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

摘要

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 Ti^IV 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. C>71, 9–18] was used to remove their contributions to the overall intensity data.