Iodide and acetate promotion of oxidative addition of MeI to Rh(I) carbonyl complexes

Axial Bonding Capabilities of Square Planar d8-ML4Complexes. Theoretical Study and Structural Correlations

“…Consistently, it has been found that the binding of a primary ammonium ion to [RhCl 2 (CO) 2 ] - diminishes its nucleophilicity . On the other hand, the fact that the addition of LiI to [RhCl 2 (CO) 2 ] - results in a stronger nucleophilic character of the complex is explained by the competition between the iodide and the Li + ions, with the former being the prevailing effect …”

“…The nucleophilic character of square planar complexes in a number of reactions has been proposed by several authors for compounds of Os(0), Rh(I), , Co(I), − and Pt(II) and the addition of a fifth ligand (iodide, − amines, or acetate 25 ) to square planar complexes has been reported to enhance their nucleophilicity.…”

“…17,18,[30][31][32] If the first step of such reaction is the nucleophilic attack of the metal atom to an alkyl halide, 17,18,22,32 it should be favored by the previous coordination of a Lewis base, as discussed above. A rate-enhancing effect of an added Lewis base on the oxidative addition reaction of alkyl halide over square planar complexes of Rh(I) [23][24][25][26] and Ir(I) 27 has in fact been detected experimentally. Even if pentacoordinate intermediate species have not been detected in most cases, these have been postulated as reaction intermediates because kinetic experiments have shown that pentacoordinate complexes are better nucleophiles than tetracoordinate ones.…”

“…The nucleophilic character of square planar complexes in a number of reactions has been proposed by several authors for compounds of Os(0), 16 Rh-(I), 17,18 Co(I), [19][20][21] and Pt(II). 22 Furthermore, the nucleophilicity of reduced cobaloximes has been found to depend on the nature of the axial ligand, 19 and the addition of a fifth ligand (iodide, [23][24][25][26][27] amines, 24 or acetate 25 ) to square planar complexes has been reported to enhance their nucleophilicity.…”

“…26 On the other hand, the fact that the addition of LiI to [RhCl 2 (CO) 2 ] -results in a stronger nucleophilic character of the complex is explained by the competition between the iodide and the Li + ions, 26 with the former being the prevailing effect. 25 Oxidative addition reactions of the ML 4 complexes result in the coordination of both a donor and an acceptor (eq 3, where AB can be a hydrogen halide or an alkyl halide 28,29 ). In many instances, such reactions have been claimed to proceed through an associative S N 2 mechanism.…”