Crystal structures of a novel NNN pincer ligand and its dinuclear titanium(IV) alkoxide pincer complex

Abstract

This report describes a synthetic protocols and the crystal structures involving a novel pincer-type H3[NNN] ligand, namely di-μ-bromido-μ-{2-(2,2-dimethylpropanimidoyl)-N-[2-(2,2-dimethylpropanimidoyl)-4-methylphenyl]-4-methylaniline}-bis[(diethyl ether)lithium], [Li2Br2(C24H33N3)(C4H10O)2] (1) and a dinuclear metal complex, namely di-μ-bromido-2:3κ4 Br:Br-bis{2-(2,2-dimethylpropanimidoyl)-N-[2-(2,2-dimethylpropanimidoyl)-4-methylphenyl]-4-methylaniline}-1κ3 N,N′,N′′;4κ3 N,N′,N′′-tetra-μ-isopropanolato-1:2κ4 O:O;3:4κ4 O:O-diisopropanolato-1κO,4κO-2,3-dilithium-1,4-dititanium, [Li2Ti2Br2(C24H32N3)2(C3H7O)6] or {[NHNNH]Ti(OiPr)3(LiBr)2}2 (2). Complex 1, which sits on a twofold rotation axis, is a rare example of a pincer-type ligand which bears ketimine side arms. A unique feature of complex 1 is that the ketimine N atoms have an LiBr(Et2O) fragment bonded to them, with the Li atom adopting a distorted tetrahedral geometry. This particular fragment creates an LiBr bridge between the two ketimine sidearms, which leads to a cage-type appearance of the ligand. Complex 2 consists of the previously described ligand and a TiIV metal atom in an octahedral environment, and is located on an inversion center. Complex 2 crystallizes as a dinuclear species with the metal atoms being bridged by an LiBr entity [the Br atoms are disordered and refined in two positions with their site occupation factors refining to 0.674(12)/0.372(12)], and the Li cation being bonded to the isopropoxide O atoms (Li having a tetrahedral coordination as in 1). The organic ligand of compound 2 exhibits disorder in its periphery groups; isopropyl and tert-butyl groups (occupation factors fixed at 0.6/0.4). The novel [NNN]H3 pincer-type ligand was characterized by multinuclear and multidimensional NMR, HRMS and X-ray crystallography. The dinuclear metal complex 2 was characterized by X-ray crystallography. Although each structure exhibits donor N - H groups, no hydrogen bonding is found in either one, perhaps due to the bulky groups around them. One of the ethyl groups of the ether ligand of 1 is disordered and refined in two parts with site-occupation factors of 0.812(8) and 0.188(8). One and a half toluene solvent molecules are also present in the asymmetric unit of 2. The toluene molecules were significantly disordered and could not be modeled properly, thus SQUEEZE [Spek (2015). Acta Cryst. C71, 9-18] was used to remove their contributions to the overall intensity data.