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

The (C(5)H5-nMe(n))(2)Ti[eta(2)-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(trimethylsilyl)acetylene (BTMSA). All of them were characterized by spectroscopic methods and (C(5)HMe(4))(2)Ti[eta(2)-C-2(SiMe(3))(2)] (1E) by the X-ray crystal analysis. The complexes decompose at temperatures in the range 100-200 degrees C. Those with n = 0-3 yield (mu-eta(5):eta(5)-fulvalene)(di-mu-hydrido)bis(eta(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 (eta(3):eta(4)-1,2-dimethyl-4,5-dimethylenecyclopentenyl)(eta(5)-tetramethylcyclopentenyl)titanium (2Ea) and (eta 3:eta 4-1,3-dimethyl-4, 5-dimethylenecyclopentenyl)(eta(5)-tetramethylcyclopentadienyl)titanium (2Eb) have been so far isolated as minor products. The C(5)Me(5) complex 1F yields quantitatively (eta(3):eta(4)-1,2,3-trimethyl-4,5-dimethylenecyclopentenyl)(pentamethylcyclopentadienyl)titanium (2F) and BTMSA is hydrogenated to a mixture of cis- and trans-bis(trimethylsilyl)ethene.