Mesityl- and pentachlorophenyl-nickel(II) complexes with the cyclic alkoxyvinyl group or alkyl(alkoxy)carbene ligand: the relative Bronsted acidity and the rotational barrier about the nickel–carbon bønd

Abstract

Cyclic α-alkoxyvinylnickel(II) complexes of the types trans-[NiRL₂([graphic omitted])] and trans-[NiRL₂-([graphic omitted])](R = C₆H₂Me₃-2,4,6 or C₆Cl₅ and L = PMe₃ or PMe₂Ph) have been prepared from trans-[NiRL₂X](X = Cl or Br) and 2,3-dihydro-5-lithiofuran or 2,3-dihydro-6-lithiopyran. Treatment of these complexes with aqueous perchloric acid gives the corresponding cationic cyclic carbene complexes, trans-[NiRL₂([graphic omitted])][ClO₄] and trans-[NiRL₂([graphic omitted])][ClO₄]. The carbene complexes of trans-Ni(C₆H₂Me₃-2,4,6)L₂ have a lower Brønsted acidity than those of trans-Ni(C₆Cl₅)L₂ and the barriers to rotation of the cyclic alkoxyvinyl groups and the cyclic alkyl(alkoxy)carbene ligands about the Ni–C bond are lower for the former complexes than for the latter. These results are intepreted in terms of the stronger trans influence of the C₆H₂Me₃-2,4,6 group.