DI- AND POLY-NUCLEAR TRANSITION METAL COMPLEXES AS CATALYSTS FOR THE METAL CARBONYL SUBSTITUTION REACTION. THE ROLE OF SUPPORTED METALS AND METAL OXIDES AS CATALYST PROMOTERS

Article abstract of DOI:10.1016/0022-328X(87)80159-6

Various di- and poly-nuclear transition metal complexes have been investigated as catalysts for the metal carbonyl substitution reaction.The complexes <<(η⁵-C5H4R)Fe(CO)2>2> (R=H, Me, CO2Me, OMe, O(CH2)4OH) and <<(η⁵-C5H5)Ru(CO)2>2> are active catalysts for a range of substitution reactions including the probe reaction t)>+Bu^tNC->t)2>+CO. <<(η⁵-C5Me5)Fe(CO)2>2> is catalytically active only on irradiation with visible light.For <<(η⁵-C5H5)Fe(CO)2>2> and a range of isocyanides RNC (R=Bu^t, C6H5CH2, 2,6-Me2C6H3), catalyst modification by substitution with isocyanide is a major factor influencing the degree of the catalytic effects observed, e.g. <<(η⁵-C5H5)Fe(CO)(CNBu^t)>2> is approximately 35 times as active as <(η⁵-C5H5)2Fe2(CO)3(CNBu^t)> for the t)>->t)2> conversion.Mechanistic studies on this system suggest that the catalytic substitution step probably involves a rapid intermolecular attack of isonitrile, possibly on a labile catalyst-substrate radical intermediate such as <<η⁵-C5H5)Fe(CO)2>>^*, or on a reactive radical cation such as ⁺ generated via electron transfer between the substrate and the catalyst.Other transition metal complexes which also catalyze the substitution of CO by isocyanide in (and (M=Cr, Mo, W), , ) include , , (M=Co, Ir) and .These reactions conform to the general mechanistic patterns established for <<(η⁵-C5H5)Fe(CO)2>2>, suggesting a similar mechanism.A range of materials, notably PtO2, PdO and Pd/C, act as promoters for the homogeneous di- and poly-nuclear transition metal catalysts, and can even be used to induce activity in normally inactive dimer and cluster complexes e.g. .This promotion is attributed to at least three possible effects: the removal of catalyst inhibitors, a catalyzed substitution of the homogeneous catalyst partner, and a possible homogeneous-heterogeneous interaction which promotes the formation of catalytic intermediates.