Add time:08/15/2019         Source:sciencedirect.com

The cyclotrimerization of 1-phenyl-2-(trimethylsilyl)acetylene (PTMSA) catalysed by the TiCl4/Et2AlCl (Ti: Al = 10–20) system affords 1,3,5-triphenyl-2,4,6-tris(trimethylsilyl)benzene (I) (minor product) and ethyl-triphenyl-bis(trimethylsilyl)benzene (II) (major product) in low yields. An X-ray crystal structural study ofI revealed that there are two different conformers in the unit cell. CompoundI has a planar central ring with alternating values of angles at carbon atoms bearing the trimethylsilyl group (av. 116.8(6)°) and at carbon atoms bearing the Ph group (av. 123.1(9)°). The steric hindrance between the substituents is relieved by the almost perpendicular orientation of the Ph rings with respect to the central ring (81 ± 5°). The replacement of one trimethylsilyl group by an Et group from Et2AlCl probably precedes the ring closure yieldingII. The presence of trimethylsilyl groups on the carbon atoms involved in this step hinders the ring closure and gives rise to what are probably linear oligomers of PTMSA.

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