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341.
The mechanistic details on enamine formation between dimethylamine and propanal are unraveled using the ab initio and density functional theory methods. The addition of secondary amine to the electrophile and simultaneous proton transfer results in a carbinolamine intermediate, which subsequently undergoes dehydration to form enamine. The direct addition of amine as well as the dehydration of the resulting carbinolamine intermediate is predicted to possess fairly high activation barrier implying that a unimolecular process is unlikely to be responsible for enamine formation. Different models are therefore proposed which could explain the relative ease of enamine formation under neat condition as well as under the influence of methanol as the co-catalyst. The explicit inclusion of either the reagent or the co-catalyst is considered in the transition states as stabilizing agents. The participation of the reagent or the co-catalyst as a monofunctional ancillary species is found to stabilize the transition states relative to the unassisted or the direct addition/dehydration pathways. The reduction in enthalpy of activation is found to be much more dramatic when two co-catalysts participate in an active bifunctional mode in the rate-determining dehydration step. The transition structures exhibited characteristic features of a relay proton transfer mechanism. The free energy of activation associated with the two methanol-assisted pathway is found to be 16.7 kcal/mol lower than that of the unassisted pathway. The results are found to be in concurrence with the available reports on the rate acceleration by co-catalysts in the Michael reaction between enamine and methyl vinyl ketone under neat conditions. 相似文献
342.
Heteroleptic half-sandwich Ru(II), Rh(III) and Ir(III) complexes based on 5-ferrocenyldipyrromethene
Mahendra Yadav 《Journal of organometallic chemistry》2011,696(3):758-763
The synthesis and characterization of heteroleptic complexes with the formulations [(η6-arene)RuCl(fcdpm)] (η6-arene = C6H6, C10H14) and [(η5-C5Me5)MCl(fcdpm)] (M = Rh, Ir; fcdpm = 5-ferrocenyldipyrromethene) have been reported. All the complexes have been characterized by elemental analyses, IR, 1H NMR and electronic spectral studies. Structures of [(η6-C6H6)RuCl(fcdpm)] and [(η6-C10H14)RuCl(fcdpm)] have been determined crystallographically. Chelating monoanionic linkage of fcdpm to the respective metal centres has been supported by spectral and structural studies. Further, reactivity of the representative complex [(η6-C10H14)RuCl(fcdpm)] with ammonium thiocyanate (NH4SCN) and triphenylphosphine (PPh3) have been examined. 相似文献
343.
Petuškova J Patil M Holle S Lehmann CW Thiel W Alcarazo M 《Journal of the American Chemical Society》2011,133(51):20758-20760
Carbene-stabilized [L(3)P](+3) cations have been synthesized for the first time by a reaction between 1-chloro-2,3-bis(dialkylamino)cyclopropenium salts and P(SiMe(3))(3). In addition, the first structural characterization of such an entity is reported. Consistent with the X-ray data, density functional calculations indicate that these P-centered cations, despite their high positive charge, still feature a nonbonding electron pair on the P-atom (HOMO) and a very low-lying LUMO depicting them as poor σ-donors and excellent π-acceptors. 相似文献
344.
We have synthesized the nickel(II) 2,3-bis(haloethynyl)-5,10,15,20-tetraphenylporphyrins with -Br (2a) or -I (2b) at the alkyne termini position from the corresponding 2,3-diethynyl analogue (1). The cross coupling of nickel(II) 2,3-dibromo-5,10,15,20-tetraphenylporphyrin with trimethyl(trimethylstannanylethynyl)silane in the presence of a Pd0 catalyst and subsequent deprotection with base under aqueous conditions yields the nickel(II) 2,3-diethynyl-5,10,15,20-tetraphenylporphyrin (1). Subsequent reaction of 1 with N-bromo- or N-iodosuccinimide in dry acetone in the presence of AgNO3 yields 2,3-bis(haloethynyl)-5,10,15,20-tetraphenylporphyrins in 70% (2a) and 68% (2b) yields. The X-ray crystal structures of 2a,b show that the porphyrin backbone deviates significantly from planarity due to a Ni(II)-induced mixture of the classic ruffle and saddle distortions. Thermolysis of 2a at 190 degrees C for 6 h in chlorobenzene and 30-fold 1,4-cyclohexadiene (CHD) generates the Bergman cyclized nickel(II) dibromopicenoporphyrin product (3) in 65% yield, which derives from diradical addition across the adjacent meso-phenyl substituents. Similarly, nickel(II) 2,3-bis(iodoethynyl)-5,10,15,20-tetraphenylporphyrin, 2b, cyclizes at 190 degrees C in chlorobenzene/CHD via high-temperature substitution of iodine by hydrogen (from CHD) or chlorine (from solvent) to afford a mixture of 4 (15%) and 5 (45%). Remarkably, ambient temperature incubation of 2a in MeOH/CHCl3 (1:3, 22 h) or chlorobenzene/CHD (3:1, 24 h) leads to generation of 3 in 15% and 22% isolated yields, respectively. Addition of 1.2 equiv of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in CHCl3/MeOH dramatically accelerates the rate of reaction, producing 3 in 30% yield within 0.5 h. The origin of the ambient temperature activation of 2a derives from the ability of electron-withdrawing functionalities at the alkyne termini to decrease the activation barrier to the Bergman product. 相似文献
345.
Heteroleptic rhodium(I) complexes with the general formulations [(η4-C8H12)Rh(L)] [η4-C8H12 = 1,5-cyclooctadiene; L = 5-(4-cyanophenyl)dipyrromethene, cydpm; 5-(4-nitrophenyl)dipyrromethene, ndpm; and 5-(4-benzyloxyphenyl)dipyrromethene, bdpm; 5-(4-pyridyl)dipyrromethene, 4-pyrdpm; 5-(3-pyridyl)dipyrromethene, 3-pyrdpm] have been synthesized. The complex [(η4-C8H12)Rh(4-pyrdpm)] have been used as a synthon in the construction of homo-bimetallic complex [(η4-C8H12)Rh(μ-4-pyrdpm)Rh(η5-C5Me5)Cl2] and hetero-bimetallic complexes [(η4-C8H12)Rh(μ-4-pyrdpm)Ir(η5-C5Me5)Cl2], [(η4-C8H12)Rh(μ-4-pyrdpm)Ru(η6-C10H14)Cl2] and [(η4-C8H12)Rh(μ-4-pyrdpm)Ru(η6-C6H6)Cl2]. Resulting complexes have been characterized by elemental analyses and spectral studies. Molecular structures of the representative mononuclear complexes [(η4-C8H12)Rh(ndpm)] and [(η4-C8H12)Rh(4-pyrdpm)] have been authenticated crystallographically. 相似文献
346.
S. Shylaja K. N. Mahendra K. B. R. Varma T. Narasimhamurthy R. S. Rathore 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(7):o361-o363
The title salt, C13H12N3+·H2PO4−, contains a nonplanar 2‐(2‐aminophenyl)‐1H‐benzimidazol‐3‐ium cation and two different dihydrogen phosphate anions, both situated on twofold rotation axes in the space group C2. The anions are linked by O—H...O hydrogen bonds into chains of R22(8) rings. The anion chains are linked by the cations, via hydrogen‐bonding complementarities and electrostatic interactions, giving rise to a sheet structure with alternating rows of organic cations and inorganic anions. Comparison of this structure with that of the pure amine reveals that the two compounds generate characteristically different sheet structures. The anion–anion chain serves as a template for the assembly of the cations, suggesting a possible application in the design of solid‐state materials. 相似文献
347.
Pseudohalogenogermylenes versus Halogenogermylenes: Difference in their Complexation Behavior towards Group 6 Metal Carbonyls 下载免费PDF全文
Mahendra Kumar Sharma Soumen Sinhababu Dhirendra Yadav Goutam Mukherjee Prof. Gopalan Rajaraman Prof. Selvarajan Nagendran 《化学:亚洲杂志》2018,13(10):1357-1365
Pseudohalogenogermylenes [(iBu)2ATI]GeY (Y=NCO 4 , NCS 5 ) show different coordination behavior towards group 6 metal carbonyls in comparison to the corresponding halogenogermylenes [(iBu)2ATI]GeX (X=F 1 , Cl 2 , Br 3 ) (ATI=aminotroponiminate). The reactions of compounds 4 – 5 and 1 – 3 with cis‐[M(CO)4(COD)] (M=Mo, W, COD=cyclooctadiene) gave trans‐germylene metal complexes {[(iBu)2ATI]GeY}2M(CO)4 (Y=NCO, M=Mo 6 , W 11 ; Y=NCS, M=Mo 7 ) and cis‐germylene metal complexes {[(iBu)2ATI]GeX}2M(CO)4 (M=Mo, X=F 8 , Cl 9 , Br 10 ; M=W, X=Cl 12 ), respectively. Theoretical studies on compounds 7 and 9 reveal that donor–acceptor interactions from Mo to Ge atoms are better stabilized in the observed trans and cis geometries than in the hypothetical cis and trans structures, respectively. 相似文献
348.
Tan DC Wijaya IP Andreasson-Ochsner M Vasina EN Nallani M Hunziker W Sinner EK 《Lab on a chip》2012,12(15):2726-2735
We report the use of a novel microfluidics-based method to detect weak protein-protein interactions between membrane proteins. The tight junction protein, claudin-2, synthesised in vitro using a cell-free expression system in the presence of polymer vesicles as membrane scaffolds, was used as a model membrane protein. Individual claudin-2 molecules interact weakly, although the cumulative effect of these interactions is significant. This effect results in a transient decrease of average vesicle dispersivity and reduction in transport speed of claudin-2-functionalised vesicles. Polymer vesicles functionalised with claudin-2 were perfused through a microfluidic channel and the time taken to traverse a defined distance within the channel was measured. Functionalised vesicles took 1.19 to 1.69 times longer to traverse this distance than unfunctionalised ones. Coating the channel walls with protein A and incubating the vesicles with anti-claudin-2 antibodies prior to perfusion resulted in the functionalised vesicles taking 1.75 to 2.5 times longer to traverse this distance compared to the controls. The data show that our system is able to detect weak as well as strong protein-protein interactions. This system offers researchers a portable, easily operated and customizable platform for the study of weak protein-protein interactions, particularly between membrane proteins. 相似文献
349.
Yadav M Patel C Patel M Mishra T Baxi GA Singhal P Shrivastav PS 《Journal of chromatographic science》2011,49(2):101-107
A simple, sensitive, selective, and rapid high-performance liquid chromatography-tandem mass spectrometry method is developed and validated for the quantitation of naratriptan, using sumatriptan as internal standard (IS). The method included liquid-liquid extraction of naratriptan and IS with methyl-tert-butyl ether and dichloromethane mixture from 100 μL human plasma. The chromatographic separation is achieved on ACE C18 (50 mm × 2.1 mm, 5 μm) analytical column under isocratic conditions, using 0.1% acetic acid and acetonitrile (15:85, v/v) at a flow-rate of 0.4 mL/min. The precursor → product ion transitions for naratriptan (m/z 336.10 → 98.06) and IS (m/z 296.09 → 251.06) were monitored on a triple quadrupole mass spectrometer, operating in the multiple reaction monitoring (MRM) and positive ion mode. The linearity of the method for naratriptan is determined in the range of 103-20690 pg/mL with the analysis time of 1.5 min. The method is fully validated according to USFDA guidelines. A systematic post-column infusion study is conducted for ion-suppression due to endogenous matrix components. The process efficiency of analyte (96%) and IS (93%) from spiked plasma samples was consistent and reproducible. The application of the method is demonstrated by a bioequivalence study of 2.5 mg naratriptan tablet formulation in 31 healthy volunteers under fasting conditions. 相似文献
350.
The right path : The mechanism of organocatalyzed Michael addition between propanal and methyl vinyl ketone is investigated using the density functional and ab intio methods. The kinetic preference for the formation of key intermediates is established in an effort to identify the competing pathways associated with the reaction. The effect of co‐catalyst/protic solvent on the energetics of the reaction is also studied