Synthesis and structure of diamine bis(phenolate) complexes containing the Ti(OEt)–O–Ti(OEt) function

Reaction of diamine-bis(phenol) ligands containing a mixture of N-methyl and N,N′-dimethyl-N,N-bis(2-hydroxy-3,5-dimethylbenzyl)ethylenediamine, H2L1 and H2L3, with [Ti(OCHMe2)4 in absolute ethanol under reflux without exclusion of air and moisture gives [(L1)Ti (OEt–O–Ti(OEt)(L1)] (1). [(L3)Ti(OEt)–O–Ti(OEt)(L3)] (2) forms when the remaining solution containing [(L3)Ti(OEt)2] (3) (characterised by X-ray crystallography) is hydrolysed with H2O. For the N-methyl and N,N′-dimethyl ligand mixture H2L2 and H2L4, which contain tert-butyl groups on the ortho-positions of the aryl rings, [(L2)Ti(OEt)–O–Ti(OEt)(L2)] (4) forms much more slowly and [(L4)Ti(OEt)2] (5) does not hydrolyse when H2O is added. When the N-protonated ligand N,N-bis(2-hydroxy-3-methyl-5-tert-butylbenzyl)ethylenediamine, H2L5, is used, rapid hydrolysis to two isomers of [(L5)Ti(OEt–O–Ti(OEt)(L5)] (6) occurs without addition of water. For N,N-bis(2-hydroxy-3,5-di-tert-butylbenzyl)ethylenediamine, H2L6, hydrolysis to [(L6)Ti(OEt)–O–Ti(OEt)(L6)] (7) occurs slowly when H2O is added. For pendant NMe2 ligand N,N-dimethyl-N′,N′-bis(2-hydroxy-3-methyl-5-tert-butylbenzyl)ethylenediamine, H2L7, the hydrolysis reaction readily gives [(L7)Ti(OEt)–O–Ti(OEt)(L7)] (8) for which an X-ray crystal structure was obtained. The ortho-tert-butyl ligand derivative H2L8 formed a complex analysing as [(L8)Ti(OEt)–O–Ti(OEt)(L8)] (9) which could not be studied further due to insolubility. Pendant pyridine ligand N-(2-pyridylmethyl)-N,N-bis(2′-hydroxy-3′-methyl-5′-tert-butylbenzyl)amine, H2L9, apparently forms isomers of [(L9)Ti(OEt)–O–Ti(OEt)(L9)] and possibly [{(L9)Ti(O)}2] from [(L9)Ti(OEt)2] (10). The ortho-tert-butyl ligand derivative H2L10 formed [(L10)Ti(OEt)–O–Ti(OEt)(L10)] (11) for which an X-ray crystal structure was obtained.

Graphical abstractReaction of diamine bis(phenolate) alkoxo titanium complexes, [LTi(OEt)2] with water in ethanol solution hydrolyses only one of the alkoxo ligands to give the oxo-bridged complexes [LTi(OEt)–O–Ti(OEt)L].Figure optionsDownload full-size imageDownload as PowerPoint slide