Synthesis, characterisation and photochemistry of Pt-IV pyridyl azido acetato complexes

Pt-II azido complexes[Pt(bpy)(N-3)(2)] (1), [Pt(phen)(N-3)(2)] (2) and trans-[Pt(N-3)(2)(py)(2)] (3) incorporating the bidentate diimine ligands 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen) or the monodentate pyridine (py) respectively, have been synthesised from their chlorido precursors and characterised by X-ray crystallography; complex 3 shows significant deviation from square-planar geometry (N-3-Pt-N-3 angle 146.7 degrees) as a result of steric congestion at the Pt centre. The novel Pt-IV complexes trans, cis-[Pt(bpy)(OAc)(2)(N-3)(2)] (4), trans, cis-[Pt(phen)(OAc)(2)(N-3)(2)] ( 5), trans, trans, trans-[Pt(OAc)(2)(N-3)(2)(py)(2)] (6), were obtained from 1-3 via oxidation with H2O2 in acetic acid followed by reaction of the intermediate with acetic anhydride. Complexes 4-6 exhibit interesting structural and photochemical properties that were studied by X-ray, NMR and UV-vis spectroscopy and TD-DFT (time-dependent density functional theory). These Pt-IV complexes exhibit greater absorption at longer wavelengths (epsilon = 9756 M-1 cm(-1) at 315 nm for 4; epsilon = 796 M-1 cm(-1) at 352 nm for 5; epsilon = 16900 M-1 cm(-1) at 307 nm for 6, in aqueous solution) than previously reported Pt-IV azide complexes, due to the presence of aromatic amines, and 4-6 undergo photoactivation with both UVA (365 nm) and visible green light (514 nm). The UV-vis spectra of complexes 4-6 were calculated using TD-DFT; the nature of the transitions contributing to the UV-vis bands provide insight into the mechanism of production of the observed photoproducts. The UV-vis spectra of 1-3 were also simulated by computational methods and comparison between Pt-II and Pt-IV electronic and structural properties allowed further elucidation of the photochemistry of 4-6.