1,2-Diselenolene ligands and related metal complexes: Design, synthesis and applications

• 1,2-Diselenolene species can behave as noninnocent species in their relevant metal complexes. • 1,2-Diselenolene ligands origin homoleptic and heteroleptic metal complexes. • 1,2-Diselenolene metal complexes belong to extended redox electron-transfer series. • Bis(1,2-Diselenolene) complexes of d 8 metal ions shown Vis-NIR electrochromism and solvatochromism. • Solid-state properties of 1,2-diselenolene metal complexes are affected by Se···Se contacts. 1,2-Diselenolene metal complexes show a variety of chemical and physical properties, such as redox activity, visible–near-infrared absorption, optical nonlinearity, conductivity, and magnetism, which render them attractive for applications spanning from new generations of devices to catalysis. This review provides an extensive report on the synthetic pathways leading to the different classes of homoleptic and heteroleptic metal complexes featuring 1,2-diselenolene ligands, discussing their structural features, properties, and main applications. A comparison between this class of coordination compounds and their much more widely investigated 1,2-dithiolene isologues illustrates similarities and differences.