METAL-METAL BONDING IN PENTAMETHYLCYCLOPENTADIENYLMOLYBDENUM(IV) DINUCLEAR COMPOUNDS - CHLORIDE ABSTRACTION FROM NONBONDED CP-ASTERISK-2MO2CL6 TO AFFORD BONDED [CP-ASTERISK-2MO2CL5]

Chloride abstraction from Cp2Mo2Cl6 (Cp*=eta(5)-C(5)Me(5)) is accompl ished by interaction with the Lewis acid AlCl3 to afford the structura lly characterized salt [Cp2Mo2Cl5](+)[AlCl4](-). Crystal data: tricli nic, space group P (1) over bar, a=8.3903(13), b=15.797(3), c=24.036(2 ) Angstrom, alpha=86.766(11), beta=80.916(10), gamma=81.616(14)degrees , V=3110.5(8) Angstrom(3), D-c=1.726 Mg m(-3), mu(Mo K alpha)=1.618 mm (-1), R=0.0637. The structure exhibits two four-legged piano stools jo ined by three bridging Cl atoms. The Mo-Mo distance of 2.866(2) Angstr om is significantly longer than all other reported bonded Mo(IV)-Mo(IV ) distances and longer than the single bond (sigma(2) delta(2)delta(2 )) distance in the related Mo(III) complexes [(ring)MoCl2](2) (ring=su bstitute cyclopentadienyl ring). The reasons for this lengthening are analyzed and discussed on the basis of structural data and Fenske-Hall MO calculations. [Cp2Mo2Cl5](+) reacts rapidly with Cl- to afford [C pMoCl4](-) and exhibits a reversible one-electron oxidation to a neut ral Cp2Mo2Cl5 species at -0.13 V versus ferrocene/ferricinium. The no n-existence of a metal-metal bonded isomeric form of the Cp2Mo2Cl5 pa rent compound is also discussed.