195Pt NMR Spectra of Head‐to‐Head and Head‐to‐Tail Amidato‐Bridged Platinum(III) Dinuclear Complexes

Abstract

Abstract195Pt chemical shifts and 1JPt–Pt coupling constants were measured for a series of head‐to‐head (HH) and head‐to‐tail (HT) amidato‐bridged cis‐diammineplatinum(III) dinuclear complexes involved in the axial water substitution reactions with halide ions (X– = Cl–, Br–): HH‐[Pt2(NH3)4(μ‐amidato)2L1L2]n+ ≡ [L1–Pt(N2O2)–Pt(N4)–L2]n+ (amidato = α‐pyridonato, α‐pyrrolidonato, and pivalamidato) and HT‐[Pt2(NH3)4(μ‐α‐pyridonato)2L1L2]n+ ≡ [L1–Pt(N3O)–Pt(N3O)–L2]n+; the diaqua (L1, L2 = H2O, n = 4), the aquahalo (L1 = X–, L2 = H2O, n = 3), and the dihalo complexes (L1, L2 = X–, n = 2). The 195Pt NMR spectroscopic data were considered in relation to the lability in the axial ligand substitution reaction and the electron distribution along the Pt–Pt bond. The NMR spectroscopic data suggested different electron distributions along the Pt–Pt bonds in all the HH dimers and in the HT aquahalo dimers, such as [L1–PtIV(N2O2)–PtII(N4)–L2]n+ and [X–PtIV(N3O)–PtII(N3O)–OH2]3+, respectively. Relative shifts of the 195Pt NMR signals for each substitution step indicate that the replacement of the axial water ligand by X– affects more effectively the electron density of the opposite Pt atom than that of the substituted one. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)