Ancillary Tethering Influences σ³-P vs σ⁵-P Speciation and Enables Intermolecular S–H Oxidative Addition to Nontrigonal Phosphorus Compounds

Abstract

The design and synthesis of a nontrigonal phosphorus(III) triamide (2) bearing a peripheral ethylene bridge is described. By comparison to a compound lacking the ethylene bridge (1, (P{N[o-NMe-C 6 H 4 ] 2 })), 2 is shown to exclusively form σ 5 -P oxidative addition products upon E−H addition (E = OR, SR) in preference to a σ 3 -P adduct from cooperative addition across one P−N bond. The resulting pentacoordinate phosphoranes have been characterized by multinuclear NMR spectroscopy and X-ray crystallography. DFT calculations on relative energies of σ 3 -P and σ 5 -P species indicate that the ethylene linker in 2 energetically destabilizes the σ 3 -P tautomer of the phosphorane product (2•[H][E]) by constraining rotation along the C−N bond, favoring formation of σ 5 -P phosphoranes by ring−chain tautomerism. Article pubs.acs.org/Organometallics

Deoxyfluorination of 1°, 2°, and 3° Alcohols by Nonbasic O–H Activation and Lewis Acid-Catalyzed Fluoride Shuttling

“…In line with this hypothesis, σ 3 -P compound 5 (prepared by reaction of (±)-2a with chlorodiazaphospholene in the presence of base, see SI Section VII for details) is converted to fluorinated product (±)-3a in 74% yield by exposure to 1.05 equiv Ph 3 CF and 5 mol % B1 (Figure ). Along complementary lines, utilizing hydridoalkoxyphosphorane 6 ·[H]­[OR] (a structurally constrained analogue of 1 that can only exist as the σ 5 -P tautomer) results in no deoxyfluorinated product 3b ; instead, fluoroalkoxyphosphorane 6 ·[F]­[OR] stemming from hydride abstraction and fluoride addition to a cationic P center is observed. Indeed, fluoroalkoxyphosphoranes are the primary alcohol-derived side products observed under the reported synthetic reaction conditions (Figure , indicated by asterisks), and the amount observed is inversely correlated to substrate performance under deoxyfluorination conditions.…”

σ3/σ5-P Tautomerism and Coordination Behavior of α,α-Dialkyl-2-(diphenylphosphino)benzenemethanols

“…Notwithstanding the proposal that 6 was a metastable species (vide infra), a clear link between structures 5 and 6 is the large steric demand about the carbon bearing the oxygen atom, which, through steric relaxation, could conceivably act as the driving force favoring the σ 5 -P tautomers (steric relaxation at phosphorus could potentially also be a factor in the case of 3 versus 4 ). Along similar lines, Radosevich and co-workers have shown that the geometric constraints imposed by the ethylene bridge in structure 8 reinforce a σ 5 -P structure, whereas the analogue 7 , lacking the bridge, exists in solution as a mixture of σ 3 /σ 5 -P tautomers . Given the instability of 5 , in order to gain further insight into the factors favoring the σ 5 -P tautomers 5 and 6 , we decided to examine further the chemistry of 6 , and this subsequently led to a re-examination of the chemistry of 2 .…”

Ligand-enforced geometric constraints and associated reactivity in p-block compounds

“…183 An additional modification to the ligand framework adding an ethylene linker between the aryl rings to form a seven-membered ring in the backbone was also reported, finding similar reactivity. 184 In addition to the protic O-H and N-H bonds, compound 56 was also found to be capable of activating the hydridic B-H bond in pinacolborane via a ligand cooperative pathway. 185 This B-H activation was then able to be utilized for the catalytic hydroboration of imines (Fig.…”