ansa-Niobocene Complexes:  Synthesis and Characterization of Novel Complexes [Me₂Si(η⁵-C₅H₄)₂]NbCl₂and [Me₂Si(η⁵-C₅H₄)₂]NbCl(RC⋮CR) (R = Me, Ph). X-ray Crystal Structure of [Me₂Si(η⁵-C₅H₄)₂]NbCl(MeC⋮CMe)

Abstract

The ansa-niobocene(IV) dichloride complex [Me2Si(η5-C5H4)2]NbCl2 (1) has been prepared by the reaction of NbCl4(THF)2 and [Me2Si(C5H4)2]Tl2 in THF. The reduction of 1 by sodium amalgam in the presence of an alkyne (2-butyne or diphenylacetylene) yielded the ansa-niobocene(III) monochloride alkyne complexes [Me2Si(η5-C5H4)2]NbCl(RC⋮CR) (R = Me (2), Ph (3)). Compounds 1−3 were characterized by IR, ESR, and NMR spectroscopy. In addition, the structure of 2 was determined by single-crystal X-ray diffraction.

Mono(cyclopentadienyl) and ansa-bis(cyclopentadienyl)imido derivatives of Group 5 and 6 transition metals; crystal structures of [M{(η-C5H4)CMe2(η-C5H4)}(NR)X] (M = Nb, R = SiMe3, X = Cl; R = But, X = Cl, Br or I; M = Ta, R = But, X = Cl) †

“…We and other workers have noted that lower yields are obtained when the dilithium salt is employed in this system. 5, 10 The crystal structure of compound 4 has been determined and its molecular structure, with atomic numbering scheme, is shown in Fig. 1.…”

New Group 4 Metallocene and Niobocene Complexes Containing Phosphane-Functionalizedansa-Ligands

“…As an extension of our previous work related to ansa ‐metallocene complexes of zirconium and niobium4,5d,8,9 we now report the synthesis and characterization of the first phosphane‐substituted ansa ‐cyclopentadienyl ligands and their incorporation in new metallocene complexes of the group 4 and 5 elements.…”

“…In 1996 we reported the first ansa ‐niobocene complexes, in which both cyclopentadienyl rings are bound only in an η 5 mode to niobium,4 and since then several complexes of this type have been described 5…”

Sandwich and Half‐Sandwich (Imido)niobium Complexes

“…In 1996 we reported the first ansa-niobocene complexes in which both cyclopentadienyl rings are bound only in an η 5 -mode to the niobium atom [64] and following from this work we prepared the ansa-(imido)niobocene complex [Nb(ϭ NtBu){Me 2 Si(η 5 -C 5 H 4 ) 2 }Cl] (51) [Equation (15)]. [58] The 1 H NMR spectrum reveals the presence of a system similar to that obtained for its non-ansa analogues.…”