BIS[(ETA(8)-CYCLOOCTATETRAENE)TITANIUM] COMPLEX WITH PERPENDICULARLY BRIDGING BIS(TRIMETHYLSILYL) ACETYLENE

The reduction of [(eta(8)-C8H8)Ti(THF)(mu -Cl)](2) by magnesium in the presence of bis(trimethylsilyl)acetylene (BTMSA) afforded the diamagn etic complex eta(8)-C8H8)Ti](2)[mu-eta(2):eta(2)-Me3SiC=CSiMe3] (I) in high yield. The crystal structure of 1 revealed that BTMSA is a four- electron ligand which binds two equivalent (eta(8)-C8H8)Ti moieties un der the angle of av. 69 degrees. The average C-C distance of 1.51 Angs trom in the acetylene ligand is close to that of sp(3) carbon atoms, h owever, a high thermal stability and enormously large down-field chemi cal shift of the acetylenic carbon atoms (delta 292.8 ppm) points to a n unusually high contribution of pi-back-bonding to the Ti-acetylene b ond. An analogous reduction in the presence of diphenylacetylene affor ded a tetraphenylcyclobutadiene complex (eta(8)-C8H8)Ti(eta(4)-C4Ph4) and hexaphenylbenzene. (C) 1998 Elsevier science S.A. All rights reser ved.