Novel Aryltitanium(IV) complexes containing h3-NCN-pseudofacial- and h3-NCN-meridional-bonded [C6H3(CH2NMe2)2-2,6]- (abbreviated as NCN) ligands. The crystal structures of [TiCl2(h3-fac-NCN)(O-i-Pr)], [TiCl(h3-mer-NCN)(O-i-Pr)(OTf)] containing an h1-O-bonded triflate anion and the seven-coordinated [Ti(h3-mer-NCN)(O-i-Pr)(OTf)2] containing h1-O- and h3-O,O'-bonded triflate anions

Abstract

Titanium(IV) derivatives of the chelating monoanionic aryldiamine ligand [C6H3(CH2NMe2)2-2,6]- (abbreviated as NCN) are prepared by treating [TiCl3(OR)] (R = i-Pr, C6H4OMe-4) with [Li(NCN)]2. [TiCl2(NCN)(O-i-Pr)] is smoothly methylated by methyllithium in toluene to give [TiClMe(NCN)(O-i-Pr)] and [TiMe2(NCN)(O-i-Pr)]. Enhancement of the Lewis acidity of the titanium center has been studied by substituting chloro ligands for triflato ligands to give [TiCl(NCN)(O-i-Pr)(OTf)] and [Ti(NCN)(O-i-Pr)(OTf)2]. X-ray studies of the dichloride and triflate complexes feature 3-pseudofacial and 3-meridional bonding modes for the NCN ligand, respectively. These different NCN bonding modes are explained in terms of the trans influence of the alkoxy and triflato ligands. A rare example of an organo titanium(IV) complex with a seven-coordinate titanium center is observed in the bis(triflate) complex as a result of bidentate O,O'-bonding mode of the triflato anion to one titanium center that is unprecedented in early transition metal chemistry. The triflato ligands exhibit a strong covalent bonding to titanium both in the solid state and in solution; the latter is demonstrated by the observation that cationic species are not formed upon addition of Lewis bases like THF, acetonitrile, and 1,2-bis(dimethylamino)ethane.