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

Routes to the formation of the 1,10-phenanthroline (phen) ligated organopalladium complexes [(phen) Pd(C6H5)](+) and [(phen)(2)Pd(C6H5)](+) via thermal extrusion of CO2 or SO2 from mono-nuclear, monocarboxylate or sulfinate complexes [(phen)(n)Pd(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)(2)Pd(O2SC6H5)](+) fragments to form [(phen)(2)Pd(C6H5)](+). In contrast, [(phen)(2)Pd(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)(2)Pd(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. (C) 2018 Elsevier B.V. All rights reserved.