New palladium(II) complexes with bis(pyrazol-1-yl)alkanes

The replacement of chloride ligands in [Pd(N-N)Cl-2] (N-N = bpzm: bis(pyrazol-1-yl)methane, bpzm*: bis(3,5-dimethylpyrazol-1-yl)methane) by a weak donor ligand such as acetonitrile has been achieved by treating the dichloro complexes with AgClO4 in this solvent. The reactivity of the new precursors [Pd(N-N)(CH3CN)(2)][ClO4](2) towards a variety of neutral N- and P-donor ligands L (pyridine, triphenylphosphine, triethylphosphine) or L-2 (1,2-bis(diphenylphosphino) ethane, ethylenediamine, N,N,N',N'-tetramethylethylenediamine, 2,2'-bipyridine, o-phenylenediamine) has been studied. When chloride abstraction from [Pd(N-N)Cl-2] is carried out in Me2CO/H2O, the cationic hydroxo-bridged dimeric complexes [(N-N)Pd(mu-OH)(2)Pd(N-N)](2+) are isolated as their perchlorate salts. The hydroxo complexes react with the protic electrophiles H(L-L) (acetylacetone, salicylaldehyde and 2-pyrrol carbaldehyde) in a 1:2 molar ratio to give the corresponding mononuclear complexes [Pd(N-N)(L-L)][ClO4]. The C-13 and H-1 NMR assignments have been made on the basis of NOE studies and H-1-H-1 COSY and H-1-C-13 HETCOR experiments. The structures of [Pd(bpzm)(tmeda)][ClO4](2) and [Pd(bpzm*)(sal)][ClO4] have been determined by single-crystal X-ray diffraction studies; in both complexes the bis(pirazolyl)alkanes act as chelating ligands with coordination around the palladium atom slightly distorted from the square-planar geometry. (C) 1999 Elsevier Science S.A. All rights reserved.