Catalyst Complexity in a Highly Active and Selective Wacker-Type Markovnikov Oxidation of Olefins with a Bioinspired Iron Complex

Abstract

Palladium-catalyzed Wacker-type reactions occupy a central place in organic synthesis with important implications in industry. Pursuing more benign protocols by replacing palladium with first-row transition metals allowed the identification of iron as a privileged one in the last few years. Although the anti-Markovnikov selectivity for iron catalysts is well developed, the Markovnikov-selective reactions still afford significant quantities of alcohol side-products, and identification of reaction intermediates has remained elusive so far. Herein, we present an iron catalyst that affords Markovnikov ketone products from (hetero)aromatic and aliphatic olefins in up to 99% selectivity under ambient conditions with 190,000 turnover numbers and turnover frequencies of 74 h–1 at 50 °C. The catalyst design is based on the promiscuous activity encountered in the family of the cytochromes P-450 enzymes, and it enables the formation of iron-hydride species under catalytically relevant reaction conditions. Substrate scope assessment and mechanistic investigations suggest that the Markovnikov-selective catalytic cycle competes with unprecedented three additional catalytic cycles (alcohol formation, hydrogenation, and reductive homo-coupling) depending on the nature of the olefin and the reaction conditions.