NMR-STUDY OF THE DYNAMIC BEHAVIOR OF [(2-PROPYNYLBORNYL)MO-2(CO)(4)CP(2)](BF4-)-B-- NONFLUXIONAL MOLYBDENUM COBALT CLUSTERS AS THE KEY TO UNDERSTANDING THE MECHANISM OF THE FORMATION OF METAL-STABILIZED CATIONS( )

Treatment of (2-propynylborneol)Co-2(CO)(6) with [(CpMo(CO)(3)](-) yie lds (2-propynylborneol)CoMo(CO)(5)Cp as a mixture of diastereomers, 4a and 4b, which can be separated and individually protonated. The resul ting cations [(2-propynylbornyl)CoMo(CO)(5)Cp](+), 5a and 5b, are non- fluxional. In contrast, the variable-temperature H-1 and C-13 NMR data on [(2-propynylbornyl)Mo-2(CO)(4)Cp(2)](+), 1, reveal two different p rocesses with barriers of 13 and 18 kcal mol(-1), respectively. These observations, in conjunction with numerous other literature results, a re used to show that the diastereomer ratios found for metal-stabilize d cationic clusters can be directly correlated to the ionization proce ss itself. It is proposed that, in all cases, elimination of water is anchimerically assisted by the metal and proceeds through an anti-peri planar transition state.