21438-99-3Relevant articles and documents
The Ever-surprising chemistry of boron: Enhanced acidity of phosphine·boranes
Hurtado, Marcela,Yanez, Manuel,Herrero, Rebeca,Guerrero, Andres,Juan Z. Davalos,Jose-Luis, M. Abboud,Khater, Brahim,Guillemin, Jean-Claude
supporting information; experimental part, p. 4622 - 4629 (2009/12/29)
The gas-phase acidity of a series of phosphines and their corresponding phosphine·borane derivatives was measured by FT-ICR techniques. BH 3 attachment leads to a substantial increase of the intrinsic acidity of the system (from 80 to 110 kJ mol-1). This acidity-enhancing effect of BH3 is enormous, between 13 and 18 orders of magnitude in terms of ionization constants. This indicates that the enhancement of the acidity of protic acids by Lewis acids usually observed in solution also occurs in the gas phase. High- level DFT calculations reveal that this acidity enhancement is essentially due to stronger stabilization of the anion with respect to the neutral species on BH3 association, due to a stronger electron donor ability of P in the anion and better dispersion of the negative charge in the system when the BH3 group is present. Our study also shows that deprotonation of ClCH2PH2 and ClCH 2PH2·BH3 is followed by chloride departure. For the latter compound deprotonation at the BH3 group is found to be more favorable than PH2 deprotonation, and the subsequent loss of Cl- is kinetically favored with respect to loss of Cl - in a typical SN2 process. Hence, ClCH2PH 2·BH3 is the only phosphine·borane adduct included in this study which behaves as a boron acid rather than as a phosphorus acid.
α-Stabilization by Silyl and Phosphino Substitution
Roemer, Bettina,Gatev, Geo G.,Zhong, Meili,Brauman, John I.
, p. 2919 - 2924 (2007/10/03)
The electron affinity of the bis(dimethylphosphino)methyl radical was measured to be 35.3+/-0.2 kcal/mol, using electron photodetachment spectroscopy in an ion cyclotron resonance spectrometer.Using equilibrium measurements, ΔHacido of bis(dimethylphosphino)methane and bis(trimethylsilyl)methane was determined to be 370+/-3 and 373+/-3 kcal/mol, respectively.From measured and known electron electron affinities and gas-phase acidities, we derive C-H bond dissociation energies: bis(dimethylphosphino)methane, 92+/-3 kcal/mol, and bis(trimethylsilyl)methane, 95+/-3 kcal/mol. ΔHacido of trimethylphosphine was bracketed at 383-387 kcal/mol.The α-stabilization effect of silyl and phosphino substitution is large and comparable in size to stabilization by thio and chloro substitution.Possible mechanisms of stabilization are discussed.
Reactions of the Benzyne Radical Anion in the Gas Phase, the Acidity of the Phenyl Radical, and the Heat of Formation of o-Benzyne
Guo, Yili,Grabowski, Joseph J.
, p. 5923 - 5931 (2007/10/02)
The thermally equilibrated ion-molecule reactions of the o-benzyne radical anion have been examined in the gas phase with the flowing afterglow technique.By using the bracketing technique between o-C6H4.- and Broensted acids of known acidity, we have established the gas-phase acidity of the phenyl radical as ΔG degacid.> = 371-3+6 kcal mol-1.Combination of our experimental acidity of the phenyl radical with appropriate thermochemical data from the literature yields a variety of substantially improved thermochemical values of C6H4 and C6H5. species, most notably, ΔHfdeg = 105 kcal mol-1.In addition to behaving as a Broensted base, o-benzyne radical anion is found to undergo a number of other reactions, including electron transfer, H/D exchange, H2+ transfer, and direct addition.The reaction between o-C6H4.- and the simple aliphatic alcohols is shown to be a competition between proton transfer and H2+ transfer while that between o-C6H4.- and dioxygen or 1,3-butadiene is found to be exclusively an associative detachment process.One unanticipated, novel observation from these studies is the facile formation of an addition complex between the o-benzyne radical anion and carbon dioxide, leading to a distonic radical anion (benzoate-type anion, phenyl-type radical) that offers a unique opportunity for examining radical chemistry in ion-molecule encounter complexes.
The Ionic Hydrogen Bond and Ion Solvation. 7. Interaction Energies of Carbanions with Solvent Molecules
Meot-Ner (Mautner), Michael
, p. 3858 - 3862 (2007/10/02)
The bonding energy of a water molecule to carbanions range from 11.0 kcal/mol for c-C5H5- to 13 - 15 kcal/mol for CH2CN-, CH2CHO-, and CH2COCH3- and to 16.2 kcal/mol for HCC-.Alcohols bond to c-C5H5- more strongly, by up to 20.6 kcal/mol for the strongly acidic CF3CH2OH, and the attachment energies show an inverse linear correlation with the acidities of the alcohols.The c-C5H5- ion exhibits unusual behavior in that it bonds to the hydrogen donor H2O more weakly (11.0 kcal/mol) than to CH3CN (15.5 kcal/mol).In contrast, the more localized pyrrolide ion c-C4H4N- bonds to the two solvents by comparable strength, 15.8 and 15.7 kcal/mol, respectively.These observations indicate a specific N-*OH hydrogen bonding contribution in c-C4H4N-*H2O, and/or an unusual C-*HC type hydrogen bonding contribution in c-C5H5-*CH3CN.As to structures, correlations between ΔHoD and ΔHoacid suggest that ligands may hydrogen bond to the ? system of c-C5H5-, and to the oxygen atoms in CH2CHO- and CH3COCH2-.The latter is supported by solvent shell effects in CH3COCH2-*nH2O.
Gas-Phase Negative Ion Chemistry of Methyl Isocyanide
Filley, Jonathan,DePuy, Charles H.,Bierbaum, Veronica M.
, p. 5992 - 5995 (2007/10/02)
The gas-phase negative ion chemistry of methyl isocyanide (CH3NC) has been studied at 0.4 Torr in a flowing afterglow apparatus and compared with that of its isomer acetonitrile (CH3CN).Methyl isocyanide has been determined to be 1.8 +/- 0.4 kcal/mol less acidic than acetonitrile in the gas phase, yielding ΔH0 acid(CH3NC) = 374 +/- 3 kcal/mol.The isocyano group has been found to stabilize an adjacent radical site better than does the cyano group.Methyl isocyanide reacts with bases by competing proton abstraction and SN2 processes.The reaction of the isocyanomethyl anion with a number of neutral reagents has also been studied.It undergoes hydrogen-deuterium exchange with D2O while cyanide ion is a major product upon reaction with O2, SO2, N2O, COS, CS2, and C6H5CHO.Other ions are also produced in smaller amounts with many of these reagents.The rates of reaction of the isomeric anions with CH3Br have also been determined.
