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′ 2 Ti(A) 2 ] 2+ [Cl − ] 2 [Cp′ = η 5 ‐(CH 3 )C 5 H 4 and A = glycine, 1 ; 2‐methylalanine, 2 ; N ‐methylglycine, 3 ; L ‐alanine, 4 ; and D ‐alanine 5 ] were prepared by the reaction of Cp′ 2 TiCl 2 and the appropriate α‐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, 1 H, 13 C and 14 N NMR spectroscopy. The structure of compound 3 was determined by single crystal X‐ray crystallography: orthorhombic P bca No. 61 , a = 9.5310(3), b = 18.2980(5), c = 26.6350(5) Å, V = 4654 Å 3 , Z = 8. Hydrolytic stability of all compounds in D 2 O was investigated using 1 H 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)(D 2 O)] 2+ , [Cp′ 2 Ti(D 2 O) 2 ] 2+ and respective α‐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 © 2005 John Wiley & Sons, Ltd.