Co-ordinatively unsaturated diene complexes of tungsten(II) and their reactions with nucleophilesto give six- and seven-co-ordinate derivatives

Abstract

[{WBr₂(CO)₄}₂] reacts with the ‘dienes’(L′) cyclo-octa-1,5-diene (cod), cyclo-octatetraene (cot), and norbornadiene (bicyclo[2.2.1] hepta-2,5-diene, nbd) to give co-ordinatively unsaturated complexes [WBr₂(CO)₂L′]. These react with Lewis bases L [= CNBu^t, PMe₂Ph, or P(OMe)₃](1 : 1 molar ratio) to give co-ordinatively unsaturated diene complexes [WBr₂(CO)LL′]via intermediate 1 : 1 adducts [WBr₂(CO)₂LL′] isolated in the case of the norbornadiene complexes. With a 3 : 1 molar ratio of ligand : metal, displacement of cod or cot occurs to give [WBr₂(CO)₂L₃][L = P(OMe)₃, PMe₂Ph, or CNBu^t], while a 4 : 1 molar ratio (L = CNBu^t) gives [WBr₂(CO)(CNBu^t)₄]. In contrast, [WBr₂(CO)₂(nbd)] forms monocarbonyl diene complexes [WBr₂(CO) L₂(nbd)][L = P(OMe)₃ or PMe₂Ph, L₂= 2,2′-bipyridyl]. Proton and ³¹P n.m.r. studies of [WBr₂(CO)₂L₃][L = P(OMe)₃ or PMe₂Ph] reveal the presence of two isomeric forms which exhibit dynamic stereochemistry at ambient temperature while the static form of one isomer could be detected at lower temperatures.