The Noble Addendum of a Phosphenium Ligand to a Base Metal: Coordination, Activation, and Hydrogenation of Alkenes and Alkynes on a Chromium Complex

Abstract

AbstractThe synthesis of a new bis‐NHP complex (NHP=N‐heterocyclic phosphenium) of chromium via salt metathesis and studies of its reactivity are reported. Photochemical reactions with H2 and selected olefins give rise to non‐isolable H2‐ and π‐alkene complexes identified spectroscopically, while internal alkynes react via activation of the triple bond to yield isolable metalla‐phospha‐cyclobutenes characterized by spectroscopic and XRD data. DFT studies give a preliminary account of the bonding in H2‐ and alkene‐complexes and explain the different reactivity towards alkenes and alkynes as the consequence of kinetic effects. Photolysis of the bis‐NHP‐complex in the presence of H2 and olefins or alkenes enables the catalytic hydrogenation of the organic substrates, while the π‐ethene complex mediates the catalytic hydrogenation of ethene in a dark reaction. The similarities and differences between both catalytic processes are shortly discussed.