ABSTRACT
We report the preparation and characterization of the dinuclear AuII hydroxide complex AuII 2(L)2(OH)2 (L=N,N'-bis (2,6-dimethyl) phenylformamidinate) and study its reactivity towards weak X-H bonds. Through the interplay of kinetic analysis and computational studies, we demonstrate that the oxidation of cyclohexadiene follows a concerted proton-coupled electron transfer (cPCET) mechanism, a rare type of reactivity for Au complexes. We find that the Au-Au σ-bond undergoes polarization in the PCET event leading to an adjustment of oxidation levels for both Au centers prior to C(sp3)-H bond cleavage. We thus describe the oxidation event as a valence tautomerism-induced PCET where the basicity of one reduced Au-OH unit provides a proton acceptor and the second more oxidized Au center serves as an electron acceptor. The coordination of these events allows for unprecedented radical-type reactivity by a closed shell AuII complex.
ABSTRACT
Crystallographic distances and the electron density of bi- and tri-nuclear gold(I) compounds reveal that the existence of multiple Auâ¯Au interactions increases their individual strength in the order of 0.9-2.9 kcal mol-1. We observed this behaviour both experimentally and theoretically in multinuclear systems, confirming a novel important cooperative character in aurophilic contacts.
ABSTRACT
We studied the influence of changing the degree of fluorination in eight new gold(i) derivatives containing both JohnPhos phosphine and polyfluorinated thiolates: [Au(SRF)(JPhos)], JPhos = P(C6H4-C6H5)(t-But)2 and RF = C6F5 (1), C6HF4 (2), C6H3F2-3,5 (3), C6H3F2-2,4 (4), C6H4F-2 (5), C6H4F-3 (6), C6H4F-4 (7) and CF3 (8). We determined the molecular and crystal structures of all new compounds by single crystal X-ray diffraction. Later, we characterised the chemical bonding scenario with quantum chemical topology tools, specifically the Quantum Theory of Atoms in Molecules (QTAIM) and the analysis of the NCI-index. Our QTAIM results indicate that while the linear S-Au-P moiety is unaffected by the variation of the fluorine content on the thiolates and that Au-S and Au-P bond strengths are mostly constant for all compounds in the series, the π character of gold bonds seems to be modified by the fluorination of the substituents at the thiolate ligand. Besides, the examination of the NCI-index reveals the presence of weak Au-πPhenyl non-covalent interactions in all compounds. Overall, this study shows the relevance of (i) the π-backbonding properties of the metal centre and (ii) different non-covalent interactions in the stability of JohnPhos gold(i) compounds.
