Synthesis, Structure, and Reactivity of Niobocene Imido Complexes Containing Alkynyl Ligands. X-ray Crystal Structure of [Nb(NPh)(η5-C5H4SiMe3)2(C⋮CPh)]

The following alkynyl niobocene imido complexes have been prepared: [Nb(NBut)(η5-C5H5)2(C⋮CR)] (R = Me (1), SiMe3 (2), But (3), CH2Ph (4)), [Nb(NC6H4Me-4)(η5-C5H5)2(C⋮CR)] (R = SiMe3 (5), But (6)), [Nb(NBut)(η5-C5H4SiMe3)2(C⋮CR)] (R = SiMe3 (7), But (8)), [Nb(NPh)(η5-C5H4SiMe3)2(C⋮CR)] (R = Ph (9), But (10)), [Nb(NC6H4Me-4)(η5-C5H4SiMe3)2(C⋮CR)] (R = SiMe3 (11), But (12)), [Nb(NC6H4OMe-4)(η5-C5H4SiMe3)2(C⋮CR)] (R = SiMe3 (13), But (14)), and [Nb(NBut){Me2Si(η5-C5H4)2}(C⋮CR)] (R = SiMe3 (15), But (16)). The synthetic path involved the reaction of either BrMg(C⋮CR) or Mg(C⋮CR)2 with the metallocene imido complex Nb(NR')(Cp)2Cl, Cp = η5-cyclopentadienyl. The molecular structure of 9 has been determined by single-crystal X-ray diffraction studies. Protonation of 2 by CF3COOH and 9 by HBF4 gave the cationic amide species [Nb(NHBut)(η5-C5H5)2(C⋮CSiMe3)]+ (17) and [Nb(NHPh)(η5-C5H4SiMe3)2(C⋮CPh)]+ (18), respectively.