P-Alkynyl functionalized benzazaphospholes as transmetalating agents

Abstract

Exposure of 10π-electron benzazaphosphole 1 to HCl, followed by nucleophilic substitution with the Grignard reagent BrMgCCPh afforded alkynyl functionalized 3 featuring an exocyclic –CC–Ph group with an elongated P–C bond (1.7932(19) Å).

Synthesis and Structure of P-Halogenated Benzazaphospholes and Their Reactivity toward Pt(0) Sources

“…The X-ray crystallographic analysis also shows that the N-atom of related P-halogenated benzazaphospholes 1–F through 1–I is planar (sp 2 ); therefore, their exocyclic P–X bonds are also susceptible to N LP → σ*(P–X) negative hyperconjugation. Previously, a DFT/NBO comparison of 1– and 3–Cl with their corresponding P–CCPh derivatives indicated that the shorter P–X (X = Cl, CCPh) bonds observed in functionalized benzazaphospholes were a result of less-extensive N-lone pair delocalization into the P–X σ* orbitals than the NHP analogues (one vs two nitrogen donors) . With the halogen series of P-heterocycles 1 and 3 completed, additional comparisons can be made, as presented in Table .…”

“…Synthesis and Structures of Dearomatized and P-Halogenated Benzazaphospholes (1). Dearomatization of the five-membered ring of N-Dipp (Dipp = 2,6-diisopropyl-phenyl)-substituted benzazaphosphole 22 2 with HCl afforded 1−Cl, 18 which has been previously characterized by NMR spectroscopy, elemental analysis, and X-ray crystallography. Given that 1−Cl served as an excellent precursor to iodo analogue 1−I via its treatment with trimethylsilane (TMS)− I, 23 we hypothesized that related substitution reactions would generate 1−F and 1−Br, respectively (Scheme 2).…”

“…To summarize, all P-halogenated benzazaphospholes (1) exhibit C 1 symmetry in the solid state, 18 and the ground-state C 1 geometry featuring a covalent P−X bond is maintained in solution.…”

“… However, during the development of P-alkynyl transmetalating agents, 1–Cl and 1–I were synthesized. Despite only a difference in the identity of the halogen, NMR studies illustrated that 1–Cl had the expected C 1 symmetry in solution, while the broad spectrum of 1–I led to the suggestion that it might be ionic . Since NHPs (structure shown above in Figure ) are accessed in wide-ranging yields from their corresponding chloro, , bromo, and iodo precursors using a variety of Lewis acids or directly via a one-step redox process with diimines and PI 3 , we sought a more complete understanding of the structure, bonding, and reactivity of the entire series of P-halogenated derivatives of 1–X and their relationships to the corresponding phosphenium cations (Scheme ).…”

“…Despite only a difference in the identity of the halogen, NMR studies illustrated that 1−Cl had the expected C 1 symmetry in solution, while the broad spectrum of 1−I led to the suggestion that it might be ionic. 18 Since NHPs (structure shown above in Figure 1) are accessed in wideranging yields from their corresponding chloro, 2,19 bromo, 16b and iodo 20 precursors using a variety of Lewis acids or directly via a one-step redox process with diimines and PI 3 , 21 we sought a more complete understanding of the structure, bonding, and reactivity of the entire series of P-halogenated derivatives of 1−X and their relationships to the corresponding phosphenium cations (Scheme 1). Here, we describe the synthesis and crystallographic characterization of the remaining fluoro (1−F) and bromo (1−Br) analogues, analysis of their structures in solution by NMR spectroscopy and computationally with density functional theory (DFT) calculations, and document the reactivity of these P-halogenated species toward Pt(0).…”