caa a22 4500 606173706 CHVBK 20210128100734.0 cr unu---uuuuu 210128e20150901xx s 000 0 eng 10.1007/s11244-015-0417-6 doi (NATIONALLICENCE)springer-10.1007/s11244-015-0417-6 The Role of Low Valent Transition Metal Complexes in Homogeneous Catalysis: An EPR Investigation [Elektronische Daten] [Emma Carter, Damien Murphy] Electron paramagnetic resonance (EPR) spectroscopy is an extremely versatile technique for the characterisation of homogeneous catalysts involving paramagnetic centres. The paramagnetic parent pre-catalyst, the activated catalyst itself or any resulting reactive intermediates, can all be monitored in situ in order to delineate the role of the formal metal oxidation state and the influence of ligand structure on the resulting catalytic activity. In this review of our recent results, we describe how highly reactive, low valent transition metal complexes of formal oxidation states Ni(I), Fe(I) and Cr(I) coordinated by N-heterocyclic carbene (NHC) or phosphine ligands and which are active for a range of cross-coupling reactions or ethylene oligomerisation, have been investigated by EPR. Analysis of the EPR spectra revealed (i) how the influence of the NHC ring size affects the electronic properties of the Ni(I) centre, (ii) how low spin Fe(I) intermediates are catalytically competent on-cycle species in cross-coupling reactions and (iii) how intramolecular structural rearrangements involving Cr(I) centres occur following the addition of a co-catalyst to the reaction medium. These results demonstrate the utility of EPR to probe the structure-reactivity relationships in paramagnetic homogeneous catalysts, providing information not readily accessible by other techniques. Springer Science+Business Media New York, 2015 EPR spectroscopy nationallicence Low-valent nationallicence Homogeneous catalysis nationallicence Cross-coupling nationallicence Oligomerisation nationallicence Transition metals nationallicence Carter Emma School of Chemistry, Cardiff University, Main Building, Park Place, CF10 3AT, Cardiff, UK aut Murphy Damien School of Chemistry, Cardiff University, Main Building, Park Place, CF10 3AT, Cardiff, UK aut Topics in Catalysis Springer US; http://www.springer-ny.com 58/12-13(2015-09-01), 759-768 1022-5528 58:12-13<759 2015 58 11244 https://doi.org/10.1007/s11244-015-0417-6 text/html Onlinezugriff via DOI BK010053 XK010053 XK010000 Metadata rights reserved Springer special CC-BY-NC licence nationallicence 1 research-article jats NATIONALLICENCE NATIONALLICENCE NL-springer NATIONALLICENCE 856 40 https://doi.org/10.1007/s11244-015-0417-6 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Carter Emma School of Chemistry, Cardiff University, Main Building, Park Place, CF10 3AT, Cardiff, UK aut NATIONALLICENCE 700 1- Murphy Damien School of Chemistry, Cardiff University, Main Building, Park Place, CF10 3AT, Cardiff, UK aut NATIONALLICENCE 773 0- Topics in Catalysis Springer US; http://www.springer-ny.com 58/12-13(2015-09-01), 759-768 1022-5528 58:12-13<759 2015 58 11244