Rh4(CO)12-Catalyzed Hydroformylation of Cyclopentene Promoted with HMn(CO)5. Another Example of Rh4(CO)12/HMn(CO)5 Bimetallic Catalytic Binuclear Elimination

Abstract

A detailed in situ high-pressure FTIR spectroscopic study was performed to investigate the bimetallic origins of catalytic synergism in homogeneous catalysis. The reaction chosen was the homogeneous catalyzed hydroformylation of cyclopentene to cyclopentanecarboxaldehyde, starting with unmodified rhodium and manganese carbonyls as catalyst precursors in n-hexane as solvent. The spectra were analyzed by an advanced signal processing and statistical technique. Only four organometallic spectra could be found. These were RCORh(CO)4, Rh4(CO)12, HMn(CO)5, and Mn2(CO)10. A very significant increase in aldehyde formation was observed in the experiments when both rhodium carbonyl and manganese carbonyl complexes were used simultaneously. The kinetics of product formation shows a distinct linear−bilinear form in observable organometallics; k1[RCORh(CO)4][H2][CO]-1 + k2[RCORh(CO)4][HMn(CO)5][CO]-1.6. The determined activation parameters for the bilinear term were ΔH⧧ = 47 ± 8 kJ/mol and ΔS⧧ = −88 ± 28 J/(mol K). The...