Oxidative Addition Of Methyl Iodide Research Articles

Synthesis, structure and reactivity of cis-[PtL 2(1-alkenyl) 2] complexes

The synthesis and characterization of several new bis(1-alkenyl)platinum(II) complexes have been carried out. The structure of cis-[Pt(dppp)((CH 2) 6CH CH 2) 2] has been determined by X-ray crystallography. The stability and reactivity of the compounds, cis-[PtL 2((CH 2) n CH CH 2) 2] ( n = 3 or 4 and L 2 = 1,3-bis(diphenylphosphino)propane (dppp), 1,2-bis(diphenylphosphino)ethane (dppe), L = PPh 3) is strongly dependent on the nature of ligand systems. It is found that the insertion of carbon monoxide into the metal–carbon bonds of the platinum alkenyl complexes is possible. Other reactions including transmetalation, intermolecular alkenyl migrations, oxidative addition of methyl iodide are described and the thermal decomposition of the bis(alkenyl) complexes are also reported.

A kinetic study of the oxidative addition of methyl iodide to [Rh((C 4H 3S)COCHCOCF 3)(CO)(PPh 3)] utilizing UV/vis and IR spectrophotometry and 1H, 19F and 31P NMR spectroscopy. Synthesis of [Rh((C 4H 3S)COCHCOCF 3)(CO)(PPh 3)(CH 3)(I)

IR and UV/vis spectrophotometric and 1H, 19F and 31P NMR spectroscopic techniques have been utilized to study the kinetics of oxidative addition of CH 3I to [Rh(tta)(CO)(PPh 3)] with Htta = (C 4H 3S)COCH 2COCF 3 = 2-thenoyltrifluoroacetone. Two definite reactions steps involving isomers of at least two distinctly different classes of Rh III-alkyl and a Rh III-acyl species were observed. NMR spectroscopy revealed that each reaction product exists in solution of two observable isomers in equilibrium with each other. The observed rate of oxidative addition of iodomethane to the different [Rh(tta)(CO)(PPh 3)] isomers was the same, but the rate of formation of the two isomers of the final Rh III-alkyl2 reaction product, [Rh(tta)(CO)(CH 3)(PPh 3)(I)], differs. Results provided the following reaction mechanism. [Display omitted] The equilibrium K 2 was fast enough to be maintained during the [Rh(tta)(CO)(PPh 3)] depletion in the first reaction step and during the Rh III-alkyl2 formation in the second reaction step. The molecular formulae of all the Rh III-alkyl and Rh III-acyl species are [Rh(tta)(CH 3)(CO)(PPh 3)(I)] and [Rh(tta)(COCH 3)(PPh 3)(I)], respectively, but the geometries are different due to different co-ordination positions of the ligands. The final Rh III-alkyl2 reaction product is isolated and characterized.

Optically active rhodium complexes with indenyl-linked phosphane ligands

The optically active indenyl-linked phosphane ligands ( S)-[2-(3 H-inden-1-yl)-1-phenylethyl]diphenylphosphane ( L 1 ) and ( S)-[2-(4,7-dimethyl-3 H-inden-1-yl)-1-phenyl-ethyl]diphenylphosphane ( L 2 ) were synthesized in three steps from ( R)-1-phenylethane-1,2-diol in excellent yields. Their lithium salts reacted with [Rh(μ-Cl)(η 2-CH 2CH 2) 2] 2 at −78 °C in THF affording the planar chiral complexes ( S, R pl + S pl )-[Rh(η 5-indenyl-CH 2CH(Ph)PPh 2- kP)(η 2-CH 2CH 2)] and ( S, R pl + S pl )-[Rh(η 5-4,7-dimethylindenyl-CH 2CH(Ph)PPh 2- kP)(η 2-CH 2CH 2)] as 61:39 and 15:85 mixtures of diastereomers. The complexes were isolated in optically pure form by column chromatography. The stereochemical configuration of one of the diastereomers was determined by X-ray crystallography. The complexation of L 2 was studied in different solvents and with several Rh precursors and diastereomeric excesses up to 76% were achieved. The ability of the chiral ligands to control the stereochemistry at the metal center was tested by oxidative addition of methyl iodide. Diastereomeric excesses greater than 98% were observed.

1,8-Bis(imidazolin-2-yliden-1-yl)carbazolide (bimca): A New CNC Pincer-Type Ligand with Strong Electron-Donating Properties. Facile Oxidative Addition of Methyl Iodide to Rh(bimca)(CO)

The synthesis of a new CNC pincer-type ligand based on an N-heterocyclic carbene substituted carbazole is presented. The resulting 3,6-di-tert-butyl-1,8-bis(3-methylimidazolin-2-yliden-1-yl)carbazolide (bimca) is a monoanionic, meridionally coordinating tridentate ligand that was generated in situ by deprotonation of the imidazolium salt (bimca)·2HI (3a) or (bimca)·2HBF4 (3b) and characterized by NMR spectroscopy as the Li complex 4. The successful transmetalation to rhodium upon reaction with [Rh(CO)2Cl]2 yielded Rh(bimca)(CO) (5). This complex shows a very small wavenumber in the IR spectrum for the ν(CO) band, thus indicating strong σ-donor and weak π-acceptor properties of the bimca ligand. The highly nucleophilic character of the Rh(I) center was proven by the formal oxidative addition of methyl iodide to Rh(bimca)(CO) (5), a reaction that proceeded more quickly than with any other Rh(I) complex reported so far. The complex Rh(bimca)(CH3)I(CO) (6) as well as Rh(bimca)(CO) (5) were characterized by X-...

Highly Diastereoselective Oxidative Addition of Methyl Iodide to a Chiral Square-Planar Complex

Oxidative addition of methyl iodide to the chiral square-planar complex IrI(CO)(duphos) shows a high level of diastereoselectivity. The basis for the diastereoselectivity of the reaction is best explained based on the crystal structure of IrI(CO)(duphos) in which methyl iodide approach across the two faces is differentiated by the chiral ligand.

Hydridodimethylplatinum(IV) Complexes with Bis(pyridine) Ligands: Effect of Chelate Ring Size on Reactivity

The effect of changing the bite angle of the dipyridyl ligand LL on the reactivity of the dimethylplatinum(II) complexes [PtMe2(LL)] has been studied, by comparing complexes with the ligands LL = di-2-pyridylamine (DPA) or di-2-pyridyl ketone (DPK), which form a six-membered chelate ring, to compounds with 2,2‘-bipyridyl derivatives, which form a five-membered chelate ring. The complex [PtMe2(DPA)] undergoes easy oxidative addition of methyl iodide to give the corresponding platinum(IV) complex [PtIMe3(DPA)]. Both [PtMe2(DPA)] and [PtMe2(DPK)] are protonated by acids HX at low temperature to give the hydridodimethylplatinum(IV) complexes [PtHXMe2(NN)] and [PtH(S)Me2(NN)]X (S = solvent), which can exist in two isomeric forms with H trans to X or N. The structure of the complex [PtHClMe2(DPK)] was determined crystallographically. In a solution containing excess CD3OD, extensive hydrogen/deuterium exchange occurs into the methylplatinum groups and methane product at low temperature, indicating very easy reversibility of the exchange between hydridomethylplatinum(IV) and (methane)platinum(II) complexes. The hydridomethylplatinum(IV) complexes reductively eliminate methane at room temperature in solution but have significantly higher thermal stability and undergo more extensive H−D exchange than when NN = 2,2‘-bipyridyl. The reaction of [PtMe2(DPA)] with excess HCl gave [PtCl2(DPA)], and the reaction of [PtMe2(DPK)] with excess CF3SO3H gave the aqua complex [Pt(OH2)2(DPK)](CF3SO3)2 or the binuclear hydroxo complex [Pt2(μ-OH)2(DPK)2](CF3SO3)2, depending on the experimental conditions.

Oxidative Addition of Methyl Iodide to a New Type of Binuclear Platinum(II) Complex: a Kinetic Study

A new organodiplatinum(II) complex cis,cis-[Me2Pt(mu-NN)(mu-dppm)PtMe2] (1), in which NN = phthalazine and dppm = bis(diphenylphosphino)methane, is synthesized by the reaction of cis,cis-[Me2Pt(mu-SMe2)(mu-dppm)PtMe2] with 1 equiv of NN. Complex 1 has a 5d(pi)(Pt) --> pi(imine) metal-to-ligand charge-transfer band in the visible region, which was used to easily follow the kinetics of its reaction with MeI. Meanwhile, the complex contains a robust bridging dppm ligand that holds the binuclear integrity during the reaction. A double MeI oxidative addition was observed, as shown by spectrophotometry and confirmed by a low-temperature 31P NMR study. The classical S(N)2 mechanism was suggested for both steps, and the involved intermediates were suggested. Consistent with the proposed mechanism, the rates of the reactions at different temperatures were slower in benzene than in acetone and large negative deltaS values were found in each step. However, some abnormalities were observed in the related rate constants and deltaS values, which were demonstrated to be due to the associative involvement of the polar acetone molecules in the reactions. The rates are almost 6 times slower in the second step as compared to the first step because of the electronic effects transmitted through the ligands and the steric effects.

Revisiting the Methyl Iodide Oxidative Addition to Rhodium Complexes: A DFT Study of the Activation Parameters

Oxidative addition of methyl iodide to rhodium complexes, the first and rate-determining step in the rhodium-catalyzed methanol carbonylation process, has been studied computationally by means of D...

Kinetic study of the oxidative addition of methyl iodide to Vaska’s complex in ionic liquids

Oxidative addition of methyl iodide to Vaska’s complex in the ionic liquids 1-butyl-3-methylimidazolium triflate [C 4mim][OTf], [C 4mim] bis(trifluormethylsulfonyl)imide [Tf 2N], and N-hexylpyridinium [C 6pyr][Tf 2N] occurred cleanly to give the expected Ir(III) oxidative addition product. Pseudo-first order rate constants were determined for the oxidative addition reaction in each solvent ([Vaska’s] = 0.25 mM, [CH 3I] = 37.5 mM). The observed rate constants under these conditions were 5–10 times slower than the rate seen in DMF. At high methyl iodide concentrations (>23 mM), the expected first order dependence on methyl iodide was not observed. In each ionic liquid, there was no change in the reaction rates within experimental error over the methyl iodide concentration range of 23–75 mM. At lower methyl iodide concentration, a decrease in rate was observed in [C 4mim][Tf 2N] with decreasing concentration of methyl iodide.

Oxidative addition to dimethylplatinum (II) compounds containing bulky nitrogen ligands: crystal structures of compounds [PtMe 3I{(Me 2NCH 2CH 2NCH)Ar}] (Ar = phenanthryl or anthryl)

Oxidative addition of methyl iodide to platinum (II) compounds [PtMe 2{(Me 2NCH 2CH 2NCH)Ar}] (Ar = phenanthryl or anthryl) produced the corresponding platinum (IV) compounds. Processes aimed at reducing the steric crowding at the coordination sphere of the platinum (IV) centre such as C–C restricted rotation of the pendant part of the ligand leading to rotamers and isomerisation of the C N moiety have been detected in solution. The obtained platinum (IV) compounds were characterised by elemental analyses, mass spectrometry and NMR spectroscopy. According to the crystallographic characterisation, the anthracene derivative gave an E conformer while a Z conformation was obtained for the phenanthrene derivative. In order to rationalize the experimental results, DFT calculations have been performed.

Oxidative Addition of Methyl Iodide to Dinuclear Gold(I) Amidinate Complex: Schmidbaur’s Breakthrough Reaction Revisited with Amidinates

Abstract Oxidative-addition of methyl iodide, CH3I, to the dinuclear gold amidinate [Au2(o-Me2-form)2] in THF generates a metal-metal bonded Au(II) product, formulated as [Au2(o-Me2-form)2CH3I], in quantitative yield under nitrogen at 0 °C and in absence of light. The product is characterized by 1H NMR, elemental analysis and preliminary X-ray crystallography.

Oxidative addition of methyl iodide to [Rh(CO) 2I] 2: synthesis, structure and reactivity of neutral rhodium acetyl complexes, [Rh(CO)(NCR)(COMe)I 2] 2

Reaction of [Rh(CO) 2I] 2 ( 1) with MeI in nitrile solvents gives the neutral acetyl complexes, [Rh(CO)(NCR)(COMe)I 2] 2 (R=Me, 3a; t Bu, 3b; vinyl, 3c; allyl, 3d). Dimeric, iodide-bridged structures have been confirmed by X-ray crystallography for 3a and 3b. The complexes are centrosymmetric with approximate octahedral geometry about each Rh centre. The iodide bridges are asymmetric, with Rh–(μ-I) trans to acetyl longer than Rh–(μ-I) trans to terminal iodide. In coordinating solvents, 3a forms mononuclear complexes, [Rh(CO)(sol) 2(COMe)I 2] (sol=MeCN, MeOH). Complex 3a reacts with pyridine to give [Rh(CO)(py)(COMe)I 2] 2 and [Rh(CO)(py) 2(COMe)I 2] and with chelating diphosphines to give [Rh(Ph 2P(CH 2) n PPh 2)(COMe)I 2] ( n=2, 3, 4). Addition of MeI to [Ir(CO) 2(NCMe)I] is two orders of magnitude slower than to [Ir(CO) 2I 2] −. A mechanism for the reaction of 1 with MeI in MeCN is proposed, involving initial bridge cleavage by solvent to give [Rh(CO) 2(NCMe)I] and participation of the anion [Rh(CO) 2I 2] − as a reactive intermediate. The possible role of neutral Rh(III) species in the mechanism of Rh-catalysed methanol carbonylation is discussed.

Optically active iridium complexes with cyclopentadienyl-phosphine ligands: synthesis and oxidative addition of methyl iodide

The dimer [Ir(μ-Cl)(C 8H 14) 2] 2 reacts with the ligands ( S)-(C 5H 4CH 2CH(Ph)PPh 2)Li and ( R)-(C 5H 4CH(Cy)CH 2PPh 2)Li to give ( S)-[Ir(η 5-C 5H 4CH 2CH(Ph)PPh 2-κ P)(C 8H 14)] and ( R)-[Ir(η 5-C 5H 4CH(Cy)CH 2PPh 2-κ P)(C 8H 14)], which upon treatment with CH 3I at room temperature afford the cationic iridium(III) compounds ( S, S Ir )-[Ir(η 5-C 5H 4CH 2CH(Ph)PPh 2-κ P)(CH 3)(C 8H 14)][I] as a single diastereomer, and ( R)-[Ir(η 5-C 5H 4CH(Cy)CH 2PPh 2-κ P)(CH 3)(C 8H 14)][I] as a 9:1 mixture of two diastereomers. If the oxidative addition reaction is performed at reflux in methylene chloride, the starting complexes convert to the neutral compounds ( S)-[Ir(η 5-C 5H 4CH 2CH(Ph)PPh 2-κ P)(CH 3)(I)] and ( R)-[Ir(η 5-C 5H 4CH(Cy)CH 2PPh 2-κ P)(CH 3)(I)] as 1.6:1 and 3.3:1 mixtures of diastereoisomers, respectively. Carbonyl iridium complexes are synthesized by reacting [IrCl(CO)(PPh 3) 2] with the ligands to afford ( S)-[Ir(η 5-C 5H 4CH 2CH(Ph)PPh 2-κ P)(CO)] and ( R)-[Ir(η 5-C 5H 4CH(Cy)CH 2PPh 2-κ P)(CO)]. They give upon treatment with CH 3I the cationic species ( S)-[Ir(η 5-C 5H 4CH 2CH(Ph)PPh 2-κ P)(CH 3)(CO)][I] and ( R)-[Ir(η 5-C 5H 4CH(Cy)CH 2PPh 2-κ P)(CH 3)(CO)][I] as 1.6:1 and 3:1 mixture of diastereomers, respectively. No migratory-insertion of the methyl group into the carbonyl–metal bond has been observed even after prolonged heating.

Isolation and structural characterization of an optically active intermediate in the oxidative addition of methyl iodide on a rhodium(I) centre.

The optically pure cationic complex (S,S(Rh))-[Rh(eta5-C(5)H(4)CH(2)CH(Ph)PPh(2)-kappaP)(eta2-CH(2)CH(2))(CH(3))][I] is the first example of a key intermediate in the oxidative addition reaction of methyl iodide on a rhodium(I) centre which has been structurally characterized by X-ray diffraction.

Kinetic Evidence of an Arm-Off Mechanism in Complexes of Hemilabile Hybrid Ligands. Oxidative Addition of Methyl Iodide to the Rhodium(I) Complex [Rh(2,6-bis(benzylthiomethyl)pyridine)(CO)]PF6 via Competitive Pathways

Kinetic experiments of the oxidative addition of methyl iodide to the cationic rhodium(I) carbonyl complex [Rh(L)(CO)]PF6 (1; L = 2,6-bis(benzylthiomethyl)pyridine) forming the observable rhodium(III) methyl species [RhI(L)(CO)Me)]PF6 have been performed by FT-IR. The reaction yields the isolable rhodium acyl complex [RhI(L)(COMe)]PF6. Plots of kobs versus concentration of methyl iodide indicate that the reaction proceeds by two parallel pathways, one which is first order in complex 1 and zero order in MeI (k1) and one which is first order in complex 1 and first order in MeI (k2). The first-order pathway displays scarce dependence on the nature of the solvent (k1 (31 °C): 6.7 × 10-6 s-1, acetone; 1.1 × 10-5 s-1, dichloromethane; 1.7 × 10-5 s-1, acetonitrile), while a larger solvent effect is observed for the second-order pathway (k2 (31 °C): 6.4 × 10-6 M-1 s-1, dichloromethane; 5.9 × 10-5 M-1 s-1, acetone; 1.4 × 10-4 M-1 s-1, acetonitrile), in agreement with the dissociative and associative character of...

Oxidative addition of methyl iodide to dimethylplatinum (II) compounds containing bulky and/or chiral ligands. Crystal structure of compound [PtMe 3I{1-(Me 2NCH 2 CH 2NCH)C 10H 7}

Compound [PtMe 2{1-(Me 2NCH 2CH 2NCH)C 10 H 7}] ( 2a) gave upon reaction with methyl iodide platinum (IV) compound [PtMe 3I{1-(Me 2NCH 2CH 2NCH)C 10H 7}] ( 3a) as a single isomer which was characterised structurally. Upon standing in solution, two isomers of 3a were detected by 1H NMR. New chiral compounds [PtMe 2( N, N ′-chelate)] ( N, N ′=2-(( S)-CHNCH(Me)C 6H 5)C 9H 6N ( 2b), 2-(( R)-CHNCH(Me)C 10H 7)C 5H 4N ( 2c) and 2-(( R)-CHNCH(Me)C 10H 7)C 9H 6N ( 2d)) were obtained from [Pt 2Me 4(μ-SMe 2) 2] and the corresponding diimines. The oxidative addition of methyl iodide to compounds 2b– 2d gave two diastereomers each of compounds [PtMe 3I( N, N ′-chelate] in nearly equal amounts. All new platinum (II) and platinum (IV) compounds were fully characterised.

Oxidative Addition of Methyl Iodide and CO Migratory Insertion in a Cationic Rhodium Complex of a S,N,S Tridentate Ligand

The cationic rhodium(I) carbonyl complex mer-[Rh(L)(CO)]PF6 coordinated by a tridentate S,N,S donor ligand (L = 2,6-bis(benzylthiomethyl)pyridine) reacts with MeI to give the corresponding acetyl derivative [Rh(L)(COMe)I]PF6, by consecutive oxidative addition−migratory insertion reactions via observable methyl−rhodium(III) intermediate complexes. Rate constants and activation parameters have been obtained for both reaction steps in MeCN, and compared with those of complexes coordinated by mono- and bidentate ligands. This is the first report on the organometallic reactivity of a rhodium(I) and carbonyl complex of S,N,S ligands.

DFT-studies of cis- and trans-[Rh(CO) 2X 2] + (X=PH 3, PF 3, PCl 3, PBr 3, PI 3 or P(CH 3) 3) and oxidative addition of CH 3I to them

We have performed B3LYB density functional calculations for oxidative addition of CH 3I to [Rh(CO) 2X 2] + (X=PH 3, PF 3, PCl 3, PBr 3, PI 3 or P(CH 3) 3). This species is similar to the catalyst used in industrially important Monsanto process. Our goal is to see if the catalytic process could be enhanced by modifying the ligands. We have taken a set of phophine ligands and calculated the oxidative addition of methyl iodide to both the cis- and trans-forms of the modified catalysts. In our calculations, we found concerted mechanisms for the oxidative additions studied. Our results show that the activation parameters of the oxidative additions have a clear correlation to the ligand type and ligand size. With PCl 3 and PBr 3, our results show lower activation parameters than for the experimentally observed cis-[Rh(CO) 2I 2] −.

Steric and electronic effects on the reactivity of rh and ir complexes containing P-S, P-P, and P-O ligands. Implications for the effects of chelate ligands in catalysis.

Kinetic studies of the reactions of [M(CO)(L-L)I] [M = Rh, Ir; L-L = Ph(2)PCH(2)P(S)Ph(2) (dppms), Ph(2)PCH(2)CH(2)PPh(2) (dppe), and Ph(2)PCH(2)P(O)Ph(2) (dppmo)] with methyl iodide have been undertaken. All the chelate ligands promote oxidative addition of methyl iodide to the square planar M(I) centers, by factors of between 30 and 50 compared to the respective [M(CO)(2)I(2)](-) complexes, due to their good donor properties. Migratory CO insertion in [Rh(CO)(L-L)I(2)Me] leads to acetyl complexes [Rh(L-L)I(2)(COMe)] for which X-ray crystal structures were obtained for L-L = dppms (3a) and dppe (3b). Against the expectations of simple bonding arguments, methyl migration is faster by a factor of ca. 1500 for [Rh(CO)(dppms)I(2)Me] (2a) than for [Rh(CO)(dppe)I(2)Me] (2b). For M = Ir, alkyl iodide oxidative addition gives stable alkyl complexes [Ir(CO)(L-L)I(2)R]. Migratory insertion (induced at high temperature by CO pressure) was faster for [Ir(CO)(dppms)I(2)Me] (5a) than for its dppe analogue (5b). Reaction of methyl triflate with [Ir(CO)(dppms)I] (4a) yielded the dimer [[Ir(CO)(dppms)(mu-I)Me](2)](2+) (7), which was characterized crystallographically along with 5a and [Ir(CO)(dppms)I(2)Et] (6). Analysis of the X-ray crystal structures showed that the dppms ligand adopts a conformation which creates a sterically crowded pocket around the alkyl ligands of 5a, 6, and 7. It is proposed that this steric strain can be relieved by migratory insertion, to give a five-coordinate acetyl product in which the sterically crowded quadrants flank a vacant coordination site, exemplified by the crystal structure of 3a. Conformational analysis indicates similarity between M(dppms) and M(2)(mu-dppm) chelate structures, which have less flexibility than M(dppe) systems and therefore generate greater steric strain with the "axial" ligands in octahedral complexes. Ab initio calculations suggest an additional electronic contribution to the migratory insertion barrier, whereby a sulfur atom trans to CO stabilizes the transition state compared to systems with phosphorus trans to CO. The results represent a rare example of the quantification of ligand effects on individual steps from catalytic cycles, and are discussed in the context of catalytic methanol carbonylation. Implications for other catalytic reactions utilizing chelating diphosphines (e.g., CO/alkene copolymerization and alkene hydroformylation) are considered.

A mechanistic investigation of oxidative addition of methyl iodide to [Tp*Rh(CO)(L)

Reaction of methyl iodide with square planar [kappa(2)-Tp*Rh(CO)(PMe(3))] 1a (Tp* = HB(3,5-Me(2)pz)(3)) at room temperature affords [kappa(3)-Tp*Rh(CO)(PMe(3))(Me)]I 2a, which was fully characterized by spectroscopy and X-ray crystallography. The pseudooctahedral geometry of cationic 2a, which contains a kappa(3)-coordinated Tp* ligand, indicates a reaction mechanism in which nucleophilic attack by Rh on MeI is accompanied by coordination of the pendant pyrazolyl group. In solution 2a transforms slowly into a neutral (acetyl)(iodo) rhodium complex [kappa(3)-Tp*Rh(PMe(3))(COMe)I] 3a, for which an X-ray crystal structure is also reported. Kinetic studies on the reactions of [kappa(2)-Tp*Rh(CO)(L)] (L = PMe(3), PMe(2)Ph, PMePh(2), PPh(3), CO)] with MeI show second-order behavior with large negative activation entropies, consistent with an S(N)2 mechanism. The second-order rate constants correlate well with phosphine basicity. For L = CO, reaction with MeI gives an acetyl complex, [kappa(3)-Tp*Rh(CO)(COMe)I]. The bis(pyrazolyl)borate complexes [kappa(2)-Bp*Rh(CO)(L)] (L = PPh(3), CO) are much less reactive toward MeI than the Tp* analogues, indicating the importance of the third pyrazolyl group and the accessibility of a kappa(3) coordination mode. The results strengthen the evidence in favor of an S(N)2 mechanism for oxidative addition of MeI to square planar d(8) transition metal complexes.