Metallaphosphinidene Coupling with a Phosphorus Ylide to Form a Phosphavinyl [P═CH ₂ ] ⁻ Ligand

High Resolution Image Download MS PowerPoint Slide 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 {P 2 } motif, [{(PCP)(OC)Ir} 2 (η 2,η 2;μ 2 -P 2 )] ( 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, PhMe 2 PCH 2, the photointermediate is intercepted, leading to a unique phosphavinyl complex, [(PCP)Ir(P═CH 2 )] ( 4 ), in 60% spectroscopic yield. Complex 2 also reacts thermally with PhMe 2 PCH 2 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 CH 2 groups couple to a [C 3 ] fragment in a new ylide, PhMe 2 PCHCOCH 3 . Structural characterization, isotopic labeling, and IR and NMR spectroscopic studies, along with quantum simulations, unveil a rigid, π-bonded [P═CH 2 ] − moiety in 4, having magnetically inequivalent hydrogens at room temperature. Complex 4 comprises a deprotonated ligand form of the elusive phosphaethylene molecule (HP═CH 2 ) 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═CH 2 ] − fragments, leading to a linear {Ir═P═CH 2 } transition geometry for this molecular switch. Lastly, we utilize the phosphavinyl ligand to form other rare π-constructs with an organic azide.