Titanocene-bis(trimethylsilyl)acetylene complexes: effects of methyl substituents at the cyclopentadienyl ligands on the structure of thermolytic products

Abstract

The (C 5H 5− n Me n Ti[ η 5-C 2(SiMe 3) 2] ( n = 0–5) ( 1A–1F) complexes were prepared by the reduction of corresponding titanocene dichlorides with magnesium in THF in the presence of bis(trimethylsily)acetylene (BTMSA). All of them were characterized by spectroscopic methods and (C 5HMe 2Ti[ η 5-C 2(SiMe 3) 2] ( 1E) by the X-ray crystal analysis. The complexes decompose at temperatures in the range 100–200°C. Those with n = 0–3 yield ( μ- η 5 : η 5-fulvalene)(di-μ-hydrido)bis ( η 5-cyclopentadienyltitanium) ( 2A) and its methylated analogues ( 2B–2D) whereas BTMSA is released. The crystal structure of 2D showed that the hexamethylfulvalene ligand contains non-methylated carbon atoms in inner alternate positions. Complex 1E afforded a mixture of products. Among them only volatile isomers ( η 3: η 4-1,2-dimethyl-4,5-dimethylcyclopenteny)( η 5-tetramethylcyclopentadienyl)titanium ( 2Ea) and ( η 3: η 4-1,3-dimethyl-4, 5-dimethylenecyclopentenyl)( η 5-tetramethylcyclopentadienyl)titanium (2Eb) have been so far isolated as minor products. The C 5Me 5 comples 1F yields quantitatively ( η 3: η 4-1,2,3-trimethyl-4,5-dimethylenecyclopentyl)(pentamethylcyclopentadienyl)titanium ( 2F) and BTMSA is hydrogenated to a mixture of cis- and trans-bis(trimethylsilyl)ethene.