Alkylation and reductive dimerization of half-sandwich imido vanadium dichlorides

Article abstract of DOI:10.1016/0022-328X(95)00113-5

The vanadium imido complex ArNVCl3 (2) (Ar=2,6-C6H3-(i-Pr)2) can be converted to the half-sandwich imido vanadium complex CpV(NAr)Cl2 (3) by reaction with CpSiMe3.Reaction of 3 and of CpV(N-p-tolyl)Cl2 (1) with alkylating reagents did not allow the isolation of the pure dialkyl complexes but showed extensive reduction of vanadium.Reaction of 1 with AlMe3 leads to the formation of a mixture of diamagnetic dimeric, imido-bridged complexes (CpV)2(μ-N-p-tolyl)2 MeR (R=Me or Cl), which canbbe converted to the pure chloro compound 2 (4) reaction with HCl.Dimerization is preveted when the more bulky ArN ligand is used.Alkylation of 4 with MeLi proceeds cleanly to give the methyl compound 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-Cl 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 Broensted acids.The 51V NMR chemical shifts of the new complexes are reported and compared with the chemical shifts of known imido vanadium complexes.Keywords: Vanadium; Half-sandwich complexes; Imido complexes; Alkylation; Reduction