THERMODYNAMIC ACTIVATION PARAMETERS IN THE FLUXIONAL BEHAVIOR OF CH2[(ETA-5-C5H4)M(CO)]2(MU-CO), WHERE M = RH OR IR - CRYSTAL-STRUCTURE OF CH2[(ETA-5-C5H4)IR(CO)]2(MU-CO)

The systhesis and molecular structure of CH2[(eta-5-C5H4)Ir(CO)]2(mu-CO) is reported. (CO)-C-13 enrichment of the analogous rhodium complex, CH2[(eta-5-C5H4)Rh(CO)]2(mu-CO), is also reported. Variable-temperature H-1 NMR studies of CH2[(eta-5-C5H4)Ir(CO)]2(mu-CO) and corresponding H-1 and C-13 NMR studies of its rhodium analogue have been carried out. The low-temperature limiting spectra of both compounds have been fully analyzed. Coalescence temperatures for each of the three pairs of exchanging protons for the Rh and Ir complexes have been recorded, and the coalescence temperatures for the carbonyls in the rhodium compound have been recorded. Calculated DELTA-G double-ended-dagger values for the rhodium complex support a mechanism in which the ring and carbonyl motions are coupled. Comparisons of DELTA-G double-ended-dagger values for the rhodium and iridium complexes reveals a substantially higher barrier for the iridium compound than for the rhodium.