Phosphiranes, Phosphirenes, and Heavier Analogues

Glueck, David S.

doi:10.1016/b978-0-12-409547-2.14761-4

Cited by 6 publications

(6 citation statements)

References 95 publications

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“…To meet these criteria, we have chosen the radicals 2 , 8 , 12 , and 21 for further studies. Indeed, all of these radicals have remarkable RSE values, and the precursors to these radicals, namely, phosphirenes, phospholes, − phosphinines , (phosphabenzenes), and phosphepins, can be synthesized using well-established and effective techniques.…”

Section: Resultsmentioning

confidence: 99%

Stability of Carbocyclic Phosphinyl Radicals: Effect of Ring Size, Delocalization, and Sterics

2022

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In this computational study, we report on the stability of cyclic phosphinyl radicals with an aim for a systematical assessment of stabilization effects. The radical stabilization energies (RSEs) were calculated using isodesmic reactions for a large number of carbocyclic radicals possessing different ring sizes and grades of unsaturation. In general, the RSE values range from −1.2 to −14.0 kcal·mol–1, and they show practically no correlation with the spin populations at the P-centers. The RSE values correlate with the reaction Gibbs free energies calculated for the dimerization of the studied simple radicals. Therefore, the more easily accessible RSE values offer a cost-effective estimation of global stability in a straightforward manner. To explore the effect of unsaturation on the RSE values, delocalization energies were determined using appropriate isodesmic reactions. Introducing unsaturations beside the P-center into the backbone of the rings leads to an additive increase in the magnitude of the delocalization energy (∼10, 20, and 30 kcal·mol–1, respectively, for radicals with one, two, and three CC bonds in the conjugation). Parallelly, the spin populations at the P-centers also dwindle gradually by ∼0.1 e in the same order, indicating that the lone electron delocalizes over the π-system. Radicals containing exocyclic CC π-bonds were also investigated, and all of these radicals have rather similar stabilities independently of the ring size, outlining the primary importance of the two exocyclic π-bonds in the conjugation. Among the radicals involved in our study, those with the best electronic stabilization are the unsaturated three-, five-, six-, and seven-membered rings containing the maximum number of conjugated vinyl fragments. The largest delocalization energy of 31.5 kcal·mol–1 and the lowest obtained spin population of 0.665 e were found for the fully unsaturated seven-membered radical (phosphepin derivative). Importantly, the electronic stabilization effects alone are insufficient for stabilizing the radicals in monomeric forms epitomized by the exothermic dimerization energies (−40 to −58 kcal·mol–1). Therefore, it is essential to apply sterically demanding bulky substituents on the α-C-atoms. Tweaking the steric congestion enabled us to propose radicals that are expected to be stable against dimerization and, consequently, may be realistic target species for synthetic investigations. The effects contributing to the stability of radicals having sterically encumbered substituents have also been explored.

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Section: Resultsmentioning

confidence: 99%

Stability of Carbocyclic Phosphinyl Radicals: Effect of Ring Size, Delocalization, and Sterics

2022

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“…3 However, this idea has been little explored beyond a BASF patent on the use of Gruẗzmacher's phosphirane BABAR-Phos (Chart 1) in Rh-catalyzed hydroformylation. 4 The P−N bond in BABAR-Phos and its bicyclic structure are unusual in phosphiranes, 5 so we wanted to test the simpler P-stereogenic phosphiranes syn-and anti-Mes*PCH 2 CHPh (1−2) 6 , which formed stable Vaska-type rhodium complexes trans-RhL 2 (CO)(Cl) (Mes* = 2,4,6-(t-Bu) 3 C 6 H 2 , Chart 1). 7 Experimental and computational evidence suggests that phosphiranes are slightly poorer σ-donors than the analogous phosphines, and, in contrast to the earlier hypothesis, their πacceptor properties are similar.…”

Section: Introductionmentioning

confidence: 99%

Displacement of P-Stereogenic Phosphiranes from Rhodium by CO in Hydroformylation Catalysis

Tipker,

Hughes,

Glueck

et al. 2024

Organometallics

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The P-stereogenic phosphiranes syn-and anti-Mes*PCH 2 CHPh (1−2, Mes* = 2,4,6-(t-Bu) 3 C 6 H 2 ) formed precatalysts for the hydroformylation of propylene using the precursor Rh(acac)(CO) 2 . Stoichiometric reactions gave the complexes Rh(acac)(L)(CO) (3−4). High-pressure NMR spectroscopy showed that Rh complex 3 was formed in the catalytic mixture, but on treatment with syngas (CO/H 2 ), the phosphirane was displaced from rhodium. These observations were consistent with a density functional theory study, which found that the equilibrium between Rh(acac)(CO) 2 , phosphiranes 1−2, CO, and Rh(acac)(L)(CO) (3−4) favored the starting materials. These results emphasized the competition between CO and phosphine ligands for coordination to rhodium during hydroformylation and the importance of strong Rh-L coordination to ensure control of catalyst properties.

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“…Like the isoelectronic epoxides and aziridines, phosphiranes are potentially useful as “spring-loaded” building blocks in organophosphorus chemistry because of their strained three-membered rings. P-quaternization increases the strain further, promoting ring opening, but coordination of Lewis or Brønsted acids to phosphiranes is limited by their low Lewis basicity and proton affinity . In contrast to other phosphines, phosphiranes do not readily form adducts with BH 3 , and P-methylation requires the highly reactive electrophile methyl triflate .…”

Section: Introductionmentioning

confidence: 99%

“…P-quaternization increases the strain further, 3 promoting ring opening, but coordination of Lewis or Brønsted acids to phosphiranes is limited by their low Lewis basicity and proton affinity. 4 In contrast to other phosphines, phosphiranes do not readily form adducts with BH 3 , 5 and P-methylation requires the highly reactive electrophile methyl triflate. 6 Similarly, protonation of phosphiranes has until recently only been observed in the gas phase, where the parent P–H phosphiranium cation [C 2 H 4 PH 2 ] + has been observed by mass spectrometry 7 and studied computationally.…”

Section: Introductionmentioning

confidence: 99%

Protonation of P-Stereogenic Phosphiranes: Phospholane Formation via Ring Opening and C–H Activation

Tipker

Muldoon

et al. 2023

ACS Omega

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Protonation of cyclopropanes and aziridines is well-studied, but reactions of phosphiranes with acids are rare and have not been reported to result in ring opening. Treatment of syn-Mes*PCH 2 CHR (Mes* = 2,4,6-(t-Bu) 3 C 6 H 2 , R = Me or Ph, syn-1-2) or anti-Mes*PCH 2 CHPh (anti-2) with triflic acid resulted in regiospecific anti-Markovnikov C-protonation with ring opening and cyclophosphination of a Mes* ortho-t-Bu group to yield the phospholanium cations [PH(CH 2Me or Ph, 3−4), which were deprotonated with NEt 3 to give phospholanes 5−6. Enantioenriched or racemic syn-1 both gave racemic 3. The byproduct [Mes*PH(CH 2 CH 2 Me)(OH)][OTf] (7) was formed from syn-1 and HOTf in the presence of water. Density functional theory calculations suggested that P-protonation followed by ring opening and hydride migration to C yields the phosphenium ion, [Mes*P(CH 2 CH 2 Me)][OTf], which undergoes C−H oxidative addition of an o-t-Bu methyl group. This work established a new reactivity pattern for phosphiranes.

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Phosphiranes, Phosphirenes, and Heavier Analogues

Cited by 6 publications

References 95 publications

Stability of Carbocyclic Phosphinyl Radicals: Effect of Ring Size, Delocalization, and Sterics

Stability of Carbocyclic Phosphinyl Radicals: Effect of Ring Size, Delocalization, and Sterics

Displacement of P-Stereogenic Phosphiranes from Rhodium by CO in Hydroformylation Catalysis

Protonation of P-Stereogenic Phosphiranes: Phospholane Formation via Ring Opening and C–H Activation

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