Synthesis and chemistry of titanium(IV) complexes with triamido-amine, triaryloxo-amine, beta-diketonate/phenoxide and bis(beta-diketonate) ligands

The synthesis of titanium(IV) complexes with tetradentate nitrogen- and oxygen-rich ligands and the subsequent testing of their ability to mediate chemical reactions is described. The novel Ti(NMe2)(N(CH2 CH2NTs)3) complex, incorporating an electron-poor trisulfonamido ligand, has an unusual distorted six-coordinate structure in which one of the sulfonamide oxygens coordinates to titanium. Its high reactivity with water and alcohols prompted the synthesis of more acidic tris(amido)amine molecules. The prepared acyl sulfonamides N(CH2CONHSO2R) 3 gave complex mixtures of products with Ti(OtBu) 4 and Ti(NMe2)4, and the tris(trifluoromethanesulfonamide) N(CH2CH2NHSO2CF3)3 was inert towards Ti(OtBu)4, and formed multiple products with Ti(NMe2)4.; Titanium(IV) complexes stable to hydrolysis were obtained using a tris(aryloxo)amine supporting ligand. A series of monomeric complexes LTi(X) was prepared, where L = N(CH2C6H2tBu 2O)3 and X = OtBu, OCH 3, OOCCF3, Cl, OH, OTiL. The LTi(OH) compound could not be obtained by direct hydrolysis of an alkoxide precursor and undergoes unexpectedly facile alcoholysis. It is an active catalyst for sulfide oxidation, but it did not activate peroxides for alkene's epoxidation or catalyze the retro aldol reaction of diacetone alcohol. An explanation for the complex's catalytic inactivity based on the inequivalence of its binding sites trans to a potential substrate is suggested.; Exploring the above assumption, a ligand possessing a beta-diketonate moiety and two phenoxide arms, 1,3-bis(2'-(3'',5''-di-tert-butyl-2''-hydroxystyryl)phenyl)propane-1,3-dione, was prepared, but its metalation with titanium did not lead to well defined products. The observed preference for coordination of two beta-diketonate fragments, before the chelation of a second phenoxide arm to a given metal center, suggested a new ligand bearing two beta-diketonate functional groups.; Among the prepared ligands with interconnected bis(beta-diketonate) fragments, the 2,2'-bis(methylene)biphenyl-linked 2,2'-bis(4-R-2,4-dioxobutyl)biphenyl, R2BobH2, (R = tBu or p-Tol) showed excellent selectivity upon coordination with titanium. It forms only monomeric complexes with the (R)-Λ/(S)-Delta cis-alpha stereochemistry. The (R2Bob)Ti-framework proved to be a poor catalyst for epoxidation, but very stable, which allowed the preparation of neutral and cationic derivatives. Three cationic titanium complexes were isolated and structurally characterized. The ionic [(Tol2Bob)Ti(OC (CH3)2CH2COCH3)]BArF can undergo a slow exchange process with (CD3)2CO, as a result of retro-aldol reaction.