Dual Reactivity of a Geometrically Constrained Phosphenium Cation

A geometrically constrained phosphenium cation in bis(pyrrolyl)pyridine based NNN pincer type ligand (1(+) ) was synthesized, isolated and its preliminary reactivity was studied with small molecules. 1(+) reacts with MeOH and Et(2)NH, activating the O−H and N−H bonds via a P‐center/ligand assisted path. The reaction of 1(+) with one equiv. of H(3)NBH(3) leads to its dehydrogenation producing 5. Interestingly, reaction of 1(+) with an excess H(3)NBH(3) leads to phosphinidene (P(I)) species coordinating to two BH(3) molecules (6). In contrast, [1(+) ][OTf] reacts with Et(3)SiH by hydride abstraction yielding 1‐H and Et(3)SiOTf, while [1(+) ][B(C(6)F(5))(4)] reacts with Et(3)SiH via an oxidative addition type reaction of Si−H bond to P‐center, affording a new P(V) compound (8). However, 8 is not stable over time and degrades to a complex mixture of compounds in matter of minutes. Despite this, the ability of [1(+) ][B(C(6)F(5))(4)] to activate Si−H bond could still be tested in catalytic hydrosilylation of benzaldehyde, where 1(+) closely mimics transition metal behaviour.