Prediction of Boron-Boron Triple-Bond Polymers Stabilized by Janus-Type Bis(N-heterocyclic) Carbenes.

A class of polymeric compounds containing boron-boron triple bonds stabilized by N-heterocyclic biscarbenes is proposed. Since a triply bonded B2 is related to its third excited state, the predicted macromolecule would be composed by several units of an electronically excited first-row homonuclear dimer. Moreover, it is shown that the replacement of biscarbene with N2 or CO as spacers could change the bonding profile of the boron-boron units to a cumulene-like structure. Based on these results, different types of diboryne polymers are proposed, which could lead to an unprecedented set of boron materials with distinct physical properties. The novel diboryne macromolecules could be synthesized by the reaction of Janus-type biscarbenes with tetrabromodiborane, B2 Br4 , and sodium naphthalenide, [Na(C10 H8 )], similarly to Braunschweig's work on the room temperature stable boron-boron triple bond compounds (Science, 2012, 336, 1420).