14 For example, C s-symmetric phosphorus triamide A can promote oxidative addition of alcohols and amines. 13 Fortunately, by distorting phosphines away from their classic three-fold symmetry, their frontier orbitals can become energetically accessible. Yet, unlike TMs that have closely spaced HOMO–LUMO gaps, MG compounds feature orbitals that are far apart energetically, which limits their ability to engage in TM-type reactivity like oxidative addition, insertion, and reductive elimination. An environmentally friendly and sustainable TM alternative would be to use a more benign and earth-abundant Main Group (MG) element such as phosphorus as the active center. 12 These metal–ligand platforms are both expensive and toxic, resulting in a delicate balance between the benefits of chemical synthesis and its harmful effects to the environment and human health. 2 However, some of the most commonly employed metals like Ru, 3 Rh, 4 Ir, 5 Pd, 6 and Pt 7 are scarce, while the supporting ligands are often phosphines, 8 N-heterocyclic carbenes (NHCs), 9 and/or other elaborate scaffolds including chiral diols, 10 functionalized cyclopentadienyl ligands ( ansa-metallocenes), 11 and rare and/or non-naturally occurring amines. Introduction Transition metal (TM) catalysis 1 has revolutionized the chemical industry, enabling the conversion of cheap feedstocks into valuable products for pharmaceuticals, polymers, and other specialty chemicals. The complex 19F NMR spectra of 5 and 6 observed experimentally, were reproduced by simulations with MestreNova. Treatment of 5 with ( p-CH 3)C 6H 4MgBr generated crystalline P-( p-Tol) derivative 6, which was characterized by NMR spectroscopy, elemental analysis, and X-ray crystallography. Pincer 2 featuring four benzylic CF 3 groups was expected to strengthen the O–P–O bond of the target, but after metal–halogen exchange and quenching with PCl 3, unexpected cyclization with loss of CH 3Cl was observed to give monochlorinated 5.

However, subjecting 1 to a metalation/phosphination/reduction sequence afforded cyclotriphosphane 3, resulting from trimerization of the P( I) center unbound by its oxygen donors. Here, OCO pincers 1 and 2 were synthesized, operating under the hypothesis that the more electron-withdrawing oxygen donors would better stabilize the 3-center, 4-electron O–P–O bond of the 10–P–3 target and the sp 3-hybridized benzylic carbon atoms would prevent the formation of aromatic P-heterocycles. Using an NCN pincer, previous efforts to enforce this planarized geometry at P resulted in the formation of a C s-symmetric, 10π-electron benzazaphosphole that existed as a dynamic “bell-clapper” in solution. In order to stabilize a 10–P–3 species with C 2v symmetry and two lone pairs on the central phosphorus atom, a specialized ligand is required.

Coupling constants mestrenova