On the Way to Heptahexaenylidene Complexes:  Trapping of an Intermediate with the Novel MCCCCCCCR₂ 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 BF 3 ·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 ε C ζ bond of the intermediate heptahexaenylidene complex (CO) 5 W C α C β C γ C δ C ε C ζ C η (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.