Molecular engineering of coordination pockets in chloro-tris-phenoxo complexes of titanium(IV)

Abstract

The chloro-tris-phenoxo complexes [TiCl(OAr) 3] (OAr = OC 6H 4CMe 3-4 ( 1), OC 6H 3Me 2-2,4 ( 2), OC 6H 2Me 3-2,4,6 ( 4), OC 6H 3(CHMe 2) 2-2,6 ( 5), OC 6H 3(CMe 3) 2-2,4 ( 6) and OC 6H 4Ph-2 ( 8) are prepared by heating 3 equivalents of the phenol and [TiCl 4] in toluene. X-ray crystal structure determinations show that 2 is a phenoxy-bridged dimer with the ortho-methyl groups making the beginning of a pocket about the terminal chloro ligand and 6 is a tetrahedral monomer in which the pocket is more well developed by the ortho- tert-butyl groups. Both 2 and 6 react with dmbipy to give [TiCl(OAr) 3(dmbipy)] [OAr = OC 6H 3Me 2-2,4 ( 3) and OC 6H 3(CMe 3) 2-2,4 ( 7)] in which the original pocket is destroyed. Reaction of TiCl 4 with 3 equivalents of LiOC 6H 4Ph-2 in diethyl ether gives [TiCl(OC 6H 4Ph-2) 3(diethyl ether)] ( 9) for which an X-ray crystal structure determination shows a trigonal bipyramidal coordination geometry with the diethyl ether lying trans to the chloro ligand. The three phenoxide ligands make up the equatorial plane which takes the 2-phenyl substituent on each phenoxo ligand away from the chloro ligand resulting in a partially collapsed cavity. The tied-back analogues of 2 and 6, [TiCl{(OC 6H 2Me 2-2,4-CH 2-6) 3N}] ( 11) and [TiCl({OC 6H 2(CMe 3) 2-2,4-CH 2-6} 3N)] · diethyl ether ( 12), are prepared by adding (HOArCH 2) 3N [Ar = C 6H 2Me 2-2,4 and C 6H 2(CMe 3) 2 2,4] to [TiCl(OCHMe 2) 3] in diethyl ether. An X-ray crystal structure of 12 showed a trigonal bipyramidal structure with a coordination environment about the terminal chloro ligand similar to that found in 6. Complex 12 reacts with pyridine to form the 6-coordinate complex [TiCl({OC 6H 2(CMe 3) 2-2,4-CH 2-6} 3N)(py)] ( 13).