Synthesis and Reactivity of Mixed-Ligand Palladium(II) Organometallic Complexes with Phosphites and Bis(pyrazol-1-yl)methane

New cationic organometallic palladium(II) complexes of general formula [PdMe(NN)P(OR)3]ClO4 {NN = bis(pyrazol-1-yl)methane (BPM) and bis(3,5-dimethylpyrazol-1-yl)methane (Me2BPM); P(OR)3 = phosphites} have been synthesized and characterized. The isolation of the intermediate reaction products has highlighted the formation mechanism of these species. By reacting [PdMe(BPM)P(OEt)3]ClO4 with the Cl- and SeCN- ions the neutral species PdClMe(BPM)P(OEt)3 and PdMe(SeCN)(BPM)P(OEt)3 have been prepared, the last one as a mixture of isomers. The NMR data suggest that these neutral complexes are stabilized by an anagostic interaction between a hydrogen atom of the BPM methylene bridge and the palladium center. The reaction of [PdMe(BPM)P(OEt)3]ClO4 with CO and tosylmethyl isocyanide allowed the isolation of the corresponding insertion products. Preliminary studies showed that the cationic acyl complex [Pd(COMe)(BPM)P(OEt)3]ClO4 is an active catalyst toward styrene polymerization in the presence of CO.