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 Me2NC=CNMe2 affords two complexes: the binuclear complex [(CO)(5)W=C(NMe2)(Me2N)C=W(CO)(5)] (2) and the insertion product [(CO)(5)W=C(NMe2)C(NMe2)=C(Ph)H] (3). Sequential reaction of the (dimethylamino)ethynylcarbene complex [(CO)(5)W=C(NMe2)C=CH] (4a) with nBuLi, W(CO)(6), and F3CSO3Me yields the new ethynediyl-bridged binuclear alkoxycarbene-aminocarbene complex [(CO)(5)W=C(NMe2)C=C(MeO)C=W(CO)(5)] (5). Treatment of 4a and of [(CO)(5)Cr=C(NMe2)C=CH] (4b) with nBuLi and iodine gives the new iodine-substituted complexes [(CO)(5)M=C(NMe2)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(NMe2)C=CSn(nBu)(3)] (7a,b) the butadiynediyl-bridged bis(carbene) complexes [(CO)(5)M=C(NMe2)(C=C)(2)(Me2N)C=M(CO)(5)] (8a,b) are obtained. Analogously, from [(CO)(5)W=C(NMe2)(C=C)(x)H] (x = 2, 3) and nBuLi/I-2 amino(iodobutadiynyl)carbene and amino(iodohexatriynyl)carbene complexes [(CO)(5)W=C(NMe2)(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(NMe2)(2)- and C-14(NMe2)(2)-bridged complexes [(CO)(5)W=C(NMe2)(C=C)(x)(Me2N)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.