Phenoxide Anion Research Articles

Basicity and bulkiness effects of 1,8-diaminonaphthalene, 8-aminoquinoline and their alkylated derivatives on the different efficiencies of η5-C5H5 and η5-C5Me5 ruthenium precatalysts in allylic etherification reactions

The different behaviours of Ru(η5-C5H5) and Ru(η5-C5Me5) precatalysts, [Ru(η5-C5R5)(NCMe)(N,N)]PF6 (R = H, Me), in the allylic etherification reaction of cinnamyl chloride using the phenoxide anion as a nucleophile was considered. The N,N ligands are the commercial products 1,8-diaminonaphthalene and 8-aminoquinoline, and their derivatives obtained by alkylation of the amino nitrogen atoms: alkyl substituents that are also bulky chiral C2-symmetric frameworks allow modulation of the basicity and steric demand of the ligands. Some of the precatalysts, [Ru(η5-C5R5)(NCMe)(N,N)]PF6 (R = H, Me), were also synthesized and characterized. The cinnamyl phenyl ether isomers were obtained with very high B/L regioselectivity values, either with Ru(η5-C5H5) or Ru(η5-C5Me5) precatalysts. The highest B/L regioselectivity values achieved with Ru(η5-C5Me5) precatalysts were found with the N,N ligand 1,8-diaminonaphthalene and its derivatives; with Ru(η5-C5H5) precatalysts best B/L values were obtained with ligands derived from 8-aminoquinoline. A correlation between the B/L regioselectivity, and the σ-donor power and bulkiness of the substituents at the nitrogen atoms of the N,N coordinated ligand was established, but the Ru(η5-C5H5) or Ru(η5-C5Me5) precatalysts followed an opposite trend. It was also found that the low ee values did not depend on the diastereomeric composition of the chiral-at-metal precatalyst [Ru(η5-C5R5)(NCMe)(N,N)]PF6.

N-Heterocyclic Carbene-Catalyzed Enantioselective Mannich Reactions with α-Aryloxyacetaldehydes

N-Heterocyclic carbenes (NHCs) catalyze a new Mannich-type reaction to form beta-amino acid derivatives in high yield and enantioselectivity. The reaction is initiated by the addition of an NHC to an alpha-aryloxyaldehyde followed by elimination of a phenoxide anion which generates an enol/enolate. A Mannich addition to a tosylimine proceeds with excellent control over enantioselectivity. In a new carbene catalysis concept, catalyst regeneration is promoted by return, or rebound, and acylation of the phenoxide group which served as the activating component in the first step of the catalytic cycle. The activated ester products formed in situ are manipulated to form a variety of useful compounds including beta-amino acids, beta-amino amides, and peptides.

Experimental and Theoretical Studies on the Nucleofugality Patterns in the Aminolysis and Phenolysis of S-Aryl O-Aryl Thiocarbonates

The reactions of S-phenyl, S-(4-chlorophenyl), and S-(2,3,4,5,6-pentafluorophenyl) 4-nitrophenyl thiocarbonates (9, 11, and 16, respectively) with a series of secondary alicyclic (SA) amines and those of S-(4-methylphenyl) 4-nitrophenyl thiocarbonate (8) and compounds 9 and 11 with a series of phenols are subjected to a kinetic investigation in 44 wt % ethanol-water, at 25.0 degrees C and an ionic strength of 0.2 M. The reactions were followed spectrophotometrically. Under nucleophile excess, pseudo-first-order rate coefficients (k(obsd)) were found. For all these reactions, plots of k(obsd) vs. free amine or phenoxide anion concentration at constant pH are linear, the slope (k(N)) being independent of pH. The Brønsted-type plots (log k(N) vs. pK(a) of the conjugate acids of the nucleophiles) for the aminolysis of 9, 11, and 16 are linear with slopes beta = 0.85, 0.90, and 0.67, respectively. The two former slopes are consistent with a stepwise mechanism, through a zwitterionic tetrahedral intermediate, which breaking to products is rate determining. The latter beta value is consistent with a concerted mechanism. The Brønsted-type plots for the phenolysis of thiocarbonates 8, 9, and 11 are linear with slopes beta = 0.62, 0.70, and 0.69, respectively. These beta values and the absence of curvature at pK(a) = 7.5 confirm a concerted mechanism. In all these reactions, except those of 16, the main nucleofuge is 4-nitrophenoxide, being the thio benzenethiolate the minor nucleofuge. For the reactions of thiocarbonate 16 the main nucleofuge is pentafluorobenzenethiolate whereas little 4-nitrophenoxide was found. The reactions of two SA amines with S-(3-chlorophenyl) 4-nitrophenyl thiocarbonate (10) were subjected to product analysis, showing 60% 4-nitrophenoxide and 40% 3-chlorobenzenethiolate. The study is completed with a theoretical analysis based on the group electrophilicity index, a reactivity descriptor that may be taken as a measure of the ability of a group or fragment to depart from a molecule with the bonding electron pair. The theoretical analysis is in accordance with the experimental results obtained and predicts relative nucleofugalities of O-aryl vs. S-aryl groups in a series of diaryl thiocarbonates not experimentally evaluated to date.

Rearrangement and predissociation processes in negative molecular ions of nitrobenzenes

The reactions of resonant electron capture by the molecules of benzene nitroderivatives has been studied in the gas phase. Some fragment negative ions were found to be unstable with respect to electron autodetachment. This circumstance has been used for the determination of their structure. In particular, it has been established that the low measured appearance energy of neutral component of [M-H](-) ion beam is a result of isomerization of nitrobenzenes' molecular ion, leading to the 2-nitrosophenol structure with the subsequent formation of the phenoxide anion in the autodetaching state. The effective yield curves of some types of fragment ions demonstrate fine vibrational structures, testifying the predissociation mechanism of ion formation. For all detected ions, the absolute cross sections of formation have been measured.

Substituent effects on the thermodynamic stability of imines formed from glycine and aromatic aldehydes: implications for the catalytic activity of pyridoxal-5'-phosphate.

Equilibrium constants for addition of glycine to substituted benzaldehydes to form the corresponding imines and pK(a)'s for ionization of the iminium ions were determined by (1)H NMR analysis in D(2)O. The introduction of a phenoxide anion substituent into the aromatic ring of benzaldehyde leads to a substantial increase in the pK(a) of the iminium ion from 6.3 to 10.2 for p-hydroxybenzaldehyde and to 12.1 for salicylaldehyde. An analysis of the differential effect of ortho- versus para-substitution shows that the iminium ion to salicylaldehyde is stabilized by an intramolecular hydrogen bond in aqueous solution, with an estimated energy ca. 3 kcal/mol larger than can be accounted for by a simple electrostatic interaction. A comparison of the o-O(-) substituent effect on the acidity of the iminium ions of glycine to benzaldehyde and 4-pyridine-carboxaldehyde provides evidence for the existence of an internal hydrogen bond of similar strength in pyridoxal 5'-phosphate (PLP) iminium ions in water. The effects of other ring substituents on the stability of PLP iminium ions are discussed.

Regio- and enantioselectivity in the alkylation and etherification reactions of cinnamyl allylic derivatives catalyzed by [(η 5-C 5R 5)Ru(N–N*)(NCCH 3)]PF 6 (R = H, Me) complexes containing N–N* bulky chiral ligands of different rigidity and flexibility

[(η 5-C 5R 5)Ru(N–N*)(NCMe)]PF 6 (R = H, N–N* = (Sa)- 1, 5; (Sa)- 2, 6; (R,R)- 3, 7; (R,R)- 4; 8; R = Me, N–N* = (Sa)- 1, 9) complexes containing N–N* bulky chiral ligands of different rigidity and flexibility were synthesized by reacting the precursor [(η 5-C 5R 5)Ru(NCMe) 3]PF 6 (R = H, Me) with the N–N* ligand in a 1:1 molar ratio. The more bulky (η 5-C 5Me 5) ligand gave low stability to the complexes [(η 5-C 5Me 5)Ru(N–N*)(NCMe)]PF 6, when N–N* = (Sa)- 2, (R,R)- 3, (R,R)- 4, in comparison to (η 5-C 5H 5) ligand and prevented their characterization. The catalytic activity of complexes 5– 9 in allylic alkylation and etherifications reactions, using malonate and phenoxide anions as nucleophiles respectively, were investigated and compared to the results obtained with corresponding precursors [(η 5-C 5H 5)Ru(NCMe) 3]PF 6 and [(η 5-C 5Me 5)Ru(NCMe) 3]PF 6. The effect of bulkiness and of rigidity and flexibility ligand features is discussed.

Are Carboxyl Groups the Most Acidic Sites in Amino Acids? Gas-Phase Acidities, Photoelectron Spectra, and Computations on Tyrosine, p-Hydroxybenzoic Acid, and Their Conjugate Bases

Deprotonation of tyrosine in the gas phase was found to occur preferentially at the phenolic site, and the conjugate base consists of a 70:30 mixture of phenoxide and carboxylate anions at equilibrium. This result was established by developing a chemical probe for differentiating these two isomers, and the presence of both ions was confirmed by photoelectron spectroscopy. Equilibrium acidity measurements on tyrosine indicated that deltaG(acid)(o) = 332.5 +/- 1.5 kcal mol(-1) and deltaH(acid)(o) = 340.7 +/- 1.5 kcal mol(-1). Photoelectron spectra yielded adiabatic electron detachment energies of 2.70 +/- 0.05 and 3.55 +/- 0.10 eV for the phenoxide and carboxylate anions, respectively. The H/D exchange behavior of deprotonated tyrosine was examined using three different alcohols (CF3CH2OD, C6H5CH2OD, and CH3CH2OD), and incorporation of up to three deuterium atoms was observed. Two pathways are proposed to account for these results, and all of the experimental findings are supplemented with B3LYP/aug-cc-pVDZ and G3B3 calculations. In addition, it was found that electrospray ionization of tyrosine from a 3:1 (v/v) CH3OH/H2O solution using a commercial source produces a deprotonated [M-H]- anion with the gas-phase equilibrium composition rather than the structure of the ion that exists in aqueous media. Electrospray ionization from acetonitrile, however, leads largely to the liquid-phase (carboxylate) structure. A control molecule, p-hydroxybenzoic acid, was found to behave in a similar manner. Thus, the electrospray conditions that are employed for the analysis of a compound can alter the isomeric composition of the resulting anion.

Phenolysis of diaryl thiolcarbonates and thionocarbonates

AbstractThe phenolysis of phenyl S‐4‐nitrophenyl thiolcarbonate (1), 4‐chlorophenyl S‐4‐nitrophenyl thiolcarbonate (2), phenyl 4‐nitrophenyl thionocarbonate (3), 3‐chlorophenyl 4‐nitrophenyl thionocarbonate (4) and 3‐methoxyphenyl 4‐nitrophenyl thionocarbonate (5) are studied kinetically in 44 wt% ethanol–water, at 25.0 °C, ionic strength 0.2 M. The Brønsted plots (log kN vs. pKa of phenols) for the reactions of 1 and 2 are linear and those of 3, 4 and 5 are curved. The Brønsted slopes for 1 and 2 are 0.64 and 0.60, respectively, which suggest a concerted mechanism for these reactions. The curved Brønsted plots for the reactions of 3, 4 and 5 show slope values of 1.0, 1.1 and 1.1, respectively, at low pKa, and 0.39, 0.28 and 0.34, respectively, at high pKa. The shape and slope values of these Brønsted plots are in accordance with a stepwise mechanism. The reactivity towards phenoxides of the thiocarbonates increases with the increase in the Hammett σ value for the substituents in the non‐leaving group. The fact that the phenolysis of 3 is stepwise, whereas that of phenyl 4‐nitrophenyl carbonate is concerted can be attributed to the destabilization of the intermediate T−. A similar argument explains the stepwise phenolysis of 3, in contrast to the concerted phenolysis of 1, where there is an additional destabilization of T− caused by the change of the leaving group, from 4‐nitrophenoxide in 3 to 4‐nitrobenzenethiolate in 1. Thiolcarbonates 1 and 2 in 44 wt% ethanol–water are less reactive towards phenoxide anions (ca. 100‐fold) than their corresponding oxycarbonates in water. Copyright © 2008 John Wiley & Sons, Ltd.

NHC-Catalyzed Reactions of Aryloxyacetaldehydes: A Domino Elimination/Conjugate Addition/Acylation Process for the Synthesis of Substituted Coumarins

N-heterocyclic carbenes (NHCs) catalyze a domino Michael addition/acylation reaction to form 3,4-dihydrocoumarins. The reaction proceeds through addition of the NHC to an aryloxyaldehyde followed by elimination of a phenoxide leaving group, generating an enol intermediate. This transient nucleophile generated in situ performs a 1,4-addition onto a conjugate acceptor, and the carbene catalyst is regenerated upon acylation of the phenoxide anion resulting in formation of 3,4-dihydrocoumarins.

Liquid chromatography/electrospray ionization/ion mobility spectrometry of chlorophenols with full flow from large bore LC columns

Chlorophenols (CPs) as a mixture of fourteen congeners from mono- to pentachlorophenol were determined using liquid chromatography/electrospray ionization/ion mobility spectrometry (LC/ESI/IMS) to describe the response and analytical performance of a mobility spectrometer as a detector for liquid chromatography. The mobility spectrometer was equipped with an interface so that flows from a large bore column could be electrosprayed directly into the drift tube at flow rates up to 500 μL/min without splitting of flow. A linear gradient of the mobile phase from 40% to 90% methanol and 60% to 10% acetic acid (AcOH)–ammonium acetate buffer solution over 40 min with a C18 column provided baseline separations though mobility spectra for CPs were influenced by mobile phase composition. Product ions formed from CPs with ESI included phenoxide anions CPO−, AcOH·CPO−, CPOH·CPO−, and Na+·(CPO−)2 and were found to be governed by the drift gas temperature. Ions were identified using LC/ESI/mass spectrometry (MS) and supported by results from computational modeling. Quantitative response was affected by congener structure through the acidities of the OH moiety and by the composition of the mobile phase. Limits of detection ranged from 0.135 mg/L for 2,3,5-trichlorophenol and pentachlorophenol to 2.23 mg/L for 2-chlorophenol; corresponding linear ranges were 20 and 70.

Polyoxometalate (POM) Oxidation of Phenols: Effect of Aromatic Substituent Groups on Reaction Mechanism

The kinetics of the oxidation of a series of substituted phenols by polyoxometalate (POM), K5[SiVW11O40] · 12H2O were investigated. Under all conditions studied second‐order kinetics were observed. Electron‐transfer from neutral phenols (k1) was slower than that from the corresponding phenoxide anions (k2), and the reaction rate was highly dependent on the nature of the substituent groups. The observed rate constants decreased in the order: p‐methoxyphenol ( 1 )>p‐methylphenol ( 2 )>m‐methylphenol ( 4 )>m‐methoxyphenol ( 3 )>phenol ( 5 )>p‐chlorophenol ( 6 )>p‐bromophenol ( 7 )>m‐chlorophenol ( 8 )>m‐nitrophenol ( 9 ). A Hammett plot of the data revealed a better correlation with σ+ than with σ, suggesting a reaction involving the formation of an electron‐deficient radical intermediate with the rate‐determining step being an electron‐transfer from a neutral substrate. Depending on the concentration of POM, oxidized phenolic and oxidative coupling products were detected.

3,4,5-Trimethoxyphenol: A combined experimental and theoretical thermochemical investigation of its antioxidant capacity

The standard (p∘=0.1MPa) molar enthalpies of combustion and sublimation of 3,4,5-trimethoxyphenol were measured, respectively, by static bomb combustion calorimetry in oxygen atmosphere and by Calvet microcalorimetry. From these measurements, the standard molar enthalpy of formation in both the crystalline and gaseous phase, at T=298.15K, were derived: −(643.4±1.9)kJ·mol−1 and −(518.1±3.6)kJ·mol−1, respectively. Density functional theory calculations for this compound and respective phenoxyl radical and phenoxide anion were also performed using the B3LYP functional and extended basis sets, which allowed the theoretical estimation of the gaseous phase standard molar enthalpy of formation through the use of isodesmic reactions and the calculation of the homolytic and heterolytic O–H bond dissociation energies. There is good agreement between the calculated and experimental enthalpy of formation. Substituent effects on the homolytic and heterolytic O–H bond dissociation energies have been analysed.

Gas-phase acidities of the 20 protein amino acids

The gas-phase acidities of the 20 protein amino acids (PAAs) have been determined using an electrospray ionization–quadrupole ion trap instrument. Three different methods were used to determine both the absolute acidities and the relative acidity ordering of the PAAs. The extended kinetic method was used to determine absolute acidities for all 20 PAAs with substituted carboxylic acids and substituted phenols as reference acids. Acidities were obtained with an average uncertainty of ±10 kJ/mol, which is large compared to some of the differences between amino acids with similar acidities. To determine the relative acidity ordering, single-reference kinetic method experiments were performed using both the reference acids from the absolute acidity studies and tryptophan and threonine as reference acids. Additional ordering information was obtained from kinetic method experiments in which proton-bound dimer ions comprising pairs of amino acids were generated and dissociated in the ion trap. The recommended acidity ordering is Gly < Ala < Pro < Val < Leu < Ile < Lys < Trp < Phe < Tyr < Met < Ser < Thr < Cys < Gln < Gln < Arg < Asn < His < Glu < Asp. Isodesmic acidity values were also obtained at the B3LYP/6-311++G**//B3LYP/6-31+G* level of theory with acetic acid as the reference acid. The theoretical acidities are in excellent agreement with the absolute acidities obtained from the extended kinetic method studies. The calculations predict that the preferred isomer for protonated cysteine and tyrosine is not a carboxylate anion, but rather a thiolate anion and a phenoxide anion, respectively.

Calculation of the relative acidities and oxidation potentials of para-substituted phenols. A model for α-tocopherol in solution

Relative acidities (Delta pK(a)) of phenols and oxidation potentials (Delta E(ox)) of the phenoxide anions have been calculated for nine para-substituted phenols using density functional theory. Solvent effects were incorporated using the conductor-like polarisable continuum method. Using the calculated Delta pK(a) and Delta E(ox) values in a thermodynamic cycle, the DeltaBDE (bond dissociation enthalpy) of the phenols were also determined with all values calculated to within 1.5 kcal mol(-1) of experiment. The Delta pK(a) and Delta E(ox) values were calculated for 6-hydroxy-2,2,5,7,8-pentamethylchroman (HPMC), a model for alpha-tocopherol for which there are no known experimental values. The acidity of this compound is raised by 2.4 pK(a) units and lowered by -0.79 V relative to phenol with a calculated Delta BDE of -14.9 kcal mol(-1). There is a negative correlation (r(2) = 0.86) between the Delta pK(a) and the Delta BDE values. A stronger and positive correlation is found between the Delta E(ox) (r(2) = 0.98) and the Delta BDE values. Using these correlations it is uncovered that hydrogen abstraction of phenols, as measured by the Delta BDE, is driven by electron transfer rather than by proton transfer.

DFT/B3LYP study of the substituent effect on the reaction enthalpies of the individual steps of sequential proton loss electron transfer mechanism of phenols antioxidant action: Correlation with phenolic C [sbnd]O bond length

The reaction enthalpies related to the individual steps of sequential proton loss electron transfer (SPLET) mechanism, for phenol and 30 meta- and para-substituted phenols (ArOH) were calculated using DFT/B3LYP method. This newly discovered mechanism represents an alternative way to the extensively studied hydrogen atom transfer (HAT) mechanism. Except the comparison of calculated reaction enthalpies with available experimental and theoretical values, obtained enthalpies were correlated with Hammett constants. We have found that electron-donating substituents induce the rise in the proton affinities of phenoxide anions ArO − (reaction enthalpy of the first step). Electron-withdrawing groups induce the increase in the reaction enthalpy of the second step of SPLET where electron from ArO − is abstracted. Found results indicate that dependences of reaction enthalpies on Hammett constants of the substituents are linear. Moreover, we found, that proton affinities and electron transfer enthalpies from ArO − can be successfully correlated with the length of phenolic C O bonds of the studied substituted phenol molecules.

The Loss of Carbon Dioxide from Activated Perbenzoate Anions in the Gas Phase: Unimolecular Rearrangement via Epoxidation of the Benzene Ring

The unimolecular reactivities of a range of perbenzoate anions (X-C6H5CO3-), including the perbenzoate anion itself (X = H), nitroperbenzoates (X = para-, meta-, ortho-NO2), and methoxyperbenzoates (X = para-, meta-OCH3) were investigated in the gas phase by electrospray ionization tandem mass spectrometry. The collision-induced dissociation mass spectra of these compounds reveal product ions consistent with a major loss of carbon dioxide requiring unimolecular rearrangement of the perbenzoate anion prior to fragmentation. Isotopic labeling of the perbenzoate anion supports rearrangement via an initial nucleophilic aromatic substitution at the ortho carbon of the benzene ring, while data from substituted perbenzoates indicate that nucleophilic attack at the ipso carbon can be induced in the presence of electron-withdrawing moieties at the ortho and para positions. Electronic structure calculations carried out at the B3LYP/6-311++G(d,p) level of theory reveal two competing reaction pathways for decarboxylation of perbenzoate anions via initial nucleophilic substitution at the ortho and ipso positions, respectively. Somewhat surprisingly, however, the computational data indicate that the reaction proceeds in both instances via epoxidation of the benzene ring with decarboxylation resulting--at least initially--in the formation of oxepin or benzene oxide anions rather than the energetically favored phenoxide anion. As such, this novel rearrangement of perbenzoate anions provides an intriguing new pathway for epoxidation of the usually inert benzene ring.

Resequencing of Comonomer Units of Well-Defined Vectra Oligomers during MALDI-TOF Mass Spectral Measurements

To aid in the detailed characterization of the LCP polymer Vectra A950, 20 alternating dimers and 10 alternating tetrameric model oligomers were synthesized and subjected to detailed MALDI and ESI spectral characterization. The model compounds were synthesized using stepwise reactions on 4-hydroxybenzoic and 6-hydroxy-2-naphthoic acids using protection−deprotection strategies. MALDI-TOF spectra of these compounds in both the positive and negative modes were determined using dithranol, 2-(4-hydroxyphenylazo)-benzoic acid (HABA), and and its methyl ester (MHABA) as matrixes and in the presence or absence of silver trifluoroacetate. The “coolest” matrix, leading to least fragmentation, proved to be dithranol with silver trifluoroacetate, while the “hottest” was dithranol alone. On the positive side, the majority of ions detected other than the parent ions proved to be acylium ions resulting from cleavage of the unexpectedly fragile aryloxy-to-carbonyl bond. At higher applied laser power, the extrusion of oxybenzoyl groups as p-quinonemethide molecules from both the chain middles and ends, followed by recombination, led to extensive resequencing of the original monomer units. Similar behavior was observed in the negative ion spectra, allowance being made for the suppression of negative ions by carboxylic and phenolic functional groups. ESI spectra on the positive side, in contrast, gave much less fragmentation but more complicated spectra resulting from the occurrence of noncovalent molecular complexes. On the negative side, much fragmentation accompanied the complex spectra, reasonably resulting from the ready formation of carboxylate and phenoxide anions. In the ESI spectra, the original monomer sequences were cleanly maintained and identified. Our results demonstrate both the power and limitations of MALDI and ESI in the characterization of Vectra A950, which by implication extend to the characterization of other commercially important polymers based on 4-hydroxybenzoic acid as well.

Lewis Base-catalyzed Alkynylation of Carbonyl Compounds with Trimethylsilylacetylenes

Abstract Alkynylation of carbonyl compounds with trimethylsilylacetylenes in the presence of a catalytic amount of Lewis bases such as acetate or phenoxide anion is described. The alkynylation proceeded under mild conditions and afforded the corresponding propargyl alcohols in good to excellent yields.

Solvent effects on spectrophotometric titrations and vibrational spectroscopy of 5,10,15-triphenyl-20-(4-hydroxyphenyl)porphyrin in aqueous DMF

The spectrophotometric titration by sodium hydroxide of 5,10,15-triphenyl-20-(4-hydroxyphenyl)porphyrin ((OH) 1PH 2) is studied as a function of solvent composition of DMF–H 2O binary solvent mixture ([OH −] = 0.04 M). Combining the structure changes of the porphyrin and the “four orbital” model of Gouterman, many features of the optical spectra of this deprotonated para-hydroxy-substituted tetraphenylporphyrin in different composition of binary solvent mixtures can be rationalized. In highly aqueous solvents, the changes of the titration curves are shown to be mainly due to hydrogen-bonding of the oxygen of the phenoxide anion group by the hydroxylic solvent, Which decreases the energy of the phenoxide anion π orbital. Thus the phenoxide anion π orbital cannot cross over the porphyrin π orbital being a different HOMO. However, its energy is close to that of the porphyrin π orbitals. As a result, in the visible region, no charge-transfer band is observed, while in the visible-near region, the Soret peak split into two components. In nonaqueous solvents, the changes are mainly attributed to further deprotonation of pyrrolic-Hs of (OH) 1PH 2 by NaOH and coordination with two sodium ions to form the sodium complex of (OH) 1PH 2, which turns hyperporphyrin spectra of deprotonated of phenolic-H of (OH) 1PH 2 into three-banded spectra of regular metalloporphyrin.

Reactivity of 1‐Hydro‐5‐carbaphosphatrane Based on Tautomerization between Pentavalent Phosphorane and Trivalent Cyclic Phosphonite

The reaction behavior of 1-hydro-5-carbaphosphatrane (1 a) was examined. Treatment of 1 a with oxidants such as 3-chloroperoxybenzoic acid (mCPBA) and tBuOCl gave cyclic phosphonate 2 and 1-chloro-5-carbaphosphatrane (4), respectively, via cyclic phosphonite 3, a tautomer of 1 a. Compound 4 was readily hydrolyzed to afford 2. Compound 1 a was also sulfurized via 3 by elemental sulfur to afford cyclic thioxophosphonate 5, which was also obtained by reactions in the presence of bases. Treatment of 1 a with bases also proceeded through 3 to give an equilibrium mixture of the corresponding phenoxide anion 10 and the phosphoranide anion 9, which was quenched with MeI to afford a mixture of 11 and 1-methyl-5-carbaphosphatrane (1 b). Such reactivities are typical for neutral phosphoranes. Theoretical investigations of these reactivities were also performed.