Filling a Niche in “Ligand Space” with Bulky, Electron‐Poor Phosphorus(III) Alkoxides

Abstract

The chemistry of phosphorus(III) ligands, which are of key importance in coordination chemistry, organometallic chemistry and catalysis, is dominated by relatively electron‐rich species. Many of the electron‐poor PIII ligands that are readily available have relatively small steric profiles. As such, there is a significant gap in “ligand space” where more sterically bulky, electron‐poor PIII ligands are needed. This contribution discusses the coordination chemistry, steric and electronic properties of PIII ligands bearing highly fluorinated alkoxide groups of the general form PRn(ORF)3−n, where R=Ph, RF=C(H)(CF3)2 and C(CF3)3; n=1–3. These ligands are simple to synthesize and a range of experimental and theoretical methods suggest that their steric and electronic properties can be “tuned” by modification of their substituents, making them excellent candidates for large, electron‐poor ligands.

Synthesis of a Perfluorinated Phenoxyphosphorane and Conversion to Its Hexacoordinate Anions

“…[17] After optimization,t his reaction gave [Li] [P(OC 6 F 5 ) 6 ]( 6)i na lmostq uantitative yield on a1 5gscale, and this salt was amenablet oc ation-exchange using [NBu 4 ] [SiPh 3 F 2 ]t og ive the targeted 4 followinge liminationo fL iF and Ph 3 SiF (Scheme 2b). [17] After optimization,t his reaction gave [Li] [P(OC 6 F 5 ) 6 ]( 6)i na lmostq uantitative yield on a1 5gscale, and this salt was amenablet oc ation-exchange using [NBu 4 ] [SiPh 3 F 2 ]t og ive the targeted 4 followinge liminationo fL iF and Ph 3 SiF (Scheme 2b).…”

“…Thus, treatment of 1 with one equivalent of LiOC 6 F 5 in MeCN was attempted, following a recently reported synthesis of P(OC(CF 3 ) 3 ) 3 from PCl 3 and NaOC(CF 3 ) 3 in this strongly donating solvent . After optimization, this reaction gave [Li][P(OC 6 F 5 ) 6 ] ( 6 ) in almost quantitative yield on a 15 g scale, and this salt was amenable to cation‐exchange using [NBu 4 ][SiPh 3 F 2 ] to give the targeted 4 following elimination of LiF and Ph 3 SiF (Scheme b).…”

Ligand-enforced intimacy between a gold cation and a carbenium ion: impact on stability and reactivity

“…A rapid screening of the product of these reactions by 31 P NMR spectroscopy were inconsistent with the formation of the targeted cationic phosphines. Indeed, the products of these reactions, referred to as [2]OTf, [3]OTf and [4]OTf give rise to 31 P NMR resonances at 8.6 ppm for [2]OTf, 3.4 ppm for [3]OTf, and 3.9 ppm for [4]OTf, consistent with the presence of phosphonium centers and indicative of cyclization reactions as depicted in Scheme 1. The formation of these cyclized phosphonium species has been confirmed by X-ray analysis (see SI).…”

“…1,2 While the coordination chemistry of phosphine ligands has traditionally emphasized their donor properties, recent efforts have explored the induction of -acidity by incorporation of electron withdrawing substituents. [3][4][5][6][7][8] This strategy, which rests on an energy lowering of phosphorus-centered *-orbitals, 3 has been revitalized by the advent of cationic phosphines [9][10][11][12] such as A, 13,14 B, 15 C, 16 and D 17 (Figure 1). These phosphines bear a carbenium ion directly connected to the phosphorus center, setting the stage for an inductive depletion of electron density at the phosphorus center.…”

“…1,2 While the coordination chemistry of phosphine ligands has traditionally emphasized their donor properties, recent efforts have explored the induction of π-acidity by incorporation of electron withdrawing substituents. 3–8 This strategy, which rests on an energy lowering of phosphorus-centered σ*-orbitals, 3 has been revitalized by the advent of cationic phosphines 9–12 such as A , 13,14 B , 15 C , 16 and D 17 ( Fig. 1 ).…”