2,2'-Dithiotolane pincer ligands with an electronically non-innocent central π-CC ligating unit and their coordination chemistry to transition metals.

The synthesis of a family of 2,2'-dithiotolane ligands with different substitution patterns is reported. The ligands feature an electronically non-innocent alkyne backbone with two thioether donor arms in the wing-positions. This enables pincer-type coordination to early and mid transition metals, as shown for tantalum, molybdenum, rhenium, and ruthenium. The resulting complexes exhibit subtle yet distinct differences in reactivity, demonstrating the electronic adaptability of the pincers and highlighting their potential as ancillary ligands for transition metals. Furthermore, the reduction of selected molybdenum complexes was explored, revealing a pronounced tendency towards dimerisation and enabling the isolation and characterisation of two constitutional isomers featuring Mo-Mo bonding. The latter was further elucidated by quantum-chemical modelling.