Metal Olefin Complexes: Revisiting theDewar−Chatt−DuncansonModel and Deriving Reactivity Patterns from Carbon‐13 NMR Chemical Shift

Abstract

† Dedicated to the memory of our dear friend, colleague, and mentor Richard A. Andersen. This work emanates from many discussions regarding the teaching of organometallic chemistry at the graduate and undergraduate level at UC Berkeley, ETH Zürich, and the University of Tokyo.Metal olefin complexes that are ubiquitous intermediates in catalysis are investigated by a detailed analysis of their 13 C-NMR chemical shift tensors. This analysis allows evidencing specific electronic features, namely the olefin-to-metal σ-donation and the metal-to-olefin π-backdonation as proposed in the DewarÀ ChattÀ Duncanson model. Apart from these interactions, the chemical shift tensor analysis reveals an additional ligand-to-metal πdonation of the olefin σ(C=C) orbital in systems with suitably oriented vacant d-orbitals. This interaction which is not accounted for in the DewarÀ ChattÀ Duncanson model explains the reactivity of this type of metal olefin complexes towards oxidative cyclization (olefin insertion) and protonolysis.Keywords: olefin complexes, NMR spectroscopy, density functional calculations, chemical shift analysis, frontier molecular orbitals. the DewarÀ ChattÀ Duncanson model of olefins binding to metals. b) Two Lewis structures used to represent ethylene as a neutral (left) and a di-anionic (right) ligand.

Photo-epoxidation of (α, β)-pinene with molecular O2 catalyzed by a dioxo-molybdenum (VI)-based Metal–Organic Framework

“…4). The oxygen atom transfer process is based on the (nucleophile) olefin attack on an empty (electrophile) Mo-O + π* orbital in agreement with the Dewar-Chatt-Duncanson model for the OAT process [54]. Previously, Rappé and Goddard proposed an intrinsic polarity effect of the bonds Mo δ+ -O δ− , analogous to the carbonyl group which is due to the presence of a second geminal group, allows the stabilization of the respective metal-oxygen dipole through the known oxo-spectator effect [55][56][57][58].…”

Colloidal-ALD-Grown Core/Shell CdSe/CdS Nanoplatelets as Seen by DNP Enhanced PASS–PIETA NMR Spectroscopy

“…In order to further delineate this trend, we decomposed the calculated shielding of all possible combinations within the formula [Cd­(XH 2 ) 4– n (YH 2 ) n ] 2+ (X, Y = O, S, Se, Te) into diamagnetic, paramagnetic, and spin–orbit contributions (not to be confused with the bulk properties diamagnetism and paramagnetism). − The diamagnetic contributions arise from a molecule’s electronic ground state and generally shield the nucleus. They are mostly affected by core orbitals and hence are rather independent of a nucleus’ chemical environment.…”

Deciphering Metal–Oxide and Metal–Metal Interplay via Surface Organometallic Chemistry: A Case Study with CO2 Hydrogenation to Methanol

“…Notably, these correlations are only possible where the π-interaction of ligand and metal occurs, that is, where symmetry-appropriate unoccupied d-orbitals are present on the metal center. 93 Using the combination of ΔH ads,pyridine and δ iso (CH 3 O), it was possible to demonstrate that methanol formation rates (extrapolated to 0% conversion) correlate directly with Lewis acid strength, as observed in earlier studies on Cu/MO x /Al 2 O 3 (vide supra), while CO formation rates were largely independent and similar to those observed for Cu/SiO 2  indicating that the formation of CO occurs on Cu 0 surfaces, as described in the earlier literature. 50,95,96 The outcome of this systematic study of the implications of Lewis acidity and the cooperative activation of CO 2 at the metal−support interface further supports the bifunctional nature of catalysts proficient in the conversion of CO 2 to methanol.…”