Reactions of {TiO(salen)}n [salen=N,N′-bis(salicylidene)ethylenediamine] in aromatic aldehydes and ketones

• Published in: Polyhedron 2012-02, Vol.33 (1), p.97-106
• Main Authors: Nielson, Alastair J., Telfer, Shane G., Waters, Joyce M.
• Format: Article
• Language: English
• Subjects: C–C bond formation; Oxotitanium(iv) Schiff base complexes; Reactions in aldehydes and ketones; X-ray structures
• ISSN: 0277-5387
• DOI: 10.1016/j.poly.2011.11.013

Polymeric {Ti(salen)O}n reacts with aromatic acids generated by air oxidation of aromatic aldehydes or with the acid itself to form Ti salen complexes containing a carboxylato ligand and a Ti–O–Ti bridging system. In acetophenone addition of PhCOCH2 to the salen ligand CN bond carbon occurs. Polymeric {TiO(salen)}n prepared from [Ti(OCHMe2)2(acac)2] and salen-H2 in MeOH and with an apparent chain structure, is mostly insoluble but dissolves when strongly heated in aromatic aldehydes or ketones, depositing the insoluble form again on cooling. p-Tolualdehyde performed differently, giving a red solution from which insoluble red crystals were deposited. X-ray crystallography showed the complex was [{Ti(salen)(O2CC6H4Me-4)-O-Ti(salen)(O2CC6H4Me-4)]. Solvent (1) (solvent=p-tolualdehyde or p-toluic acid) containing a Ti–O–Ti bridge. Reaction of {TiO(salen)}n with p-tert-butylbenzoic acid in the presence of excess p-tolualdehyde gave [{Ti(salen)(O2CC6H4CMe3-4)-O-Ti(salen)(O2CC6H4CMe3-4) ]. 4-CH3C6H4CHO (2) for which an X-ray crystal structure determination indicated similar connectivity around the metal as for (1). {TiO(salen)}n heated strongly in isobutyrophenone (PhCOCHMe2) also gave red crystals which X-ray analysis showed structural similarity to (1) and (2) but incorporating a PhCO2-ligand. {TiO(salen)}n heated in acetophenone gave a product which X-ray analysis showed was a dioxo-bridged dimer (4) in which C–C bond formation had occurred on one side of each salen ligand.