Effect of the nature of carbene fragments in the tungsten complexes PhMe2E-CH=W(NAr)(OR')2 and Me3E-CH=W(NAr)(OR')2 (E = C, Si) on their catalytic properties in olefin metathesis reactions

Catalytic properties of the silicon-containing carbene complexes of tungsten Me3Si-CH=W(NAr)(OR')(2)(1) and PhMe2Si-CH=W(NAr)(OR')(2) (2) and their hydrocarbon analogs Me3C-CH=W(NAr)(OR')(2) (3) and PhMe2C-CH=W(NAr)(OR')(2) (4) (Ar = 2,6-Pr-i 2C6H3, R' = CMe2CF3) were studied in homometathesis of hex-1-ene, metathesis polycondensation of deca-1,9-diene, and ring opening metathesis polymerization of cyclooctene. The nature of the carbene fragment in the tungsten catalysts substantially affects their catalytic activity. Silicon-containing catalysts 1 and 2 were found to be 3-5 times less active than their hydrocarbon analogs 3 and 4. Metathesis polymerization of cyclooctene in the bulk with initiators 1-4 completed within a few minutes to form a block. Stereoregularity of the formed polyoctenamers depends to a considerable extent on the nature of the carbene fragments in the starting initiators. Initiators 1-2 lead to polyoctenamers mainly containing the cis-units, whereas the use of complexes 3 and 4 affords polyoctenamers mainly containing the trans-units. The structures of novel compound 2 and known complexes 1, 3, and 4 were determined by X-ray diffraction analysis.