Synthesis and chemistry of organoimidovanadium(V) compounds and their role in the formation of vanadium nitrides.

摘要

A series of vanadium(V) compounds of the formula (η5-C ₅Me₅)V(NR)Cl₂ (R = 1-adamantyl, tert-butyl, para-tolyl) have been prepared by the reaction of (η5 -C₅Me₅)V(O)Cl₂ with RNCO or by oxidation of [(η5-C₅Me₅)VCl₂] ₃ with azide. The para-tolylimido compound undergoes chloride metathesis with monoanionic reagents NaOtBu, LiNEt ₂, and Mg(CH₂SiMe₃)₂ to produce mono- and disubstituted products. A discussion of ligand strength in this system using 51V NMR is presented.; Ammonolysis of the dichloro compounds produces the symmetrically-bridged [(η5-C₅Me₅)V(μ-N)Cl]₂, in yields consistent with the basicity of the organoimido ligand. A comparison of this reactivity with that of (η5-C₅Me ₅)V(NSiMe₃)Cl₂ is presented. An X-ray structural study of (η5-C₅Me₅)V(NtBu)Cl ₂ exhibits a 173° V-N-C imido linkage and V-N triple bond.; Synthesis of (η5-tBuC₅H ₄)V(NR)Cl₂ compounds was performed utilizing (t-Bu)C ₅H₄SiMe₃ as the cyclopentadiene reagent with V(NR)Cl ₃. In contrast to the metathesis of V(NR)Cl₃ compounds with Li(tBu)C₅H₄, reduction of the vanadium(V) is not observed. An X-ray crystal structure of (η5- tBuC₅H₄)V(N-ptol)Cl₂ reveals linear V-N-C bonding, and a short N-C bond of 139 pm. This is explained by delocalized bonding, which incorporates the imido carbon atoms as well as nitrogen and vanadium. Details of the structure and valence-bond descriptions are of this compound are presented.; Organoimidotrichlorovanadium(V) compounds bind ligands L₂ (L₂ = 1,2-dimethoxyethane; N,N,N,N-tetramethylethylenediamine) to produce adducts V(NR)Cl₃L₂. The V(NR)Cl₃L ₂ compounds thermally react to form terminal nitrides V(N)Cl₂L ₂ via an unprecedented cleavage of the N-C bond of the organoimido ligand, with reactivity following the order t-butyl > 1-adamantyl > p-tolyl. The downfield 51V NMR shifts of the adducts relative to starting materials is discussed using crystal-field models. X-ray crystal structures of V(NAd)Cl₃(DME) and V(N ptol)Cl₃(TMEDA) are presented, and details of the imido bonding in the adducts are discussed. A comparison with silylimido reactivity in the formation of nitrides in this system is also presented.