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1.
The 1H NMR spectra of a series of cis and trans-3R,4 X-cyclohexanones (-2,2,6,6-d4) are analysed. By comparison of their 3J coupling constants with those of cyclohexane homologues we obtain information about the chair–chair equilibrium constants for R = CH3, X = CN, the chair structure of cis isomers with an equatorial t-butyl group, and a conformational heterogeneity with trans (CH3)3C and CN groups. This latter situation is analysed by means of a simplified but controlled Karplus relationship, on the basis of a mixture of two conformers; this involves a diequatorial chair and a boat form with a dihedral angle Φ34 of about ?6°.  相似文献   

2.
A series of heterocyclic trans-dichloro-β-diketonato-cis-diorganoantimony(V) compounds of the type R2SbCl2X (R2 = (CH2)4, (CH2)5, o,o′−C6H4C6H4, o,o′−C6H4CH2C6H4; X = Acac, Dpm) has been synthesized. The stereochemistry of these compounds has been deduced from PMR spectroscopic and molecular dipole moment data. Since the cis-dichloro-β-diketonato-trans-diorganoantimony(V) compounds R2SbCl2Acac (R = Me, Et, Ph) were known previously, a set of both cis- and trans-diorgano main group organometallic complexes has thus been made available, which allows a comparative study of the influence of stereochemistry on the strength of metal—ligand interactions in this type of octahedral d10 metal complex. β-Diketonate—ligand exchange reactions have been studied by PMR spectroscopy, and a marked influence of stereochemistry observed. trans-Dichloro-β-diketonato-cis-diorganoantimony(V) compounds undergo ligand exchange only slowly, if at all, whereas cis-dichloro-β-diketonato-trans-diorganoantimony(V) compounds react instantaneously. Both PMR chemical shift data and IR spectroscopic data point to the occurrence of a stronger antimony-β-diketonate interaction in trans-dichloro-β-diketonato-cis-diorganoantimony than in cis-dichloro-β-diketonato-trans-diorganoantimony compounds. This can be understood in terms of the hybridization of the antimony valence orbitals. The results are in line with the assumption that Sb---O bond rupture is the rate-determining step in β-diketonate ligand exchange.  相似文献   

3.
Cyclometallated complexes of the type cis-bis(2-phenylpyridine)platinum(II) (C22H16N2Pt) and cis-bis(2-(2′-thienyl)pyridine)platinum(II) (C18H12N2S2Pt) undergo thermal or photochemical oxidative addition (TOA or POA) reactions with a number of substrates. TOA (with CH3I, CH3CH2I etc.) yield mixtures of several isomers which rearrange slowly (within ca. one week at room temperature) to one of the possible cis-isomers. CH2Cl2, CHCl3, or (E)? ClCH?CHCl, e.g., do not react thermally. POA yield directly complexes of Pt(IV) with the halide and a σ-bonded C-atom in cis-position. The configuration, as assigned by extensive use of 1H-NMR data, can be characterized for the two chelating ligands C …? N and C′ …? N′ by C,C′-cis; N,N′-cis and C(chelate), Cl-trans.  相似文献   

4.
Complexes of general formula [ReOX2{(C5H4N)CH(O)CH2(C5H4N)}] (X?=?Cl,?I) were prepared by reaction of trans-[ReOCl3(PPh3)2] and trans-[ReOI2(OEt)(PPh3)2] with cis-1,2-di-(2-pyridyl)ethylene (DPE) in ethanol and benzene in air. The coordinated DPE ligand undergoes addition of water at the ethylenic carbon atoms, and the (C5H4N)CH(O)CH2(C5H4N) moiety acts as a uninegative terdentate N,O,N-donor ligand. X-ray crystal structures of both complexes have been determined and show distorted octahedral geometry at the rhenium(V) centre.  相似文献   

5.
2‐X‐1, 2‐Difluoroalk‐1‐enylxenon(II) salts were prepared by the reaction of XeF2 with XCF=CFBF2 (X = F, trans‐H, cis‐Cl, trans‐Cl, cis‐CF3, cis‐C2F5) but no organoxenon(II) compounds were obtained when the trans‐isomers of boranes, trans‐XCF=CFBF2 (X = CF3, C4F9, C4H9, Et3Si), were used under similar conditions.  相似文献   

6.
The single‐crystal X‐ray structure determinations of the title complexes, cis‐di­chloro‐trans‐di­methyl‐cis‐bis(N‐methyl­pyr­rolidin‐2‐one‐O)­tin(IV), [Sn(CH3)2Cl2(C5H9NO)2], cis‐di­bromo‐trans‐di­methyl‐cis‐bis(N‐methyl­pyrrolidin‐2‐one‐O)tin­(IV), [SnBr2(CH3)2(C5H9NO)2], and cis‐di­iodo‐trans‐di­methyl‐cis‐bis(N‐methyl­pyrrolidin‐2‐one‐O)­tin(IV), [Sn(CH3)2I2(C5H9NO)2], show that those tin complexes in which coordination of the lactam ligand to SnIV is realized via oxygen exhibit a distorted octahedral geometry.  相似文献   

7.
The hydrodeboration of the (fluoroorgano)trifluoroborates K [RFBF3] [RF = C6F5, XCF=CF (X = F, cis‐ and trans‐Cl, C3F7O, cis‐C2F5, trans‐C4F9, ‐C4H9) and C6F13] and of the organotrifluoroborates K [RBF3] (R = C6H5, cis‐ and trans‐C4H9CH=CH, C4H9 and C8H17) with CH3CO2H (100 %), CF3CO2H (100 %), aqueous HF and anhydrous HF was investigated. In the alkenyltrifluoroborates K [R'CF=CFBF3] the formal replacement of BF3 by a proton occurred stereospecifically under retention of the configuration. The 19F NMR spectra of K [RFBF3] in acids indicate strong interactions of the BF3 group with protons or acid molecules.  相似文献   

8.
The oxidative addition of XRCN to PtL4 yields cis-and/or trans-PtX(RCN)L2 (X = Cl, Br; R = (CH2)n, n = 1, 2, 3; L = PPh3, PPh2CH3, AsPh3). L is readily displaced by more basic phosphines or by a diphosphine. In each case the trans complex is the thermodynamically more stable isomer and cis-trans isomerization catalyzed by free L occurs in dichloromethane. Insertion of CO in the σ Pt? C bond takes place quantitatively in the case of cyanoethyl and cyanopropyl. Abstraction of X by AgBF4 gives cis or trans cationic complexes with N-bonded CN group.  相似文献   

9.
A series of ruthenium hydride compounds containing substituted bidentate pyrrole‐imine ligands were synthesized and characterized. Reacting RuHCl(CO)(PPh3)3 with one equivalent of [C4H3NH(2‐CH=NR)] in ethanol in the presence of KOH gave compounds {RuH(CO)(PPh3)2[C4H3N(2‐CH=NR)]} where trans‐Py‐Ru‐H 1, R = CH2CH2C6H9; cis‐Py‐Ru‐H 2, R = Ph‐2‐Me; and cis‐Py‐Ru‐H 3, R = C6H11. Heating trans‐Py‐Ru‐H 1 in toluene at 70°C for 12 hr resulted a thermal conversion of the trans‐Py‐Ru‐H 1 into its cis form, {RuH(CO)(PPh3)2[C4H3N(2‐CH=NCH2CH2C6H9)]} (cis‐Py‐Ru‐H 1) in very high yield. The 1H NMR spectra of trans‐Py‐Ru‐H 1, cis‐Py‐Ru‐H 2, cis‐Py‐Ru‐H 3, and cis‐Py‐Ru‐H 1 all show a typical triplet at ca. δ–11 for the hydride. The trans and cis form indicate the relative positions of pyrrole ring and hydride. The geometries of trans‐Py‐Ru‐H 1, cis‐Py‐Ru‐H 1, and cis‐Py‐Ru‐H 3 are relatively similar showing typical octahedral geometries with two PPh3 fragments arranged in trans positions.  相似文献   

10.
Chlorodiphenylphosphine and 2,2′-biphenylylenephosphorochloridite react with 2-hydroxy-2′-(1,4-bisoxo-6-hexanol)-1,1′-biphenyl to yield the new α,ω-bis(phosphorus-donor)-polyether ligands, 2-Ph2PO(CH2CH2O)2–C12H8-2′-OPPh2 (1) and 2-(2,2′-O2C12H8)P(CH2CH2O)2–C12H8-2′-P(2,2′-O2C12H8) (2). These ligands react with Mo(CO)4(nbd) to form the monomeric metallacrown ethers, cis-Mo(CO)4{2-Ph2PO(CH2CH2O)2–C12H8-2′-OPPh2} (cis-3) and cis-Mo(CO)4{2-(2,2′-O2C12H8)P(CH2CH2O)2–C12H8-2′-P(2,2′-O2C12H8)} (cis-4), in good yields. The X-ray crystal structures of cis-3 and cis-4 are significantly different, especially in the conformation of the metal center and the adjacent ethylene group. The very different 13C-NMR coordination chemical shifts of this ethylene group in cis-3 and cis-4 suggest that the solution conformations of these metallacrown ethers are also quite different. Both metallacrown ethers undergo cistrans isomerization in the presence of HgCl2. Although the cistrans equilibrium constants for the isomerization reactions are nearly identical, the isomerization of cis-3 is more rapid. Phenyl lithium reacts with cis-3 to form the corresponding benzoyl complexes but does not react with either trans-3 or cis-4. Both the slower rate of cistrans isomerization of cis-4 and its lack of reaction with PhLi are consistent with weaker interactions between the hard metal cations and the carbonyl oxygens in both trans-3 and cis-4.  相似文献   

11.
Directed tridentate Lewis acids based on the 1,3,5‐trisilacyclohexane skeleton with three ethynyl groups [CH2Si(Me)(C2H)]3 were synthesised and functionalised by hydroboration with HB(C6F5)2, yielding the ethenylborane {CH2Si(Me)[C2H2B(C6F5)2]}3, and by metalation with gallium and indium organyls affording {CH2Si(Me)[C2M(R)2]}3 (M=Ga, In, R=Me, Et). In the synthesis of the backbone the influence of substituents (MeO, EtO and iPrO groups at Si) on the orientation of the methyl group was studied with the aim to increase the abundance of the all‐cis isomer. New compounds were identified by elemental analyses, multi‐nuclear NMR spectroscopy and in some cases by IR spectroscopy. Crystal structures were obtained for cis‐trans‐[CH2Si(Me)(Cl)]3, all‐cis‐[CH2Si(Me)(H)]3, all‐cis‐[CH2Si(Me)(C2H)]3, cistrans‐[CH2Si(Me)(C2H)]3 and all‐cis‐[CH2Si(Me)(C2SiMe3)]3. A gas‐phase electron diffraction experiment for all‐cis‐[CH2Si(Me)(C2H)]3 provides information on the relative stabilities of the all‐equatorial and all‐axial form; the first is preferred in both solid and gas phase. The gallium‐based Lewis acid {CH2Si(Me)[C2Ga(Et)2]}3 was reacted with a tridentate Lewis base (1,3,5‐trimethyl‐1,3,5‐triazacyclohexane) in an NMR titration experiment. The generated host–guest complexes involved in the equilibria during this reaction were identified by DOSY NMR spectroscopy by comparing measured diffusion coefficients with those of the suitable reference compounds of same size and shape.  相似文献   

12.
Intramolecular Diels–Alder (IMDA) transition structures (TSs) and energies have been computed at the B3LYP/6‐31+G(d) and CBS‐QB3 levels of theory for a series of 1,3,8‐nonatrienes, H2C?CH? CH?CH? CH2? X? Z? CH?CH2 [? X? Z? =? CH2? CH2? ( 1 ); ? O? C(?O)? ( 2 ); ? CH2? C(?O)? ( 3 ); ? O? CH2? ( 4 ); ? NH? C(?O)? ( 5 ); ? S? C(?O)? ( 6 ); ? O? C(?S)? ( 7 ); ? NH? C(?S)? ( 8 ); ? S? C(?S)? ( 9 )]. For each system studied ( 1 – 9 ), cis‐ and trans‐TS isomers, corresponding, respectively, to endo‐ and exo‐positioning of the ? C? X? Z? tether with respect to the diene, have been located and their relative energies (ErelTS) employed to predict the cis/trans IMDA product ratio. Although the ErelTS values are modest (typically <3 kJ mol?1), they follow a clear and systematic trend. Specifically, as the electronegativity of the tether group X is reduced (X?O→NH or S), the IMDA cis stereoselectivity diminishes. The predicted stereochemical reaction preferences are explained in terms of two opposing effects operating in the cis‐TS, namely (1) unfavorable torsional (eclipsing) strain about the C4? C5 bond, that is caused by the ? C? X? C(?Y)? group’s strong tendency to maintain local planarity; and (2) attractive electrostatic and secondary orbital interactions between the endo‐(thio)carbonyl group, C?Y, and the diene. The former interaction predominates when X is weakly electronegative (X?N, S), while the latter is dominant when X is more strongly electronegative (X?O), or a methylene group (X?CH2) which increases tether flexibility. These predictions hold up to experimental scrutiny, with synthetic IMDA reactions of 1 , 2 , 3 , and 4 (published work) and 5 , 6 , and 8 (this work) delivering ratios close to those calculated. The reactions of thiolacrylate 5 and thioamide 8 represent the first examples of IMDA reactions with tethers of these types. Our results point to strategies for designing tethers, which lead to improved cis/trans‐selectivities in IMDAs that are normally only weakly selective. Experimental verification of the validity of this claim comes in the form of fumaramide 14 , which undergoes a more trans‐selective IMDA reaction than the corresponding ester tethered precursor 13 .  相似文献   

13.
1H NMR spectra of several aliphatic and phenyl substituted alkenediynes have been obtained. Chemical shifts and coupling constants of these compounds are discussed in conjunction with some compounds described in the literature. Chemical shifts of the protons from isomeric alkenediynes R? C?C? C?C? CH?CH2, R? CH?CH? C?C? C?CH and R? CH?CH? C?C? C?C? CH3 (R = H, alkyl, C6H5, C6H4OCH3-p) are well correlated with cis/trans-isomerism and electronic effects of substituents at the C?C bond. The coupling constants were found to be only slightly dependent on the substitution at the double bond. We could resolve couplings over a maximum of eight bonds in the alkenediyne system.  相似文献   

14.
Abstract

Cobalt(III) complexes of the type [Co(en)2(chel)]X.nH2O where en = ethylenediamine, chel = phthalato = C6H4CO2)2? 2, maleato = (O2CCH = CHCO2)2?, succinato = (O2CCH2CH2CO2)2?, homophthalato = (O2CC6H4(CH2)CO2)2?, citraconato = (O2CC(CH3) = CHCO2)2?, itaconato = (CH2 = C(CO2)CH2CO2)2?, X = NO? 3, Br?, (O2CC6H4CO2H)?, (O2CHC = CHCO2H)?, (O2C(CH2)2CO2H)?, (O2CC6H4(CH2)CO2H)?, (O2CHC = C(CH2)-CO2H)?, and (O2C-CH2?C(= CH2)-CO2H)?, [Co(en)2(malonato)]X.2H2O (where malonato = (O2CCH2CO2)2?, X = Cl?, Br?, and NO? 3) and [Co(en)2CO3]Cl.2H2O have been investigated for their bacterial activity against Escherichia coli B growing on EMB agar and in minimal glucose media both in lag and log phases. Among the most active are where chel = phthalato and homophthalato. The effects are distinct from those known for compounds of Pt, e.g., cis?[Pt(NH3)2Cl2] and rhodium, e.g., trans?[Rh(C5H5N)4,Cl2].6H2O. Antagonisms are reported.  相似文献   

15.
The Crystal Structure of cis‐ and trans‐N‐iso‐Propylamidodimethyl Indium, [(CH3)2In‐N(H)iC3H7]2 According to the X‐ray structure determination [(CH3)2In‐N(H)iC3H7]2 (prepared from InMe3 (Me = CH3) and H2NiPr (iPr = CH(CH3)2) crystallizes in the monoclinic space group P21/n with 3 dimeric trans as well as 3 dimeric cis isomers per unit cell. The centrosymmetric form has a planar In2N2 core with In—N bonds of 222.1(4) and 222.9(5) pm, respectively, the skeleton of the cis isomer with In—N bonds of 221.4(4) pm is slightly folded (13.7°). Some 1H, 13C NMR, IR, and Raman data are reported.  相似文献   

16.
The cyclohexyl esters of a series of carboxylic acids, RCO2H, spanning a range of electronegativities and quotients of steric hindrance for the R substituent (R=Me, Et, iPr, tBu, CF3, CH2Cl, CHCl2, CCl3, CH2Br, CHBr2, and CBr3) were prepared. Their conformational equilibria in CD2Cl2 were examined by low‐temperature 1H NMR spectroscopy to study the axial or equatorial orientation of the ester functionality with respect to the adopted chair conformation of the cyclohexane ring. The ab initio and DFT geometry‐optimized structures and relative free energies of the axial and equatorial conformers were also calculated at the HF/6‐311G**, MP2/6‐311G**, and B3LYP/6‐31G** levels of theory, both in the gas phase and in solution. In the latter case, a self‐consistent isodensity polarized continuum model was employed. Only by including electron correlation in the modeling calculations for the solvated molecules was it possible to obtain a reasonable correlation between ΔG°calcd and ΔG°exp. Both the structures and the free energy differences of the axial and equatorial conformers were evaluated with respect to the factors normally influencing conformational preference, namely, 1,3‐diaxial steric interactions in the axial conformer and hyperconjugation. It was assessed that hyperconjugative interactions, σC? C/σC? H and σ*C? O, together with a steric effect—the destabilization of the equatorial conformer with increasing bulk of the R group—were the determinant factors for the position of the conformational equilibria. Thus, because hyperconjugation is held responsible as the mitigating factor for the anomeric effect in 2‐substituted, six‐membered saturated heterocyclic rings, and since it is also similarly responsible, at least partly, in these monosubstituted cyclohexanes for a preferential shift towards the axial conformer, the question is therefore raised: can the anomeric effect really be construed as anomalous?  相似文献   

17.
New neutral platinum(II) monohydridocarborane complexes of general formula cis- and trans-L2PtH(σ-carb), where L = (C2H5)3P, (C6H5)3P, (C6H5)2(CH3)P, (C6H5)(CH3)2P and carb = 2-R-1,2- or 7-R-1,7-B10C2H10? (R = H, CH3, C6H5), have been prepared. The configurations of the complexes obtained have been assigned by 1H NMR spectroscopy. The cis-monohydridocarborane complexes here reported are the first examples of neutral cis-monohydrido derivates of platinum(II) containing platinum—carbon σ bonds. 1H NMR chemical shifts and coupling constants of the prepared complexes are also reported, and used in a tentative evaluation of the trans-influence of the carbonage ligands.  相似文献   

18.
Imidazolium salts, [RS(O)? CH2(C3H3N2)Mes]Cl (R=Me ( L1 a ), Ph ( L1 b )); Mes=mesityl), make convenient carbene precursors. Palladation of L1 a affords the monodentate dinuclear complex, [(PdCl2{MeS(O)CH2(C3H2N2)Mes})2] ( 2 a ), which is converted into trans‐[PdCl2(NHC)2] (trans‐ 4 a ; N‐heterocyclic carbene) with two rotamers in anti and syn configurations. Complex trans‐ 4 a can isomerize into cis‐ 4 a (anti) at reflux in acetonitrile. Abstraction of chlorides from 4 a or 4 b leads to the formation of a new dication: trans‐[Pd{RS(O)CH2(C3H2N2)Mes}2](PF6)2 (R=Me ( 5 a ), Ph ( 5 b )). The X‐ray structure of 5 a provides evidence that the two bidentate SO? NHC ligands at palladium(II) are in square‐planar geometry. Two sulfoxides are sulfur‐ and oxygen‐bound, and constitute five‐ and six‐membered chelate rings with the metal center, respectively. In acetonitrile, complexes 5 a or 5 b spontaneously transform into cis‐[Pd(NHC)2(NCMe)2](PF6)2. Similar studies of thioether–NHCs have also been examined for comparison. The results indicate that sulfoxides are more labile than thioethers.  相似文献   

19.
Single‐crystal X‐ray diffraction analysis of [2,6‐(Me2NCH2)2C6H3]2SnF2 reveals that only one of the two dimethylaminomethyl groups of each pincer‐type ligands [2,6‐(CH2NMe2)2C6H3]? is coordinated to the tin atom at Sn‐N distances of 2.576(2) and 2.470(2) Å, inducing chirality of the latter. The tin atom exhibits a distorted octahedral trans(C,C)cis(N,N)cis(F,F) configuration. Extensive intra‐ and intermolecular C‐H···F hydrogen bonding is observed with the latter giving rise to formation of polymeric chains.  相似文献   

20.
The reaction of sulfur with primary or secondary amines and formaldehyde has been studied. A simple one step process for the preparation of thioformamides (RR′NCHS; R ? H, R′ ? CH3, C2H5; R ? R′ ? CH3, C2H5; R+R′ ? ? (CH2), ? (CH2), ? C2H4OC2H) and the amine salts of N, N-dialkyl-dithiocarbamic acids (R2NCS2 · H2NR2, R ? CH3, C2H5, C4H9; R2 ? ? (CH2), ? (CH2), ? C2H4OC2H) is reported. In addition, the isolation of diethylamidosulfoxylic acid, (C2H5)2NSOH · 1/2 H2O, the first derivative of a new class of compounds, is described. The physical properties and the 1H-NMR. spectra of the above mentioned compounds are given.  相似文献   

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