SYNTHESIS OF SIGMA,ETA(2)-ALKYNYL-BRIDGED BIMETALLIC COMPLEXES CONTAINING ANSA-METALLOCENE AND LOW-VALENT NICKEL-MONOCARBONYL ENTITIES

The reaction of the ansa-titanocene dichlorides )-C(5)H(3)R(1))(eta(5) -C(5)H(3)R(2))SiMeR(3)]TiCl2 (1a, R(1) = R(2) = H, R(3) = Me; 1b, R(1) = H, R(2) = SiMe(3), R(3) = Me; 1c, R(1) = R(2) = SiMe(3), R(3) = Ph) with 2 equiv of LiC=CSiMe(3) (2) yields the bis(alkynyl) ansa-titanoc enes ))(eta(5)-C(5)H(3)R(2))-SiMeR(3)]Ti(C=CSiMe(3))(2) (3a, R(1) = R( 2) = H, R(3) = Me; 3b, R(1) = H, R(2) = SiMe(3), R(3) = Me; 3c, R(1) = R(2) = SiMe(3), R(3) = Ph). These compounds react with Ni(CO)(4) (4) to afford (5)-C(5)H(3)R(2))SiMeR(3)]Ti(C=CSiMe(3))(2)}Ni(CO) (5a, R(1) = R(2) = H, R(3) = Me; 5b, R(1) = H, R(2) = SiMe(3), R(3) = Me; 5c, R (1) = R(2) = SiMe(3), R(3) = Ph) in high yields. Compounds 5a-c contai n a low-valent nickel-monocarbonyl fragment, which is stabilized by th e chelating effect of both alkynyl ligands of 3. In contrast, the ansa -zirconocene dichloride eta(5)-C5H4)(eta(5)-C(5)H(3)SiMe(3))-SiMe(2)]Z rCl2 (6) leads with 2 equiv of LiC=CSiMe(3) (2) to a variety of reacti on products, of which the sigma,eta(2)-doubly alkynyl-bridged dinuclea r zirconocene )(eta(5)-C(5)H(3)SiMe(3))SiMe(2)]-Zr(C=CSiMe(3))}2 (7) c an be crystallized. Compound 7 can be synthesized in much better yield s by reacting 6 first with LiC=CSiMe(3) and secondly with n-butyllithi um; a possible mechanism for the formation of 7 will be discussed. In 7 the alkynyl ligands act both as sigma- and pi-donors. Compound 7 con tains two formal Zr-III centers. The X-ray structure analyses of 1b, 3 a, and 7 are reported. Crystals of 1b and 3a are monoclinic, space gro up P2(1)/n (1b) and P2(1)/a (3a): 1b, cell constants a = 7.516(2) Angs trom, b = 19.86(6) Angstrom, c = 12.275(3) Angstrom, beta = 91.47(2)de grees, V = 1831.8 Angstrom(3), and Z = 4; 3a, cell constants a = 10.78 6(6) Angstrom, b = 20.01(2) Angstrom, c = 11.88(2) Angstrom, beta = 99 .86(9)degrees, V = 2526.2 Angstrom(3), and Z = 4. Complex 7 crystalliz es in the triclinic space group P1 $($) over bar$$ with the cell const ants a = 12.354(6) Angstrom, b = 19.15(1) Angstrom, c = 20.28(1) Angst rom, alpha = 68.59(5)degrees, beta = 89.30(5)degrees, gamma = 86.77(5) degrees, V = 4458.1 Angstrom(3), and Z = 4. The properties of the MeRS i-bridged titanocenes 3 and 5 in comparison to the appropriate unbridg ed species are discussed.