Reactivity of the pyrazolatopalladium(II) complexes [Pd(dmpz)2(Hdmpz)2] and [Pd2(μ-dmpz)2(dmpz)2(Hdmpz)2] towards carboxylic acids:: Hydrogen bonds as the driving force that determines the nature of the final products

The compound [Pd(Hdmpz)(4)](O2CCH2NHCOCH3)(2) (1; (Hdmpz = 3,5-dimethylpyrazole) has been obtained by treatment of [Pd(dmpz)(2)(Hdmpz)(2)] (A) with two equivalents of N-acetylglycine (HO2CCH2NHCOCH3). The X-ray study on a crystal of 1 revealed that the N-acetylglycinate anion links to the cationic complex [Pd(HdmpZ)(4)](2+) through the carboxylate group by charge assisted N-H(+)...O(-) hydrogen bonds. Additionally, the remaining N-H and C=O groups allow the N-acetylglycinate anions to self-assemble through N-(HO)-O-... hydrogen bonds to generate infinite chains. The compounds [Pd-2(mu-dmpz)(2)(O2CCH2NHCOCH3-kO)(2)(Hdmpz)(2)] (2) and [Pd-2(mu-dmpz)(2)(O2CC6H4-R-kO)(2)(Hdmpz)(2)] [R = m-NO2 (3a), p-N(CH3)(2) (3b), p-NH2 (3c), p-OCH3 (3d), p-OH (3e)] have been obtained by treatment of [Pd-2(mu-dmpz)(2)(dmpz)(2)-(Hdmpz)(2)] (B) with two equivalents of the monocarboxylic acids N-acetylglycine (HO2CCH2NHCOCH3) and the benzoic derivatives HO2CC6H4R [R = m-NO2, p-N(CH3)(2), p-NH2, p-OCH3, p-OH] respectively. The X-ray study on complexes 3d and 3e shows that in these complexes the carboxylate anion bonded to one Pd atom and the terminal Hdmpz group bonded to the other one have the right arrangement to establish an N-(HO)-O-... hydrogen bond. The (HO)-O-... and (NO)-O-... distances are in the range of those corresponding to charge-assisted N-H(+)...O(-) interactions. In complexes 3a-3e, the H atoms of the terminal Hdmpz groups can be replaced by Ag+ to give the mixed-metal complexes [Pd2Ag2(mu-dmpz)(4)(mu-O2CC6H4-R-kO)(2)(Hdmpz)(2)] [R = m-NO2 (4a), p-N(CH3)(2) (4b), p-NH2 (4c), p-OCH3 (4d), p-OH (4e)]. Compounds 4a-4e, which exhibit a transoid conformation of the carboxylate groups with respect to the (PdPd)-Pd-... line, isomerise to the cisoid species (4a'-4e'). The X-ray structure of the DMSO adduct of 4d' is also reported. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006).