non-bonding d-p interactions between the filled d orbitals in the metal and the lone electron pairs in the heteroatom.12 Answering this question would improve the understanding of the reactivity of compounds containing strong -donor ligands such as fluoride. Spectroscopic data have been of critical importance to support the concept of repulsive d-p interactions The availability of spectroscopic data for many pincer complexes of the type [(iPrPCP)M-L] containing widely different anionic ligands L provides an unique opportunity for investigating their correlation to their / donor capacity of L. With the aim of extending this comparison, we have prepared some new derivatives with L = triflate, nitrate, acetate, methyl, phenyl and hydride. Results and Discussion. Synthesis of new pincer derivatives of Ni and Pd. We have described previously the hydroxo, alkoxo and amido derivatives of Ni and Pd stabilized by the iPrPCP pincer ligand.5 In this section we detail the synthesis of new complexes [(iPrPCP)M-L] containing anionic ligands L with widely different electron-donor strengths, including different halides, triflates, nitrates, alkyls and hydrides. We originally synthesized the nickel precursor [(iPrPCP)Ni-Br] by oxidative addition of 1-bromo-2,6- bis(diisopropylphosphino)methylbenzene (iPrPCBrP) to Ni(cod)2. A similar reaction was used to prepare the Pd analogue [(iPr(PCP)Pd-Br], using [Pd(5-Cp)(3-C3H5)], generated in situ from [Pd(3-C3H5)(-Cl)]2 and NaCp, as the Pd(0) source (see Experimental part). For the synthesis of [(iPrPCP)Pd-Cl], we relied on literature procedures for involving direct palladation of the diphosphine 2,6-bis(diisopropylphosphino)methylbenzene (iPrPCHP) by Pd(II) sources.15 Several pincer derivatives of nickel have also been prepared by direct metallation,16 including the chloro derivative [(iPrPCP)Ni-Cl].17 This method can be regarded more practical than those based on oxidative addition methods because it does not require the previous synthesis of organometallic precursors. Hence, we developed a new synthesis of [(iPr(PCP)Ni-Br] involving direct reaction of (iPrPCP)H and NiBr2(dme), using triethylamine to 3 neutralize the resulting HBr. This method leads to the desired nickel complex in nearly the same yield as achieved by oxidative addition (ca. 80 %). Scheme 1 As shown in Scheme 1, complexes [(iPr(PCP)Ni-Br] and [(iPrPCP)Pd-Cl] are starting materials for the synthesis of other compounds. We previously reported that the palladium nitrate complex is readily obtained by reacting the corresponding chloro precursor with silver nitrate.5a Similarly, the nickel analogue is also prepared from the corresponding bromide precursor and AgNO3, but in this case special care should be taken to adjust 1:1 Ni/Ag stoichiometry. This is because an excess of the silver reagent causes the oxidation of the product to an stable Ni(III) complex, [(iPrPCP)Ni(NO3)2], which will be described elsewhere.18 The acetate complexes [(iPrPCP)M-OAc] are obtained in analogous fashion from the halide precursors and an stoichiometric amount of silver acetate. Transmetallation reactions of halide precursors with methyl or phenyllithium also proceed easily, affording the corresponding derivatives [(iPrPCP)M-R] (R = Me or Ph) in good yields. The Pd phenyl derivative was mentioned in the literature before.15a We characterized the nickel methyl and phenyl complexes by X-ray diffraction. Figures 1 and 2 represent one of the two crystallographically independent molecules found in the unit cells of these complexes. The methyl complex has a typical square-planar configuration without remarkable features. Figure 2 shows that the rings of the phenyl and the pincer ligands are approximately perpendicular. Although electron - backdonation from the Ni center to each of the aromatic systems is expected to be different due to their different orientations with regard to the metal coordination plane, the Ni-C bond distances are very similar (Ni1-C1: 1.940(2); Ni1-C21, 1.925(2) Å). The methyl and phenyl complexes are thermally stable and they resist exposure to air for some time in the solid state. However, during one of the attempts to crystallize the nickel methyl complex we isolated colorless crystals which we subsequently identified as the diphosphine oxide 1-Me-2,6-(iPr2P(O)CH2)2C6H3·H2O (Figure 3). Interestingly, a methyl group saturates the ipso position originally bound to nickel, suggesting that the reaction with oxygen induces the reductive coupling of the methyl and the pincer ligand. Although the molecule has no crystallographically imposed symmetry, it adopts a symmetric arrangement with both phosphine oxide 4 functionalities associated to a single water molecule through strong hydrogen bridges (oxygen-oxygen distances = 2.766(2) and 2.841(2) Å). Figure 1. Crystal structure of [(iPrPCP)NiMe] (one of two independent molecules). Selected bond distances (Å) : Ni1-C1, 1.954(2); Ni1-C21, 1.991(2); Ni1-P1, 2.1418(15); Ni1-P2, 2.1445(15). Angle between mean planes: ring C1-C6 NiP2C2, 9.1º. Figure 2. Crystal structure of [(iPrPCP)NiPh] (one of two independent molecules) Selected bond distances (Å): Ni1-C1, 1.940(2); Ni1-C21, 1.925(2); Ni1-P1,2.1470(6); N11-P2, 2.1484(6). Angles between mean planes (deg): Ph NiP2C2, 79.3; Ring C1-C6 NiP2C2, 11.1; Ph ; Ring C1-C6, 88.1. . Figure 3. Crystal structure of 1-Me-2,6-(iPr2P(O)CH2)2C6H3·H2O. Selected distances (Å) and angles (deg) : C1-C21, 1.509(3); P1-O1, 1.4978(14); P2-O2, 1.4867(13); O1-H3BO, 1.884(17); O3-H3BO, 0.881(15); O1-O3, 2.763(3); O2-H3AO, 1.93(2); O3-H3AO, 0.921(15); O2-O3, 2.842(3); O1-H3BO-O3, 175(2); O2-H3AO-O3, 174(2); H3BO-O3-H3AO, 104(2). Both the nickel bromide and the palladium chloride react smoothly with MeI at 60 ºC affording the iodides [iPr(PCP)M-I] 15a,16d in high yield. This appears to be a very general reaction for pincer complexes,19 and other iPrPCP derivatives of Ni or Pd we tried react in a similar fashion with MeI. This reaction provides a simple method for recycling mixtures of these compounds, since the iodide complexes can easily be recovered by column chromatography on silica. The synthesis of the palladium triflate [(iPrPCP)PdOTf] from the chloride complex and silver triflate has been described previously in the literature.15b We found that the readily available Ni and Pd methyl derivatives react with triflic acid affording the corresponding triflates in good yields (Eq 1). This is a versatile route to complexes containing weakly coordinating anions that avoids the use of expensive and potentially reactive silver salts. 5 M P P Me iPriPr iPriPr M = Ni, Pd; M P P OTf iPriPr iPriPr HOTf (1) Nickel hydride complexes containing RPCP ligands (R = iPr, tBu, cyclohexyl) have been synthesized by the reaction of the corresponding halide precursors and different hydride sources.17 In our hands, the reaction of [(iPrPCP)Ni-Br] with LiBHEt3 (superhydride) was clean and essentially complete, but the purification of the hydride from the boron byproducts was problematic, leading to erratic isolated yields. Alternatively, this compound can be prepared reacting [(iPrPCP)Ni-OMe] with triethoxysilane. As shown in Scheme 2, the Ni methoxide is prepared by the previously reported method,5b from the amide [(iPrPCP)Ni-NH2] and methanol. It is not necessary to isolate the amido and methoxide intermediates because all three steps of this synthesis can be performed in sequential manner. Since most reagents and byproducts (methanol, HSi(OEt)3, ammonia and Si(OMe)(OEt)3) are volatile, this method minimizes side reactions and simplifies product isolation. The palladium hydride [(iPrPCP)Pd-H] has also been prepared in the same way, in spite of the thermal instability of the corresponding amido complex [(iPrPCP)Pd- NH2].5c The identity of the latter intermediate has been confirmed spectroscopically and full NMR data (1H, 13C and 31P) are supplied in the Experimental Section. The crystal structure of the nickel hydride is shown in Figure 4. The crystals of this compound contain three crystallographically independent molecules and are isomorphous with those of the nickel fluoride derivative. Both complexes share an unusual crystal packing model, which is described in detail below for the fluoride complex. Although the quality of the X-ray data is not excellent, the hydride ligand was located at ca. 1.60 Å of the Ni center. The lengths of the N-C bonds in the three independent molecules are slightly different (1.943, 1.911 and 1.893 Å). The average length of the Ni-C bond found in the unit cell is 1.916 Å, somewhat shorter than in the methyl and phenyl complexes (1.94 – 1.95 Å) and very similar in the hydroxo and amido derivatives (1.917 and 1.929 Å), in spite of the widely different strengths of the trans influence of such ligands. This suggests that these M- C bonds can be significantly biased by the rigidity of the pincer scaffold and are not good indicators of the trans influence exerted by the anionic ligand. M P P XiPriPr iPriPr M = Ni, X = Br M = Pd, X = Cl M P P NH2iPriPr iPriPr NaNH2MeOH M P P OMeiPriPr iPriPr HSi(OEt)3 - NaX - NH3M P P HiPriPr iPriPr M = Ni, Pd -Si(OMe)(OEt)3 Scheme 2. 6 Figure 4. ORTEP view of [(iPrPCP)Ni-H] (one of three independent molecules in the crystal). Selected bond distances (Å): Ni-H, 1.597(15); Ni1- C1, 1.946(13); Ni1-P1, 2.112(3); Ni1-P2, 2.121(3). Angle between mean planes ring C1-C6 and NiP2C2, 14.1º. Synthesis of Ni and Pd fluoride complexes. In order to synthesize these compounds, we explored two general methods commonly used for the preparation of organometallic transition metal fluoride complexes: halide exchange with AgF and protonation of suitable precursors with Et3N·3HF (TREAT-HF) (Scheme 3).1a We investigated the reaction of the halide precursors [(iPrPCP)Ni-Br] and [(iPrPCP)Pd-Cl] with an excess of AgF in toluene, assisted with ultrasounds. Under these conditions, the Ni precursor is transformed into the corresponding fluoride complex [(iPrPCP)Ni-F] in good yield, but the Pd chloro complex only reacts very sluggishly. Grushin observed that palladium iodide complexes are better precursors for this purpose, probably because such exchange reactions are driven by the insolubility of AgI.20 Hence, [(iPrPCP)Pd-F] complex was satisfactorily obtained from the corresponding palladium iodide [(iPrPCP)Pd-I] and AgF. We found that an excess of ≥ 2equiv of AgI was necessary to complete the formation of the nickel and palladium fluorides (Scheme 3). Although this could be attributed to the transformation of AgF into a less reactive mixed halide compound, analysis of the salt residue by powder X ray diffraction gave no indication of inorganic phases different from AgF and AgBr or AgI. Monitoring the halide exchange reactions by 31P{1H} NMR shows that after 12h of sonication, the initial resonances of the nickel bromide or palladium iodide precursors fully disappear and are replaced by broader signals of the products. Analytically pure samples of the yellow (M = Ni) or colorless (M = Pd) fluoride complexes [(iPrPCP)M-F] were obtained after recrystallization from hexane. The 31P{1H} signals of the pure materials appear splitted in doublets by coupling with 19F. These are significantly narrower and appear a few ppm below those observed for the crude reaction mixtures. The differences of line shape and chemical shifts of the 31P spectra of the reaction mixtures could be due to the presence of small amounts of water, which is known to promote rapid intermolecular fluoride exchange.21 However, since efforts were made to maintain rigorously anhydrous conditions, it can not be ruled out that the presence of small amounts of AgF could induce similar effects to those of water in the NMR spectra of the crude solutions. The reaction of hydroxo complexes with TREAT-HF has proven to be an useful and versatile route for the synthesis of fluoride derivatives.20 In addition, we showed that the methylnickel complex [NiMe2(dippe)] also reacts readily with TREAT-HF, affording the methyl-fluoride complex [NiMeF(dippe)].9 Since methyl derivatives [(iPrPCP)M-Me] are robust and readily available, we decided to investigate their reaction with TREAT-HF. This reaction proceeds rapidly for M = Ni, affording [(iPrPCP)Ni-F] in high yield. As with the AgF method, the 31P{1H} spectrum of the crude product is somewhat broad, but in this case the line broadening persists after recrystallization. This suggests the presence of small amounts of HF, probably retained in the form of fluxional bifluoride species that cannot be easily removed by recrystallization.21 However, we found that THF solutions of the 7 crude material are effectively cleaned by stirring with CaH2 for 24 h, affording [iPr(PCP)Ni-F] with well resolved spectra. Presumably, CaH2 reacts with the HF but not with the nickel fluoride complex, forming highly insoluble CaF2. At room temperature, the reaction of [(iPrPCP)Pd-Me] with an equivalent amount of TREAT-HF is slow and incomplete. However, using an excess of the acidic reagent to force the reaction leads to ill-defined products that could not be purified by recrystallization. Treating this mixture with CaH2 was unsuccessful because it leads to the formation of [(iPrPCP)Pd-H], identified by its characteristic low-field 31P signal at 71.7 ppm. Monitoring the reaction of TREAT-HF with [(iPrPCP)Pd-Me] by 31P{1H} shows that full neutralization requires gentle warming at 50 ºC for 1 – 2 h. Clean samples of [(iPrPCP)Pd-F] are obtained when a somewhat less than the stoichiometric amount of TREAT-HF is reacted with [(iPrPCP)Pd-Me] at 50 ºC, since all the HF contained in the acidic reagent is consumed under these conditions. Therefore, careful adjustment of the TREAT-HF and the reaction temperature is essential for the successful preparation of [(iPrPCP)Pd-F]. This can be routinely done by a two-stage addition method, as described in the Experimental Section. M P P XiPriPr iPriPr AgF (5 equiv) Ultrasonds - AgX M P P FiPriPr iPriPr [(iPrPCP)M-F] M = Ni, Pd [(iPrPCP)M-X]: M = Ni, X = Br M = Pd, X = I M P P Me iPriPr iPriPr TREAT-HF [(iPrPCP)M-Me] M = Ni, Pd M = Ni, R. T. M = Pd, 50 ºC Scheme 3 The room temperature 31P{1H} spectra of pure fluoride complexes [(iPrPCP)M-F] in C6D6 show signals at 54.3 ppm (M = Ni) or 57.5 ppm (M = Pd), splitted in doublets by coupling to 19F. The coupling constant 2JPF is larger for M = Ni (36.7 Hz) than for M = Pd (5.9 Hz). The trans 19F – 13C coupling is transmitted more efficiently in the case of the palladium complex, which gives a broad doublet at 155.2 ppm in its 13C{1H} spectrum for C ipso with 2JCF = 48.8 Hz, while the analogous signal of the Ni complex appears unresolved at 152.1 ppm. This signal splits in a doublet of triplets with 2JCF = 27.3 Hz and 2JCP = 16.0 Hz when the carbon spectrum is recorded at -75 ºC. The 19F signals, which appear at -295.0 and -245.3 ppm for the Ni and the Pd complexes respectively, are too broad to allow resolving the 19F-31P splitting. The nickel fluoride complex has been characterized by X-ray diffraction. The unit cell of the crystal contains three crystallographically independent molecules. These show no significant differences in their general configuration or intramolecular bond distances or angles. One of them is shown in Figure 5. The Ni center is found in a square-planar coordination environment, with nearly zero tetrahedral distortion. Intramolecular bond distances and angles are unexceptional. The Ni-F bond lengths are 1.844(2), 1.861(2) and 1.846(2) Å (1.850(2) Å in average), which are comparable to other monomeric nickel fluoride complexes. As mentioned previously, the nickel fluoride and hydride complexes form isomorphous crystals characterized by very similar cell parameters. The 8 crystal packing of these compounds is worth some comment. This is shown in Figure 6 for [(iPrPCP)Ni-F]. The molecules pile themselves, forming columnar structures separated by narrow channels of about 1.6 Å wide. Each C1-Ni-L vector (L = H or F) is twisted ca. 120º with respect to the next one, in such a way that the columns resemble screw threads making one turn for each set of three molecules. The Ni-L bonds are oriented pointing outwards from the columns. This arrangement allows short inter-columnar contacts involving the fluoride or hydride and the C-H bonds of neighboring molecules. Although in the case of the fluoride complex it would be tempting to attribute these contacts to non-classical hydrogen bridges, this appears less likely for the hydride since the Ni-H bond is much less polar than the Ni-F. No signs of other intermolecular interactions, e. g., -stacking, seem to stabilize the columnar arrangement. Thus, it seems likely that the peculiar crystal packing of these compounds stems from the shape of their molecules, rather than from the existence of strong intermolecular forces. Figure 5. Crystal structure of [(iPrPCP)Ni-F] (one of three independent molecules). Selected bond distances (Å): Ni1-F1, 1.844(2) ;Ni1-C1, 1.901(4); Ni1-P1; 2.1606(13); Ni1-P2, 2.1608(12). Figure 6. Crystal packing of [(iPrPCP)Ni-F]. A) view along axis C, showing the columnar motif from the top . B) Detail of one of the columns formed by three crystallographically independent molecules. Assessment of the  and  bonding strength of anionic ligands L- on the basis of the 13C NMR spectra of [(iPrPCP)M-L] complexes. The special reactivity of late transition metal complexes containing strongly -basic ligands such as fluoride, alkoxo or amido complexes has been explained in the light of different theories.1,22 One of the most appealing ideas is the existence of nonbonding d-p interactions between the filled d orbitals in the metal and the ligand lone pairs.12 These would destabilize the metal-ligand bond, increasing the reactivity of the complexes. Unfortunately, quantification of such effects has proven to be a difficult task. Precise measurements of the relative metal-alkoxide and metal-amido bond strengths in Ni(II) , Pt(II) and Ru(II) complexes have been interpreted in terms of electrostatic and covalent contributions to essentially  bonds, leading to the conclusion that d-p interactions are weak or non-existent.23 However, analysis of spectroscopic data for late transition metal 9 complexes containing -donor ligands has led to different conclusions. A study by Caulton and Eisenstein on Ru(II) carbonyl complexes [RuHL(CO)(PR3)2] showed that the frequency of the (CO) band depends on the relative - donor strength of the anionic ligands L- present in the molecule, decreasing in the order I < Br < Cl < F < OEt.14 Since the metal d orbitals of  symmetry are all occupied, the observed decrease (CO) was assumed to be induced by a push-pull effect: the metal d orbitals become destabilized by the nonbonding M-L p− d interactions, which exalt the -backbonding capacity of the Ru(II) center to the carbonyl. Theoretical calculations supported this interpretation and reproduced the experimental trend of the (CO) frequency. This suggested that (CO) provides an indication of the intensity of the filled-filled  interactions. Accordingly, fluoride and alkoxide are among the stronger  donor ligands towards the Ru center. Grushin has applied similar ideas to the analysis of the bonding in a series of palladium complexes of the type trans-Pd(Ar)(X)(PPh3)2 (Ar = Ph, 4-C6H4NO2; X = F, Cl, Br, I). 24 In these compounds, the 13C signal of the metal-bound carbon atom (C ipso) experiences a significant shift of ca. 10 ppm, growing increasingly shielded on going from iodide to fluoride. The trend is counterintuitive, because the trans influence25 of the halide ligands, and therefore their electron-donor capacity, increases in the opposite order (as confirmed by the structural data gathered for this particular set of complexes). As a rationale, it was proposed that a  push-pull effect analogous to that suggested by Caulton and Eisenstein actually increases the electron density at the ipso carbon as the halogen varies from I to F, shifting 13C resonance to lower frequency. This is schematically shown in Figure 7, A. Figure 7. Mechanisms explaining the influence of the metal fragment on 13C NMR shifts of the aryl ring. A) ligand promoted -electron backdonation (push-pull effect). B) paramagnetic contribution to the chemical shift, due the to the mixing of the ground and excited states. The availability of a series of iPrPCP pincer complexes of Ni and Pd provides an opportunity to extend the comparison to various monoanionic ligands besides halides. X-ray structural data are of little use for this purpose, because the influence of the anionic ligands on the rigid pincer fragment is small. However, the structural invariance of the [(iPrPCP)M] moiety is a positive factor for analyzing spectroscopic properties, since any variations can be directly attributed to electronic effects. Table 1 collects selected 13C NMR data for [(iPrPCP)M-L] derivatives, analogous to the signals considered by Grushin in the analysis of arylpalladium complexes. Most of the 13C data come from spectra recorded in C6D6, but in some cases the spectra were recorded in CD2Cl2 for solubility reasons. Although solvent effects on chemical shifts are fairly small, these have been minimized with the use of coordination shifts,  C, i.e. the differences between the chemical shifts of each signal in the complex and those in the free ligand (in the same solvent) Table 1. Coordination shifts () for selected 13C signals of [(iPrPCP)M-L] complexes relative to free PrPCHP ligand.a 16 ca. 35 ppm. The magnitude of the coordination shift is nearly identical for the nickel and palladium complexes, and is related to the qualitative -donor capacity of the anionic ligands. This is supported by a good correlation between the coordination shifts of C ipso and the electronegativity of the monoatomic ligands (hydride and halides). This relationship can be used to gauge the -donor capacity of the anionic ligands towards the Ni and Pd centers, which increases in the order OTf < NO3 < F < OAc < OMe < Cl < OH ≈ Br < I < NH2 < Ph < Me < H. Analysis of the chemical shifts of the para and meta resonances revealed a completely different pattern that could be related to the -donor capacity of the ligands. The differences between the chemical shifts of the para and meta carbons are more negative in complexes containing strong −donor ligands (OH, F, NH2 or OMe) than those without this capacity (H, Me). This is consistent with an enhancement of -backdonation from the metal to the aryl ring caused by nonbonding p-d interactions. These results are largely in agreement with long-standing ideas on the electronic properties of simple anionic ligands (e. g., fluoride is a weak -donor ligand, but a stronger  donor than the rest of the halides), but the new data offer the opportunity to directly compare very different ligands that are seldom found within the same system. Two methods have been applied for the synthesis of the fluoride derivatives [(iPrPCP)M-F]: halide exchange with AgF and protonation of the methyl derivatives [(iPrPCP)M-Me] with TREAT-HF. Fluoride complexes [(iPrPCP)M- F] exhibit an interesting reactivity pattern. The fluoride ligand is readily displaced from nickel or palladium by lithium alkoxides, cleanly leading to the corresponding pincer alkoxo derivatives. The fluoride complexes also react with dodecyl iodide affording iodide complexes and alkyl fluoride. Although analogous halide exchange reactions also take place between dodecyl iodide and chloride or bromide pincer complexes, these react much more slowly than the fluorides, indicating that the latter are more nucleophilic. Furthermore, the reaction of the fluorides with dodecyl iodide is at least 20 times faster for the palladium than for the nickel derivative. It is difficult to justify this difference on the basis of the degree of polarization of the M-F bonds since this is probably similar in the Ni and Pd complexes. However, the higher nucleophilicity of the palladium fluoride can be qualitatively explained by the larger degree of destabilization of the fluoride lone pairs by the filled metal d orbitals, which are more spatially extended in second than in first row transition elements. The nucleophilic reactivity of the fluoride pincer complexes was exploited in a catalytic halide exchange reaction between AgF and RI to afford alkyl fluorides. Both nickel and palladium catalysts improve the selectivity of the reaction of AgF with dodecyl iodide, probably by avoiding the formation of reactive carbocationic intermediates. However, only the palladium complexes lead to a significant acceleration of the reaction, presumably due to the much higher nucleophilic reactivity of the fluoride complex. Experimental Section. All procedures and chemical manipulations were carried out under Ar or N2 using Schlenk or glove box techniques. Solvents were rigorously dried and degassed before use. Commercially available reagents were used as received. The pincer ligand precursor, 2,6-bis(diisopropylphosphino)benzene35 (iPrPCHP) and the complex [(iPrPCP)Pd-Cl]15b were prepared according to literature methods. The brominated precursor 1-bromo-2,6- bis(diisopropylphosphino)benzene36 (iPrPCBrP) was prepared analogously to iPrPCHP from 1-bromo-,’- dibromoxylene. NMR spectra were recorded on Bruker DRX 300, 400 and 500 MHz spectrometers. Assignment of signals was assisted by combined monodimiensional (gated 13C) and bidimensional techniques (HSQC). Chemical 17 shifts (δ) are in ppm. Solvent 1H and 13C{1H} resonances were used as the internal standard but the chemical shifts are reported with respect to TMS, and 31P spectra are referenced to external PPh3 in C6D6 (δ −6.0 ppm). Multiplicity abbreviation is reported as: br, broad; s, singlet, d, doublet; t, triplet; m, mutiplet; v, virtual; dvt, doublet of virtual triplets. IR spectra were recorded in nujol mull on Bruker Vector 22 or Tensor 27 spectrophotometers. GC and GCMS analyses were carried out in Agilent 6890 and Thermoquest Trace GC chromatographs equipped with a FID detector and an AutomassMulti mass spectrometer, respectively, using capillary polymethylsiloxane columns. Microanalyses were performed by the Microanalytical Service of the Instituto de Investigaciones Químicas. Synthesis of complexes. [(iPrPCP)Ni-Br]: A solution of PrPCHP in THF (0.5 M, 10 mL, 5 mmol) was added to a suspension of NiBr2(dme) (dme= dimethoxyethane) (1.54 g, 5 mmol) in THF (60 mL) at −78 ºC , the resulting mixture was stirred and allowed to reach room temperature. Et3N (5.5 mL, 50 mmol) was added and the reaction mixture heated at 125 ºC for 3 h. The solvent was evaporated under reduced pressure and the residue extracted with Et2O (3 × 40 mL). The combined extracts were concentrated and cooled to -20 ºC, affording the [(iPrPCP)Ni-Br] as a yellow solid in 90% yield. 1H NMR (CD2Cl2, 25 ºC, 300 MHz) δ 1.17 (dvt, 12H, 3JHH ≈ J*HP ≈ 6.9 Hz, CH3), 1.44 (dvt, 12H, 3JHH ≈ J*HP ≈ 7.7 Hz, CH3), 2.36 (m, 4H, CH), 3.09 (vt, 4H, J*HP = 4.0 Hz, CH2), 6.90 (m, 3H, 2×CarHm, CarHp). 13C{1H} NMR (CD2Cl2, 25 ºC, 300MHz) δ 18.3 (s, CH3), 19.0 (s, CH3), 24.2 (vt, J*CP = 11.2 Hz CH), 33.0 (vt, J*CP = 12.9 Hz, CH2), 122.4 (vt, J*CP = 8.9 Hz, CarHm), 125.5 (s, CarHp), 152.8 (vt, J*CP = 13.2 Hz, Car-o), 159.5 (t, 2JCP = 15.9 Hz, Car-i). 31P{1H} NMR (CD2Cl2, 25 ºC, 300MHz) δ 60.5. Anal. Calcd. for C22H35BrNiP2: C, 50.46; H, 7.41; found: C, 50.35; H, 7.32. [(iPrPCP)Pd-Br]: 12 mL of a 0.085 M solution of NaCp in THF (1.02 mmol) were added to a solution of the palladium chloro(allyl) dimer [Pd(3-C3H5)(-Cl)]2 (0.183 g, 0.5 mmol) in 40 ml of THF stirred at -80 ºC. The resulting red mixture was stirred for 1 h at room temperature and then cooled again to -80 ºC. A solution of PrPCBrP (0.5 M in THF, 2 mL, 1mmol) was added. The mixture was allowed to warm at room temperature and stirred for 12 h. The solvent was evaporated under vacuum, and the resulting solid extracted with diethyl ether (3 x 20 mL). The solution was taken to dryness again and the residue purified by chromatography on a silica gel column, using diethyl ether/hexane 5:1 as eluent. The product was isolated as a pale yellow solid in 40 % yield. 1H NMR (CD2Cl2, 25 ºC, 300 MHz) δ 1.14 (dvt, 12H, 3JHH ≈ J*HP ≈ 7.0 Hz, CH3), 1.37 (dvt, 12H, 3JHH ≈ J*HP ≈ 7.0 Hz, CH3), 2.34 (m, 4H, CH), 3.19 (vt, 4H, J*HP = 4.0 Hz, CH2), 6.91 (t, 1H, 3JHH = 7.4 Hz, CarHp), 7.01 (d, 2H, 3JHH = 7.6 Hz, 2×CarHm). 13C{1H} NMR (CD2Cl2, 25 ºC, 300MHz) δ 18.1 (s, CH3), 18.9 (s, CH3), 24.4 (vt, J*CP = 11.2 Hz CH), 33.4 (vt, J*CP = 11.5 Hz, CH2), 122.9 (vt, J*CP = 10.8 Hz, CarHm), 125.2 (s, CarHp), 151.0 (vt, J*CP = 10.7 Hz, Car-o), 159.3 (s, Car-i). 31P{1H} NMR (CD2Cl2, 25 ºC, 300MHz) δ 61.4. Anal. Calcd. for C22H35BrNiP2: C, 50.12; H, 7.36; found: C, 50.42; H, 7.43. [(iPrPCP)Ni-I]: To a solution of (iPrPCP)Ni-Br (0.095 g, 0.2 mmol) in THF (5 mL), MeI (0.152 mL, 1 mmol) was added and the resulting mixture was heated at 60 ºC for 72 h. The solvent was removed under reduce pressure, and the residue extracted with hexane. The product was obtained as a yellow solid after evaporating the solvent under reduced pressure. Yield 70%. 1H NMR (CD2Cl2, 25 ºC, 300 MHz): δ 1.15 (dvt, 3JHH ≈ J*HP ≈ 6.9 Hz, 12H, 18 CH3), 1.43 (dvt, 3JHH ≈ J*HP ≈ 7.7 Hz, 12H, CH3), 2.48 (m, 4H, CH), 3.14 (vt, J*HP = 4.1 Hz, 4H, CH2), 6.95 (m, 3H, 2×CarHm, CarHp). 13C{1H} NMR (CD2Cl2, 25 ºC, 300 MHz): δ 18.4 (s, CH3), 19.3 (s, CH3), 25.2 (vt, J*CP = 11.8 Hz, CH), 34.1 (vt, J*CP = 13.0 Hz, CH2), 122.4 (vt, J*CP = 8.9 Hz, CarHm), 125.6 (s, CarHp), 152.5 (vt, J*CP = 12.9 Hz, Car−o), 163.8 (t, 2JCP = 15.9 Hz, Car-i). 31P{1H} NMR (CD2Cl2, 25 ºC, 300 MHz): δ 63.1. Anal calcd for C20H35INiP2: C, 45.93; H, 6.74; found C, 45.59, H, 5.81. [(iPrPCP)Pd-I]: MeI (0.152 mL, 1 mmol) was added to a solution of [(iPrPCP)Pd-Cl] (0.095 g, 0.2 mmol) in THF (5 mL), and the resulting mixture was heated at 60 ºC for 24 h. The solvent was removed under reduced pressure, the residue extracted with hexane, and the solution was taken to dryness affording [(iPrPCP)Pd-I] as a colourless solid. Yield 80%. 1H NMR (CD2Cl2, 25 ºC, 300 MHz): δ 1.10 (dvt, 3JHH ≈ J*HP ≈ 7.2 Hz, 12H, CH3), 1.37 (dvt, 3JHH ≈ J*HP ≈ 8.0 Hz, 12H, CH3), 2.44 (m, 4H, CH), 3.26 (vt, J*HP = 4.3 Hz, 4H, CH2), 6.97 (t, 3JHH = 7.4 Hz, 1H, CarHp), 7.07 (d, 3JHH = 7.6 Hz, 2H, CarHm). 13C{1H} NMR (CD2Cl2, 25 ºC, 75 MHz): δ 18.1 (s, CH3), 19.3 (s, CH3), 25.3 (vt, J*CP = 11.9 Hz, CH), 34.9 (vt, J*CP = 11.6 Hz, CH2), 122.7 (vt, J*CP = 10.7 Hz, CarHm), 125.4 (s, CarHp), 150.8 (vt, J*CP = 10.6 Hz, Car−o), 165.2 (s, Car−i). 31P{1H} NMR (CD2Cl2, 25 ºC, 121 MHz): δ 62.4. Anal calcd for C20H35IP2Pd: C, 42.09; H, 6.18; found C, 42.27, H, 5.81. [(iPrPCP)Ni-ONO2]: A solution of [(iPrPCP)Ni-Br] (2.05 g, 4.3 mmol) in THF (50 mL) was added to a flask charged with AgNO3 (0.750 g, 4.4 mmol). The reaction mixture was stirred at room temperature for 36 h. The solvent was evaporated under vacuumand the residue extracted with Et2O (3×50 mL). The complex [(iPrPCP)Ni-ONO2] was obtained as a yellow crystals after evaporating the solvent under reduced pressure and crystallizing from hexane to −30 ºC. 1H NMR (CD2Cl2, 25 ºC, 300MHz) δ 0.91 (dvt, 12H, 3JHH ≈ J*HP ≈ 7.0 Hz, CH3), 1.25 (dvt, 12H, 3JHH ≈ J*HP ≈ 7.7 Hz, CH3), 1.79 (m, 4H, CH), 2.58 (vt, 4H, J*HP = 4.1 Hz, CH2), 6.73 (d, 2H, 3JHH =7.4 Hz, CarHm), 6.95 (t, 1H, 3JHH = 7.4 Hz, CarHp). 13C{1H} NMR (CD2Cl2, 25 ºC, 300MHz) δ 17.6 (s, CH3), 18.2 (s, CH3), 23.5 (vt, J*CP = 10.1 Hz CH), 30.4 (vt, J*CP = 13.6 Hz, CH2), 122.4 (vt, J*CP = 8.6 Hz, CarHm), 125.6 (s, CarHp), 149.3 (t, 2JCP = 16.6 Hz, Car-i), 152.6 (vt, J*CP = 12.5 Hz, Car-o) .31P{1H} NMR (CD2Cl2, 25 ºC, 300MHz) δ 58.6 ppm. Anal. Calcd. for C20H35NO3P2Ni: C, 52.43; H, 7.70. N, 3.06; found: C, 52.51; H, 7.89. N, 2.97. IR (Nujol mull) ν(NO2) 1456 cm-1, ν(NO2) 1282 cm-1, ν(NO) 1026 cm-1. [(iPrPCP)Ni-OAc] and [(iPrPCP)Pd-OAc]: A solution of [(iPrPCP)Ni-Br] (0.238 g, 0.5 mmol) or [(iPrPCP)Pd-Cl] (0.240 g, 0.5 mmol) in THF (25 mL) was transferred to a flask charged with AgOAc (0.083 g, 0.5 mmol) and the resulting mixture was stirred at room temperature for 12 h. The solvent was evaporated under reduce pressure and the residue extracted with Et2O (3 × 25 mL). The complex [(iPrPCP)Ni-OAc] was obtained as a yellow crystalline solid after addition of some hexane and cooling to −30 ºC. Yield 75%. 1H NMR (CD2Cl2, 25 ºC, 300 MHz) δ 1.24 (dvt, 12H, 3JHH ≈ J*HP ≈ 6.9 Hz, CH3), 1.36 (dvt, 12H, 3JHH ≈ J*HP ≈ 8.6 Hz, CH3), 1.73 (s, 3H, OCOCH3), 2.18 (m, 4H, CH), 3.02 (vt, 4H, J*HP = 4.1 Hz, CH2), 6.79 (m, 3H, 2×CarHm, CarHp). 13C{1H} NMR (CD2Cl2, 25 ºC, 75 MHz) δ 18.1 (s, CH3), 18.7 (s, CH3), 24.1 (vt, J*CP = 10.0Hz, CH), 24.3 (s, COOCH3), 31.4 (vt, J*CP = 13.4 Hz, CH2), 122.2 (vt, J*CP = 8.6 Hz, CarHm), 125.1 (s, CarHp), 153.1 (vt, J*CP = 13.1 Hz, Car-o), 153.6 (t, 2JCP = 17.3 Hz, Car-i), 175.9 (s, OCOCH3). 31P{1H} NMR (CD2Cl2, 25 ºC, 121 MHz) δ 56.6 ppm. . Anal. Calcd. for C22H38NiO2P2: C, 58.05; H, 8.41;found: C, 58.09; H, 8.37. The complex [(iPrPCP)Pd-OAc] was obtained as a colourless microcrystalline solid after evaporating the solvent under reduce pressure. Yield 75%.1H NMR (CD2Cl2, 25 ºC, 300 MHz): δ 1.19 (dvt, 19 3JHH ≈ J*HP ≈ 7.3 Hz, 12H, CH3), 1.28 (dvt, 3JHH ≈ 7.9 J*HP ≈ 7.9 Hz, 12H, CH3), 1.85 (s, 3H, OCOCH3) 2.29 (m, 4H, CH), 3.15 (vt, J*HP = 4.3 Hz, 4H, CH2), 6.88 (t, 3JHH = 8.6 Hz, 1H, CarHp), 6.96 (d, 3JHH = 7.5 Hz, 2H, CarHm). 13C{1H} NMR (CD2Cl2, 25 ºC, 75 MHz): δ 18.0 (s, CH3), 18.8 (s, CH3), 24.2 (br s, OCOCH3), 24.7 (vt, J*CP = 10.9 Hz, CH), 32.4 (vt, J*CP = 11.7 Hz, CH2), 122.7 (vt, J*CP = 10.6 Hz, CarHm), 125.8 (s, CarHp), 151.4 (vt, J*CP = 10.6 Hz, Car−o), 155.4 (s, Car−i), 175.7 (s, OCOCH3). 31P{1H} NMR (CD2Cl2, 121 MHz): δ 59.5. IR (Nujol mull) ν(C=O) 1580 cm-1. Anal calcd for C22H38O2P2Pd: C, 52.54; H, 7.62; found C, 52.50, H, 7.48. [(iPrPCP)Ni-Me] and [(iPrPCP)Pd-Me]: A solution of MeLi in Et2O (1.6 M, 0.29 mL, 0.47 mmol) was added to a solution of [(iPrPCP)Ni-Br] (0.148 g, 0.31 mmol) in Et2O (25 mL) or [(iPrPCP)Pd-Cl] (0.149 g, 0.31 mmol) at –50 ºC. The resulting mixture allowed to stir for 2 h at room temperature. Methanol (0.29 mL) was added and the reaction mixture stirred for 15 additional min. The mixture was evaporated under reduced pressure and the residue extracted with Et2O (3×15 mL). The complex [(iPrPCP)Ni-Me] was obtained as an orange solid after evaporating the solvent under reduced pressure, and was recrystallized from hexane. Yield: 73%. 1H NMR (CD2Cl2, 25 ºC, 300 MHz): δ −0.77 (t, 3JHP = 8.0 Hz, 3H, NiCH3), 1.11 (dvt, 3JHH ≈ J*HP ≈ 6.6 Hz, 12H, CH3), 1.25 (dvt, 3JHH ≈ J*HP ≈ 7.5 Hz, 12H, CH3), 2.24 (m, 4H, CH), 3.20 (vt, J*HP = 4.0 Hz, 4H, CH2), 6.82 (t, 3JHH = 7.3 Hz, 1H, CarHp), 6.95 (d, 3JHH = 7.5 Hz, 2H, CarHm). 13C{1H} NMR (CD2Cl2, 25 ºC, 75 MHz): δ −17.8 (t, 2JCP = 21.7 Hz, NiCH3), 18.4 (s, CH3), 19.0 (vt, J*CP = 2.3 Hz, CH3), 23.8 (vt, J*CP = 10.3 Hz, CH), 37.0 (vt, J*CP = 13.1 Hz, CH2), 121.0 (vt, J*CP = 8.5 Hz, CarHm), 124.4 (s, CarHp), 151.2 (vt, J*CP = 13.8 Hz, Car−o) 176.6 (t, 2JCP = 13.5 Hz, Car−i). 31P{1H} NMR (CD2Cl2, 25 ºC, 121 MHz): δ 62.4. Anal calcd for C21H38P2Ni: C, 61.34; H, 9.32; found C, 31.34, H, 9.32.The complex [(iPrPCP)Pd-Me] was obtained as a white solid after evaporating the solvent under reduce pressure. Yield: 62%. 1H NMR (CD2Cl2, 25 ºC, 300 MHz): δ −0.34 (t, 3JHP = 5.2 Hz, PdCH3), 1.09 (dvt, 3JHH ≈ J*HP ≈ 6.9 Hz, 12H, CH3), 1.23 (dvt, 3JHH ≈ J*HP ≈ 7.8 Hz, 12H, CH3), 2.25 (m, 4H, CH), 3.35 (vt, J*HP = 4.1 Hz, 4H, CH2), 6.86 (t, 3JHH = 7.4 Hz, 1H, CarHp), 7.05 (d, 3JHH = 7.4 Hz, 2H, CarHm). 13C{1H} NMR (CD2Cl2, 25 ºC, 75 MHz): δ −18.6 (t, 2JCP = 10.1 Hz, PdCH3), 18.2 (s, CH3), 19.1 (vt, J*CP = 2.8 Hz, CH3), 24.5 (vt, J*CP = 10.8 Hz, CH), 38.7 (vt, J*CP = 11.9 Hz, CH2), 121.1 (vt, J*CP = 9.6 Hz, CarHm), 124.1 (s, CarHp), 149.8 (vt, J*CP = 10.8 Hz, Car−o) 178.2 (t, 2JCP = 4.1 Hz, Car−i). 31P{1H} NMR (CD2Cl2, 25 ºC, 121 MHz) : δ 59.2. Anal calcd for C21H38P2Pd: C, 54.96; H, 8.35; found C, 54.90, H, 8.30. [(iPrPCP)Ni-Ph and [(iPrPCP)Pd-Ph]: A solution of PhLi in hexane (2.0 M, 0.15 mL, 0.3 mmol) was added to a solution of [(iPrPCP)Pd-Cl] (0.149 g, 0.31 mmol) or [(iPrPCP)Ni-Br] (0.148 g, 0.31 mmol) in Et2O (25 mL) at –80 ºC. The cooling bath was removed and the mixture was allowed to stir until it warmed to the room temperature. The solvent was evaporated under reduced pressure and the remaining residue was extracted with Et2O (3 × 10 mL). The extract evaporated under vacuum and the residue was taken up in hexane (20 mL). The products crystallized when the hexane solutions were concentrated to 1 or 2 mL and cooled to −30 ºC. [(iPrPCP)Ni-Ph]: yellow solid. 1H NMR (CD2Cl2, 25 ºC, 300 MHz): δ 0.86 (dvt, 3JHH ≈ J*HP ≈ 7.4 Hz, 12H, CH3), 1.09 (dvt, 3JHH ≈ J*HP ≈ 6.9 Hz, 12H, CH3), 2.04 (m, 4H, CH), 3.18 (vt, J*HP = 4.0 Hz, 4H, CH2), 6.61 (t, 3JHH = 7.2 Hz, 1H, CPhHp), 6.80 (m, 3H, CarHp, and 2×CPhHm), 6.91 (d, 3JHH = 7.4 Hz, 2H, CarHm), 7.42 (dd, 2H, 3JHH = 7.8 Hz, 1JHH = 1.3 Hz, CPhHo). 13C{1H} NMR (CD2Cl2, 25 ºC, 75 MHz): δ 17.7 (s, CH3), 18.5 (s, CH3), 23.6 (vt, J*CP = 11.0 Hz, CH), 36.9 (vt, J*CP = 13.0 Hz, CH2), 120.5 (s, CPhHp), 121.1 (vt, J*CP = 8.7 Hz, CarHm), 124.8 (s, CarHp), 125.5 (s, CPhHm), 140.1 (vt, J*CP = 2.5 Hz, CphHo), 152.1 (vt, J*CP = 10.8 Hz, Car−o), 164.2 (t, 2JCP = 26.1 Hz, Car−i), 174.3 (t, 2JCP = 13.2 Hz, Car−i). 31P{1H} NMR (CD2Cl2, 25 ºC, 121 MHz) : δ 56.3. Anal calcd for C26H40P2Ni: C, 65.99; H, 8.52; found C, 65.95, H, 8.63. 20 [(iPrPCP)Pd-Ph]: white solid, 62% yield. 1H NMR (CD2Cl2, 25 ºC, 300 MHz): δ 1.02 (dvt, 3JHH ≈ J*HP ≈ 7.7 Hz, 12H, CH3), 1.13 (dvt, 3JHH ≈ J*HP ≈ 7.2 Hz, 12H, CH3), 2.13 (m, 4H, CH), 3.41 (vt, J*HP = 4.2 Hz, 4H, CH2), 6.77 (t, 3JHH = 7.3 Hz, 1H, CPhHp), 6.94 (m, 1H, CarHp) 6.93 (t, 3JHH = 7.4 Hz, 2H, CPhHm), 7.08 (dd, 2H, 3JHH = 7.4 Hz, CarHm), 7.51 (dd, 2H, 3JHH = 7.6 Hz, 1JHH = 1.3 Hz, CPhHo). 13C{1H} NMR (CD2Cl2, 25 ºC, 75 MHz): δ 17.9 (s, CH3), 18.6 (s, CH3), 24.4 (vt, J*CP = 11.3 Hz, CH), 38.2 (vt, J*CP = 12.1 Hz, CH2), 121.0 (s, CPhHp), 121.3 (vt, J*CP = 9.3 Hz, CarHm), 124.6 (s, CarHp), 126.1 (s, CPhHm), 140.6 (vt, J*CP = 2.5 Hz, CphHo), 150.8 (vt, J*CP = 10.8 Hz, Car−o), 164.4 (t, 2JCP = 12.1 Hz, CPh−i), 175.1 (t, 2JCP = 4.1 Hz, Car−i). 31P{1H} NMR (CD2Cl2, 25 ºC, 121 MHz) : δ 55.1. Anal calcd for C26H40P2Pd: C, 59.94; H, 7.74; found C, 59.99, H, 7.77. [(iPrPCP)Ni-OTf]: A solution of trifluoromethanesulfonic (triflic) acid (0.7M, 0.3 mL, 0.21 mmol) was added to a solution of [(iPrPCP)Ni-Me] (0.082 g, 0.2 mmol) in Et2O (15 mL) at −78 ºC. The product precipitated as a red solid when the mixture was allowed to warm to room temperature. The solution was filtered off, and the solid was washed with Et2O (10 mL), dried under vacuum and recrystallized from dichloromethane-toluene. Yield 50%. 1H NMR (C6D6, 25 ºC, 300MHz) δ 0.81 (dvt, 12H, 3JHH ≈ J*HP ≈ 6.9 Hz, CH3), 1.45 (dvt, 12H, 3JHH ≈ J*HP ≈ 7.9 Hz, CH3), 2.16 (m, 4H, CH), 2.52 (vt, 4H, J*HP = 3.7 Hz, CH2), 6.66 (d, 2H, 3JHH =7.4 Hz, CarHm), 6.91 (t, 1H, 3JHH = 7.4 Hz, CarHp). 13C{1H} NMR (C6D6, 25 ºC, 75 MHz) δ 18.2 (s, CH3), 19.2 (s, CH3), 23.8 (vt, J*CP = 10.4 Hz CH), 29.5 (vt, J*CP = 13.9 Hz, CH2), 120.2 (q, J*CF = 318.4 Hz, CF3), 122.9 (vt, J*CP = 8.5 Hz, CarHm), 126.3 (s, CarHp), 144.7 (t, 2JCP = 16.2 Hz, Car-i) and 152.8 (vt, J*CP = 12.5 Hz, Car-o) .31P{1H} NMR (C6D6, 25 ºC, 121 MHz) δ 60.1 ppm. IR (Nujol mull) ν(SO) 1320, 1203, 1167 cm-1. Anal. Calcd. for C21H35F3NiOP2S: C, 46.21; H, 6.45; S, 5.88 ; found: C, 46.21; H, 6.47; S, 5.98. [(iPrPCP)Pd-OTf]: A solution of trifluoromethanesulfonic (triflic) acid (0.7M, 0.3 mL, 0.21 mmol) was added to a solution of [(iPrPCP)Pd-Me] (0.092 g, 0.2 mmol) in Et2O (15 mL) at −78 ºC and the reaction mixture was allowed to warm to room temperature. The solvent was evaporated under reduced pressure and the residue extracted with CH2Cl2, the solution filtered and taken to dryness. The white residue was recrystallized from Et2O at −30ºC to afford the product as colorless crystals. Yield 40%. 1H NMR (C6D6, 25 ºC, 400MHz) δ 0.76 (dvt, 12H, 3JHH ≈ J*HP ≈ 7.2 Hz, CH3), 1.33 (dvt, 12H, 3JHH ≈ J*HP ≈ 7.7 Hz, CH3), 2.15 (m, 4H, CH), 2.58 (vt, 4H, J*HP = 4.7 Hz, CH2), 6.79 (d, 2H, 3JHH =7.5 Hz, CarHm), 6.94 (t, 1H, 3JHH = 7.5 Hz, CarHp). 13C{1H} NMR (C6D6, 25 ºC, 100 MHz) δ 18.0 (s, CH3), 19.1 (s, CH3), 24.8 (vt, J*CP = 11.0 Hz CH), 30.8 (vt, J*CP = 11.9 Hz, CH2), 121.2 (c, J*CF = 318.7 Hz, CF3), 123.5 (vt, J*CP = 10.5 Hz, CarHm), 125.9 (s, CarHp), 149.5 (t, 2JCP = 11.2 Hz, Car-i), 151.1 (vt, J*CP = 10.3 Hz, Car-o) .31P{1H} NMR (C6D6, 25 ºC, 161 MHz) δ 63.2 ppm. Anal. Calcd. for C21H35F3OP2PdS: C, 42.54; H, 5.95; S, 5.41 ; found: C, 42.50; H, 5.78; S, 5.14. IR (Nujol mull) ν(SO3) 1314 , 1203 , 1161 cm-1. Synthesis of [(iPrPCP)Ni-H and [(iPrPCP)Pd-H]: The synthesis of these two compounds involves a protocol for the consecutive generation of the amides [iPr(PCP)M-NH2],5b,c and methoxides [iPr(PCP)M-OMe],5b,c which are then reacted with trimethoxysilane. The intermediate complexes have been reported before,5 except for the palladium amide derivative. Due to its thermal instability, this compound was characterized by NMR only, and data are reported below. a) Generation of amide complexes [iPr(PCP)M-NH2]: A solution of [(iPrPCP)Pd-Cl] (1.59 g, 3.3 mmol) or [(iPrPCP)Ni- Br] (1.57 g, 3.3 mmol) in THF (60 mL) was transferred to a flask charged with NaNH2 (1.29 g, 33.2 mmol), and the 21 resulting suspension sonicated for 2 h. The initially colourless solution turned red. NaNH2 in excess was eliminated by centrifugation. For NMR characterization, the solution containing [(iPrPCP)Pd-NH2] was taken to dryness and dissolved in C6D6: 1H NMR (C6D6, 25 ºC, 400 MHz) δ -0.42 (s, 2H, NH2.), 0.93 (dvt, 12H, 3JHH ≈ J*HP ≈ 6.9 Hz, CH3), 1.27 (dvt, 12H, 3JHH ≈ J*HP ≈ 7.6 Hz, CH3), 1,89 (m, 4H, CH), 2.95 (vt, 4H, J*HP = 3.8 Hz, CH2), 7.09 (m, 3H, 2×CarHm, CarHp). 13C{1H} NMR (C6D6, 25 ºC, 100 MHz) δ 18.1 (s, CH3), 19.1 (s, CH3), 24.1 (vt, J*CP = 10.6 Hz, CH), 35.9 (vt, J*CP = 12.0 Hz, CH2), 122.0 (vt, J*CP = 10.1 Hz, CarHm), 124.0 (s, CarHp), 149.7 (vt, J*CP = 10.9 Hz, Car-o), 164.4 (s, Car-i). 31P{1H} NMR (C6D6, 25 ºC, 161 MHz) δ 58.8 ppm. b) Generation of methoxide complexes complexes [iPr(PCP)M-OMe]: After removal of NaH2, THF solutions of the amido complexes were treated with 0.20 mL of methanol (5 mmol) at room temperaure. The resulting solutions were taken to dryness and the residue was taken up in 20 mL THF or hexane and used for the synthesis of the hydrides as follows. c) Reaction of methoxide complexes with triethoxysilane: A solution of the appropriate methoxide complex in THF (Ni) or hexane (Pd), prepared as indicated above, was cooled to 0 ºC and treated with an excess of triethoxysilane (0.9 mL, 5 mmol). The mixture was allowed to warm at room temperature and the volatiles were removed under vacuum. The nickel hydride [(iPrPCP)Ni-H] was obtained as yellow needles after recrystallization from pentane at - 30 ºC. Yield, 60 %. 1H NMR (C6D6, 25 ºC, 400 MHz) δ −9.92 (t, 2JHP = 55.4 Hz, 1H, Ni-H) 0.96 (dvt, 12H, 3JHH ≈ J*HP ≈ 6.9 Hz, CH3), 1.20 (dvt, 12H, 3JHH ≈ J*HP ≈ 7.6 Hz, CH3), 1,92 (m, 4H, CH), 3.15 (vt, 4H, J*HP = 3.9 Hz, CH2), 7.24 (m, 3H, 2×CarHm, CarHp). 13C{1H} NMR (C6D6, 25 ºC, 100 MHz) δ 18.4 (s, CH3), 19.5 (s, CH3), 24.6 (vt, J*CP = 11.9 Hz, CH), 37.5 (vt, J*CP = 12.3 Hz, CH2), 121.0 (vt, J*CP = 10.1 Hz, CarHm), 124.7 (s, CarHp), 151.3 (vt, J*CP = 13.7 Hz, Car-o), 178.1 (t, 2JCP = 11.1 Hz, Car-i). 31P{1H} NMR (C6D6, 25 ºC, 161 MHz) δ 76.9 ppm. IR (Nujol mull) = 1761 and 1743 cm─1 ( Ni-H); IR (C6D6 solution) νmax (cm-1): 1735 ( Ni-H); Anal calcd for C20H36P2Ni: C, 60.49; H, 9.14; found: C, 60.21; H, 9.01. [(iPrPCP)Pd-H]: Colorless solid, 90 % yield. 1H NMR (C6D6, 300 MHz, 25 ºC): δ −3.77 (t, 1H, 2JHP = 17.0 Hz, Pd−H), 0.91 (dvt, 3JHH = 7.2 Hz, J*HP = 7.2 Hz, 12H, CH3), 1.17 (dvt, 3JHH = 7.8 Hz, J*HP = 7.8 Hz, 12H, CH3), 1.88 (m, 4H, CH), 3.24 (vt, J*HP = 4.1 Hz, 4H, CH2), 7.23 (t, 3JHH = 7.4 Hz, 1H, CarH), 7.28 (d, 3JHH = 7.4 Hz, 2H, CarH). 13C{1H} NMR (C6D6, 75 MHz, 25 ºC): δ 18.7 (CH3), 20.1 (vt, J*CP = 3.4 Hz, CH3), 25.3 (vt, J*CP = 11.6 Hz, CH), 39.8 (tv, J*CP = 11.7 Hz, CH2), 121.4 (tv, J*CP = 9.6 Hz, CarHm), 125.0 (CarHp), 150.3 (vt, J*CP = 10.7 Hz, Car─o), 179.7 (t, 2JCP = 3.8 Hz, Car─i). 31P{1H} NMR (C6D6, 121 MHz) = δ 71.7; IR (Nujol mull) = 1787 and 1763 cm─1 ( Pd-H); IR (C6D6 solution) νmax (cm-1): 1721 ( Pd-H); Anal calcd for C20H36P2Pd: C, 54.00; H, 8.16; found: C, 53.49; H, 8.24. [(iPrPCP)Ni-F]: a) From [(iPrPCP)Ni-Br]: A solution of the nickel bromide complex (0.381 g, 0.8 mmol) in THF (20 mL) was added to a suspension of AgF (0.203 g, 1.6 mmol) in toluene (10 mL) and the resulting suspension was sonicated for 12 h. The solvent was removed under reduced pressure and the residue extracted with hexane (3 × 25 mL). The combined extracts were centrifugued,concentrated and cooled −30ºC, affording the product as yellow crystals in 80% yield. b) From [(iPrPCP)Ni-Me]: A solution of TREAT-HF in THF (0.25 M, 6.0 mL, 1.5 mmol) was added to a solution of [(iPrPCP)Ni-Me] (1.23 g, 3 mmol) in THF (80 mL) at −78 °C. The reaction mixture was allowed to reach room temperature. The Et3N·3HF excess was eliminated transferring the solution to a flask charged with CaH2 (2.0 g) and the suspension resulting was stirred for 24 h. The reaction mixture was centrifuged and filtered to afford a yellow solution. The solvent was evaporated under reduced pressure, the residue extracted with hexane (3 × 50 mL), and the solution taken to dryness. Yield 62%. 1H NMR (CD2Cl2, 25 ºC, 300MHz) δ 1.28 22 (dvt, 12H, 3JHH ≈ J*HP ≈ 7.0 Hz, CH3), 1.43 (dvt, 12H, 3JHH ≈ J*HP ≈ 7.7 Hz, CH3), 2.19 (m, 4H, CH), 2.99 (vt, 4H, J*HP = 5.1 Hz, CH2), 6.73 (d, 2H, 3JHH =6.9 Hz, CarHm), 6.78 (t, 1H, 3JHH =6.6 Hz, CarHp). 13C{1H} NMR (CD2Cl2, 25 ºC, 75 MHz) δ 18.2 (s, CH3), 18.9 (s, CH3), 23.3 (vt, J*CP = 9.7 Hz, CH), 30.7 (vt, J*CP = 12.9 Hz, CH2), 122.2 (vt, J*CP = 8.7 Hz, CarHm), 124.7 (s, CarHp), 152.1 (bs, Car-i), 153.3 (t, 2JCP = 10.9 Hz, Car-o). 31P{1H} NMR (CD2Cl2, 25 ºC, 121 MHz) δ 54.3 ppm (d, 2JFP= 36.7 Hz). 19F{1H} NMR (CD2Cl2, 25 ºC, 376 MHz) δ −287.0 ppm. Anal. Calcd. for C20H35FNiP2: C, 57.86; H, 8.50; found: C, 57.99; H, 8.48. [(iPrPCP)Pd-F]: a) From [(iPrPCP)Pd-I] and AgF: A solution of the palladium iodide complex (0.457 g, 0.8 mmol) in THF (20 mL) was added to flask charged with AgF (0.203 g, 1.6 mmol) and the resulting suspension was sonicated for 12 h. The solvent was removed under reduced pressure and the residue was extracted with hexane (3 × 25 mL). The complex [(iPrPCP)Pd-F] was obtained as a colourless solid after cooling to −30ºC. b) From [(iPrPCP)Pd- Me and TREAT-HF. For the success of this method, the correct adjustment of the reagents ratio is essential. Since the weighting of TREAT-HF may involve significant error, we used a standard solution of this reagent in THF. The TREAT-HF content of this solution was estimated by reacting a sample of this solution with half the required amount of [(iPrPCP)Pd-Me] at 50 ºC for 2 h, and then analyzing the ratio product : starting material by 31P{1H} NMR. Once the concentration of the TREAT-HF is accurately known, the synthesis can be carried out as follows: A solution of TREAT-HF in THF (0.1 M, 3.4 mL, 0.34 mmol) was added to a solution of [(iPrPCP)Pd-CH3] (0,467 g, 1.02 mmol) in THF (10 mL) at room temperature. The resulting mixture was heated at 50ºC for 2 h. The solvent was evaporated under reduce pressure and the residue extracted with hexane (3 × 25 mL). The complex [(iPrPCP)Pd-F] was obtained as a colourless solid after cooling to −30ºC. Yield: 42%. 1H NMR (C6D6, 25 ºC, 300 MHz): δ 1.00 (dvt, 3JHH ≈ J*HP ≈ 7.2 Hz, 12H, CH3), 1.34 (dvt, 3JHH ≈ J*HP ≈ 7.9 Hz, 12H, CH3), 1.96 (m, 4H, CH), 2.75 (vt, J*HP = 4.0 Hz, 4H, CH2), 6.91 (d, 3JHH = 7.4 Hz, 2H, CarHm), 7.00 (t, 3JHH = 7.4 Hz, 1H, CarHp). 13C{1H} NMR (C6D6, 25 ºC, 100 MHz): δ 18.2 (s, CH3), 19.0 (s, CH3), 24.1 (vt, J*CP = 10.4 Hz, CH), 32.4 (vt, J*CP = 10.3 Hz, CH2), 122.8 (vt, J*CP = 10.3 Hz, CarHm), 124.6 (s, CarHp), 151.2 (vt, J*CP = 10.9 Hz, Car−o), 155.2 (d, 2JCF = 48.2 Hz, Car−i). 31P{1H} NMR (C6D6, 121 MHz): δ 57.5 (d, 2JFP = 5.9 Hz). 19F{1H} NMR (C6D6, 25 ºC, 376 MHz) δ −245.3 ppm Anal calcd for C20H35FP2Pd: C, 51.90; H, 7.62; found C, 51.52, H, 7.72. Reactions of Fluoride Complexes with LiOMe. To a solution of [(iPrPCP)Ni-F] (0.66 g, 1.6 mmol, see below) or [(iPrPCP)Pd-F] (0.74, 1.6 mmol, see below) in THF (25 mL) was added a solution of MeOLi (2.4 mmol) in THF (20 mL) at −78 ºC. The resulting mixture was allowed to warm at room temperature and stirred for 20 min. According to the 31P{1H} spectra of the reaction mixtures, the fluoride complexes were cleanly and quantitatively converted in the corresponding methoxides. Lithium fluoride was removed by centrifugation, the solvent evaporated under reduced pressure and the residue extracted with hexane. The complexes [(iPrPCP)Pd-OMe]5c and [(iPrPCP)Ni-OMe]5b were obtained after concentration and cooling to −30 ºC. Reaction of Halide Complexes with Dodecyl Iodide. 23 Solutions of the halide complexes [(iPrPCP)Ni-Br], [(iPrPCP)Ni-I], [(iPrPCP)Ni-F], [(iPrPCP)Pd-I] or [(iPrPCP)Pd-Cl] (0.02 mmol) and n-iododecane (50 L, 0.2 mmol) in C6D6 (0.6 mL) containing a small amount of pcymene as internal standard for 1H integration were transferred to NMR tubes capped with J. Young® valves and placed in a pre-heated oil bath at 100 ºC. The course of the reactions was monitored by 1H and 31P{1H} NMR. The reaction of [(iPrPCP)Pd-F] with dodecyl iodide was studied directly in the NMR probe at the same temperature. Catalytic fluorination of Dodecyl Iodide. To a suspension of AgF (0.065 g, 0.52 mmol) in toluene (1 mL) was added a solution of [(iPrPCP)Ni-Br], [(iPrPCP)Ni-I], [(iPrPCP)Ni-F], [(iPrPCP)Pd-I] or [(iPrPCP)Pd-F] (0.035 mmol) in toluene (2 mL). The resulting suspension was stirred for 3 h at 100 ºC. Aliquots were taken out for GC analysis. Yields and conversions were calculated by GC using p-cymene as internal standard. X-ray structure analysis for [(iPrPCP)Ni-F], [(iPrPCP)Ni-H], [(iPrPCP)Ni-Me], [(iPrPCP)Ni-Ph] and [iPr(P(O)C(Me)P(O)]·H2O. A summary of crystallographic data and structure refinement results for these new crystalline compounds is given in the Table 3. Crystals coated with dry perfluoropolyether were mounted on glass fibers and fixed in a cold nitrogen stream (T = 100 or 120 K). Intensity data were collected on a Bruker SMART CCD diffractometer operating with graphite monochromated Mo-Kα radiation (λ = 0.71073 Å), except for compound [(iPrPCP)Ni-Me] whose intensity data were collected on an Enraf-Nonius FR590-Kappa CCD 2000 diffractometer equipped with a graded multilayer mirror providing monochromated Cu-Kα radiation (λ = 1.54178 Å). For the Bruker diffractometer the data were reduced by SAINT37 while for the Enraf-Nonius diffractometer the data were reduced by HKL-Denzo and Scalepak.38 The data were in all cases corrected for absorption effects by the multi-scan method (SADABS).36 The structures were solved by direct methods (SIR-2002, SHELXS)39,40 and refined against all F2 data by full-matrix least-squares techniques (SHELXTL-6.12)37 minimizing w[Fo2-Fc2]2. All non-hydrogen atoms were refined with anisotropic thermal parameters. Hydrogen atoms were included in calculated positions and allowed to ride on the attached carbon atoms with the isotropic temperature factors (Uiso values) fixed at 1.2 times (1.5 times for the methyl groups) those Ueq values of the corresponding carbon atoms. Table 3. Summary of crystallographic data and structure refinement results for [(iPrPCP)Ni-F], [(iPrPCP)Ni-H], [(iPrPCP)Ni-Me], [(iPrPCP)Ni-Ph] and [iPr(P(O)C(Me)P(O)]·H2O Compound [(iPrPCP)Ni-F] [(iPrPCP)Ni-H] [(iPrPCP)Ni-Me] [(iPrPCP)Ni-Ph] [iPr(P(O)C(Me)P(O)]·H2O Chemical formula C20H35FNiP2 C20H36NiP2 C21H38NiP2 C26H40NiP2 C21H38O2P2•H2O Formula Mass 415.13 397.14 411.16 473.23 402.47 24 Crystal system Monoclinic Monoclinic Monoclinic Triclinic Monoclinic a/Å 18.316(1) 18.038(4) 10.998(9) 10.4777(10) 13.5036(11) b/Å 19.001(2) 18.938(5) 13.794(9) 13.9169(14) 12.3747(11) c/Å 19.963(2) 20.036(5) 28.90(3) 18.1873(18) 14.2276(12) α/° 90.00 90.00 90.00 81.963(2) 90.00 β/° 113.933(2) 113.393(4) 96.038(14) 76.658(1) 107.045(2) γ/° 90.00 90.00 90.00 77.812(2) 90.00 Unit cell volume/Å3 6350.2(10) 6282(3) 4360(6) 2510.7(4) 2273.0(3) Temperature/K 100(2) 100(2) 120(2) 100(2) 100(2) Space group P2(1)/n P2(1)/n P2(1)/n P 1 P2(1)/c No. of formula units per unit cell, Z 12 12 8 4 4 Radiation type MoKα MoKα CuKα MoKα MoKα Absorption coefficient, μ/mm-1 1.076 1.078 2.648 0.910 0.208 No. of reflections measured 41108 39578 36997 30622 14665 No. of independent reflections 15961 15516 6775 12620 5757 Rint 0.0863 0.0937 0.0788 0.0379 0.0546 Final R1[a] values [F2>2σ(F 2)] 0.0679 0.0728 0.0476 0.0383 0.0470 Final wR2(F2) [b] values [F 2>2σ(F2)] 0.1428 0.1637 0.1159 0.0708 0.0687 Final R1[a] values (all data) 0.1168 0.1359 0.0586 0.0560 0.0787 Final wR(F2) [b] values (all data) 0.1647 0.1939 0.1224 0.0745 0.0743 Goodness of fit on F2, S[c] 1.003 0.993 0.997 0.835 0.980 [a] R1(F)=F0 −Fc)/ F0  . [b] wR2(F2)=w(Fo2−Fc2)2    / (F0 2)2    1/2 . [c] S=w(Fo2−Fc2)2   / (n−p)    1/2 (n = number of reflections, p = number of parameters). Acknowledgement Financial support from the DGI (Project CTQ2009-11721), Junta de Andalucía (Project FQM6276) and European Union (FEDER funds) is gratefully acknowledged. L. M. M.-P. thanks a predoctoral grant from the Junta de Andalucía. References 1) a) Vigalok, A. Organometallics, 2011, 30, 4802 – 4810. b) Grushin, V. V. Acc. Chem. Res. 2010, 43, 160 – 171. c) van der Vulgt, J. I. Chem. Soc. Rev. 2010, 39, 2302–2322. d) Gunnoe, B. T. Eur. J. Inorg. Chem., 2007, 1185-1203. e) Roesky, H. W.; Singh, S.; Yusuff, K. K. M.; Maguire, J. A. Hosmane. N. S. Chem. Rev., 2006, 106, 3813-3843. f) Fulton, J. R.; Holland, A. W.; Fox, D. J.; Bergman, R. G. Acc. Chem. Res. 2002, 35, 44–56. g) Fryzuk, M. D.; Montgomery, C. D. Coord. Chem. Rev. 1989, 95, 1 – 40. h) Bryndza, H. E.: Tam, W. Chem. Rev. 1988, 88, 1163-1188. 2) a) Lappert, M. F.; Power, P. P.; Protchenko, A. V.; Seeber, A. L. Metal Amide Chemistry, John Wiley & Sons, West Sussex, 2009. b) Bradley, D. C; Mehrotra, R. C.; Rothwell, I. P. ; Singh, A. Alkoxo and Aryloxo Derivatives of Metals; Academic Press, Cornwall, Great Britain. 2001. 3) a) Baratta, W.; Ballico, M.; Del Zotto, A.; Herdteweck, E.; Magnolia, S.; Peloso, R.; Siega, K.; Tonutti, M.; Zangrando, E.; Rigo, P. Organometallics, 2009, 28, 4421-4430. b) Samec, J. S. M.; Backvall, J. E.; Andersson, P. G.; Brandt, P. Chem. Soc. Rev. 2006, 35, 237 – 248. c) Sigman, M. S.; Jensen D. R. Acc. 25 Chem. Res., 2006, 39, 221. Hartwig, J. F. Nature, 2008, 455, 314 – 322. d) Shannon S. S. Angew. Chem. Int. Ed., 2004, 43, 3400. 4) For leading references, see for example: a) Furuya, T.; Benitez, D.; Tkatchouk, E.; Strom, A. E.; Tang, P.; Goddard, W. A.; Ritter, T. J. Am. Chem. Soc., 2010, 132, 3793-3807. b) Gnanaprakasam, B.; Zhang, J.; Milstein, D. Angew. Chem. Int. Ed., 2010, 49, 1468-1471. c) Hanley, P. S.; Markovi, D.; Hartwig, J. F. J. Am. Chem. Soc., 2010, 138, 6302 - 6303. d) Ball, N. D.; Sanford, M. S. J. Am. Chem. Soc., 2009, 131, 3796 - 3797. e) Neukom, J. D.; Perch, N. S. Wolfe, J. P. J. Am. Chem. Soc., 2010, 132, 6276 - 6277. f) Matas, I.; Cámpora, J.; Palma, P.; Álvarez E. Organometallics, 2009, 28, 6515 - 6523. g) Smythe, N. A.; Grice, K. A.; Williams, B. S.; Goldberg K. I. Organometallics, 2009, 28, 277 - 278. h) Trend R. M.; Stoltz. B. M. J. Am. Chem. Soc., 2008, 130, 15957 - 15966. i) Stambuli, J. P. Weng, Z.; Incarvito, C. D.; Hartwig, J. F. Angew. Chem. Int. Ed., 2007, 44, 7674 - 7677. j) Zhao, J.; Hesslink, H.; Hartwig, J. F.. Organometallics, 2001, 123, 7220 – 7227. k) Hartwig, J. F.; Richards, S.; Barañano, D.; Paul, F. . J. Am. Chem. Soc., 1996, 118, 3626 – 3633. 5) a) Cámpora, J.; Palma, P.; del Río, D. Álvarez, E. Organometallics, 2004, 23, 1652 - 1655. b) Cámpora, J.; Palma, P.; del Río, D.; Conejo, M. M.; Álvarez, E. Organometallics, 2004, 23, 5653 – 5655. c) Melero, C.; Martínez-Prieto, L. M.; Palma, P.; del Río, D.; Álvarez, E.; Cámpora, J. Chem. Commun. 2010, 46, 8851 – 8853. 6) Clot, E.; Eisenstein, O.; Jasim, N.; Macgregor, S. A.; McGrady, J. E.; Perutz.R. N. Acc. Chem. Res., 2011, 44, 333-348. 7) a) Grushin, V. V. Chem. Eur. J., 2002, 8, 1006. b) Watson, D. A.; Su, M.; Teverovskiy, G.; Zhang, Y.; García- Fortanet, J.; Kinzel, T.; Buchwald, S. L.. Science 2009, 325, 1661–1664. 8) Grushin, V. V. Angew. Chem. Int. Ed. 1998, 37, 994 – 996. 9) a) Cámpora, J.; Matas, I.; Palma, P.; Graiff, C.; Tiripicchio, A. Organometallics, 2005, 24, 28217. b) Cámpora, J.; Matas, I.; Palma, P.; Álvarez, E.; Graiff, C.; Tiripicchio, A. Organometallics, 2007, 26, 5712. 10) a) Ball, N. D.; Kampf J. W.; Sanford, M. S. Dalton Trans., 2009, 39, 632 – 640. b) Huacuja, R.; Herbert, D. E.; Fafard, C. M.; Ozerov, O. V. J. Fluorine Chem., 2010, 131, 1257. 11) Slander, N.; Szabó, K. Chem. Rev. 2011, 111, 2048 – 2076. 12) a) Caulton, K. G. New J. Chem. 1994, 18, 25 – 41. b) Mayer, J. M. Comments Inorg. Chem. 1988, 8, 125 – 135. 13) a) Parshall, G. W. J. Am. Chem. Soc, 1966, 20, 704 – 708. b) Clark, H. C.; Ward, J. E. H. J. Am. Chem. Soc, 1974, 96, 1741 – 1747. c) Manna, J.; Kuehl, C. J.; Whiteford, J. A.; Stang, P. J. Organometallics, 1997, 16, 1897 -1905. 14) Poulton, J. T.; Sigalas, M. P.; Folting, K.; Streib, W. E.; Eisenstein, O.; Caulton, K.; G. Inorg. Chem 1994, 33 1476-1485. 15) a) Ohff, M. Ohff, A. van der Boom M. E.; Milstein D. J. Am. Chem. Soc., 1997, 119, 11687 -11688. b) Frech, C. M.; Shimon, L. J. W. Milstein, D. Angew. Chem. Int. Ed., 2005, 44, 1709 – 1711. 16) a) Moulton, C. J.; Shaw, B. L. J. Chem. Soc. Dalton Trans. 1976, 1020 – 1024. b) Rimml, H.; Venanzi. L. M. J. Organomet. Chem. 283, 259, C6-C7. c) A. R. Kennedy, R. J. Cross, K. W. Muir. Inorg. Chim. Acta, 1995, 231, 195 – 200. d) van der Boom, M. E.; Liou, S. – Y.; Shimon, L. J. W.; Ben-David, Y.; Milstein, D. Inorg. Chim. Acta, 2004, 357, 4015 – 4023.