Physical insights into mechanistic processes in organometallic chemistry: an introduction

The challenges of research into the mechanisms of 4d versus 3d late transition metal homogeneous catalysts is considered here, particularly catalysts containing hydrides. Included are case studies of C-H bond activation as studied in a collaboration of the Weller and McIndoe groups where a ruthenium (4d) hydride intermediate is detected using ESI-MS analysis of the catalytic mixture, and as studied in a collaboration of the Thomas and Neidig groups where a hydride transfer step involving low valent iron (3d) catalytic species is investigated using low temperature methods including Mössbauer spectroscopy. In the asymmetric hydrogenation of olefins, mechanisms are considered for rhodium (4d) vs. the newly discovered cobalt (3d) metal catalysts from the Shevlin and Chirik groups. The Hintermair group has recently described a study of a Noyori ruthenium catalyst for the ATH of acetophenone in basic 2-PrOH using a variety of flow sampling methods including flow NMR. This mechanism is highlighted along with our iron hydride work in homogeneous asymmetric hydrogenation.