Borane-Stabilized Isomeric Dimers of the Phosphaethynolate Anion.

The reactions of the phosphaethynolate anion ([PCO]- ) with a range of boranes were explored. BPh3 and [PCO]- form a dimeric anion featuring P-B bonds and is prone to dissociation at room temperature. The more Lewis acidic borane B(C6 F5 )3 yields a less symmetric dimer of [PCO]- with P-B and P-O bonds. Less sterically demanding HB(C6 F5 )2 and H2 B(C6 F5 ) boranes form a third isomer with [PCO]- featuring both boranes bound to the same phosphorus atom. Despite the unexpected thermodynamic preference for P-coordination, computational data illustrate that electronic and steric features impact the binding modes of the resulting dianionic dimers.