Guenter Helmchen
Jun 26, 2023
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Chemistry
Abstract
Introduction of Crabtree's iridium-based hydrogenation catalyst in 1977 marked a paradigm shift both with respect to the role of iridium in homogeneous catalysis as well as catalytic hy-dro-genation of olefins. In 1998, Pfaltz introduced an improved catalyst, by use of BARF- as anion, and established the first chiral variant of the Crabtree catalyst. This led to nume-rous practical highly enantioselective syntheses. Elucidation of mechanistic de-tails posed great problems because of instability of the crucial intermediates. A remarkable breakthrough was achieved by Brandt, Andersson et al. in 2003, based on dft calculations. These authors replaced a previously assumed IrI/IrIII catalytic cycle by a novel IrIII/IrV cycle. The proposal was experimentally verified by Pfaltz in 2014 and corroborated by advanced quantum chemical calculations. This essay is an attempt to de-scribe a fascinating interplay of experi-ments and quantum chemical calculations for an important syn-thet-ic method.