A Lewis base can be "frustrated" if, because of crowding, it cannot get its dono...

A Lewis base can be "frustrated" if, because of crowding, it cannot get its donor pair close enough to a Lewis acid for a reaction to occur. For example, do not react directly because of crowding between the lone pair of phosphorus and the boron. However, if an equimolar mixture of is mixed with 1 bar of the gas in bromobenzene solution, a white product is formed in good yield. A variety of NMR evidence has been gathered on the product: there is a single are consistent with a 4-coordinate boron atom; and indicates two nonequivalent nitrogen atoms. In addition, no gas is released in the reaction.

a. Suggest the role of in this reaction.

b. Propose a structure of the product (See E. Otten, R. C. Neu, and D. W. Stephan, J. Ant. Chew. Soc., 2009, 132, 9918.)