16331-65-0Relevant academic research and scientific papers
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.
Kinetics of the reduction of dialkyl peroxides. New insights into the dynamics of dissociative electron transfer
Donkers, Robert L.,Maran, Flavio,Wayner, Danial D. M.,Workentin, Mark S.
, p. 7239 - 7248 (2007/10/03)
The concerted dissociative reduction of di-tert-butyl peroxide (DTBP), dicumyl peroxide (DCP), and di-n-butyl peroxide (DNBP) is evaluated by both heterogeneous and homogeneous electron transfer using electrochemical methods. Electrochemical and thermochemical determination of the O-O bond energies and the standard potentials of the alkoxyl radicals allow the standard potentials for dissociative reduction of the three peroxides in N,N-dimethylformamide and acetonitrile to be evaluated. These values allowed the kinetics of homogeneous ET reduction of DTBP and DCP by a variety of radical anion donors to be evaluated as a function of overall driving force. Comparison of the heterogeneous ET kinetics of DTBP and DNBP as a function of driving force for ET allowed the distance dependence on the reduction kinetics of the former to be estimated. Results indicate that the kinetics of ET to DTBP is some 0.8 order of magnitude slower in reactivity than DNBP because of a steric effect imposed by the bulky tert-butyl groups. Experimental activation parameters were measured for the homogeneous reduction of DTBP with five mediators, covering a range of 0.4 eV in driving force over the temperature range -30 to 50°C in DMF. The temperature dependence of the kinetics leads to unusually low preexponential factors for this series. The low preexponential factor is interpreted in terms of a nonadiabatic effect resulting from weak electronic coupling between the reactant and product surfaces. Finally, the data are discussed in the context of recent advances of dissociative electron transfer reported by Saveant and by German and Kuznestov. In total the results suggest that these peroxides undergo a nonadiabatic dissociative electron transfer and represent the first reported class of compounds where this effect is reported.
Gas-phase ionic reactions of benzyl and methoxide anions
Gatev, Geo G.,Zhong, Meili,Brauman, John I.
, p. 531 - 536 (2007/10/03)
Gas-phase reactions of benzyl and methoxide anions with alkyl formate and other esters were compared using Fourier transform io cyclotron resonance spectroscopy. Although these anions have similar basicities, in many cases the reaction pathways differ.
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.
Bond strengths of ethylene and acetylene
Ervin, Kent M.,Gronert, Scott,Barlow,Gilles, Mary K.,Harrison, Alex G.,Bierbaum, Veronica M.,DePuy, Charles H.,Lineberger,Ellison, G. Barney
, p. 5750 - 5759 (2007/10/02)
Negative ion photoelectron spectroscopy and gas-phase proton transfer kinetics were employed to determine the CH bond dissociation energies of acetylene, ethylene, and vinyl radical: D0(HCC-H) = 131.3 ± 0.7 kcal mol-1, D0(CH2CH-H) = 109.7 ± 0.8 kcal mol-1, and D0(CH2C-H) = 81.0 ± 3.5 kcal mol-1. The strengths of each of the other CH and CC bonds in acetylene and ethylene and their fragments were derived. The energy required to isomerize acetylene to vinylidene was also determined: HC≡CH → H2C=C: ΔHisom,0 = 47.4 ± 4.0 kcal mol-1. As part of this study, proton transfer kinetics in a flowing afterglow/selected-ion flow tube apparatus were used to refine the acidities of ethylene, acetylene, and vinyl. The gas-phase acidity of acetylene was tied to the precisely known values for hydrogen fluoride, ΔGacid,298(HF) = 365.6 ± 0.2 kcal mol-1, and water, ΔGacid,298(H2O) = 383.9 ± 0.3 kcal mol-1, yielding ΔGacid,298(HCC-H) = 369.8 ± 0.6 kcal mol-1. The gas-phase acidity equilibria of acetylene with isopropyl alcohol and tert-butyl alcohol were also measured. Combined with relative acidities from the literature, these measurements yielded improved acidities for the alcohols, ΔGacid,298((CH3)2CHO-H) = 370.1 ± 0.6 kcal mol-1, ΔGacid,298((CH3)3CO-H) = 369.3 ± 0.6 kcal mol-1, ΔGacid,298(C2H5O-H) = 372.0 ± 0.6 kcal mol-1, and ΔGacid,298(CH3O-H) = 375.1 ± 0.6 kcal mol-1. The gas-phase acidity of ethylene was measured relative to ammonia, ΔGacid,298(NH3) = 396.5 ± 0.4 kcal mol-1, giving ΔGacid,298(C2H4) = 401.0 ± 0.5 kcal mol-1. The gas-phase acidity of vinyl radical was bracketed, 375.1 ± 0.6 kcal mol-1 ≤ ΔGacid,298(CH2C-H) ≤ 380.4 ± 0.3 kcal mol-1. The electron affinities of ethynyl, vinyl, and vinylidene radicals were determined by photoelectron spectroscopy: EA(HCC) = 2.969 ± 0.010 eV, EA(CH2CH) = 0.667 ± 0.024 eV, and EA(CH2C) = 0.490 ± 0.006 eV.
Nucleophilic attack on carbon monoxide in carbonyl phosphine complexes of rhodium(I) and ruthenium(II): A novel route to complexes of rhodium(-I)
Johnston, Gregory G.,Hommeltoft, Sven I.,Baird, Michael C.
, p. 1904 - 1909 (2008/10/08)
Reaction of [Rh(CO)2(triphos)]PF6 (triphos = MeC(CH2PPh2)3) with sodium borohydride in CD2Cl2 results in the formation of the hydride RhH(CO)(triphos) and the formyl complex Rh(HCO)(CO)(triphos). In contrast, treatment of [Rh(CO)2(triphos)]PF6 with excess methyllithium in THF results in the formation of the rhodium(-I) complex Li[Rh(CO)(triphos)]. The mechanism of this unusual reaction appears to involve (i) nucleophilic attack of MeLi on a carbonyl carbon of [Rh(CO)2(triphos)]PF6 to yield the acetyl complex Rh(MeCO)(CO)(triphos), (ii) attack by a second mole of MeLi on the acetyl group to produce the complex Li[Rh(Me2CO)(triphos)], and (iii) elimination of acetone to form product. In the presence of excess MeLi, the acetone reacts further to form tert-butoxide, which is also detected in the reaction mixture. The rhodium(-I) complex Li[Rh(CO)(triphos)] reacts with proton sources to yield the hydride RhH(CO)(triphos), with alkyl and acyl halides to form the alkyl complexes RhR(CO)(triphos) (R = Me, Et, Ph, MeCO), with trimethyltin chloride to form Rh(SnMe3)(CO)(triphos), and with CO to form Li[Rh(CO)2(η2-triphos)], with a pendant phosphine. The complex [Ru(CO)3(triphos)][AlCl4]2 can be synthesized by treating [RuCl-(CO)2(triphos)]Cl with AlCl3 under an atmosphere of CO. The dicationic complex [Ru(CO)3(triphos)]2+ is very susceptible to nucleophilic attack at CO and reacts with ethanol, water, and NaBH3CN to form the alkoxycarbonyl complex [Ru(CO2Et)(CO)2(triphos)]+, the hydride complex [RuH(CO)2(triphos)]+ (presumably via [Ru(CO2H)(CO)2(triphos)]+), and the formyl complex [Ru(HCO)(CO)2(triphos)]+, respectively.
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.
