A SYSTEMATIC-APPROACH IN THE PREPARATION OF COMPOUNDS WITH SIGMA(2)PI(4) VANADIUM-TO-VANADIUM TRIPLE BONDS - SYNTHESIS, REACTIVITY, AND STRUCTURAL CHARACTERIZATION

A high-yield synthetic route (90% isolated yield) has been found for the first paddle-wheel divanadium compound with a sigma2pi4 triple bond, V2(DFM)4 (DFM- = [(p-tolyl)NCHN(p-tolyl)]-). The molecule has been characterized by H-1 NMR, which shows that it is diamagnetic, with a very large diamagnetic anisotropy, and by X-ray crystallography. It is dimorphous, but the molecules are essentially the same in both forms. In the tetragonal form (space group P4/n, a = 13.214(6) angstrom, c = 17.427(5) angstrom, Z = 2, V = 3043(3) angstrom3) V-V = 1.978(2) angstrom and the torsion angle is 5.4(2)-degrees. In the orthorhombic form (space group Pccn, a = 15.555(2) angstrom, b = 16.914(4) angstrom, c = 24.768(i) angstrom, Z = 4, V = 6516(2) angstrom3) V-V = 1.975(4) angstrom and the mean torsion angle is 9.6(6)-degrees. The key step in the synthesis is the use of a THF solution Of VCl3(THF)3 which has been reduced by 1 equiv of NaHBEt3. The compound V(DFM)3 has also been prepared and characterized. It is a tris-chelate compound, strongly distorted from octahedral coordination due to the small bite of the DFM ligands. It forms crystals in space group C2/c with a = 12.693(4) angstrom, b = 33.109(6) angstrom, c = 9.211(3) angstrom, Z = 4, and V = 3863(2) angstrom3.