Heptahexaenylidene Complexes: Synthesis and Characterization of the First Complexes with an MCCCCCCCR₂ Moiety (M = Cr, W)

Abstract

Silica-induced elimination of dimethylamide from [(CO)5M(C⋮C)3C(NMe2)3]- [M = Cr (4a), W (4b)] affords the first isolated and characterized heptahexaenylidene complexes [(CO)5MCCCCCCC(NMe2)2] (5a,b). Complexes 4a,b were generated by sequential reaction of Me3Si(C⋮C)3SiMe3 with LiMe·LiBr, [(Me2N)3C]+Cl-, LiBu, and [(CO)5M(thf)]. Complex 5b is inert in methanol, but adds dimethylamine across the C5C6 bond to give [(CO)5WCCCCC{CHC(NMe2)2}NMe2]. The reaction of 5a,b with LiMe·LiBr and SiO2 generates the heptahexaenylidene complexes [(CO)5MCCCCCCC(Me)NMe2] (8a,b). Trapping of 8b with HNMe2 yields pentatetraenylidene complex [(CO)5WCCCCC{CHC(Me)NMe2}NMe2].