UNTYPICAL REGIOSELECTIVITY OF CARBON-DIOXIDE COUPLING WITH TITANOCENECOMPLEXES OF PHENYL(TRIMETHYLSILYL)ACETYLENE BY USING THE SO-1,2-ETHYLENE-1,1'-BIS(ETA(5)-TETRAHYDROINDENYL) LIGAND SYSTEM

The reaction of [meso-(ebthi)TiCl2] [ebthi = 1,2-ethylene-1,1'-bis(eta (5)-tetrahydroindenyl)] with magnesium in the presence of the alkynes Me3SiC=CSiMe3 and PhC=CSiMe3 resulted in the formation of the complexe s [meso-(ebthi)Ti(eta(2)-Me3SiC2SiMe3)] (1) and [meso-(ebthi)Ti(eta(2) -PhC2SiMe3)] (2a and 2b), which were isolated and then characterized b y their NMR spectra. Due to incomplete reduction the Ti-III complex [m eso-(ebthi)Ti(THF)Cl] (3) was also obtained as a by-product of these r eactions. By insertion into the Ti-CPh bond carbon dioxide reacted wit h the titanacyclopropene structure of the alkyne complex [meso(ebthi)T i(eta(2)-PhC2SiMe3)] (2a), with untypical regioselectivity to yield th e alpha-silyl-substituted meso-(ebthi)titanafuranone 6a. In the analog ous reactions of the complexes [(thi)(2)Ti(eta(2)-PhC2SiMe3)] (thi = e ta(5)-tetrahydroindenyl), [rac-(ebthi)Ti(eta(2)-PhC2SiMe3)], and [CpT i-2(eta(2)-PhC2SiMe3)] with carbon dioxide typical regioselectivity (i nsertion into the M-CSi bond of the titanacyclopropene) was observed, yielding the beta-silyl-substituted titanafuranones 7, 8a, and 9. Thes e results show that insertion of carbon dioxide into the M-C bond of t he titanacyclopropene structure of the alkynemetallocene complexes is governed by the substitution pattern of the alkyne and the steric envi roment around the metal center. The complexes 3, Ga,and 7 were investi gated by X-ray crystal structure analysis.