On the way to heptahexaenylidene complexes: Trapping of an intermediate with the novel M=C=C=C=C=C=C=CR(2) moiety

Sequential treatment of the in situ generated heptatriyne Me(3)SiC=CC=CC=CC(NMe(2))(3) with n-BuLi, (CO)(5)W[THF], and BF3 . OEt(2) affords the first alkenyl-substituted pentatetraenylidene complex, (CO)(5)W=C=C=C=C=C(NMe(2))C(H)=C(NMe(2))(2) (4), via addition of dimethylamine to the C-epsilon=C-zeta bond of the intermediate heptahexaenylidene complex (CO)(5)W=C-alpha=C-beta=C-gamma=C-delta=C-epsilon=C-zeta=C-eta(NMe(2))(2). In addition, the alkynyl(butatrienyl)carbene complex (CO)(5)W=C(C=CSiMe(3))C(Bu)=C=C=C(NMe(2))(2) (5) is formed.