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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. 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. 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. 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. 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 3 Cl was observed to give monochlorinated 5. Treatment of 5 with ( p -CH 3 )C 6 H 4 MgBr generated crystalline P-( p -Tol) derivative 6, which was characterized by NMR spectroscopy, elemental analysis, and X-ray crystallography. The complex 19 F NMR spectra of 5 and 6 observed experimentally, were reproduced by simulations with MestreNova. 

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). Stoichiometric experiments revealed that treatment of trans -Pd(PEt 3 ) 2 (Ar)( i ) (Ar = p -Me ( C ) or p -F ( D )) with 3 generated trans -Pd(PEt 3 ) 2 (Ar)(CCPh) (Ar = p -Me ( E ) or p -F ( F )), 5 , which is the result of ligand exchange between P–I byproduct 4 and C/D , and the reductively eliminated product (Ar–CC–Ph). Cyclic voltammetry studies showed and independent investigations confirmed 4 is also susceptible to redox processes including bimetallic oxidative addition to Pd(0) to give Pd( i ) dimer 6-Pd2-(P(t-Bu)3)2 and reduction to diphosphine 7 . During catalysis, we hypothesized that this unwanted reactivity could be circumvented by employing a source of fluoride as an additive. This was demonstrated by conducting a Sonogashira-type reaction between 1-iodotoluene and 3 in the presence of 10 mol% Na 2 PdCl 4 , 20 mol% P( t -Bu)Cy 2 , and 5 equiv. of tetramethylammonium fluoride (TMAF), resulting in turnover and the isolation of Ph–CC–( o -Tol) as the major product.