KINETIC-STUDIES OF CO SUBSTITUTION OF METAL-CARBONYLS IN THE PRESENCEOF O-ATOM TRANSFER REAGENTS

Kinetic studies of CO substitution of metal carbonyls in the presence of O-atom transfer reagents show the reaction rates are first-order in metal carbonyl and in O-atom transfer reagent concentrations, but zer o-order in entering-ligand concentration. This suggests an associative mechanism where a carbonyl C-atom is attacked by the O-atom of the re agent, affording the good leaving group CO2 and generating an active i ntermediate which readily reacts with the entering ligand to produce t he monosubstituted product. Metal carbonyls that have been investigate d include the mononuclear compounds M(CO)6 (M = Cr, Mo, W), M(CO)5L, a nd M(CO)5 (M = Fe, Ru, Os) as well as the cluster compounds (M3(CO)12 (M = Fe, Ru, Os), M2(CO)10 (M = Mn, Re), M3(CO)11L(M = Fe, Ru, Os), an d M4(CO)12(M = Co, Ir). Most of the studies involve reactions with (CH 3)3NO, but other O-atom transfer reagents studied include C6H5IO, othe r amine oxides, pyridine oxides, (p-CH3OC6H4)2EO (E = Se, Te), (C6H5)3 EO (E = P, As, Sb), and (C6H5)2SO. Various factors relating to the met al carbonyls and to the O-atom transfer reagents that effect the rates of CO substitution are discussed.