STABILITY OF BRIDGED AND UNBRIDGED ETA(2)-ALKYNE-TITANOCENE AND ETA(2)-ALKYNE-ZIRCONOCENE COMPLEXES - INFLUENCE OF METALS, ALKYNE SUBSTITUENTS, CP SUBSTITUTION AND ADDITIONAL LIGANDS

The influence of metals, alkyne substituents, Cp substitution and addi tional ligands on the stability of bridged and unbridged eta(2)-alkyne -titanocene and -zirconocene complexes has been investigated. The redu ction of the complex [(eta(5)C(5)H(4)) -SiMe2-(eta(5)-C5H4)]TiCl2 with magnesium in the presence of tolan (PhC2Ph) does not give the expecte d alkyne-titanocene complex [(eta(5)-C5H4) -SiMe2-(eta(5)-C5H4]]Ti(eta (2)-PhC2Ph) but by coupling of two tolan molecules the corresponding t itanacyclopentadiene [(eta(5)-C5H4)-SiMe2-(eta(5)-C5H4)]TiC4Ph4 (1) wa s obtained. In the analogous reaction with Me3SiC2SiMe3 the stable eta (2)-alkyne complex without additional ligands 5H4)-SiMe2-(eta(5)-C5H4) ]Ti(eta(2)-Me-3-SiC2SiMe3) (2) was formed, due to the sterical influen ce of the alkyne substituents. The compounds without additional ligand s (thi)(2)Ti(eta(2)-PhC2Ph) (3) and (thi)(2)Ti(eta(2)-Me3SiC2SiMe3) (5 ) were isolated from the unbridged titanocene complex(thi)(2)TiCl2 (th i = tetrahydroindenyl). Two equivalents of complex 3 reacted with one equivalent of water to yield the dimeric alkylidene-mu-oxo complex [(t hi)(2)Ti(CPh=CHPh)](2)(mu-O) (6). The reaction of the unbridged zircon ocene compound (thi)(2)ZrCl2 gave the alkyne complex (thi)(2)Zr(THF) ( eta(2)-Me3SiC2SiMe3) (7) which is stabilized by THE At higher temperat ure THF was eliminated from the orange complex 7 forming the green com plex (thi)(2)Zr(eta(2)-Me3SiC2SiMe3). This behaviour was investigated in detail using NMR spectroscopy and compared to similar complexes suc h as Cp2Zr(eta(2)-Me3SiC2SiMe3) (not stable without THF), (ebthi)(2)Zr (eta(2)-Me-3-SiC2SiMe3) (ebthi = ethylenebistetrahydsoindenyl; stable without THF) and CpZr-2(eta(2)-Me3SiC2SiMe3) (Cp* = pentamethyl-Cp, s table without THF). All complexes were characterized by spectroscopic methods. X-ray structural determinations were conducted for the comple xes 1, 3 and 7. Compound 3 is the first example of a structurally char acterized tolan-titanocene complex without additional ligands.