Metallaphosphinidene Coupling with a Phosphorus Ylide to Form a Phosphavinyl [P═CH₂]^- Ligand

Metallaphosphinidenes, [M-P], contain open-shell single-atomic phosphorus but typically display uncontrollable reactivity, preventing their utilization to selectively construct elusive functional groups. Here, we report an iridium phosphaethynolate complex, [(PCP)Ir(PCO)] (2), in a halide metathesis with Na(OCP). Photolysis of 2 leads to a bimetallic, side-on bound {P₂} motif, [{(PCP)(OC)Ir}₂(η²,η²;μ₂-P₂)] (3), via the intermediacy of a putative, triplet iridium phosphinidene, [(PCP)Ir(P)(CO)] (A), probed computationally. When 2 is instead photolyzed in the presence of a phosphorus ylide, PhMe₂PCH₂, the photointermediate is intercepted, leading to a unique phosphavinyl complex, [(PCP)Ir(P═CH₂)] (4), in 60% spectroscopic yield. Complex 2 also reacts thermally with PhMe₂PCH₂ to form 4. Tracking of the extruded CO fragment uncovers a divergent reactivity landscape; in the photolytic pathway, a carbonyl complex, [(PCP)Ir(CO)](PCO), forms, whereas in the thermal pathway, one CO and two CH₂ groups couple to a [C₃] fragment in a new ylide, PhMe₂PCHCOCH₃. Structural characterization, isotopic labeling, and IR and NMR spectroscopic studies, along with quantum simulations, unveil a rigid, π-bonded [P═CH₂]^- moiety in 4, having magnetically inequivalent hydrogens at room temperature. Complex 4 comprises a deprotonated ligand form of the elusive phosphaethylene molecule (HP═CH₂) but possesses a much lower isomerization barrier (15.9(5) kcal mol^-1) than classical phosphaalkenes (>40 kcal mol^-1), owing to an interplay between the [(PCP)Ir]⁺ and [P═CH₂]^- fragments, leading to a linear {Ir═P═CH₂} transition geometry for this molecular switch. Lastly, we utilize the phosphavinyl ligand to form other rare π-constructs with an organic azide.