The Dewar-Chatt-Duncanson (DCD) model provides a successful theoretical framework to describe the nature of the chemical bond in transition-metal compounds and is especially useful in structural chemistry and catalysis. However, how to actually measure its constituents (substrate-to-metal donation and metal-to-substrate back-donation) is yet uncertain. Recently, we demonstrated that the DCD components can be neatly disentangled and the π back-donation component put in strict correlation with some experimental observables. In the present work we make a further crucial step forward, showing that, in a large set of charged and neutral N-heterocyclic carbene complexes of gold(I), a specific component of the NMR chemical shift tensor of the carbenic carbon provides a selective measure of the σ donation. This work opens the possibility of 1)to characterize unambiguously the electronic structure of a metal fragment (LAu(I)n+/0 in this case) by actually measuring its σ-withdrawing ability, 2)to quickly establish a comparative trend for the ligand trans effect, and 3)to achieve a more rigorous control of the ligand electronic effect, which is a key aspect for the design of new catalysts and metal complexes.

13CNMR Spectroscopy of N-Heterocyclic Carbenes Can Selectively Probe σ Donation in Gold(I) Complexes

ZUCCACCIA, Daniele;
2017

Abstract

The Dewar-Chatt-Duncanson (DCD) model provides a successful theoretical framework to describe the nature of the chemical bond in transition-metal compounds and is especially useful in structural chemistry and catalysis. However, how to actually measure its constituents (substrate-to-metal donation and metal-to-substrate back-donation) is yet uncertain. Recently, we demonstrated that the DCD components can be neatly disentangled and the π back-donation component put in strict correlation with some experimental observables. In the present work we make a further crucial step forward, showing that, in a large set of charged and neutral N-heterocyclic carbene complexes of gold(I), a specific component of the NMR chemical shift tensor of the carbenic carbon provides a selective measure of the σ donation. This work opens the possibility of 1)to characterize unambiguously the electronic structure of a metal fragment (LAu(I)n+/0 in this case) by actually measuring its σ-withdrawing ability, 2)to quickly establish a comparative trend for the ligand trans effect, and 3)to achieve a more rigorous control of the ligand electronic effect, which is a key aspect for the design of new catalysts and metal complexes.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11390/1101025
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