ALKYLATION AND REDUCTIVE DIMERIZATION OF HALF-SANDWICH IMIDO VANADIUM DICHLORIDES

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 dialkyl complexes but showed extensive reduction of vanadium. Reaction of 1 with AlMe(3) leads to the formation of a mixture of diamagnetic dimeric, imido-bridged complexes (CpV)(2)(mu-N-p-tolyl)(2)MeR (R=Me or Cl), which can be converted to the pure chloro compound [CpV(mu-N-p-tolyl)Cl](2) (4) by reaction with HCl. Dimerization is prevented when the more bulky ArN ligand is used. Alkylation of 4 with MeLi proceeds cleanly to give the methyl compound [CpV(mu-N-p-tolyl)Me](2) (5). The molecular structures of the formally vanadium(IV) complexes 4 and 5 have been obtained, showing a planar cyclovanadazene core with a vanadium-vanadium single bond and V-CI and V-C-Me bond lengths that are characteristic of V(V) compounds. Compound 5 reacts with CO by insertion in the V-C bond, but no reaction is observed with other small unsaturated molecules or Bronsted acids. The V-51 NMR chemical shifts of the new complexes are reported and compared with the chemical shifts of known imido vanadium complexes.