Interplay between the palladium(II) ion, unidentate ligands and hydroxyl groups from a bidentate ligand in a new complex that catalyses hydration andalcoholysis of nitrile and urea

Palladium(II) complexes containing the bidentate ligand 3,6-dithiaoctane-1, 8-diol (dtod) and chloride anions (1) or solvent molecules (2) as two unide ntate ligands were synthesized and characterized by H-1 and C-13 NMR spectr oscopy. The complex 1, which is the precursor to the catalyst 2, was also c haracterized by elemental analysis and X-ray crystallography. The crystal s tructure of I shows square planar co-ordination of two sulfur and two chlor ide ligands to palladium(II), and also a hydrogen bonding network. The comp lex 2 catalyses hydration of dichloroacetonitrile to dichloroacetamide and methanolysis of dichloroacetonitrile to (dichloromethyl)methoxymethanimine. The catalysed reactions are as much as 10(6) times faster than the uncatal ysed ones. The hydroxyl groups in the ligand dtod do not directly participa te in the hydration and methanolysis reactions of dichloroacetonitrile cata lysed by 2. The nitrile is activated for nucleophilic attack by its co-ordi nation to palladium(Ir). The nucleophile is the free water molecule or the aqua ligand in the hydration reaction and the free methanol molecule in the methanolysis reaction. Indeed, the latter reaction is first order with res pect to methanol concentration. Urea and methylurea co-ordinated to palladi um(Ir) in the complex 2 react with the hydroxyl groups of the dtod ligand a nd form alkyl carbamates. This unimolecular alcoholysis within the co-ordin ation sphere of palladium(Ir) is 240-380 times faster than the bimolecular alcoholysis involving external attack of free ethanol.