Jian-Kun Shen

Kinetic studies of CO substitution of metal carbonyls in the presence of O-atom transfer reagents

Abstract 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 zero-order in entering-ligand concentration. This suggests an associative mechanism where a carbonyl C-atom is attacked by the O-atom of the reagent, affording the good leaving group CO2 and generating an active intermediate which readily reacts with the entering ligand to produce the monosubstituted product. Metal carbonyls that have been investigated include the mononuclear compounds M(CO)6 (M = Cr, Mo, W), M(CO)5L, and 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)11 L (M = Fe, Ru, Os), and M4(CO)12 (M = Co, Ir). Most of the studies involve reactions with (CH3)3 NO, but other O-atom transfer reagents studied include C6H5IO, other amine oxides, pyridine oxides, (p-CH3OC6H4)2EO (E = Se, Te), (C6H5)3EO (E = P, As, Sb), and (C6H5)SO. Various factors relating to the metal carbonyls and to the O-atom transfer reagents that effect the rates of CO substitution are discussed.

Effect of substituents on amineN-oxides on the rates of O-atom transfer to metal carbonyls

Abstract The kinetics of CO substitution in Cr(CO)6 to afford Cr(CO)5PPh3 in the presence of different alkyl amine N-oxides, R3NO, and aryl amine N-oxides (p-X-C6H4)(CH3)2NO, are reported. Within each type of amine N-oxide. the rates of reaction increase with increasing basicity of the amine N-oxide. However, even at lower basicities, the aryl reagents react more rapidly than do the alkyl reagents. Competition experiments between py (pyridine) and P(n-Bu) for the coordinatively unsaturated intermediates “M(CO)5” show that the discrimination abilities increase in the order Cr

Kinetics and mechamisms of CO substitution of M4(CO)11L(M = Co, Ir; L = PPh3 PnBu3, P(OMe)3, P(OEt)3) with L in the presence of the Me3NO

Abstract Reported are rates of CO substitution by L of M 4 (CO) 11 L(M = Co, Ir; L = PPh 3 , P n Bu 3 , P(OMe) 3 , P(OEt) 3 ) in the presence of added Me 3 NO. The rate law is the same as that found earlier on such reactions, being first-order in the concentrations of metal carbonyl and of Me 3 NO but zero-order in ligand concentration. The Ir compounds react from 2 to 7 times faster than do the corresponding Co compounds, and for each the rates of reaction with changes in ligand decrease in the order P(OMe) 3 > P(OEt) 3 > P n Bu 3 . The results are compared with earlier studies in the M 3 (CO) 12 and M 3 (CO) 11 L (M = Fe, Ru, Os) clusters, where it was found that the reactivities decrease in the order Fe > Ru > Os. That this order differs from that now reported (Co 4 (CO) 11 L clusters is discussed in terms of the presumed important contribution of CO bridging to the rates of associative reactions in metal carbonyl clusters.

Kinetics and Mechanism of Co Substitution by Phosphites of Co4(CO)12

Abstract The otherwise very fast CO substitution of Co4(CO)12 by P(OMe)3 and P(OEt)3 in aprotic solvents, affording phosphite-monosubstituted products was retarded by the use of CHCI3 as solvent. This made it possible to investigate these reactions by conventional methods. Kinetic data were obtained by following changes in IR spectra during reaction. The rates show predominantly a ligand-dependent pathway, with the usual two-term rate law, rate = (k1 + k2 [P(OR)3])C4(CO)12. It is suggested that the rates are retarded in protonic solvents by decreasing the nucleophilicity of phosphites due to a hydrogen bonding interaction between the H atom of CHCI3 and the O atoms of the ligands.