Experimental and Theoretical Investigations of Catalytic Alkyne Cross-Metathesis with Imidazolin-2-iminato Tungsten Alkylidyne Complexes

Abstract

The imidazolin-2-iminato tungsten alkylidyne complexes [Me3CC≡W(NImR)(OR′)2] (4a: R = tBu, R′ = CMe3; 4b: R = Dipp, R′ = CMe3; 5a: R = tBu, R′ = CMe(CF3)2; 5b: R = Dipp, R′ = CMe(CF3)2 have been prepared from [Me3CC≡W(OCMe3)3] (2) and [Me3CC≡W{OCMe(CF3)2}3(dme)] (3, dme = 1,2-dimethoxyethane) by reaction with the lithium reagents Li(NImtBu) and Li(NImDipp), generated with MeLi from 1,3-di-tert-butylimidazolin-2-imine (ImtBuNH) or 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-imine (ImDippNH), respectively. Reaction of 3 with Li[N(tBu)Ar]·OEt2 (Ar = 3,5-dimethylphenyl) afforded the amido complex [Me3CC≡W{N(tBu)Ar}{OCMe(CF3)2}2] (6). Addition of Li[OCPh(CF3)2] to [Me3CC≡WCl3(dme)] (1) produced the dme-free complex [Me3CC≡W{OCPh(CF3)2}3] (7), which, upon treatment with Li(NImtBu), gave the alkylidene complex 8, presumably formed by activation and addition of an ortho-C−H bond across the W≡C bond in the intermediate alkylidyne complex. Treatment of 1 with Li[OC(CF3)3] led to the substitution of only two chloride...