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)(eta (C5H5)-C-5)(2)(C drop CR)] (R = Me (1), SiMe3 (2), Bu-t (3), CH2Ph (4)), [Nb(=NC6H4Me-4)(eta (5)-C5H5)(2)(C drop CR)] (R = SiMe3 (5), Bu-t (6)), [Nb(=NBut)(eta (5)-C5H4SiMe3)(2)(C drop CR)(3) (R = SiMe3 (7), Bu-t (8)), [Nb(=NPh)(eta (5)-C5H4SiMe3)(2)(C drop CR)(3) (R = Ph (9), Bu-t (10)), [Nb(=NC6H4Me-4)(eta (5)-C5H4SiMe3)(2)(C drop CR)] (R = SiMe3 (11), Bu-t (12)), [Nb(=NC6H4OMe-4)(eta (5)-C5H4SiMe3)(2)(C drop CR)] (R = SiMe3 (13), Bu-t (14)), and [Nb(=NBut)(Me2Si(eta (5)-C5H4)(2))(C-CR)] (R = SiMe3 (15), Bu-t (16)). The synthetic path involved the reaction of either BrMg(C drop CR) or Mg(C drop CR)(2) with the metallocene imido complex Nb(=NR ')(Cp)(2)Cl, Cp = eta (5)-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)(eta (5)-C5H5)(2)(C drop CSiMe3)](+) (17) and [Nb(NHPh)(eta (5)-C5H4SiMe3)(2)(C drop CPh)](+) (18), respectively.