New bis(aryloxy)–Ti(iv) complexes and their use for the selective dimerization of ethylene to 1-butene??

Dalton Transactions Pub Date: 2012-07-19 DOI: 10.1039/C2DT30991B

Abstract

New titanium complexes of general formula [(ArO)nTi(Oi-Pr)(4?n)] were synthesized and used as pre-catalysts for the selective dimerization of ethylene to 1-butene. The complexes were prepared in cyclohexane using [Ti(Oi-Pr)4] and one or two equivalents of the corresponding phenols (ArOH) at room temperature. In this work, both monodentate and chelating phenols were evaluated. For alkyl-substituted phenols, it was demonstrated that large steric hindrance at both ortho and ortho′ positions selectively yielded the mono-substituted complexes [(ArO)Ti(Oi-Pr)3]. Substitution at only one of the ortho positions allowed both the mono- and the di-substituted Ti complexes to be isolated. When a heteroatom was introduced on the phenol backbone, di-substitution systematically occurred except with phenols presenting a hemilabile –CH2NR2 group at the ortho position. Upon activation with 3 equiv. of AlEt3 at 20 bar and 60 °C, all the complexes selectively dimerized ethylene to 1-butene (>86% of butenes among which 99% of 1-butene). An increase of the steric bulk at the ortho position of the ligand or the introduction of a functional group led to decreased activity compared to [Ti(Oi-Pr)4].

Graphical abstract: New bis(aryloxy)–Ti(iv) complexes and their use for the selective dimerization of ethylene to 1-butene
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