Diacetylplatinum(II) Complexes with κ 2 -Coordinated Tris(pyridyl)methanol and Tris(pyridyl)methyl Ether Ligands: Structural Insight into the Ligand Dynamics in Solution

Reactions of the bis(benzylamine)platinum(II) complex [Pt(COMe)(2)(NH2Bn)(2)] (2; Bn = benzyl) with (2-py)(3)COR (2-py = 2-pyridyl), (2-py)(2)PhCOR, and (2-py)(2)(m-Tol)COR (m-Tol = 3-methylphenyl) afforded the neutral diacetylplatinum(II) complexes [Pt(COMe)(2){(2-py)(3)COR}] (R = H (3a), Me (3b), Et (3c), Bn (3d)), [Pt(COMe)(2){(2-py)(2)PhCOR}] (R = H (4a), Me (4b)), and [Pt(COMe)(2){(2-py)(2)(m-Tol)COR}] (R = H (5a) Me (5b)), respectively, having, due to a kappa(2) coordination of the ligands, a 2-pyridyl (3), a phenyl (4), or a m-tolyl (5) ring as the pendant group. The identities of all complexes were unambiguously proved by high-resolution mass spectrometric investigations and by NMR (H-1, C-13, Pt-195) and IR spectroscopy as well as by single-crystal X-ray diffraction analyses (3a-d). In methanol solution, complexes 3b-d and 5b show a dynamic behavior. The thermodynamic parameters of these dynamics have been determined by variable-temperature H-1 NMR measurements (Eyring plots). Furthermore, extensive DFT calculations will be presented, which indicate that the dynamics are caused by the interplay of hindered and respectively unhindered rotations of the substituent R and/or the pendant group.