Tris(pyrazolyl)methanesulfonates: More Than Just Analogues of Tris(pyrazolyl)borate Ligands; N,N,N-, N,N,O-, and Other Coordination Modes

The thallium(<SC>I</SC>) salts of tris(pyrazolyl)methanesulfonate (Tpms) and tris(3-tert-butylpyrazolyl)methanesulfonate (Tpms^tBu) have been used to prepare the following complexes: [(Tpms^tBu)ZnX] [X = Cl (1a), Br (1b), I (1c), Et (3), OAc (5a)], [(Tpms^tBu)NiX] [X = Cl (2a), Br (2b)], [(Tpms^tBu)CoCl(Hpz^tBu)] (3), [(Tpms^tBu)Zn(μ-OAc)(μ-OH)Zn(Tpms^tBu)] (5b), [(Tpms^tBu)Cu(CO)] (6a), and [(Tpms)Cu(CO)] (6b). The solid-state structures of 1b, 2a, 3, and 5b have been determined by X-ray analysis. The optical spectra of 2a and 3 were investigated by means of the angular overlap model to elucidate their electronic structures in view of the underlying molecular geometries. Variable-temperature NMR and IR spectroscopic studies show that Tpms and Tpms^tBu can act as N,N,N and N,N,O ligands. Both coordination modes are present in solution for the zinc complexes 1a,b and the copper carbonyl complexes 6a,b. The N,N,O bonding mode is entropically favoured in solution. For the nickel complexes 2a,b, the Tpms^tBu ligand acts as a tripodal nitrogen ligand in the solid state and in solution. For the dinuclear zinc complex 5b, one of the Tpms^tBu ligands acts as an N,N,O ligand and one as an N,O ligand. Complex 5b is one of the very few structural models of the dinuclear zinc enzymes phospholipase C and phosphotriesterase. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)