Activation of the CN Single Bond in Iso(thio)cyanates by a Phosphinine‐Borane Lewis Pair: Unravelling a Complex Reaction Network

The first example of a CN σ ‐bond activation in tert ‐butyl isocyanate and isothiocyanate by a 3,5‐bis(trimethylsilyl)‐phosphinine‐B(C 6 F 5 ) 3 Lewis pair is reported. Despite the inherently low nucleophilicity of phosphinines, the first step of the observed reactions is the unusually facile tert ‐butylation of the phosphinine via an S N 1 pathway, yielding the unprecedented 1‐ t Bu‐phosphininium cation. The high reactivity of this intermediate leads to subsequent follow‐up reactions with the excess reactant as well as side‐products, forming additional phosphorus compounds under mild conditions via a complex reaction network. In stark contrast, the reaction of t BuNCO and t BuNCS with a classical frustrated Lewis pair leads to simple decomposition of the iso(thio)cyanate. This work not only reveals a new mode of CN σ ‐bond activation in iso(thio)cyanates by compounds based on main‐group elements, but also suggests a direct pathway for the selective P‐functionalization of phosphinines, opening up avenues for the targeted synthesis of such otherwise inaccessible aromatic phosphorus heterocycles.