ALPHA-HYDROGEN, BETA-HYDROGEN AND DELTA-HYDROGEN ABSTRACTION IN THE THERMOLYSIS OF PARAMAGNETIC VANADIUM(III) DIALKYL COMPLEXES

Electron deficient paramagnetic vanadium(III) dialkyls CpV(CH2CMe2R)2(PMe3) (14 electron, R = Me (2), Ph (3)) and CpV[CH(SiMe3)2]2 (12 electron, 4) have been synthesized. At ambient temperature 2 decomposes through a-hydrogen abstraction to produce, in the presence of dmpe (1,2-bis(dimethylphosphino)ethane), the first vanadium alkylidene CpV(CHCMea)dmpe (6), which has been structurally characterized. In contrast, 3 decomposes in the presence of excess PMe3 through orthometalation of the aryl substituent to give the metallacycle complex CpV(sigma2-CH2CMe2C6H4)(PMe3)2 (7). In the absence of excess PMe3 the (mu-alkyl)2mu-aryl)2 dimer [CpV(mu2-CH2CMe2C6H4)]2(8)isformed, with a short(2.313(2)angstrom)metal-metal distance. Reaction of CpV(Me)Cl(PMe3)2 (9) with n-BuLi produces the 1-butene complex CpV(eta2-CH2=HEt)-(PMe3)2 (10) through beta-hydrogen abstraction and reductive elimination. Reactivity of the alkylidene complex 6 includes the formation of the first imido complex of trivalent vanadium, CpV[=NC(CMe3)=C(CMe3)H](dmpe) (12), with V=N = 1.707(2) angstrom and a Z-configuration around the C=C bond, in the reaction with t-BuCN. Crystallographic data for 6: P2(1)/a, a = 13.699(2) angstrom, b = 8.966(1) angstrom, c = 15.386(2) angstrom, beta = 101.87(1)-degrees, Z = 4. For 7: P1BAR, a = 9.671(2) angstrom, b = 14.261(4) angstrom, c = 8.528(2) angstrom, a = 94.89(2)-degrees, beta = 100.55(2)-degrees, gamma = 77.78(2)-degrees, Z = 2. For 8: P2(1)/c, a = 9.812(9) angstrom, b = 14.019(10) angstrom, c = 17.407(10) angstrom, beta = 96.76(6)-degrees, Z = 4. For 12: P1BAR, a = 9.147(1) angstrom, b = 11.005(1) angstrom, c = 13.489(1) angstrom, alpha = 71.95(1)-degrees, beta = 89.70(1)-degrees, gamma = 69.56(1)-degrees, Z = 2.