REACTION OF (ETA-5-C5PH5)2MO2(CO)6 WITH A CHELATING PHOSPHINE LIGAND - GENERATION OF STABLE 17-ELECTRON AND 19-ELECTRON COMPLEXES - DYNAMIC EQUILIBRIUM OF (ETA-5-C5PH5)2MO2(CO)6 AND (ETA-5-C5PH5)MO(CO)3

The synthesis of the (eta-5-C5Ph5)2Mo2(CO)6 complex is described. In solution, the dimer is in equilibrium with 2 17-electron (eta-5-C5Ph5)Mo(CO)3 monomers. The equilibrium constant for the dimer-monomer equilibrium, as determined by electronic absorption spectroscopy, is 8.7 (+/- 5.1) x 10(-5) at 23-degrees-C. (A 1 x 10(-4) M solution of the dimer is thus 40% +/- 15% dissociated.) (eta-5-C5Ph5)2Mo2(CO)6 reacts with L2 (L2 is the chelating phosphine ligand 2,3-bis(diphenylphosphino)maleic anhydride) to form the 19-electron (''18 + delta'') (eta-5-C5Ph5)Mo(CO)2(L2-P,P') and the 17-electron (eta-5-C5Ph5)Mo(CO)2L2-P) complexes. (L2-P,P' indicates two P atoms are coordinated, and L2-P indicates one P atom is coordinated.) Variable-temperature electron spin resonance (ESR) showed a dynamic equilibrium between these 19- and 17-electron complexes with lower temperature favoring the 19-electron complex, and higher temperature the 17-electron complex. The (eta-5-C5Ph5)Mo(CO)2(L2-P,P') complex has two magnetically equivalent P atoms, and the room-temperature ESR spectrum is a 1:2:1 triplet. This spectrum and its temperature-dependent behavior is compared and contrasted with the spectrum of the analogous (eta-5-C5Ph4H)Mo(CO)2(L2-P,P') complex. Infrared, ESR, and electronic spectroscopic data are reported for all of the complexes generated in this study.