Oxidative addition of methyl iodide

Oxidative addition of methyl iodide to coordinatively unsaturated, low-oxidation state d and [Pg.321]

Abdou, H.E., Mohamed, A.A. and Fackler, J.P. Jr (2004) Oxidative addition of methyl iodide to dinuclear Gold(I) amidinate complex schmidbaur s breakthrough reaction revisited with amidinates. ZeitschriJiJurNaturforschungB. A Journal of Chemical Sciences, 59, 1480-1482. 

The 16-electron square planar complex is converted into an octahedral 18-electron complex. In Figure 2.14 we have depicted the oxidative addition of methyl iodide to Vaska s complex (L=phosphine). Iodide ions accelerate the reaction and addition of an anion to the metal is the first step in that instance [10]. 

The rate-determining step in this process is the oxidative addition of methyl iodide to 1. Within the operating window of the process the reaction rate is independent of the carbon monoxide pressure and independent of the concentration of methanol. The methyl species 2 formed in reaction (2) cannot be observed under the reaction conditions. The methyl iodide intermediate enables the formation of a methyl rhodium complex methanol is not sufficiently electrophilic to carry out this reaction. As for other nucleophiles, the reaction is much slower with methyl bromide or methyl chloride as the catalyst component. 

Finally, it should be mentioned that there is one important commercial application of the organic halide carbonylation. This is in the rhodium and methyl iodide-catalyzed conversion of methanol and carbon monoxide into acetic acid (25). The mechanism of the reaction appears to involve the oxidative addition of methyl iodide to the rhodium(I) catalyst followed by CO insertion and hydrolysis ... 

The observed rate constants are given in Table V. In order to compare rate constants, values at 18°C were determined from plots of In k vs. T l see Table V). It is apparent that the rate of oxidative addition of methyl iodide to trans- [Rh(PR3)2Cl(CO)] as measured by the values of kx at 18°C increases as the phosphine is altered in the following order ... 

Tertiary phosphine groups with long alkyl chains bound directly to phosphorus or substituted at the para position of triphenylphosphine give rise to a range of interesting and potentially useful complexes. In particular these may be used to prepare polyolefin hydrogenation catalysts based on platinum(II) and palladium(II) complexes that are both more active and more selective towards reduction to monoolefins than previous catalysts based on these systems. The platinum(II) complexes are better than the palladium(II) complexes. Additionally the new phosphines are more effective than triphenylphosphine in promoting the oxidative addition of methyl iodide to trans- [Rh(PR3)2Cl(CO)]. 

Recently, a nonchain radical mechanism has been proposed402 for the oxidative addition of methyl iodide, ethyl iodide, and benzyl bromide to tris(tri-pheny lpho sphine)platinum(O) ... 

Discussion Point DPI Oxidative addition of methyl iodide to Rh(I) complexes can be greatly accelerated using electron donating phosphine ligands. Why has this effect not been taken advantage of in a commercial rhodium-catalyzed methanol carbonylation process, whereas phosphine ligands are employed in hydroformylation ... 

The decomposition of the dimethyl palladium(II) carbene complex with excess methyl iodide is a stepwise process. Although the authors [282] propose oxidative addition of methyl iodide on the palladium centre forming an octahedral palladium(IV) complex, it seems much more likely, with respect to the rarity of palladium(IV) compounds [284,285], that the first step is reductive elimination of an imidazolium salt, a decomposition pathway found to be fairly common after the initial publication of McGuinness et al. [283], Oxidative addition of methyl iodide followed by reductive elimination of ethane would account for the accumulation of iodide ligands on the palladium centre and a Pd(0)/Pd(II) redox couple. However, in the last step, a six coordinate Pd(IV) centre still seems to be necessary (see Figure 3.91). 

The oxidative addition of methyl iodide to an unsaturated cobalt carbonyl according to Equation (27) was proposed by Wender, CO insertion gives an acetyl species (28) which is thought to be hydrogenated by cobalt carbonyl hydride or H to yield acetaldehyde [4]. Numerous examples of the oxidative addition of methyl iodide to transition metal complexes with a electron configuration (e.g. Rh Ir ) ate known from the literature [66, 67]. For the carbonytaiion of methanol, the rate has been found to be the oxidative addition of methyl iodide to rhodium(l) [68]. 

Oxidative addition of methyl iodide to the coordinalively unsaturated cobalt (I) species (1) gives the methyl complex (2) which undergoes CO insertion, probably via methyl migration. Elimination of iodine from the acetyl complex (3) and oxidative addition of hydrogen gives (5). Reductive elimination of the primary product acetaldehyde leads to the unsaturaied complex (6) which oxidatively adds iodine. The catalytic cycle is closed by the elimination of hydrogen iodide from (7), which is consumed by reaction with methanol to give methyl iodide. 

Several further experimental and theoretical studies of the oxidative addition of methyl iodide to Rh(I) complexes have been reported, in part because of its importance in the rhodium-catalyzed carbonylation of methanol (see Carbonylation Processes by Homogeneous Catalysis) to... 

Another reaction of considerable mechanistic interest reported by these workers 165) is the oxidative addition of methyl iodide, allyl chloride, or vinyl chloride to Pd(CO)(PPh3)3 to give the corresponding acyl... 

It would be more interesting and useful if the reaction could be made catalytic. Actually, catalytic decarbonylation reaction was found to be possible by using chlorocarbonylbis(triphenylphosphine) rhodium (XII) (26). This complex is reasonably stable, and more importantly it is four-coordinated and coordinatedly unsaturated, so that it may expand to a six-coordinated complex by the oxidative addition of acyl halides or aldehydes. The oxidative addition of methyl iodide to similar complexes was reported by Heck (5). 

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