Tertiary trialkyl 1,4,7-triazacyclononane (R3tacn) ligands that can be used to create reactive metal oxo-, imido- and nitrido- complexes.
- The tri-tert-butyl tacn (tBu3tacn) ligand is capable of forming 4-coordinate compounds with MnII, FeII, CoII, and NiII. These complexes are unprecedented in the chemical literature.
- The synthesis of previously inaccessible tBu3tacn requires only three chemical transformations and employs simple purification techniques.
- tBu3tacn generated redox-inert tBu3tacn-cobalt and tBu3tacn-nickel complexes.
The R3tacn series of nitrogen ligands is a classic ligand series for transition metals as the ligands serve as caps for highly oxidized metal centers (e.g. NiIII and MoVI). The tBu3tacn and tri-adamantyl tacn (Adtacn) ligands, however, were not known. Drs. Scarborough and Thangavel accessed the tBu3tacn ligand via a three step synthesis in 32% overall yield. This synthesis is highly efficient and, despite the historicalsynthetic difficulty, is superior to methods currently used to access the less bulky R3tacn ligands. Complexing the ligand with MnII, FeII, CoII, and NiII generated the first four-coordinate complexes reported for these metals. The low coordinate complexes tBu3tacn CoIIand tBu3tacn NiII were difficult to reduce with redox potentials -1.76 V and -1.58 V, respectively. This preliminary work suggests that the tBu3tacn and Adtacn ligands represent interesting ligands for the exploration of new transition metal complexes.
Publication: Thangavel et al. Inorg. Chem., 2014. 52:13282-132877