Photochemical reaction of W(CO)(6) with GeCl4 as a source of germyl and germylene compounds acting as initiators for ring-opening metathesis polymerization of norbornene

摘要

Photolysis Of W(CO)(6) in a solution of n-heptane containing GeCl4 leads to the formation of two seven-coordinate compounds with direct W-Ge bonds: [(CO)(4)W(mu-Cl)(3)W(GeCl3(CO)(3)] (1) and [(mu-GeCl2){W(CO)(5)}(2)] (2). The molecular structures of these two tungsten-germanium compounds have been established by single-crystal X-ray diffraction studies. The germyl compound 1 is a previously synthesized binuclear complex of tungsten(II) with a d(4) electronic configuration, while in the new germylene compound 2 the tungsten atom is formally in the zero oxidation state with a d(6) electronic configuration and a direct W-W bond. In an attempt to establish whether compounds 1 and 2 could be used as precatalysts for the ring-opening metathesis polymerization (ROMP) of cyclic olefins, their reactivity towards norbomene has been studied. In chloroform-d(1) solution the ROMP reaction is accompanied by the formation of a new olefin, 2,2'-binorbornylidene (bi-(NBE)), as a result of carbene-carbene coupling. In reaction of norbornene carried out in benzene solution the ROMP reaction is accompanied by the formation of 2-phenylnorbornane (hydroarylation product) and small amounts of bi(NBE). In general, in the presence of olefin, compound 2 undergoes rearrangement to give an olefin compound of the type [(WCO)(5)(eta(2)-olefin)]. (c) 2006 Elsevier B.V. All rights reserved.