Syntheses and structural and electrochemical characterizations of vanadatricarbadecaboranyl analogues of vanadocene and the structural characterization of the [Li(CH3CN)(2)(+)](6-CH3-nido-5,6,9-C3B7H9-) tricarbadecaboranyl anion

A Single-crystal X-ray determination of the [Li(CH3CN)(2)(+)](6-CH3-nido-5, 6,9-C3B7H9-) salt has shown that the 6-CH3-nido-5,6,9-C3B7H9- tricarbadecab oranyl anion has a nido-cage geometry based on an octadecahedron missing th e unique six-coordinate vertex. The resulting six-membered open face is puc kered, with two of the cage carbons (C6 and C9) occupying the low-coordinat e cage positions above the plane of the four remaining atoms (C5, B7, B8, a nd B10). The Li+ ion is centered over the open face and is solvated by two acetonitrile molecules. The reactions of the 6-CH3-nido-5,6, 9-C3B7H9- anio n with various vanadium halide salts, including VCl4, VCl3, and VBr2, each resulted in the isolation of the same five paramagnetic products (2-6) of c omposition V(CH3-C3B7H9)(2) X-ray crystallographic determinations of 2-5 sh owed that the complexes consist of two octadecahedral VC3B7 fragments shari ng a common vanadium vertex and established their structures as commo-V-(1- V-4'-CH3-2',3',4'-C3B7H9)(1-V-2-CH3-2,3,4-C3B7H9) (2), commo-V-(1-V-5'-CH(3 -)2 ' ,3 " ,5 ' -C3B7H9)(1-V-4-CH3-2,3,4-C3B7H9) (3), commo-V-(1-V-5'-CH3-2 ',3',5'-C3B7H9)(1-V-2-CH3-2,3,4C(3)B(7)H(9)) (4), and commo-V-(1-V-2-CH3-2, 3,4-C3B7H9)(2) (5) These complexes can be considered as tricarbadecaboranyl analogues of vanadocene, (eta (5)-C5H5)(2)V. However, unlike vanadocene, t hese complexes are air- and moisture-stable and have only one unpaired elec tron. The five complexes differ with respect to one another in that they ei ther (1) contain different enantiomeric forms of the CH3-C3B7H9 cages, (2) have a different twist orientation of the two cages, or (3) have the methyl group of the CH3-C3B7H9 canoe located in either the 2 or 4 position of the cage. Subsequent attempts to oxidize the compounds with reagents such as B r-2 and Ag+ were unsuccessful, illustrating the ability of the tricarbadeca boranyl anion to stabilize metals in low oxidation states. Consistent with this, both the electrochemical oxidation and the reduction of 2 were much m ore positive than those of the same oxidation state changes in vanadocene. The one-electron reduction of 2 is a remarkable 2.9 V positive of that of C p2V.