Half-sandwich imido complexes of niobium bearing alkyne, benzyne and benzylidene ligands: relatives of the zirconocene family

Reactions of [Nb(C5H5)(NC6H3Pri2-2,6)Cl2] 1a and [Nb(C5Me5)(NC6H3Pri2-2,6)Cl2] 1b with 1 and 2 equivalents of benzylpotassium respectively gave the niobium benzyl derivatives [Nb(C5H5)(NC6H3Pri2-2,6)Cl(CH2Ph)] 2 and [Nb(C5Me5)(NC6H3Pri2-2,6)(CH2Ph)2] 3. Treatment of 3 with trimethylphosphine afforded the benzylidene complex [Nb(C5Me5)(NC6H3Pri2-2,6)(PMe3)(CHPh)] 4. Complex 1a reacted with phenylmagnesium chloride in the presence of PMe3 to give [Nb(C5H5)(NC6H3Pri2-2,6)Ph2(PMe3)] 5 which upon heating at 70 °C in heptane, converts to the η2-benzyne complex [Nb(C5H5)(NC6H3Pri2-2,6)(η2-C6H4)(PMe3)] 6. The niobium(III) complexes [Nb(C5H5)(NC6H4But-2)(PMe3)2] 8a and [Nb(C5Me5)(NC6H3Pri2-2,6)(PMe3)2] 8b were obtained upon magnesium reduction of 1a and 1b respectively in the presence of an excess of PMe3. They were converted into [Nb(C5H5)(NC6H4But-2)(η2-R1CCR2)(PMe3) (R1 = R2 = Ph 9a; R1 = Ph, R2 = H 9b) and [Nb(C5Me5)(NC6H3Pri2-2,6)(η2-PhCCPh)(PMe3)] 9c upon treatment with the appropriate alkyne. The molecular structures of the 2-tert-butylimido complexes [Nb(C5H5)(NC6H4But-2)Cl2] 7 and 9a have been determined.