Ligand dynamics in tetracoordinate copper(I) complexes of bis(pyrazolyl)pyridine ligands †

Several mononuclear and a binuclear copper(I)–phosphine complex with a tridentate ligand, L [2,6-bis(3,5-dimethylpyrazol-1-ylmethyl)pyridine] or L′ [2,6-bis(pyrazol-1-ylmethyl)pyridine], have been prepared and characterized. The crystal structure of [LCu(PPh2CH2CH2PPh2)CuL][ClO4]2 has been solved. All complexes exhibit interesting molecular dynamics which could be monitored by 1H NMR spectral characteristics arising from the methylene group of the ligand and also from the protons of the pyrazole part of the ligand in some cases. The complexes with unsymmetric phosphine ligands such as PPhnBu3–n with n = 1 or 2 revealed the presence of two conformations with differing populations as evidenced by temperature dependent 1H NMR spectral data. The thermodynamics of these transformations due to the fluxional character of the ligand, L, has been studied by computer simulations of the experimental spectra. The NMR spectral characteristics revealed that the methylene protons are diastereotropic