CP-ASTERISK-MO-HALIDE CHEMISTRY - RAPID HALIDE SCRAMBLING DURING THE CONPROPORTIONATION OF CP(2)ASTERISK-MO2Y4 (Y=CL,BR,I) AND CP-ASTERISK-MOX4 (X=CL, BR) - A PARAMAGNETIC H-1-NMR STUDY

The reaction of the d1 four-legged piano-Stool complexes Cp*MoX4 (X = Cl, Br) with the d3-d3 binuclear complexes Cp2*Mo2Y4 (Y = Cl, Br, I) results in electron transfer and formation of the salts [CP2*Mo2y2]+[CP*MOX4]-. Solutions of [Cp2*Mo2I4]+[CP*MoX4]- (X = Cl, Br) are stable indefinitely in chlorocarbon solvents. However, for the Cp2*Mo2Y4/CP*MoX4 (Y, X = Cl, Br) systems, conversion to the complexes Cp2*Mo2Y6-nXn is observed together with halide exchange reactions between the cation and the anion. The formation of Cp2*Mo2Y6-nXn and the halide exchange are postulated to proceed via a common associative intermediate. The rate of formation of Cp2*Mo2Y6-nXn depends mostly on the Lewis acidity of the cation [Cp2*Mo2Y4]+, which varies in the order [Cp2*Mo2Cl4]+ much greater than [Cp2*Mo2Br4]+ much greater than [CP2*MO2I4]+, and has little dependence on the nature of X.