ALKYLATION AND REDUCTIVE DIMERIZATION OF HALF-SANDWICH IMIDO VANADIUMDICHLORIDES

The vanadium imido complex ArNVCl3 (2) (Ar=2,6-C6H3-(Pr-i)(2)) can be converted to the half-sandwich imido vanadium complex CpV(NAr)Cl-2 (3) by reaction with CpSiMe(3). Reaction of 3 and of CpV(N-p-tolyl)Cl-2 ( 1) with alkylating reagents did not allow the isolation of the pure di alkyl complexes but showed extensive reduction of vanadium. Reaction o f 1 with AlMe(3) leads to the formation of a mixture of diamagnetic di meric, imido-bridged complexes (CpV)(2)(mu-N-p-tolyl)(2)MeR (R=Me or C l), which can be converted to the pure chloro compound [CpV(mu-N-p-tol yl)Cl](2) (4) by reaction with HCl. Dimerization is prevented when the more bulky ArN ligand is used. Alkylation of 4 with MeLi proceeds cle anly to give the methyl compound [CpV(mu-N-p-tolyl)Me](2) (5). The mol ecular structures of the formally vanadium(IV) complexes 4 and 5 have been obtained, showing a planar cyclovanadazene core with a vanadium-v anadium single bond and V-CI and V-C-Me bond lengths that are characte ristic of V(V) compounds. Compound 5 reacts with CO by insertion in th e V-C bond, but no reaction is observed with other small unsaturated m olecules or Bronsted acids. The V-51 NMR chemical shifts of the new co mplexes are reported and compared with the chemical shifts of known im ido vanadium complexes.