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-2:3κ4Br:Br-bis{2-(2,2-dimethylpropanimidoyl)-N-[2-(2,2-dimethylpropanimidoyl)-4-methylphenyl]-4-methylaniline}-1κ3N,N′,N′′;4κ3N,N′,N′′-tetra-μ-isopropanolato-1:2κ4O:O;3:4κ4O:O-diisopropanolato-1κO,4κO-2,3-dilithium-1,4-dititanium, [Li2Ti2Br2(C24H32N3)2(C3H7O)6] or {[NHNNH]Ti(OiPr)3(LiBr)2}2(2). Complex1, 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 complex1is 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. Complex2consists of the previously described ligand and a TiIVmetal atom in an octahedral environment, and is located on an inversion center. Complex2crystallizes 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 in1). The organic ligand of compound2exhibits disorder in its periphery groups; isopropyl andtert-butyl groups (occupation factors fixed at 0.6/0.4). The novel [NNN]H3pincer-type ligand was characterized by multinuclear and multidimensional NMR, HRMS and X-ray crystallography. The dinuclear metal complex2was 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 of1is 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 of2. The toluene molecules were significantly disordered and could not be modeled properly, thusSQUEEZE[Spek (2015).Acta Cryst.C71, 9–18] was used to remove their contributions to the overall intensity data.
Which Properties Allow Ligands to Open and Bind to the Transient Binding Pocket of Human Aldose Reductase?
