Synthesis and structure of isomeric palladium(II)-pyrazole chelate complexes with and without an N-H group as hydrogen bond donor

Four new ligands containing a pyrazole ring and either a phosphine or thioe ther were prepared and converted to their cis-dichloropalladium(II) complex es. Two of the ligands are especially notable for the attachment of a side chain at pyrazole carbon, rather than at nitrogen. The new metal complexes include dichloro[3-(diphenylphosphinomethyl)pyrazole]palladium(II) (1-PdCl2 ) and dichloro[3-(methylthiomethyl)pyrazole]palladium(II) (2-PdCl2), which both feature an N-H group as a potential proton or hydrogen bond donor. For comparison, isomeric complexes lacking an NH group were prepared: dichloro [1-(diphenylphosphinomethyl)pyrazole]palladium(II) (3-PdCl2) and dichloro[1 -(methylthiomethyl)pyrazole]palladium(II) (4-PdCl2). As determined by X-ray crystallography, all four complexes were found to have slightly distorted square planar geometry. Complexes 1-PdCl2 and 2-PdCl2, which contain an NH group, exhibit both intermolecular and intramolecular hydrogen bonding, whe reas isomers 3-PdCl2 and 4-PdCl2 do not. Single-crystal X-ray structure det erminations on the following compounds are reported: 1-PdCl2, space group P (1) over bar, a = 8.4488(9) Angstrom, b = 8.9175(13) Angstrom, c = 12.731( 2) Angstrom, Z = 2, V = 871.8(2) Angstrom(3); 2-PdCl2, space group Pbca, a = 10.8827(10) Angstrom, b = 11.7721(7) Angstrom, c = 14.874(2) Angstrom, Z =8, V = 1905.6 Angstrom(3); 3-PdCl2, space group p2(1)/c, a = 20.520(2) Ang strom, b = 12.549(2) Angstrom, c = 13.9784(13) Angstrom, Z = 8, V = 3401.1( 6) Angstrom(3); 4-PdCl2, space group Pbca, a = 10.6545(10) Angstrom, b = 12 .0205(11) Angstrom, c = 14.6474(14) Angstrom, Z = 8, V = 1875.9(3) Angstrom (3).