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排序方式: 共有289条查询结果,搜索用时 31 毫秒
1.
Two vanadyl salen complexes having peripheral styryl substituents have been reacted with 1-methyl-3-(3-mercaptopropyl)-imidazolium chloride using azoisobutyronitrile as radical initiator. The resulting compounds contain at the same time a vanadyl salen complex and one imidazolium cation. In agreement with the expectations in view of their structure, these compounds were insoluble in conventional organic solvents, but completely miscible in imidazolium ionic liquids. These vanadyl salen complexes bonded to an imidazolium cation are highly active and reusable catalysts for the cyanosilylation of aldehydes. Moderate enantiomeric excesses were obtained using the chiral version of this complex. 相似文献
2.
Alvaro M Corma A Das D Fornés V García H 《Chemical communications (Cambridge, England)》2004,(8):956-957
Preparation of hybrid organic-inorganic MCM-41 and SBA-15 silicas functionalized with perfluoroalkylsulfonic acid groups has been achieved in a single step by reacting the mesoporous silicas with 1,2,2-trifluoro-2-hydroxy-1-trifluoromethylethane sulfonic acid beta-sultone; the catalysts showed higher activity than commercial Nafion-silica composite for the esterification of long chain fatty acids with ethanol. 相似文献
3.
Qintong Huang Ningyue Chen Lichen Liu Karen S. Arias Sara Iborra Xianfeng Yi Chao Ma Weichi Liang Anmin Zheng Chuanqi Zhang Jibo Hu Zilin Cai Yi Liu Jiuxing Jiang Avelino Corma 《Chemical science》2020,11(44):12221
Aluminosilicate boggsite (Si/Al-BOG) has been hydrothermally synthesized without adding organic structure-directing agents (OSDAs) in the synthesis gel using the borosilicogermanium ITQ-47 (Si/B-ITQ-47) zeolite as seeds. The introduction of the costly and environmentally less benign phosphazene organic structure-directing agent is not required to grow the zeolite. Physicochemical characterization experiments show that Si/Al-BOG has good crystallinity, high surface area, tetrahedral Al3+ species, and acid sites. In order to test the catalytic performance of the zeolite, the synthesis of l,l-lactide from l-lactic acid was performed. Si/Al-BOG exhibits 88.2% conversion of l-lactic acid and 83.8% l,l-lactide selectivity, which are better than those of other zeolites studied up to now.Aluminosilicate boggsite (Si/Al-BOG) has been hydrothermally synthesized without adding organic structure-directing agents (OSDAs) in the synthesis gel using the borosilicogermanium ITQ-47 (Si/B-ITQ-47) zeolite as seeds. 相似文献
4.
Corma A Diaz-Cabanas MJ Rey F Nicolopoulus S Boulahya K 《Chemical communications (Cambridge, England)》2004,(12):1356-1357
The pore topology of ITQ-15 zeolite consists of an ultra-large 14-ring channel that is intersected perpendicularly by a 12-ring pore; acid sites have been introduced in its framework and this unique structure shows advantages over unidirectional ultralarge pore zeolites for diffusing and reacting large molecules. 相似文献
5.
6.
A multisite molecular mechanism for Baeyer-Villiger oxidations on solid catalysts using environmentally friendly H2O2 as oxidant 总被引:1,自引:0,他引:1
Boronat M Corma A Renz M Sastre G Viruela PM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(23):6905-6915
The molecular mechanism of the Baeyer-Villiger oxidation of cyclohexanone with hydrogen peroxide catalyzed by the Sn-beta zeolite has been investigated by combining molecular mechanics, quantum-chemical calculations, spectroscopic, and kinetic techniques. A theoretical study of the location of Sn in zeolite beta was performed by using atomistic force-field techniques to simulate the local environment of the active site. An interatomic potential for Sn/Si zeolites, which allows the simulation of zeolites containing Sn in a tetrahedral environment, has been developed by fitting it to the experimental properties of quartz and SnO2(rutile). The tin active site has been modeled by means of a Sn(OSiH3)3OH cluster, which includes a defect in the framework that provides the flexibility necessary for the interaction between the adsorbates and the Lewis acid center. Two possible reaction pathways have been considered in the computational study, one of them involving the activation of the cyclohexanone carbonyl group by Sn (1) and the other one involving hydrogen peroxide being activated through the formation of a tin-hydroperoxo intermediate (2). Both the quantum-chemical results and the kinetic study indicate that the reaction follows mechanism 1, and that the catalyst active site consists of two centers: the Lewis acid Sn atom to which cyclohexanone has to coordinate, and the oxygen atom of the Sn-OH group that interacts with H2O2 forming a hydrogen bond. 相似文献
7.
Andrés R Galakhov MV Gómez-Sal MP Martín A Mena M del Carmen Morales-Varela M Santamaría C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(4):805-811
The photochemical treatment of mu(3)-alkylidyne complexes [[TiCp*(mu-O)](3)(mu(3)-CR)] (R=H (1), Me (2), Cp*=eta(5)-C(5)Me(5)) with the amines (2,6-Me(2)C(6)H(3))NH(2), Et(2)NH, and Ph(2)NH and the imine Ph(2)C=NH leads to the partial hydrogenation of the alkylidyne moiety that is supported on the organometallic oxide, [Ti(3)Cp*O(3)], and the formation of new oxoderivatives [[TiCp*(3)(mu-CHR)(R'NR")] (R"=2,6-Me(2)C(6)H(3), R'=H, R=H (3), Me (4); R'=R"=Et, R=H (5), Me (6); R'=R"=Ph, R=H (7), Me (8)) and [[TiCp*(mu-O)](3)(mu-CHR)(N=CPh(2))] (R=H (9), R=Me (10)), respectively. A sequential transfer hydrogenation process occurs when complex 1 is treated with tBuNH(2), which initially gives the mu-methylene [[TiCp*(mu-O)](3)(mu-CH(2))(HNtBu)] (11) complex and finally, the alkyl derivative [[TiCp*(mu-O)](3)(mu-NtBu)Me] (12). Furthermore, irradiation of solutions of the mu(3)-alkylidyne complexes 1 or 2 in the presence of diamines o-C(6)H(4)(NH(2))(2) and H(2)NCH(2)CH(2)NH(2) (en) affords [[TiCp*(mu-O)](3)(mu(3)-eta(2)-NC(6)H(4)NH)] (13) and [[TiCp*(mu-O)](3)(mu(3)-eta(2)-NC(2)H(4)NH)] (14) by either methane or ethane elimination, respectively. In the reaction of 1 with en, an intermediate complex [[TiCp*(mu-O)](3)(mu-CH(2))(NHCH(2)CH(2)NH(2))] (15) is detected by (1)H NMR spectroscopy. Thermal treatment of the complexes 4-10 quantitatively regenerates the starting mu(3)-alkylidyne compounds and the amine R'(2)NH or the imine Ph(2)C=NH; however, heating of solutions of 3 or 4 in [D(6)]benzene or a equimolecular mixture of both at 170 degrees C produces methane, ethane, or both, and the complex [[TiCp*(mu-O)](3)[mu(3)-eta(2)-NC(6)H(3)(Me)CH(2)]] (16). The molecular structure of 8 has been established by single-crystal X-ray analysis. 相似文献
8.
Abarca A Galakhov MV Gracia J Martín A Mena M Poblet JM Sarasa JP Yélamos C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(10):2337-2346
Treatment of [[Ti(eta(5)-C(5)Me(5))(micro-NH)](3)(micro(3)-N)] (1) with the imido complexes [Ti(NAr)Cl(2)(py)(3)] (Ar=2,4,6-C(6)H(2)Me(3)) and [Ti(NtBu)Cl(2)(py)(3)] in toluene affords the single azatitanocubanes [[Cl(2)(ArN)Ti]( micro(3)-NH)(3)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)]].(C(7)H(8)) (2.C(7)H(8)) and [[Cl(2)Ti](micro(3)-N)(2)(micro(3)-NH)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)]] (3), respectively. Similar reactions of complex 1 with the niobium and tantalum imido derivatives [[M(NtBu)(NHtBu)Cl(2)(NH(2)tBu)](2)] (M=Nb, Ta) in toluene give the single azaheterometallocubanes [[Cl(2)(tBuN)M](micro(3)-N)(micro(3)-NH)(2)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)]] (M=Nb (4), Ta (5)), both complexes react with 2,4,6-trimethylaniline to yield the analogous species [[Cl(2)(ArN)M](micro(3)-N)(micro(3)-NH)(2)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)]].(C(7)H(8)) (Ar=2,4,6-C(6)H(2)Me(3), M=Nb (6.C(7)H(8)), Ta (7.C(7)H(8))). Also the azaheterodicubanes [M[micro(3)-N)(2)(micro(3)-NH)](2)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)](2)].2C(7)H(8) [M=Ti (8.2C(7)H(8)), Zr (9.2C(7)H(8))], and [M[(micro(3)-N)(5)(micro(3)-NH)][Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)](2)].2 C(7)H(8) (Nb (10.2C(7)H(8)), Ta (11.2C(7)H(8))) were prepared from 1 and the homoleptic dimethylamido complex [M(NMe(2))(x)] (x=4, M=Ti, Zr; x=5, M=Nb, Ta) in toluene at 150 degrees C. X-ray crystal structure determinations were performed for 6 and 10, which revealed a cube- and double-cube-type core, respectively. For complexes 2 and 4-7 we observed and studied by DNMR a rotation or trigonal-twist of the organometallic ligands [[Ti(eta(5)-C(5)Me(5))(micro-NH)](3)(micro(3)-N)] (1) and [(micro(3)-N)(micro(3)-NH)(2)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)]](1-). Density functional theory calculations were carried out on model complexes of 2, 3, and 8 to establish and understand their structures. 相似文献
9.
10.
Concepción P Corma A Silvestre-Albero J Franco V Chane-Ching JY 《Journal of the American Chemical Society》2004,126(17):5523-5532
Pt on mesostructured CeO(2) nanoparticles embedded within ultrathin layers of highly structured SiO(2) binder shows highest activity reported with 80% selectivity for the chemoselective hydrogenation of crotonaldehyde. Characterization by transmission electron microscopy (TEM), CO adsorption, and X-ray photoelectron spectroscopy (XPS) show the presence of small Pt metal particles, preferentially located on CeO(2) (70%) together with the formation of Pt-CeO(2-x) sites at the interface between Pt and CeO(2) (4 nm) nanoparticles. These sites are able to polarize the carbonyl group and facilitate the selective hydrogenation of this with respect to the double bond. 相似文献