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The goal of this doctoral thesis was to gain a better understanding of the reaction course in imine hydrogenation as well as to develop an efficient protocol for the iridium-catalysed asymmetric hydrogenation of aliphatic imines. In the course of these studies, cyclometalation of a chiral imine to an achiral iridium complex generated a chiral catalyst. The structure of the cyclometalated imine was demonstrated to influence the enantioselectivity of the catalyst as well as to be involved in the enantiodiscriminating step of the hydrogenation. The iridacycles were investigated in further detail by two-dimensional NMR studies and their preparation was improved by counterion metathesis. Deuterium labelling experiments depicted addition of hydrogen along the C-N double bond. Optimisation studies for an efficient asymmetric hydrogenation protocol for purely aliphatic imines are described. Hydrogenations could be conducted at -5 °C achieving full conversion and improving enantioselectivities up to 92%. Cyclic aliphatic imines could also be hydrogenated with these iridacycles, but required elevated reaction temperatures as well as hydrogen pressures to achieve turnover. These studies concluded that iridium-catalysed imine hydrogenation is commenced by cyclometalation of the imine substrate to form an active iridium(III) catalyst prior to hydrogenation.
About the author
Dr. York Schramm was born on September 1984. After obtaining his Matura MAR in 2004, he studied chemistry at the University of Basel, graduating with a Master of Science in 2009 under the supervision of Prof. Dr. A. Pfaltz and Prof. Dr. Guy Lloyd-Jones (Bristol, United Kingdom). From 2009 to 2013 he continued his studies in Basel towards a PhD in the research group of Prof. Dr. A. Pfaltz working on asymmetric imine hydrogenation. In 2014 he joined the research group of Prof. Dr. John F. Hartwig at Berkeley University to conduct post-doctoral studies.
