Ionic complexes of 1,1′-dimethyltitanocene(IV) dichloride with simple α-amino acids:: synthesis, structural characterisation and investigation on hydrolytic stability in aqueous solution

Five cationic complexes of the general formula [Cp'Ti-2(A)(2)](2+) [CI-](2) [Cp' = eta(5)-(CH3)C5H4 and A = glycine, 1; 2-methylalanine, 2; N-methylglycine, 3; L-alanine, 4; and D-alanine 51 were prepared by the reaction of Cp'TiCl2 and the appropriate alpha-amino acid in 1: 2 molar ratio from methanol-water solution in high yield. Air-stable crystalline solids, highly soluble in water, were characterized by means of elemental analysis, IR, Raman, H-1, C-13 and N-14 NMR spectroscopy. The structure of compound 3 was determined by single crystal X-ray crystallography: orthorhombic Pbca No. 61, a = 9.5310(3), b = 18.2980(5), c = 26.6350(5) angstrom, V = 4654 angstrom(3), Z = 8. Hydrolytic stability of all compounds in D2O was investigated using 1H NMR spectroscopy within the pD, interval of 2.9-6.5. All compounds slowly decomposed during 24 h at pD = 2.94, forming a mixture of hydrolytic products [Cp-2'Ti(A)(D2O)](2+), [Cp-2'Ti(D2O)(2)](2+) and respective alpha-amino acids. By elevating pD to 4.0 and up to 6.5, a yellowish precipitate was formed, which indicates decomposition of the complexes. These compounds were characterized using elemental analyses, IR and Raman spectroscopy and attributed to oligomeric and/or polymeric structures described empirically by the formula Ti(Cp')(x)O-y(OH)(z) (x = 0.65; y = 0.3, z = 1.9). Copyright (c) 2005 John Wiley & Sons, Ltd.