Desulfination versus decarboxylation as a means of generating three- and five-coordinate organopalladium complexes [(phen)nPd(C6H5)]+ (n = 1 and 2) to study their fundamental bimolecular reactivity

Abstract

Routes to the formation of the 1,10-phenanthroline (phen) ligated organopalladium complexes [(phen)Pd(C6H5)]+ and [(phen)2Pd(C6H5)]+ via thermal extrusion of CO2 or SO2 from mono-nuclear, mono-carboxylate or sulfinate complexes [(phen)nPd(O2XC6H5)]+ (X = C or S; n = 1 and 2) are examined using a combination of low energy collision induced dissociation experiments in an ion trap mass spectrometer and DFT calculations. [(phen)Pd(C6H5)]+ is formed from both [(phen)Pd(O2CC6H5)]+ and [(phen)Pd(O2SC6H5)]+, but only [(phen)2Pd(O2SC6H5)]+ fragments to form [(phen)2Pd(C6H5)]+. In contrast, [(phen)2Pd(O2CC6H5)]+ fragments via loss of a phen ligand to form [(phen)Pd(O2CC6H5)]+. The experimental results are consistent with DFT calculations, which show that the barriers associated with the desulfination reactions are lower than those for the decarboxylation reactions. Of the organopalladium cations [(phen)Pd(C6H5)]+ and [(phen)2Pd(C6H5)]+, only the three-coordinate complex reacts with pyridine via a ligand coordination reaction to yield [(phen)Pd(C6H5) (NC5H5)]+ and with formic acid via an acid-base reaction to form [(phen)Pd(O2CH)]+. DFT calculations highlight that the former reaction energy is −48 kcal/mol while the later reaction proceeds via a favourable six-centered transition structure.