Ligand and Metal Effects in the Gas-Phase Fragmentation of Thiomethoxymethyl Complexes

While the collision-induced dissociation (CID) of the mass-selected cation [(Ph3P)(2)Pt(CH2SCH3)](+) causes the selective liberation of PPh3, the diphosphine complex [(dppe)Pt(CH2SCH3)](+ )(dppe=1,2-bis(diphenylphosphino)ethane) ejects C2H4, CH2S, and (CH3)(2)S upon CID. The analogous palladium complexes [(Ph3P)(2)Pd(CH2SCH3)](+) and [(dppe)Pd(CH2SCH3)](+ )show similar reactivity, except that C-H-bond activation is completely lacking. For other bidentate diphosphine ligands such as dppm, dppv, dppp, dppb, dppbz, dppf, and xantphos, a correlation of the dominant reaction channels with the bite angle is observed. For bite angles > 90 degrees, hydrogen-atom transfer is favored, as evidenced by an increase in dimethyl-sulfide loss. For smaller bite angles (< 90 degrees), intramolecular activation of the thiomethoxymethyl ligand predominates, thus resulting in increased losses of thioformaldehyde and ethene. The results of the CID experiments are compared with those for [(bipy)Pt(CH2SCH3)](+), for which the loss of C(2)H(4 )is observed as the main process. DFT calculations for the complexes [(dppe)Pt(CH2SCH3)](+) and [(bipy)Pt(CH2SCH3)](+) together with the experimental findings uncover subtle differences in the underlying reaction mechanisms.