Dinuclear Titanium(IV) complexes bearing phenoxide-tethered N-heterocyclic carbene Ligands with cisoid conformation through control of hydrolysis

In situ generated N-heterocyclic carbene salt derivative Na-2(L) of 1,3-bis(4,6-di-tert-butyl-2-hydroxybenzyl)imidazolium bromide, [H-3(L)]Br, reacted with 1 equiv. of TiBr4 at -78 degrees C to give a titanium complex of the composition [(L)TiBr2(thf)] (1), while the reaction in a 2:1 ratio under the same conditions afforded bisligand titanium complex [(L)(2)Ti] (2). Two oxygen-bridged titanium dimers, {[(L)TiBr2(mu-O)} (4) and {[(L)Ti(mu-O-2) (5), were obtained by control of hydrolysis of 1 and [(L)Ti(CH2Ph)(2)] (3) in tetrahydrofuran and diethyl ether. The molecular structures of 2, 4, and 5 have been confirmed by X-ray single-crystal analysis. The phenoxide-functionalized NHC ligand adopts transoid conformation in mononuclear complex 2 but rare cisoid conformation in dinuclear complexes 4 and 5. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)