Frustrated Lewis Pair Chemistry Enables N 2 Borylation by Formal 1,3-Addition of a B-H Bond in the Coordination Sphere of Tungsten.

The first example of a formal 1,3-B-H bond addition across the M-N equivalent to N unit of an end-on dinitrogen complex has been achieved. The use of Piers' borane HB(C6F5)(2) was essential to observe this reactivity and it plays a triple role in this transformation: 1) electrophilic N-2-borylation agent, 2) Lewis acid in a frustrated Lewis pair-type B-H bond activation, and 3) hydride shuttle to the metal center. This chemistry is supported by NMR spectroscopy and solid-state characterization of products and intermediates. The combination of chelate effect and strong sigma donation in the diphosphine ligand 1,2-bis(diethylphosphino)ethane was mandatory to avoid phosphine dissociation that otherwise led to complexes where borylation of N-2 occurred without hydride transfer.