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

Reactions of [Nb(C5H5)(NC6H3Pr2i-2,6)Cl-2] 1a and [Nb(C5Me5)(NC6H3Pr2i-2,6)Cl-2] 1b with 1 and 2 equivalents of benzylpotassium respectively gave the niobium benzyl derivatives [Nb(C5H5)(NC6H3Pr2i-2,6)Cl(CH2Ph)] 2 and [Nb(C5Me5)(NC6H3Pr2i-2,6)(CH2Ph)(2)] 3. Treatment of 3 with trimethylphosphine afforded the benzylidene complex [Nb(C5Me5)(NC6H3Pr2i-2,6)(PMe3)(=CHPh)] 4. Complex la reacted with phenylmagnesium chloride in the presence of PMe3 to give [Nb(C5H5)(NC6H3Pr2i-2,6)Ph-2(PMe3)] 5 which upon heating al 70 degrees C in heptane, converts to the eta(2)-benzyne complex [Nb(C5H5)(NC6H3Pr2i-2,6)(eta(2)-C6H4)(PMe3)] 6. The niobium(III) complexes [Nb(C5H5)(NC6H4But-2)(PMe3)(2)] 8a and [Nb(C5Me5)(NC6H3Pr2i-2,6)(PMe3)(2)] 8b were obtained upon magnesium reduction of la and Ib respectively in the presence of an excess of PMe3. They were converted into [Nb(C5H5)(NC6H4But-2)(eta(2)-(RC)-C-1=CR2)(PMe3) (R-1 = R-2 = Ph 9a; R-1 = Ph, R-2 = H 9b) and [Nb(C5Me5)(NC6H3Pr2i-2,6)(eta(2)-PhC=CPh)(PMe3)] 9c upon treatment with the appropriate alkyne. The molecular structures of the 2-tert-butylimido complexes [Nb(C5H5)(NC6H4But-2)Cl-2] 7 and 9a have been determined.