Metal-iodosylarene complexes have been recently viewed as a second oxidant alongside of the well-known high-valent metal-oxo species. Extensive efforts have been exerted to unveil the structure-function relationship of various metal-iodosylarene complexes. In the present manuscript, density functional theoretical calculations were employed to investigate such relationship of a specific manganese-iodosylbenzene complex [Mn III (TBDAP)(PhIO)(OH)] 2+ (1). Our results fit the experimental observations and revealed new mechanistic findings. 1 acts as a stepwise 1e+1e oxidant in sulfoxidation reactions. Surprisingly, C-H bond activation of 9,10-dihydroanthracene (DHA) by 1 proceeds via a novel ionic hydride transfer/proton transfer (HT/PT) mechanism. As a comparison to 1, the electrophilicity of an iodosylbenzene monomer PhIO was investigated. PhIO performs concerted 2e-oxidations both in sulfoxidation and C-H activation. Hydroxylation of DHA by PhIO was found to proceed via a novel ionic and concerted proton-transfer/hydroxylrebound mechanism involving 2e-oxidation to form a transient carbonium species.
Coinage metal clusters stabilized by organic ligands such as phosphine or organothiolate are well known to possess multi-twinned gold cores, and the face-centered-cubic (fcc) metal atom packing is unstable until the cluster size reaches a certain threshold. In this study, we searched for the smallest size gold nanocrystal protected by thiolate ligands by means of the crystal facet cleavage (CFC) method. Starting from the nanocrystal-like Au28(SR)20 cluster, after cleaving two different crystal facets and patching the ligand shells, we obtained five nanocrystal-like Au20(SR)16 isomers. These fcc-structured Au20 clusters were quite different from non-fcc Au20(SPh-tBu)16; the latter's total structure was determined by single X-ray diffraction. By employing dispersion correction density functional theory (DFT-D) calculations and considering ligand effects, we found that fcc-structured Au20(SR)16 isomers had comparable or even lower energies when compared with the non-fcc structure found in Au20(SPh-tBu)16. Furthermore, the calculation of optical absorption spectra based on predicted fcc isomers indicated that the cubic nanocrystal-like isomer structure is a good candidate to understand the structure of the Au20(SCH2CH2Ph)16 cluster.
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