Titanium-catalyzed head-to-tail dimerization of tert-butylacetylene. Crystal structures of [(C 5HMe 4) 2Ti( μ-H) 2Mg(THF)( μ-Cl)] 2 (THF-tetrahydrofuran) and (C 5HMe 4) 2TiOCMe 3

Abstract

tert-Butylacetylene (TBUA) is readily dimerized exclusively to 2,4-di- tert-butyl-1-buten-3-yne, head-to-tail dimer (HTTD), in the presence of the ( η 5-C 5HMe 4) 2TiCl 2/Mg/THF system. The ESR investigation revealed the formation of Ti–Mg hydride complexes [( η 5-C 5HMe 4) 2Ti( μ-H) 2Mg(THF)( μ-Cl)] 2 ( 2) and [( η 5-C 5HMe 4) 2Ti( μ-H) 2] 2Mg ( 3) in the absence of TBUA and a tweezer-type complex, probably [( η 5-C 5HMe 4) 2Ti( η 1-CCCMe 3) 2] − [Mg(THF)Cl] + ( 4) in its presence. The catalytic system as well as complexes 2– 4 were deactivated by presumably tert-butanol contained in TBUA to give ( η 5-C 5HMe 4) 2TiOCMe 3 ( 5). Purification of TBUA improved the turnover by up to 8.8×10 3 mol TBUA per 1 mol Ti using complex 3 as a catalyst, however, complex 5 remained the only observable product of deactivation. The crystal structures of 2 and 5 were determined by X-ray diffraction analysis.