Rehse, A.; Linseis, M.; Azarkh, M.; Drescher, M.; Winter, R.F. Valence Tautomerism in Chromium Half-Sandwich Triarylmethylium Dyads †. Inorganics2023, 11, 448.
Rehse, A.; Linseis, M.; Azarkh, M.; Drescher, M.; Winter, R.F. Valence Tautomerism in Chromium Half-Sandwich Triarylmethylium Dyads †. Inorganics 2023, 11, 448.
Rehse, A.; Linseis, M.; Azarkh, M.; Drescher, M.; Winter, R.F. Valence Tautomerism in Chromium Half-Sandwich Triarylmethylium Dyads †. Inorganics2023, 11, 448.
Rehse, A.; Linseis, M.; Azarkh, M.; Drescher, M.; Winter, R.F. Valence Tautomerism in Chromium Half-Sandwich Triarylmethylium Dyads †. Inorganics 2023, 11, 448.
Abstract
Valence tautomerism (VT) may occur if a molecule contains two chemically different redox-active units, which differ only slightly in their intrinsic redox potential. Herein, we present three new half-sandwich complexes [(η6arene)Cr(CO)2L]+ with a triarylmethylium substituent appended to the -coordinated arene and different coligands L (L = CO, P(OPh)3, PPh3, 1+ 3+) at the chromium atom. Ligand substitution purposefully lowers the half-wave potential for chromium oxidation and thereby the redox potential difference towards tritylium reduction. For the PPh3-substituted complex 3+, cyclic voltammetry measurements indicate that chromium oxidation and tritylium reduction occur at (almost) the same potential. This renders the diamagnetic Cr(0)C6H4CAr2+ form 3+ and its paramagnetic diradical Cr(I)+•C6H4CAr2• valence tautomer 3+•• energetically nearly degenerate. Temperature-dependent IR spectroscopy shows indeed two pairs of carbonyl bands assignable to a Cr(0) and a Cr(I) species, coexisting in a T-dependent equilibrium with almost equal quantities for both at 70 °C. The diradical form with one unpaired spin at the trityl unit engages in a monomer ⇌ dimer equilibrium, which was investigated by means of quantitative EPR spectroscopy. The diradical species 1+•• 3+•• were found to be highly reactive, leading to several identified reaction products, which presumably result from hydrogen atom abstraction by the trityl C atom, e.g. from the solvent.
Chemistry and Materials Science, Inorganic and Nuclear Chemistry
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