Dialkynylborane Complexes of Formazanate Ligands: Synthesis, Electronic Properties, and Reactivity

Dialkynylborane complexes of N-donor ligands have received significant attention because of their application in biological imaging, as light-harvesting materials, and as the functional component of organic photovoltaics. Despite these advances, relatively few types of N-donor ligands have been explored in this context. To this end, we prepared a series of dialkynylborane complexes of formazanate ligands and explored their electronic properties and reactivity. In doing so, we demonstrated that (1) the nature of the alkynyl substituents has little influence over the UV-vis absorption properties of the title complexes, but does affect the potentials at which they are electrochemically oxidized and reduced, (2) dialkynylborane formazanate complexes can be converted to stable radical anions by chemical reduction with cobaltocene derivatives, and (3) copper-assisted alkyne-azide cycloaddition chemistry at the alkynyl substituents directly bound to boron can be used to elaborate structural diversity. These conclusions are likely to lead to the development of, and provide guiding principles for the design of, future examples of functional molecular materials based on boron complexes of N-donor ligands.