Cp★Mo-halide chemistry. Rapid halide scrambling during the conproportionation of Cp2★Mo2Y4 (Y  Cl, Br, I) and Cp★MoX4(X  Cl, Br): A paramagnetic 1H 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★Mo2 Y6-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]+å[Cp2★Mo2Br4]+å [Cp2★Mo2I4]+, and has little dependence on the nature of X.