Tungsten(II)-initiated ring-opening metathesis polymerization and other C–C bond forming reactions of 5-vinyl-2-norbornene

Abstract

The trichloro-bridged tungsten(II) dimer [(CO) 4W(μ-Cl) 3W(GeCl 3)(CO) 3] ( 1) has been demonstrated to be a very effective catalyst for the ring-opening metathesis polymerization (ROMP) of 5-vinyl-2-norbornene (V-NBE). The selectivity of ROMP reaction depends very strongly on properties of solvent in which the reaction is carried out. In CCl 4 solution the ROMP reaction is accompanied by the formation of small amounts of (V-NBE)-(CCl 4) adducts, but in benzene solution 2,2′-bi(vinylnorbornylidene) (bi-(V-NBE)) and (V-NBE)-(C 6H 6) adducts were also detected. In dichloromethane or chloroform- d 1 solution the selectivity of ROMP reaction is low because it is accompanied by formation of bi-(V-NBE). The tungsten(II) compound activates the more strained cyclic double bond of V-NBE. As was shown by 1H and 13C NMR spectroscopy, the pendant vinyl group is left intact in poly-(vinylcyclopentylenevinylene) as well as in bi-(V-NBE). A mechanism involving C–H bond activation of olefin and the formation of tungsta-vinylnorbornylidene is proposed to explain those results. In dichloromethane and chloroform- d 1 solution a tungsta-vinylnorbornylidene species undergoes a carbene–carbene coupling reaction to give bi-(V-NBE). The reaction products are identified by means of chromatography (GC–MS) and 1H and 13C NMR spectroscopy.