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 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 NBH leads to its dehydrogenation producing 5. Interestingly, reaction of 1 with an excess H NBH leads to phosphinidene (P ) species coordinating to two BH molecules (6). In contrast, [1 ][OTf] reacts with Et SiH by hydride abstraction yielding 1-H and Et SiOTf, while [1 ][B(C F ) ] reacts with Et SiH via an oxidative addition type reaction of Si-H bond to P-center, affording a new P 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 F ) ] to activate Si-H bond could still be tested in catalytic hydrosilylation of benzaldehyde, where 1 closely mimics transition metal behaviour.