ISSN:0947-6539    

DOI:10.1002/chem.19970031103

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe definition and reasons for desiring extralarge pore, crystalline molecular sieves are ennumerated. A historical perspective on the development of these materials is presented with emphasis on critical features important for practical application. Based on the known physiochemical properties of extra‐large pore materials, several avenues for their synthesis are suggested. Finally, a few issues of concern when dealing with this class of materials are presente

ISSN:0947-6539    

DOI:10.1002/chem.19970031104

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractCarbohydrate‐modified carbene complexes can be synthesised by combining a sugar electrophile with a metalate nucleophile or vice versa. Acyclic sugar skeletons adopt conformations that are controlled by the minimisation of 1,3‐interactions and are not significantly affected by the incorporation of a metal fragment. Thus, the latter can be used exclusively for reactivity tuning. Sugar carbene complexes undergo regio‐ and stereoselective ligand‐ and metal‐centred reactions such as C2‐homologisation and ben

ISSN:0947-6539    

DOI:10.1002/chem.19970031105

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

Abstract[Bis(dicyclohexylamino)phosphino]trimethylsilylcarbene (1) reacts with benzonitrile leading to the corresponding 2‐phosphino‐2H‐azirine3in 85% yield. Treatment of3with trifluoro‐methanesulfonic acid, methyl trifluoro‐methanesulfonate, or elemental sulfur leads to theP‐hydrogeno‐2‐phosphonio‐,P‐methyl‐2‐phosphonio‐, or 2‐thioxo‐phosphoranyl‐2H‐azirine (4, 5, and7) in 77, 87, and 91% yields, respectively. Irradiation of3gives rise to the 1,2λ5‐azaphosphete8(98% yield). Treatment of3with BF3·OEt2, BH3·SMe2, Lawesson's reagent, or methyl isothiocyanate gives heterocycles9(90% yield),10(76% yield),12(83% yield), or13(80% yield), while under the same experimental conditions, heterocycle8reacts with the same reagents to give9(82% yield),11(83% yield),12(86% yield), and15(56% yield), respectively. Thermolysis of theP‐hydrogeno‐2‐phosphonio‐2H‐azirine4at 55°C leads to the cationic, four‐membered heterocycle17(96% yield), while photolysis of theP‐methylazirine analogue5in the presence of dimethyl acetylenedicarboxylate affords pyrrole19(64% yield). Irradiation of the thiox‐ophosphoranyl azirine7gives the 1,3,5λ5‐thiazaphosphole20in 79% yield. The influence of the coordination state of phosphorus on the rea

ISSN:0947-6539    

DOI:10.1002/chem.19970031106

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe second‐order polarizabilities β(— 2ω; ω, ω) of six nondipolar NLO chromophores—1,3,5‐tris(isopropyl‐amino)‐2,4,6‐trinitrobenzene (1), 1,3,5‐tris(isopropylamino)‐2,4,6‐tris(trifluoro‐methylsulfonyl)benzene (2), tris(dimethyl‐imoniomethyl)methide diperchlorate (3), 2,4,6‐tris[4‐(N,N‐diethylamino)phenyl‐ethynyl]‐1,3,5‐triazine (4), 2,4,6‐tris[4‐(N,N‐diethylamino)phenyl]‐1,3,5‐triazine (5), and tris(2‐dimethylaminoethenyl)‐methinium perchlorate (6)—were studied by polarized hyper‐Rayleigh scattering (HRS). The NLO activity of these two‐dimensional NLO chromophores is attributed to three‐level contributions to the β values, for which different optimization strategies are investigated. Exceptionally large second‐order polarizabilities were observed for the conjugationally elongated structures: the β value of triazine4is 15 times larger than that of the one‐dimensional two‐level chromophore 4‐nitroaniline. Results obtained with the polarized HRS experiment are discussed with respect t

ISSN:0947-6539    

DOI:10.1002/chem.19970031107

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractModelO‐glycosylation reactions at either rim of calix[4]arenes are described with the aim of providing access to a new family of carbohydrate‐containing calixarene derivatives named calixsugars. One or two sugar moieties (D‐mannofuranose and D‐glucopyranose) were introduced at the lower rim of the parent calix[4]arene by glycosylation of the phenolic hydroxyl groups by means of a Mitsunobu reaction. Tetrapropoxy calix[4]arenes bearing two or four hydroxymethyl groups at the upper rim were coupled with perbenzoylated thioethyl D‐galactoside and D‐lactoside in the presence of the thiophilic promoter copper(III) triflate. In this way β‐linked bis‐ and tetrakis‐O‐galactosyl calix[4]arenes were obtained in good yield, the latter showing some solubility in water. For theO‐lactosyl derivatives only the bis‐substituted compound could be obtained because of the competing formation of an intramolecular ether linkage between 1,3‐hydroxymethyl groups. Preliminary binding studies showed some affinity of the galactose‐containing calixsugars toward charged carbohydrates an

ISSN:0947-6539    

DOI:10.1002/chem.19970031108

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe reactions of [(Me3Si)3CLi2thf] with Me2MCl (M = Al, Ga) afford the mixed trialkylmetallanes [(Me3Si)3‐CAlMe2·thf] (1) and [(Me3Si)3CGaMe2·thf] (2) in high yields. The coordinated THF molecule of compound2can be removed by sublimation in vacuo to yield the solvent‐free product [(Me3Si)3‐CGaMe2] (3). Hydrolysis of compound2with one equivalent of water at 0°C gives the trimeric hydroxide [{(Me3Si)3CGaMe(μ‐OH)}3] (4), while the reaction with two equivalents of water at room temperature yields the unusually stable gallium hydroxide‐water complex [{(Me3Si)3CGaMe(OH)(μ‐OH)MeGaC(SiMe3)3) H2O·2thf] (6). On heating, compound6is converted to the hydroxide [{(Me3Si)3C}4Ga4(μ‐O)2(μ ‐OH)4] (5), which has a heteroadamantane‐like core. The hydrolysis of compound1with one equivalent of water at − 25°C gives the dimeric hydroxide [{(Me3Si)3CAlMe(μ‐OH)}2·2thf] (7), while the reaction with two equivalents of water results in the formation of the novel hydroxide [{(Me3Si)3C}4Al4(μ‐O)2(μ‐OH)4] (8), which is isostructural to the gallium compound6with the adamantane‐like structure. The molecular structures of compounds1, 2, 4, 5·3THF,6, 7and8·0.5 THF have been determined by X‐ray structure analysis. Compound7is the first structurally characterised aluminium hydroxide containing methyl groups, and8is the smallest structurally characterised

ISSN:0947-6539    

DOI:10.1002/chem.19970031109

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe use of a new electron‐withdrawing germane, H2Ge[3,5‐(CF3)2C6H3]2(3), has facilitated the isolation and characterization of three new complexes implicated in the dehydrogenative coupling of bisarylgermanes by Pt0‐phos‐phane complexes. The intermediates include a digermyl species,trans‐[(Et3P)2Pt{GeH(Ar)2}2] (7), a bound digermane showing the first stage of Ge‐Ge catenation,cis‐[(Et3P)2Pt(H){Ge(Ar)2‐GeH(Ar)2}] (8), and the Ge‐H activated form of this product, [(Et3P)2HPtGe(Ar)2‐Ge(Ar)2PtH(PEt3)2] (6). Complexes such as6and8have not previously been isolated as intermediates in dehydrogenative coupling reactions. An X‐ray crystal structure was determined for complex6, confirming thecisgeometry of the hydrogen and germanium ligands; this provides yet another example of the stability of germyl hydrides towards reductive elimination. A similarcisgeometry was observed for complex8. Performing the dehydrogenative coupling reaction under a CO2atmosphere failed to yield any products containing trap

ISSN:0947-6539    

DOI:10.1002/chem.19970031110

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractTwo new molybdenum(v) hydroxyphosphates have been synthesized hydrothermally, Na2Cd3(Mo2O4OH)6‐(PO4)2(PO3OH)6[N(CH3)4]4·10H20 (1) and Cd9(Mo2O4OH)12(PO4)6(PO3OH)10‐[N(CH3)4]8·15H2O (2). Their structures have been determined from single‐crystal X‐ray diffraction. The water molecules and hydroxyl groups have been deduced from valence calculations. Both compounds crystallize in the triclinic space groupP1, with the cell parameters for1a= 12.340(2),b= 12.596(1),c= 14.717(2) Å, α = 107.24(1)°, β = 89.83(1)°, γ = 114.31(1)°,V= 1972.3(4) Å3, and for2a= 11.942(1), b = 13.339(2),c= 26.765(3) Å, α = 85.33(1)°, β = 86.87(1)°, γ = 64.08(1)°,V= 3821.3(9) Å3. The two frameworks can be described on the basis of similar [Mo6P4X31]n‐(X = O, OH) anionic clusters, but1is a tridimensional structure, whereas2exhibits

ISSN:0947-6539    

DOI:10.1002/chem.19970031111

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractMetal exchange of the solvated tripodal lithium amide [H3CC{CH2N(Li‐solv)SiMe3}3] (1, solv = ether solvent) with thallium(I) chloride leads to the previously reported pentametallated dimeric thallium amide [{H3CC(CH2NSiMe3)3}2(H)Tl5] (2) in high yield. That the redox‐induced partial demetallation of the amide presumably occurs at an intermediate stage of the metal exchange is inferred from the isolation and structural characterization of the mixed Tl‐Li amide [H3CC{CH3N(Tl) SiMe3}3][H3CC{CH2NSiMe3}3(H)(Tl)(Li‐thf)]·(toluene) (3), which has a crystal structure closely related to that of2. In both cases the central structural motif, defined by weakly attractive Tl ⃛ Tl contacts, is a tetrahedral metal array in which a triangular thallium triamide unit is capped by an exposed Tl atom of a second building block. Compound3may be converted to2by metal exchange with TlCl. The two supramolecular components of2reaggregate upon recrystallization in a nonpolar solvent such as pentane to yield the dimeric aggregate of the fully metallated thallium amide [H3CC{CH2N(Tl)‐SiMe3}3]2(4). An X‐ray crystallographic study of4established the existence of dimeric aggregation through Tl ⃛ Tl interactions leading to a more open dimeric form than2and3, which is interpreted as being due to a structural mismatch of the building blocks. Compound4may be thermally degraded by prolonged stirring in toluene at ambient temperature to yield the previously reported mixed‐valence TlITlIIamide [H3CC(C

ISSN:0947-6539    

DOI:10.1002/chem.19970031112

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY