38651-11-5Relevant academic research and scientific papers
In Situ Generated Gold Nanoparticles on Active Carbon as Reusable Highly Efficient Catalysts for a Csp3 ?Csp3 Stille Coupling
Holz, Julia,Pfeffer, Camilla,Zuo, Hualiang,Beierlein, Dennis,Richter, Gunther,Klemm, Elias,Peters, René
supporting information, p. 10330 - 10334 (2019/06/27)
Gold nanoparticle catalysts are important in many industrial production processes. Nevertheless, for traditional Csp2-Csp2 cross-coupling reactions they have been rarely used and Pd catalysts usually give a superior performance. Herein we report that in situ formed gold metal nanoparticles are highly active catalysts for the cross coupling of allylstannanes and activated alkylbromides to form Csp3-Csp3 bonds. Turnover numbers up to 29 000 could be achieved in the presence of active carbon as solid support, which allowed for convenient catalyst recovery and reuse. The present study is a rare case where a gold metal catalyst is superior to Pd catalysts in a cross-coupling reaction of an organic halide and an organometallic reagent.
Can one predict changes from SN1 to SN2 mechanisms?
Thanh, Binh Phan,Nolte, Christoph,Kobayashi, Shinjiro,Ofial, Armin R.,Mayr, Herbert
supporting information; experimental part, p. 11392 - 11401 (2011/02/27)
The reactions of substituted benzhydryl bromides Ar2CHBr with primary and secondary amines in DMSO yield benzhydryl amines Ar 2CHNRR′, benzophenones Ar2CdO, and benzhydrols Ar2CHOH. Kinetic investigations at 20°C revealed the rate law -d[Ar2CHBr]/dt = (k1 + k2[HNRR′])[Ar 2CHBr], where the amine independent term k1 gave rise to the formation of Ar2CdO and Ar2CHOH and the amine-dependent term k2[HNRR′] was responsible for the formation of Ar2CHNRR′. Clear evidence for concomitant S N1 and SN2 processes was obtained. While the rate constants of the SN1 reactions correlate with Hammett's σ+ constants (ρ = -3.22), the second-order rate constants k2 for the SN2 reactions are not correlated with the electron releasing abilities of the substituents, indicating that the transition states of the SN2 reactions do not merge with the transition states of the SN1 reactions. The correlation equation log k 20°C = s(E + N), where nucleophiles are characterized by N and s and electrophiles are characterized by E (J. Am. Chem. Soc. 2001, 123, 9500-9512), was used to calculate the lifetimes of benzhydrylium ions in the presence of amines and DMSO. The change from SN1 to SN2 mechanism occurred close to the point where the calculated rate constant for the collapse of the benzhydrylium ions with the amines just reaches the vibrational limit; that is, the concerted SN2 mechanism was only followed when it was enforced by the lifetime of the intermediate. The nucleophile-specific parameters N and s needed for this analysis were determined by studying the kinetics of the reactions of a variety of amines with amino-substituted benzhydrylium tetrafluoroborates (Ar2CH+BF4-) of known electrophilicity E in DMSO. Analogously, the rates of the reactions of laser flash photolytically generated benzhydrylium ions Ar2CH + with DMSO in acetonitrile were employed to determine the nucleophile-specific parameters N and s of DMSO, and it is reported that DMSO is a significantly stronger O-nucleophile than water and ordinary alcohols.
Kinetics of the solvolyses of benzhydryl derivatives: Basis for the construction of a comprehensive nucleofugality scale
Denegri, Bernard,Streiter, Andre,Juric, Sandra,Ofial, Armin R.,Kronja, Olga,Mayr, Herbert
, p. 1648 - 1656 (2007/10/03)
A series of 21 benzhydrylium ions (diarylmethylium ions) are proposed as reference electrofuges for the development of a general nucleofugality scale, where nucleofugality refers to a combination of leaving group and solvent. A total of 167 solvolysis rate constants of benzhydrylium tosylates, bromides, chlorides, trifluoroacetates, 3,5-dinitrobenzoates, and 4-nitroben-zoates, two-thirds of which have been determined during this work, were subjected to a least-squares fit according to the correlation equation log k 25°C = Sf(Nf + Ef), where s f and Nf are nucleofuge-specific parameters and E f is an electrofuge-specific parameter. Although nucleofuges and electrofuges characterized in this way cover more than 12 orders of magnitude, a single set of the parameters, namely sf, Nf, and E f, is sufficient to calculate the solvolysis rate constants at 25°C with an accuracy of ± 16%. Because sf ≈ 1 for all nucleofuges, that is, leaving group/ solvent combinations, studied so far, qualitative discussions of nucleofugality can be based on Nf.
Kinetics of the reactions of halide anions with carbocations: Quantitative energy profiles for SN1 reactions
Minegishi, Shinya,Loos, Robert,Kobayashi, Shinjiro,Mayr, Herbert
, p. 2641 - 2649 (2007/10/03)
Rate constants for the reactions of Laser flash photolytically generated benzhydrylium ions (diarylcarbenium ions) with halide ions have been determined in various solvents, including neat and aqueous acetonitrile as well as some alcohols. Substitution of the rate constants into the correlation equation log k = s(N + E) yields the nucleophilicity parameters N for the halide ions in different solvents. Linear correlations with negative slopes are found between the nucleophilicity parameters N for Cl- and Br- in different solvents and the solvent ionizing powers Y of the corresponding solvents. Increasing halide solvation reduces the rates of carbocation/chloride combinations by approximately half as much as it increases the rates of ionizations of benzhydryl chlorides. Comparison of the solvent dependent nucleophilicity parameters N of halide anions and the nucleophilicity parameters N1 for solvents yields a quantitative prediction of common ion rate depression, as demonstrated by the analysis of a variety of literature reported mass-law constants α. Combination of the rate constants for the reactions of benzhydrylium ions with halide ions (k-1) reported in this work with the ionization constants of benzhydryl halides (k1) and the recently reported rate constants for the reactions of benzhydrylium ions with solvents (k2) yields complete quantitative free energy profiles for solvolysis reactions. The applicability of Hammond's postulate for interpreting solvolysis reactions can thus be examined quantitatively.
Tricyclic compounds, their production and use
-
, (2008/06/13)
A compound of the formula: wherein R1 is H or a substituent; m is 1-3; Ar is an aromatic group which may be substituted; X is a bond or a divalent straight-chain group having 1-6 atoms which may be substituted; Y is —S—, —O—, or —N(R2— (R2 is H or a substituent group), Z is —N= or —C(R3)= (R3 is H or a hydrocarbon group), ring A is a benzene ring; ring B is a 5- to 7-membered ring which may be substituted, or a salt thereof is useful for eliciting a prostaglandin I2 receptor agonistic effect.
Benzylphosphonic acid inhibitors of human prostatic acid phosphatase
Schwender,Beers,Malloy,Cinicola,Wustrow,Demarest,Jordan
, p. 311 - 314 (2007/10/03)
A series of α-substituted benzylphosphonic acids is described as inhibitors of human prostatic acid phosphatase, an enzyme has been used as a model to study aryl phosphatases. The most potent inhibitors in this series are 2-trifluoromethylbenzhydrylphosphonic acid (9 μM), and α-(2-phenylethyl)benzylphosphonic acid (14 μM). The structure-activity studies suggest that bulk tolerance beyond the phosphate binding area limits the steric or hydrophobic contribution to inhibitor potency achieved through α-carbon substitution.
Phosphorus Lone Pairs Stabilization of Carbocations: the Synthesis and Dynamics of Unsymmetrical Methylene Phosphonium Ions
Heim, Udo,Pritzkow, Hans,Schoenberg, Hartmut,Gruetzmacher, Hansjoerg
, p. 673 - 674 (2007/10/02)
Halide abstractions from P-chlorinated phosphorus ylides 9a-c either by AlCl3 or SnCl2 yield unsymmetrical methylene phosphonium ions 10a-c in which energy barriers > 83 kJ mol-1 for the rotation around the P=C have been estimated by NMR techniques.The salts with AlCl4- counteranions are stable, but compounds with SnCl3- anions decompose stereoselectively to unsymmetrical methylene phosphanes, SnCl2, and t-BuCl.
