Activation of unsaturated small molecules by bio-relevant multinuclear metal-sulfur clusters

The high affinity of sulfur (S) for transition metal ions (M), as well as the flexible M-S bonding and bridging modes, enable the formation of a wide range of multi-metallic compounds called metal-sulfur (M-S) clusters. Even though M-S clusters tolerate various nuclearities in principle, the number of metals in molecular entities, particularly those applicable in catalytic reactions, are typically 4 or lower, while the highest number of 8 has been found in the biological N-2-reducing catalyst. Other than the N-2 reduction, M-S clusters in nature have been found in the conversion of small molecules such as CO2, CO, and H-2. With the detailed structures of these native M-S clusters elucidated by recent biochemical studies, we can take steps toward the development of artificial catalysts superior to enzymes and/or those for biologically inaccessible reactions, while another direction is to deeply understand the enzymatic reactions and their relationship between the M-S structures. Here we review the progress in the reaction studies on synthetic M-S clusters, focusing on their utility in the activation and transformation of small molecules. The main part of this review has been divided into three sections: i) transformations of N-2 and related small molecules, ii) reduction of CO2, and iii) transformations of organic small molecules. Remarkable recent progress includes the development of catalytic N-2-silylation toward N(SiMe3)(3) and CO2 reduction toward C-1-C-4 hydrocarbons. Tandem reduction and N-methylation of nitroarenes have also been accomplished in the last decade. Through the review process, the development of catalytic reactions by M-S clusters was found to be still challenging. Collaborative works among chemists who can synthesize M-S clusters, those who are skilled in developing homogeneous catalytic reactions, those having spectroscopic techniques, and theoretical chemists may provide new insights into this field. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

Metal-sulfur (M-S) clusters are a class of multi-metallic compounds with high affinity, forming various compounds with different nuclearities. Recent biochemical studies have elucidated the structures of native M-S clusters, allowing us to develop artificial catalysts superior to enzymes and for biologically inaccessible reactions. This review summarizes the progress in the reaction studies on synthetic M-S clusters for the activation and transformation of small molecules.