Insertion of lsocyanides into niobium– and tantalum–halogen bonds

Abstract

Isocyanides RNC (R = Me or Bu^t) insert into the metal–halogen bond of niobium and tantalum pentahalides or tantalum tribromide oxide to give the complexes [MX₄{CX(NR)}(CNR)](A : M = Nb or Ta; X = Cl or Br; R = Me or Bu^t), [TaBr₂{CBr(NMe)}₃(CNMe)], and [TaBr₂O{CBr(NMe)}(CNMe)]. The complex [NbCl₄{CCl(NMe)}(CNMe)] gives the further insertion products [NbCl₃{CCl(NMe)}₂L¹] on treatment with L¹= MeNC or PPh₃, but treatment of [MX₄{CX(NBu^t)}(CNBu^t)] with L²= PPh₃, PMe₂Ph, or PMePh₂, or L³= Ph₂PCH₂CH₂PPh₂ or cis-Ph₂PCH = CHPPh₂ displaces Bu^tNC to give [MX₄{CX(NBu^t)}L²](M = Ta, X = Cl or Br) and [MX₃{CX(NBu^t)}L³]X (M = Ta, X = Br; M = Nb, X = Cl). The complex [TaBr₃{CBr(NMe)}(dppe)]Br (dppe = Ph₂PCH₂CH₂PPh₂) has also been prepared from [TaBr₅(dppe)]. Reaction of [NbCl₃{CCl(NMe)}₂(CNMe)] with Li[AlH₄] gives dimethylamine but no higher amines. Hydrogen or deuterium chloride reacts with [NbCl₄{CCl(NMe)}(CNMe)] to give a product with N–H or N–D bonds which could not be purified. The physical properties of these complexes are reported and their structures and possible mechanism of formation are discussed.