Bis[( η8-cyclooctatetraene)titanium] complex with perpendicularly bridging bis(trimethylsilyl)acetylene

Abstract

The reduction of [( η 8-C 8H 8)Ti(THF)( μ-Cl)] 2 by magnesium in the presence of bis(trimethylsilyl)acetylene (BTMSA) afforded the diamagnetic complex [( η 8-C 8H 8)Ti] 2[ μ- η 2: η 2-Me 3SiCCSiMe 3] ( 1) in high yield. The crystal structure of 1 revealed that BTMSA is a four-electron ligand which binds two equivalent ( η 8-C 8H 8)Ti moieties under the angle of av. 69°. The average CC distance of 1.51 Å in the acetylene ligand is close to that of sp 3 carbon atoms, however, a high thermal stability and enormously large down-field chemical shift of the acetylenic carbon atoms ( δ 292.8 ppm) points to an unusually high contribution of π-back-bonding to the Ti-acetylene bond. An analogous reduction in the presence of diphenylacetylene afforded a tetraphenylcyclobutadiene complex ( η 8-C 8H 8)Ti( η 4-C 4Ph 4) and hexaphenylbenzene.