Structure and reactivity of mono(cyclopentadienyl)vanadium alkynyl and aryne complexes

Starting from CpVCl(2)(PMe(3))(2) (1) the paramagnetic mono- and bis(phenylethynyl) complexes CpVCl(2-n)(C=CPh)(n)(PMe(3))(2) [n=1 (2), 2 (3)] have been synthesized. Both compounds were characterized by X-ray diffraction and were found to be thermally more stable than other CpV(III) hydrocarbyl complexes. The CpV(III) bis(phenyl) complex CpVPh(2)(PMe(3))(2) (5) decomposes at ambient temperature through beta-hydrogen abstraction to give the first isolated vanadium benzyne complex, CPV(eta(2)-C6H4)(PMe(3))(2) (6). The molecular structure of 6 indicates that this compound can best be described as a high-spin d(2) vanadium(III) benzometallacyclopropene. The cyclopropene character is expressed in the reactivity of 6, showing insertion of unsaturated substrates. Insertion of diphenylacetylene gives CpV(eta(2)-PhC=CPhC(6)H(4))(PMe(3))(2) (7), with a planar vanadaindene structure, whereas terminal alkenes CH2=CRR' (R = H, Me; R' = H, Me) insert regioselectively to give beta-substituted metallaindanes CpV(eta(2)-CH(2)CRR'C6H4)PMe(3) (R and R' = H, 8a; R = H, R' = Me, 8b; R and R' = Me, 8c), which show a low thermal stability in case one of the beta-substituents is a hydrogen. With t-BuCN double insertion followed by rearrangement of the intermediate diazametallacycle gives the isoindolenine-substituted vanadium(III) imido complex CpV[NC(t-Bu)N=C(t-Bu)C6H4](PMe(3))(2) (9). The benzyne complex 6 reacts with dihydrogen to form the known triple-decker CpV(C6H6)VCp through partial hydrogenation of the benzyne ligand.