Synthesis of N-heterocyclic carbene palladium(II) bis-phosphine complexes and their decomposition in the presence of aryl halides

Methylpalladium(II) carbene complexes of the type [Pd(NHC)Me(P-P)]BF(4) (NHC = N-heterocyclic carbene, P-P = chelating phosphine) have been synthesised, the complex [Pd(tmiy)Me(dcype)]BF(4) (tmiy = 1,3,4,5-tetramethylimidazol-2-ylidene, dcype = 1,2-bis(dicyclohexylphosphino)ethane) being characterised crystallographically. Complexes bearing the tmiy ligands were shown to decompose in an analogous manner to complexes bearing monodentate phosphine ligands, with the rate of decomposition being nominally linked to the size of the chelate ring. The decomposition of these complexes in the presence of aryl halides-expected to yield Pd(Ar)X(P-P)-was studied and shown instead to yield PdX(2)(P-P) and [Pd(tmiy)X(P-P)]BF(4). Additionally, Pd(Me)X(P-P) and Pd(Ar)X(P-P) were observed in some cases. Intermolecular cross-over reactions between the starting complex and Pd(Ar)X(P-P) were found to be the source of these unexpected products.     

The influence of N-substitution on the reductive elimination behaviour of hydrocarbyl-palladium-carbene complexes--a DFT study

The reductive elimination of 2-hydrocarbyl-imidazolium salts from hydrocarbyl-palladium complexes bearing N-heterocyclic carbene (NHC) ligands represents an important deactivation route for catalysts of this type. We have explored the influence that carbene N-substituents have on both the activation energy and the overall thermodynamics of the reductive elimination reaction using density functional theory (DFT). Given the proximity of the N-substituent to the three-centred transition structure, steric bulk has little influence on the activation barrier and it is electronic factors that dominate the barriers' magnitude. Increased electron donation from the departing NHC ligand acts to stabilise the associated complex against reductive elimination, with stability following the trend: Cl < H < Ph < Me < Cy < iPr < neopentyl < tBu. The intimate involvement of the carbene p pi-orbital in determining the barrier to reductive elimination means N-substituents that are capable of removing pi-density (e.g. phenyl) act to promote a more facile reductive elimination.     

Influence of geometry on reductive elimination of hydrocarbyl-palladium-carbene complexes

The influence of spectator ligand bite angle and the twist angle of the carbene on the reductive elimination of N-heterocyclic carbenes (NHCs) from palladium bis-phosphine complexes has been investigated using density functional theory. The spectator bite angle was found to have a significant influence on both the activation energy (E(act)) and the enthalpy of reaction. Widening of the bite angle was found to lower E(act) and increase the enthalpy of reaction. In contrast, rotation of the carbene with respect to the PdL(2) plane was found to have little influence on E(act). At carbene twist angles approaching 0 degrees however, relief of the increased steric strain provides a considerable driving force for the decomposition reaction.     

Reductive elimination of ArCF3 from bidentate Pd(II) complexes: a computational study

The reductive eliminations of ArCF(3) from Pd(II) complexes bearing small- and large-bite-angle phosphane ligands have been investigated using computational methods. QM/QM' and QM/MM studies were applied and complemented with CP2K molecular dynamics investigations. The ligand substituents were varied and a decomposition analysis was performed to allow us to gain insights into the steric and electronic properties of the ligands. The greater reactivity of Xantphos-derived (Xantphos=4,5-bis(diphenylphosphino)-9,9-dimethylxanthene) complexes in the reductive elimination of ArCF(3) is primarily due to the lower repulsive effect of the phoshine substituents in the transition state than in the reactant complex, combined with the increased electronic interaction in the transition state. For DPPE (1,2-bis(diphenylphosphino)ethane), the steric effect of the ligand substituents is greater in the transition state, leading to a higher reaction barrier overall for reductive elimination. There is no direct correlation of the reactivity with the bite angle of the reactant complexes. Only for complexes with large ligand substituents may the bite angle of the Pd complexes be used as a guide for reactivity.     

Synthesis,characterization and catalytic activity in Suzuki–Miyaura coupling of palladacycle complexes with n‐butyl‐substituted N‐heterocyclic carbene ligands

A series of monomeric palladacycle complexes bearing n‐butyl‐substituted N‐heterocyclic carbenes, namely [Pd(NHC)X(dmba)] (dmba: dimethylbenzylamine and [Pd(NHC)X(ppy)]; NHC: 1‐n‐butyl‐3‐substituted benzylimidazol‐2‐ylidene; ppy: 2‐phenylpyridine), were prepared either by transmetallation from the corresponding silver carbene complexes or by the reaction of the corresponding acetate‐bridged palladacycle dimer with N‐heterocyclic carbene ligands in high yields. The palladium(II) complexes were characterized using elemental analyses, APCI‐MS, ¹H NMR and ¹³C NMR spectroscopies. These complexes are efficient in the Suzuki–Miyaura coupling reaction between phenylboronic acid and aryl bromides.     

Vinyl-vinyl coupling on late transition metals through C-C reductive elimination mechanism. A computational study

A detailed density functional study was performed for the vinyl-vinyl reductive elimination reaction from bis-sigma-vinyl complexes [M(CH=CH(2))(2)X(n)]. It was shown that the activity of these complexes decreases in the following order: Pd(IV), Pd(II) > Pt(IV), Pt(II), Rh(III) > Ir(III), Ru(II), Os(II). The effects of different ligands X were studied for both platinum and palladium complexes, which showed that activation barriers for C-C bond formation reaction decrease in the following order: X = Cl > Br, NH(3) > I > PH(3). Steric effects induced either by the ligands X or by substituents on the vinyl group were also examined. In addition, the major factors responsible for stereoselectivity control on the final product formation stage and possible involvement of asymmetric coupling pathways are reported. In all cases DeltaE, DeltaH, DeltaG, and DeltaG(aq) energy surfaces were calculated and analyzed. The solvent effect calculation shows that in a polar medium halogen complexes may undergo a reductive elimination reaction almost as easily as compounds with phosphine ligands.     

Reductive elimination from arylpalladium cyanide complexes

We report the isolation and characterization of arylpalladium cyanide complexes that undergo reductive elimination to form arylnitriles. The rates of reductive elimination from a series of arylpalladium cyanide complexes reveal that the electronic effects on the reductive elimination from arylpalladium cyanide complexes are distinct from those on reductive reductive eliminations from arylpalladium alkoxo, amido, thiolate, and enolate complexes. Arylpalladium cyanide complexes containing aryl ligands with electron-donating substituents undergo reductive elimination of aromatic nitriles faster than complexes containing aryl ligands with electron-withdrawing substituents. In addition, the transition state for the reductive elimination of the aromatic nitrile is much different from that for reductive eliminations that occur from most other arylpalladium complexes. Computational studies indicate that the reductive elimination of an arylnitrile from Pd(II) occurs through a transition state more closely related in structure and electronic distribution to that for the insertion of CO into a palladium-aryl bond.     

Aryl-fluoride reductive elimination from Pd(II): feasibility assessment from theory and experiment

DFT methods were used to elucidate features of coordination environment of Pd(II) that could enable Ar-F reductive elimination as an elementary C-F bond-forming reaction potentially amenable to integration into catalytic cycles for synthesis of organofluorine compounds with benign stoichiometric sources of F(-). Three-coordinate T-shaped geometry of Pd(II)Ar(F)L (L = NHC, PR(3)) was shown to offer kinetics and thermodynamics of Ar-F elimination largely compatible with synthetic applications, whereas coordination of strong fourth ligands to Pd or association of hydrogen bond donors with F each caused pronounced stabilization of Pd(II) reactant and increased activation barrier beyond the practical range. Decreasing donor ability of L promotes elimination kinetics via increasing driving force and para-substituents on Ar exert a sizable SNAr-type TS effect. Synthesis and characterization of the novel [Pd(C(6)H(4)-4-NO(2))ArL(mu-F)](2) (L = P(o-Tolyl)(3), 17; P(t-Bu)(3), 18) revealed stability of the fluoride-bridged dimer forms of the requisite Pd(II)Ar(F)L as the key remaining obstacle to Ar-F reductive elimination in practice. Interligand steric repulsion with P(t-Bu)(3) served to destabilize dimer 18 by 20 kcal/mol, estimated with DFT relative to PMe(3) analog, yet was insufficient to enable formation of greater than trace quantities of Ar-F; C-H activation of P(t-Bu)(3) followed by isobutylene elimination was the major degradation pathway of 18 while Ar/F- scrambling and Ar-Ar reductive elimination dominated thermal decomposition of 17. However, use of Buchwald's L = P(C(6)H(4)-2-Trip)(t-Bu)(2) provided the additional steric pressure on the [PdArL(mu-F)](2) core needed to enable formation of aryl-fluoride net reductive elimination product in quantifiable yields (10%) in reactions with both 17 and 18 at 60 degrees over 22 h.     

Oxidative addition of the imidazolium cation to zerovalent Ni, Pd, and Pt: a combined density functional and experimental study

Oxidative addition of different imidazolium cations to zerovalent group 10 metals, to afford heterocyclic carbene complexes, has been investigated by both density functional theory (DFT) and experimental studies. The theoretical analysis shows that addition of imidazoliums to Pt(0) and Ni(0) is more exothermic than to Pd(0), and Ni(0) is predicted to react with a much lower barrier than either Pt(0) or Pd(0). Strongly basic supporting ligands on the metal, as well as cis-chelating ligands, increase the exothermicity of the reaction and also lower the activation barrier. The addition of 2-H imidazoliums is easier and more exothermic than addition of 2-alkylimidazoliums, and a halo-imidazolium is expected to further lower the barrier to oxidative addition and increase the exothermicity. The DFT results show that all three of the metals should be able to oxidatively add imidazolium cations under appropriate conditions. Experimental studies confirmed that oxidative addition is possible, and a number of Pt- and Pd-carbene complexes were prepared via oxidative addition of imidazolium salts to M(0) precursors. Most significantly, oxidative addition of 2-H azolium salts was found to readily occur, and the reaction of 1,3-dimethylimidazolium tetrafluoroborate with Pt(PPh(3))(2) and Pt(PCy(3))(2) affords [PtH(dmiy)(PPh(3))(2)]BF(4) (10) and [PtH(dmiy)(PCy(3))(2)]BF(4) (11), while reaction between 3,4-dimethylthiazolium tetrafluoroborate and Pt(PCy(3))(2) yields [PtH(dmty)(PCy(3))(2)]BF(4) (12) (dmiy = 1,3-dimethylimidazolin-2-ylidene, dmty = 3,4-dimethylthiazolin-2-ylidene). Addition of 2-iodo-1,3,4,5-tetramethylimidazolium tetrafluoroborate to Pt(PPh(3))(4) or Pd(dcype)(dba) yields [PtI(tmiy)(PPh(3))(2)]BF(4) (9) and [PdI(tmiy)(dcype)]BF(4) (14), respectively (tmiy = 1,3,4,5-tetramethylimidazolin-2-ylidene, dcype = 1,3-bis(dicyclohexylphosphino)ethane)). X-ray crystal structures are reported for complexes 9 and 11 (cis and trans). These studies clearly show for the first time that oxidative addition of imidazolium and thiazolium cations is possible, and the results are discussed in terms of the ramifications for catalysis in imidazolium-based ionic liquids with both carbene-based and non-carbene-based complexes.     

Synthetic and computational studies of the palladium(iv) system Pd(alkyl)(aryl)(alkynyl)(bidentate)(triflate) exhibiting selectivity in C-C reductive elimination

Synthetic routes to methyl(aryl)alkynylpalladium(iv) motifs are presented, together with studies of selectivity in carbon-carbon coupling by reductive elimination from Pd(IV) centres. The iodonium reagents IPh(C[triple bond, length as m-dash]CR)(OTf) (R = SiMe(3), Bu(t), OTf = O(3)SCF(3)) oxidise Pd(II)Me(p-Tol)(L(2)) (1-3) [L(2) = 1,2-bis(dimethylphosphino)ethane (dmpe) (1), 2,2'-bipyridine (bpy) (2), 1,10-phenanthroline (phen) (3)] in acetone-d(6) or toluene-d(9) at -80 °C to form complexes Pd(IV)(OTf)Me(p-Tol)(C[triple bond, length as m-dash]CR)(L(2)) [R = SiMe(3), L(2) = dmpe (4), bpy (5), phen (6); R = Bu(t), L(2) = dmpe (7), bpy (8), phen (9)] which reductively eliminate predominantly (>90%) p-Tol-C[triple bond, length as m-dash]CR above ～-50 °C. NMR spectra show that isomeric mixtures are present for the Pd(IV) complexes: three for dmpe complexes (4, 7), and two for bpy and phen complexes (5, 6, 8, 9), with reversible reduction in the number of isomers to two occurring between -80 °C and -60 °C observed for the dmpe complex 4 in toluene-d(8). Kinetic data for reductive elimination from Pd(IV)(OTf)Me(p-Tol)(C[triple bond, length as m-dash]CSiMe(3))(dmpe) (4) yield similar activation parameters in acetone-d(6) (66 ± 2 kJ mol(-1), ΔH(?) 64 ± 2 kJ mol(-1), ΔS(?)-67 ± 2 J K(-1) mol(-1)) and toluene-d(8) (E(a) 68 ± 3 kJ mol(-1), ΔH(?) 66 ± 3 kJ mol(-1), ΔS(?)-74 ± 3 J K(-1) mol(-1)). The reaction rate in acetone-d(6) is unaffected by addition of sodium triflate, indicative of reductive elimination without prior dissociation of triflate. DFT computational studies at the B97-D level show that the energy difference between the three isomers of 4 is small (12.6 kJ mol(-1)), and is similar to the energy difference encompassing the six potential transition state structures from these isomers leading to three feasible C-C coupling products (13.0 kJ mol(-1)). The calculations are supportive of reductive elimination occurring directly from two of the three NMR observed isomers of 4, involving lower activation energies to form p-TolC[triple bond, length as m-dash]CSiMe(3) and earlier transition states than for other products, and involving coupling of carbon atoms with higher s character of σ-bonds (sp(2) for p-Tol, sp for C[triple bond, length as m-dash]C-SiMe(3)) to form the product with the strongest C-C bond energy of the potential coupling products. Reductive elimination occurs predominantly from the isomer with Me(3)SiC[triple bond, length as m-dash]C trans to OTf. Crystal structure analyses are presented for Pd(II)Me(p-Tol)(dmpe) (1), Pd(II)Me(p-Tol)(bpy) (2), and the acetonyl complex Pd(II)Me(CH(2)COMe)(bpy) (11).     

Imidazol(in)ium‐2‐Carboxylates as Efficient Precursors to N‐Heterocyclic Carbene Complexes of Copper and Silver

Copper and silver N‐heterocyclic carbene (NHC) complexes were prepared through a simple, base‐free protocol involving the decomposition of corresponding imidazol(in)ium‐2‐carboxylates under thermolytic conditions and a subsequent reaction of the in situ generated carbenes with copper(I) or silver(I) chloride, respectively. The desired NHC metal complexes were isolated with good yields after simple crystallization.     

Mechanistic information on the reductive elimination from cationic trimethylplatinum(IV) complexes to form carbon-carbon bonds

Cationic complexes of the type fac-[(L(2))Pt(IV)Me(3)(pyr-X)][OTf] (pyr-X = 4-substituted pyridines; L(2) = diphosphine, viz., dppe = bis(diphenylphosphino)ethane and dppbz = o-bis(diphenylphosphino)benzene; OTf = trifluoromethanesulfonate) undergo C-C reductive elimination reactions to form [L(2)Pt(II)Me(pyr-X)][OTf] and ethane. Detailed studies indicate that these reactions proceed by a two-step pathway, viz., initial reversible dissociation of the pyridine ligand from the cationic complex to generate a five-coordinate Pt(IV) intermediate, followed by irreversible concerted C-C bond formation. The reaction is inhibited by pyridine. The highly positive values for DeltaS()(obs) = +180 +/- 30 J K(-1) mol(-1), DeltaH(obs) = 160 +/- 10 kJ mol(-1), and DeltaV()(obs) = +16 +/- 1 cm(3) mol(-1) can be accounted for in terms of significant bond cleavage and/or partial reduction from Pt(IV) to Pt(II) in going from the ground to the transition state. These cationic complexes have provided the first opportunity to carry out detailed studies of C-C reductive elimination from cationic Pt(IV) complexes in a variety of solvents. The absence of a significant solvent effect for this reaction provides strong evidence that the C-C reductive coupling occurs from an unsaturated five-coordinate Pt(IV) intermediate rather than from a six-coordinate Pt(IV) solvento species.     

Pd-catalyzed inter- and intramolecular carbene transfer from group 6 metal-carbene complexes.

The use of group 6 metal-carbene complexes in inter- and intramolecular carbene transfer reactions has been studied. Thus, pentacarbonyl[(aryl)(methoxy)carbene]chromium(0) and tungsten complexes, 10, efficiently dimerize at room temperature in the presence of diverse Pd(0) and Pd(II)/Et(3)N catalysts. The effect of additives (PPh(3), AsPh(3), or SbPh(3)) on the nature and the isomeric ratio of the reaction products is negligible. The nature of the reaction products is more catalyst-dependent for metal carbenes 12 bearing alkyl groups attached to the carbene carbon. In these cases, either carbene ligand dimerization or beta-hydrogen elimination reactions are observed, depending on the catalyst. The carbene ligand dimerization reaction can be used to prepare conjugated polyenes, including those having metal moieties at both ends of the polyene system, as well as enediyne derivatives. The intramolecular carbene ligand dimerization of chromium bis-carbene complexes 28 and 30 allows the preparation of mono- and bicyclic derivatives, with ring sizes from six to nine members. For bis-carbene derivatives the beta-hydrogen elimination reaction is inhibited, provided that both metal centers are tethered by an o-xylylene group. Other alkyl complexes 32 form new mononuclear carbene complexes 37 or decompose to complex reaction mixtures. The results obtained in these reactions may be explained by transmetalation from Cr(0) to Pd(0) and the intermediacy of Pd-carbene complexes. Aminocarbene-chromium(0) complexes 15, need harsher reaction conditions to transfer the carbene ligand, and this transfer occurs only in the presence of deactivated olefins. The corresponding insertion/hydrolysis products 48 resulted in these cases. A catalytic cycle involving transmetalation from a chromacyclobutane to a palladacyclobutane is proposed to explain these results.     

以N-杂环卡宾为配体的金属络合物催化有机合成的反应

综述了近几年来以N-杂环卡宾为配体的金属络合物催化有机合成的反应。     

Directly observed reductive elimination of aryl halides from monomeric arylpalladium(II) halide complexes

Monomeric, three-coordinate arylpalladium(II) halide complexes undergo reductive elimination of aryl halide to form free haloarene and Pd(0). Reductive elimination of aryl chlorides, bromides, and iodides were observed upon the addition of P(t-Bu)3 to Pd[P(t-Bu)3](Ar)(X) (X = Cl, Br, I). Conditions to observe the equilibrium between reductive elimination and oxidative addition were established with five haloarenes. Reductive elimination of aryl chloride was most favored thermodynamically, and elimination of aryl iodide was the least favored. However, reductive elimination from the aryl chloride complex was the slowest, and reductive elimination from the aryl bromide complex was the fastest. These data show that the electronic properties of the halide, not the thermodynamic driving force for the addition of elimination reaction, control the rates for addition and elimination of haloarenes. Mechanistic data suggest that reversible reductive elimination of aryl bromide to form Pd[P(t-Bu)3] and free aryl bromide is followed by rate-limiting coordination of P(t-Bu)3 to form Pd[P(t-Bu)3]2.     

Reaction of molecular oxygen with a Pd(II)-hydride to produce a Pd(II)-hydroperoxide: experimental evidence for an HX-reductive-elimination pathway

The reaction of molecular oxygen with a Pd(II)-hydride species to form a Pd(II)-hydroperoxide represents one of the proposed catalyst reoxidation pathways in Pd-catalyzed aerobic oxidation reactions, but well-defined examples of this reaction were discovered only recently. Here, we present a mechanistic study of the reaction of O2 with trans-(IMes) 2Pd(H)(OBz), 1 (IMes = 1,3-dimesitylimidazol-2-ylidene), which yields trans-(IMes) 2Pd(OOH)(OBz), 2. The reaction was monitored by (1)H NMR spectroscopy in benzene-d6, and kinetic studies reveal a two-term rate law, rate = k1[1] + k2[1][BzOH], and a small deuterium kinetic isotope effect, k(Pd-H)/k(Pd-D) = 1.3(1). The rate is independent of the oxygen pressure. The data support a stepwise mechanism for the conversion of 1 into 2 consisting of rate-limiting reductive elimination of BzOH from 1 followed by rapid reaction of molecular oxygen with (IMes) 2Pd(0) and protonolysis of a Pd-O bond of the eta(2)-peroxo complex (IMes) 2Pd(O2). Benzoic acid and other protic additives (H2O, ArOH) catalyze the oxygenation reaction, probably by stabilizing the transition state for reductive elimination of BzOH from 1. This study provides the first experimental validation of the mechanism traditionally proposed for aerobic oxidation of Pd-hydride species.     

Studies of reductive elimination reactions to form carbon-oxygen bonds from Pt(IV) complexes.

The platinum(IV) complexes fac-L(2)PtMe(3)(OR) (L(2) = bis(diphenylphosphino)ethane, o-bis(diphenylphosphino)benzene, R = carboxyl, aryl; L = PMe(3), R = aryl) undergo reductive elimination reactions to form carbon-oxygen bonds and/or carbon-carbon bonds. The carbon-oxygen reductive elimination reaction produces either methyl esters or methyl aryl ethers (anisoles) and L(2)PtMe(2), while the carbon-carbon reductive elimination reaction affords ethane and L(2)PtMe(OR). Choice of reaction conditions allows the selection of either type of coupling over the other. A detailed mechanistic study of the reductive elimination reactions supports dissociation of the OR(-) ligand as the initial step for the C-O bond formation reaction. This is followed by a nucleophilic attack of OR(-) upon a methyl group bound to the Pt(IV) cation to produce the products MeOR and L(2)PtMe(2). C-C reductive elimination proceeds from L(2)PtMe(3)(OR) by initial L (L = PMe(3)) or OR(-) (L(2) = dppe, dppbz) dissociation, followed by C-C coupling from the resulting five-coordinate intermediate. Our studies demonstrate that both C-C and C-O reductive elimination reactions from Pt(IV) are more facile in polar solvents, in the presence of Lewis acids, and for OR(-) groups that contain electron withdrawing substituents.     

Oxidative Addition of 2‐Halogenoazoles—Direct Synthesis of Palladium(II) Complexes Bearing Protic NH,NH‐Functionalized NHC Ligands

The chemistry of N‐heterocyclic carbenes (NHCs) is dominated by N,N′‐dialkylated or ‐diarylated derivatives. Such NHC ligands are normally obtained by C2‐deprotonation of azolium cations or by reductive elimination from azol‐2‐thiones. A simple one‐step procedure is described that leads to complexes with NH,NH‐functionalized NHC ligands by the oxidative addition of 2‐halogenoazoles to complexes of zero‐valent transition metals.     

Thione complexes of Rh(I): a first comparison with the bonding and catalytic activity of related carbene and imine compounds

Heterocyclic mono(thione), trans-bis(thione), cis-bis(thione), trans-(carbene-thione), cis-(carbene-thione), trans-(phosphine-thione) and mono(imine) complexes of rhodium(I) have been prepared and fully characterised. Chloro(eta(4)-1,5-cyclooctadiene)(L)rhodium(I)(1a, L = 1,3-diisopropyl-4,5-dimethyl-2,3-dihydro-1H-imidazol-2-thione; 1b L = 1,3,4,5-tetramethyl-2,3-dihydro-1H-imidazol-2-thione) appear as isomers at room temperature due to slow coordination exchange on the S-donor atom. In the three structures determined, the substituent on the sulfur appears syn to Cl. Hindered rotation about the Rh-carbene bond is revealed in the NMR spectra of seven new complexes with isopropyl substituents on the heterocyclic carbene ligands. The trans influence of the thione ligands is smaller than that of carbenes but larger than that shown by imines and chloride. Thione complexes are better catalyst precursors than the carbene complexes for the hydroformylation of 1-hexene under the chosen reaction conditions: 80 degrees C, 8 MPa CO-H2(1:1), 16 h, 1:1000 catalyst to 1-hexene ratio.     

Trans influence on the rate of reductive elimination. Reductive elimination of amines from isomeric arylpalladium amides with unsymmetrical coordination spheres

To determine the trans effect on the rates of reductive eliminations from arylpalladium(II) amido complexes, the reactions of arylpalladium amido complexes bearing symmetrical and unsymmetrical DPPF (DPPF = bis(diphenylphosphino)ferrocene) derivatives were studied. THF solutions of LPd(Ar)(NMeAr') (L = DPPF, DPPF-OMe, DPPF-CF3, DPPF-OMe,Ph, DPPF-Ph,CF3, and DPPF-OMe,CF3; Ar = C6H4-4-CF3; Ar' = C6H4-4-CH3, Ph, and C6H4-4-OMe) underwent C-N bond forming reductive elimination at -15 C to form the corresponding N-methyldiarylamine in high yield. Complexes ligated by symmetrical DPPF derivatives with electron-withdrawing substituents on the DPPF aryl groups underwent reductive elimination faster than complexes ligated by symmetrical DPPF derivatives with electron-donating substituents on the ligand aryl groups. Studies of arylpalladium amido complexes containing unsymmetrical DPPF ligands revealed several trends. First, the complex with the weaker donor trans to nitrogen and the stronger donor trans to the palladium-bound aryl group underwent reductive elimination faster than the regioisomeric complex with the stronger donor trans to nitrogen and the weaker donor trans to the palladium-bound aryl group. Second, the effect of varying the substituents on the phosphorus donor trans to the nitrogen was larger than the effect of varying the substituents on the phosphorus donor trans to the palladium-bound aryl group. Third, the difference in rate between the isomeric arylpalladium amido complexes was similar in magnitude to the differences in rates resulting from conventional variation of substituents on the symmetric phosphine ligands. This result suggests that the geometry of the complex is equal in importance to the donating ability of the dative ligands. The ratio of the differences in rates of reaction of the isomeric complexes was similar to the relative populations of the two geometric isomers. This result and consideration of transition state geometries suggest that the reaction rates are controlled more by substituent effects on ground state stability than on transition state energies. In addition, variation of the aryl group at the amido nitrogen showed systematically that complexes with more electron-donating groups at nitrogen undergo faster reductive elimination than those with less electron-donating groups at nitrogen.