KINETICS AND MECHANISMS OF CO SUBSTITUTION OF (ETA-5-IND)RE(CO)3 (IND = INDENYL) WITH PHOSPHINES AND PHOSPHITES - THE INDENYL LIGAND EFFECT ON RELATED TRINDENYLMETAL CARBONYLS

Kinetic studies were performed for the reactions of (eta(5)-Ind)Re(CO)3 with phosphines and phosphites. Second-order rate laws were observed, which are first-order in metal complex and first-order in phosphine concentrations. Depending on reaction conditions, i.e., temperature and ligand concentration, two different types of products, (eta(1)-Ind)Re(CO)3L2 and (eta(5)-Ind)Re(CO)2L, were observed. The eta(1)-product changed slowly to eta(5)-product at high temperature. A reaction mechanism which requires a common intermediate for the formation of eta(1)- and eta(5)-products is proposed, which allows for simulated spectral changes in accord with what is observed experimentally. Also the reactivity of related trindenyl analogues were compared with indenyl- and cyclopentadienylmetal carbonyl complexes. The rates of reaction follow the order (eta(5)-Ind)M(CO)n > (eta(5)-Td)[M(CO)n]3 > (eta(5)-Cp)Mo(CO)n, where M = Rh (n = 2) and Re and Mn (n = 3). For a given cyclic ligand, the rates decrease in the order Rh > Re > Mn; for changes in the number of Re(CO)3 groups on a trindenyl ligand, the rates decrease in the order (eta(5)-TdH2)Re(CO)3 > (eta(5)-TdH)[Re(CO)3]2 > (eta(5)-Td)[Re(CO)3]3. These relative rates of reaction are discussed in terms of the coordination number of the metal, its size, and the extent of pi-delocalization of electron density in the transition state for reaction.