Bimetallic Complexes with Conjugated C₄, C₆, C₁₀, and C₁₄ Bridges:  Synthetic Routes to Alkynediyl-Bridged Bis(carbene) Complexes

The reaction of [(CO) 5 W C(Ph)H] with Me 2 NC⋮CNMe 2 affords two complexes: the binuclear complex [(CO) 5 W C(NMe 2 )(Me 2 N)C W(CO) 5 ] ( 2 ) and the insertion product [(CO) 5 W C(NMe 2 )C(NMe 2 ) C(Ph)H] ( 3 ). Sequential reaction of the (dimethylamino)ethynylcarbene complex [(CO) 5 W C(NMe 2 )C⋮CH] ( 4a ) with n BuLi, W(CO) 6, and F 3 CSO 3 Me yields the new ethynediyl-bridged binuclear alkoxycarbene−aminocarbene complex [(CO) 5 W C(NMe 2 )C⋮C(MeO)C W(CO) 5 ] ( 5 ). Treatment of 4a and of [(CO) 5 Cr C(NMe 2 )C⋮CH] ( 4b ) with n BuLi and iodine gives the new iodine-substituted complexes [(CO) 5 M C(NMe 2 )C⋮CI] (M = W ( 6a ), M = Cr ( 6b )). By Pd-catalyzed coupling of 6a, b with the C-stannylated ethynylcarbene complexes [(CO) 5 M C(NMe 2 )C⋮CSn( n Bu) 3 ] ( 7a, b ) the butadiynediyl-bridged bis(carbene) complexes [(CO) 5 M C(NMe 2 )(C⋮C) 2 (Me 2 N)C M(CO) 5 ] ( 8a, b ) are obtained. Analogously, from [(CO) 5 W C(NMe 2 )(C⋮C) x H] ( x = 2, 3) and n BuLi/I 2 amino(iodobutadiynyl)carbene and amino(iodohexatriynyl)carbene complexes [(CO) 5 W C(NMe 2 )(C⋮C) x I] ( x = 2 ( 10 ), 3 ( 14 )) are obtained. Pd-catalyzed coupling with the corresponding C-stannylated alkynylcarbene complexes finally affords the binuclear C 10 (NMe 2 ) 2 - and C 14 (NMe 2 ) 2 -bridged complexes [(CO) 5 W C(NMe 2 )(C⋮C) x (Me 2 N)C W(CO) 5 ] ( x = 4 ( 12 ), 6 ( 16 )). All alkynediyl-bridged bis(carbene) complexes are stable at room temperature. The spectroscopic data of 5 indicate that it is best described as a hybrid of a dipolar allenyl-type compound and an alkynylcarbene complex. In contrast, the C⋮C units in the binuclear complexes 8a, b, 12, and 16 are essentially localized.