Photochemical reaction of W(CO) 6 with GeCl 4 as a source of germyl and germylene compounds acting as initiators for ring-opening metathesis polymerization of norbornene

Abstract

Photolysis of W(CO) 6 in a solution of n-heptane containing GeCl 4 leads to the formation of two seven-coordinate compounds with direct W Ge bonds: [(CO) 4W(μ-Cl) 3W(GeCl 3)(CO) 3] ( 1) and [(μ-GeCl 2){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 norbornene 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(η 2-olefin)].