INSITU CLUSTER STABILITY STUDIES EXPLORED BY CYLINDRICAL INTERNAL REFLECTANCE (CIR) SPECTROSCOPY - 1-PENTENE HYDROFORMYLATION USING PHOSPHINE-SUBSTITUTED CO4(CO)8P2(MU-4-PPH)2 CLUSTERS

The stability of diphosphine-substituted cobalt clusters derived from Co4(CO)10(mu-4-PPh)2 has been examined under hydroformylation conditions using Cylindrical Internal Reflectance (CIR) spectroscopy. The monodentate phosphine clusters Co4(CO)8(PPh3)2(mu-4-PPh)2 (1) and Co4(CO)8[P(OMe)3]2(mu-4-PPh)2 (2) undergo rapid P-ligand loss to give the corresponding monosubstituted cluster Co4(CO)9P(mu-4-PPh)2 [where P = PPh3 or P(OMe)3] and Co4(CO)10(mu-4-PPh)2 at 130-degrees-C. No hydroformylation activity was observed at 130-degrees-C. Increasing the reaction temperature to 150-degrees-C affords the parent cluster as the only observable organometallic species. 1-Pentene hydroformylation is observed at 150-degrees-C, and the working catalyst solution shows no evidence for the fragmentation of Co4(CO)10(mu-4-PPh)2 to HCo(CO)4. In contrast, the bidentate-substituted dimethylphosphino(ethane) (dmpe) cluster Co4(CO)8(dmpe)(mu-4-PPh)2 (3) appears to function as a hydroformylation catalyst without phosphine loss or declusterification at 130-degrees-C. The greater stabilization of the dmpe-substituted cluster relative to the monodentate phosphine systems and the absence of cluster fragmentation, which has recently been reported in the hydroformylation of 1-pentene using Co4(CO)10(mu-4-PPh)2, are discussed.