Synthetic and computational study of geminally bis(supermesityl) substituted phosphorus compounds

Abstract

Reaction chemistry of an extremely sterically encumbered phosphinic chloride (Mes*)(2)P(=O)Cl (Mes* = 2,4,6-tri-t-butylphenyl, supermesityl) was investigated. This compound, as well as other compounds bearing two supermesityl groups placed geminally at the central phosphorus atom, shows extremely low reactivity at the phosphorus centre. Nevertheless, some synthetically significant transformations were possible. Reduction with hydridic reagents under forcing conditions yielded the phosphine oxide (Mes*)(2)P(=O)H and a secondary phosphine Mes*(2,4-tBu(2)C(6)H(3))PH. Deprotonation of (Mes*)(2)P(=O)H gave the corresponding phosphinite, which afforded very crowded tertiary phosphine oxides (Mes*)(2)P(=O)R (R = Me and Et) on reactions with electrophiles. While the reaction of the phosphine Mes*(2,4-tBu(2)C(6)H(3))PH with sulfur was surprisingly facile (although under forcing conditions), we have been unable to chlorinate or deprotonate this phosphine. All new compounds were fully characterised with multinuclear NMR, IR, Raman, MS, microanalyses and single crystal X-ray diffraction. Our computations (B3LYP and M06-2X level) show that strain energies of (synthetically accessible) geminally substituted compounds are extremely high (180 to 250 kJ mol(-1)), the majority of the strain is stored as boat distortions to the phenyl rings in Mes* substituents.

Crystal Structure of Bis(2,4,6-trimethylphenyl)-phosphine Oxide

“…As expected based on spectroscopic data [16] and related secondary phosphine oxides [16][17][18][19], the organophosphorus compound 1 exhibits a tetracoordinate geometry. The hydrogen atom H1 was located in the difference map and allowed to freely refine giving a P1-H1 distance of 1.319(17) Å.…”

“…The P1-O1 distance measured 1.4854(13) Å and the P1-C1 and P1-C10 distances were 1.8151(18) Å and 1.8162(18) Å, respectively. The mesityl rings exhibit a twist of 31.93 (16) • (measured as the dihedral angle between C1-C6-C10-C15) that is intermediate in magnitude when compared to diphenylphosphine oxide [17] (1.2 • , relatively unhindered) and bis(2,4,6-tri-tert-butylphenyl)phosphine oxide [19] (52.4 • , extremely congested), illustrating the influence of steric congestion on the molecular structure of the compound. In the crystal, intermolecular O···H-C contacts were identified between O1, H16C, and H17B with interatomic distances of 2.561(2) Å and 2.653(2) Å, respectively (Figure 2).…”

Low‐Temperature Isolation of the Bicyclic Phosphinophosphonium Salt [Mes*2P4Cl][GaCl4]

“…At ambient temperature,s olution NMR spectra indicate that 3a + and 3b + decompose within hours. [47] One of the decomposition products was identified as [6,[48][49][50][51] In an ext series of experiments,w ea imed to further establish the identity of low-temperature intermediate 2 + .For that purpose, 1 was treated with GaCl 3 in the presence of dimethylbutadiene (dmb) as trapping reagent. [52,53] This time, no red color was observed upon addition of GaCl 3 .According to 31 At ambient temperature,c ation 5 + is characterized by four broad signals in the 31 PNMR spectrum, indicating unresolved dynamic effects.C ooling to À80 8 8Cr evealed dynamic equilibria between several conformers or rotamers (Supporting Information, Figure S3).…”

A Systematic Survey of the Reactivity of Chlorinated N2P2, NP3 and P4 Ring Systems

“…In both cases, a tBu group of the Mes* moietyh ad been transferred onto another molecular fragment or solvent molecule, indicating decomposition of the sterically demanding substituent ( Figure 2). Cleavage of tBu groups from Mes* substituents is not uncommon in the presence of Lewis acids (or by thermalt reatment), [47][48][49][50][51] thus demonstrating the high Lewis acidity of salt 6.…”