Day, Joanna K., Baghurst, Rebecca E., Strevens, Robert R., Light, Mark E., Hursthouse, Michael B., Stengel, Bruno F., Fallis, Ian A. and Aldridge, Simon (2007) Influence of ligand backbone flexibility in group 4 metal complexes of tetradentate mixed tertiary amine/alkoxide ligands. New Journal of Chemistry, 31 (1), 135-142. (doi:10.1039/b608680b).
Abstract
Simple epoxide ring opening chemistry using the cyclic secondary amine 1,4-diazacycloheptane or the related linear species N,N'-dimethylethylenediamine, and racemic (+/-) -3,3-dimethyl-1,2-epoxybutane gives access to the pendant alcohol functionalised ditertiary amine pro-ligands [HOCH(Bu-t)CH2N(R)CH2](2) (H2L1:R-2=CH2CH2CH2; H2L2:R-2=Me-2). The contrasting reactions of H2L1 and H2L2 towards homoleptic group 4 alkoxides highlight the crucial role of ligand backbone flexibility in complex formation. Thus, the chemistry of the more conformationally rigid system (L-1)(2-) appears to be constrained by the cyclic ligand core, such that it adopts a bridging (mu(2):eta(2), eta(2)) mode of coordination towards Ti(IV), leading to dinuclear metal systems [e.g. (LTi2)-Ti-1((OPr)-Pr-i)(6)]. By contrast, the more flexible linear system (L-2)(2-) binds to both Ti(IV) and Zr(IV) in a chelating fashion leading, for example, to the synthesis of the C-2 symmetric mononuclear complex rac-(LTi)-Ti-2((OPr)-Pr-i)(2). Thus, a simple synthesis of diastereomerically pure, C-2 symmetric, geometrically cis octahedral Ti(IV) complexes from racemic precursors is presented.
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