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21.
Burford N Ragogna PJ McDonald R Ferguson MJ 《Chemical communications (Cambridge, England)》2003,(16):2066-2067
Polyphosphorus dications have been synthesised and comprehensively characterised as diphosphine (dppe, dmpe and dpph) linked Ar2P+ Lewis acids (Ar = C6H5); this application of unique homoatomic coordination chemistry provides important building blocks for extended systems. 相似文献
22.
Neil G. Connelly John G. Crossley A. Guy Orpen Henrietta Salter 《Journal of organometallic chemistry》1994,480(1-2):c12-c13
The reaction of [NBu4n]2Cu(mnt)2] with [Pt(CNMe)4][PF6]2 gives [Pt(mnt)(CNMe)2]·(NC)2C2S2CNMe, an X-ray study of which reveals co-stacking of neutral planar metal and organic molecules. 相似文献
23.
Gaballah ST Hussein YH Anderson N Lian TT Netzel TL 《The journal of physical chemistry. A》2005,109(48):10832-10845
Femtosecond, picosecond, and nanosecond transient absorbance (TA) and picosecond emission kinetics results are presented for three 5-(1-pyrenyl)-2'-deoxyuridine nucleosides each with a different two-atom linker joining pyrenyl C-1 to uracil C-5. The linkers are respectively -NHCO-, -(CH(2))(2)-, and -C[triple bond]C- for PAdU, PEdU, and PYdU. For all three nucleoside conjugates, most conformers undergo intramolecular charge transfer (CT) from their pyrenyl (1)(pi,pi) excited states to form Py(*+)/dU(*-) CT products in ultrashort times: 相似文献
24.
Burford N Cameron TS Clyburne JA Eichele K Robertson KN Sereda S Wasylishen RE Whitla WA 《Inorganic chemistry》1996,35(19):5460-5467
The phosphadiazonium cation [MesNP](+) reacts quantitatively with the fluorenylide anion, MesNH(2), and MesOH (Mes = 2,4,6-tri-tert-butylphenyl), resulting in formal insertion of the N-P moiety into the H-Y (Y = C, N, O) bonds. Specifically, reaction of MesNPCl with fluorenyllithium gives the aminofluorenylidenephosphine [crystal data: C(31)H(38)NP, monoclinic, P2(1)/c, a = 9.568(8) ?, b = 24.25(2) ?, c = 11.77(1) ?, beta = 101.38(8) degrees, Z = 4]. Similarly, reaction of [MesNP][GaCl(4)] with MesNH(2) gives the diaminophosphenium salt [MesN(H)PN(H)Mes][GaCl(4)] [crystal data: C(36)H(60)Cl(4)GaN(2)P, monoclinic, C2/c, a = 24.921(2) ?, b = 10.198(4) ?, c = 16.445(2) ?, beta = 93.32(1) degrees, Z = 4], and reaction with MesOH gives the first example of an aminooxyphosphenium salt [MesN(H)POMes][GaCl(4)]. It is proposed that the reactions involve nucleophilic attack at phosphorus followed by a 1,3-hydrogen migration from Y to N. Experimental evidence for the formation of sigma-complex intermediates is provided by the isolation of [MesNP-PPh(3)][SO(3)CF(3)] [crystal data: C(37)H(44)F(3)NO(3)P(2)S, triclinic, P&onemacr;, a = 10.663(1) ?, b = 19.439(1) ?, c = 10.502(1) ?, alpha = 103.100(7) degrees, beta = 113.311(7) degrees, gamma = 93.401(7) degrees, Z = 2]. As part of the unequivocal characterization of the aminooxyphosphenium salt, detailed solid-state (31)P NMR studies and GIAO calculations on the phosphenium cations have been performed. Contrary to popular belief, the phosphorus shielding in dicoordinate cations is not caused by the positive charge but results from efficient mixing between the phosphorus lone pair and pi orbitals. 相似文献
25.
Griffith GA Percy JM Pintat S Smith CA Spencer N Uneyama E 《Organic & biomolecular chemistry》2005,3(15):2701-2712
Highly-functionalised difluorinated cyclooctenones were synthesised from trifluoroethanol using either metallated difluoroenol acetal or carbamate chemistry, followed by a [2,3]-Wittig rearrangement or aldol reaction. Efficient RCM reactions afforded the title compounds which showed rather restricted fluxional behaviour by VT (19)F NMR. Topological characterisation by molecular modelling and NOESY/ROESY experiments offered a number of challenges, but allowed the identification of two favoured boat-chair conformers which interconverted by pseudorotation with relatively large activation barriers. 相似文献
26.
Stølen S Mohn CE Ravindran P Allan NL 《The journal of physical chemistry. B》2005,109(25):12362-12365
We discuss the importance of the topography of the potential energy hypersurface for the ionic conductivity of perovskite-related A(2)B(2)O(5) oxides. A correlation between the energetic preference of the cations for different coordination geometries and the ionic conductivity is proposed based on a first principles periodic density functional theory study of selected possible structures for Ba(2)In(2)O(5), Sr(2)Fe(2)O(5), Sr(2)Mn(2)O(5), and La(2)Ni(2)O(5). There are a large number of low-energy local minima on the potential energy hypersurfaces of the two first compounds due to an energetic preference for BO(4) tetrahedra. Tetrahedral environments are energetically unfavorable for Mn(III) in Sr(2)Mn(2)O(5) and for Ni(II) in La(2)Ni(2)O(5), and the number of low-energy configurations is relatively low in these two cases. Consistent with our findings, in contrast to Sr(2)Fe(2)O(5) and Ba(2)In(2)O(5), Sr(2)Mn(2)O(5) and La(2)Ni(2)O(5) do not exhibit transitions to disordered phases on heating, and there appear to be no reports of enhanced ionic conductivity for these compounds. Thus we suggest that the possibility of many different oxygen orderings associated with a variety of low-energy connectivity schemes within tetrahedral layers such as in the brownmillerite-based structures of Sr(2)Fe(2)O(5) and Ba(2)In(2)O(5) is a prerequisite for high ionic conductivity in perovskite-related A(2)B(2)O(5) oxides. 相似文献
27.
Thermodynamic studies were performed on 12 pairs of N-trifluoroacetyl-O-alkyl nipecotic acid ester enantiomers on diluted permethylated beta-cyclodextrin stationary phase (CP Chirasil-Dex CB). The influence of ester alkyl group structure on interaction with permethylated beta-cyclodextrin (Me-CD) and enantioselectivity was studied. The types of alkyl groups studied included n-alkyl (C1-C5) and groups containing branching at differing locations relative to the chiral center of the molecule. The results show that for a given molecular weight, the n-alkyl esters have stronger interactions with Me-CD than esters containing branched alkyl groups. However, although having weaker interactions with Me-CD, esters containing alpha-branched alkyl groups exhibit higher enantioselectivity than the corresponding n-alkyl or beta-branched isobutyl esters. From the retention data, thermodynamic parameters were estimated using the retention increment method and enthalpy-entropy compensation plots (ln R' versus deltaH) were constructed. The results suggest that ester enantiomers with branching at the alpha-carbon of the ester alkyl group have additional and/or different types of enantioselective interactions with Me-CD than the C1-C5 n-alkyl esters or beta-branched isobutyl ester. In order to obtain a qualitative sense of the interaction with Me-CD, structures of the diastereomeric complexes formed between Me-CD and some of the ester enantiomers were modeled using simulated annealing molecular dynamics. 相似文献
28.
Khlobystov AN Brett MT Blake AJ Champness NR Gill PM O'Neill DP Teat SJ Wilson C Schröder M 《Journal of the American Chemical Society》2003,125(22):6753-6761
A series of structurally related binuclear metallacycles [Cd(NO(3))(2)L](2), where L is an angular exo-bidentate ligand, have been synthesized. Each metallacycle contains two coordinatively unsaturated, chiral metal centers within a single molecule, and the assembly of these metallacycles into polymeric framework structures has been studied systematically for the first time. Stereoselective homochiral association of [Cd(NO(3))(2)L](2) leads to the formation of helical coordination polymers, whereas meso type association results in nonhelical chain structures. The type of stereoselective aggregation depends on the conditions of self-assembly as well as on ligand functionality. Both helical and nonhelical polymeric complexes have been isolated for the metallacycle [Cd(NO(3))(2)(2,4'-pyacph)](2) (2,4'-pyacph = 2,4'-(4-ethynylphenyl)bipyridyl). Homochiral association results in the formation of helical [Cd(NO(3))]( infinity ) chains which link the binuclear [Cd(NO(3))(2)(2,4'-pyacph)](2) metallacycles into racemic two-dimensional sheets which contain both P and M [Cd(NO(3))]( infinity ) helices. In contrast, meso-association leads to the formation of nonhelical one-dimensional chains. It is shown that the product of homochiral association is predominately formed at room temperature and that of meso-association is generated at elevated temperatures. Thus, it may be concluded that the homochiral association appears to be energetically less favorable than the meso-association, a conclusion that has been confirmed by theoretical calculations of the crystal lattice energy. Several high-yield syntheses of bipyridyl-type ligands used for metallacyclic assembly are also reported. 相似文献
29.
Nikhil M. Kriplani David P. Nackashi Christian J. Amsinck Neil H. Di Spigna Michael B. Steer Paul D. Franzon Ramon L. Rick Gemma C. Solomon Jeffrey R. Reimers 《Chemical physics》2006
Two efficient, physically based models for the real-time simulation of molecular device characteristics of single molecules are developed. These models assume that through-molecule tunnelling creates a steady-state Lorentzian distribution of excess electron density on the molecule and provides for smooth transitions for the electronic degrees of freedom between the tunnelling, molecular-excitation, and charge-hopping transport regimes. They are implemented in the fREEDA™ transient circuit simulator to allow for the full integration of nanoscopic molecular devices in standard packages that simulate entire devices including CMOS circuitry. Methods are presented to estimate the parameters used in the models via either direct experimental measurement or density-functional calculations. The models require 6–8 orders of magnitude less computer time than do full a priori simulations of the properties of molecular components. Consequently, molecular components can be efficiently implemented in circuit simulators. The molecular-component models are tested by comparison with experimental results reported for 1,4-benzenedithiol. 相似文献
30.
Karen V. Baker John M. Brown Neil A. Cooley Gareth D. Hughes Richard J. Taylor 《Journal of organometallic chemistry》1989,370(1-3):397-406
The palladium dibromide complexes of (S,R)-(1,1′-bis-diphenylphosphino)-2-ferrocencylthyldimethylamine and (S,R)-(1-diphenylphosphino)-2-ferrocenylethyldimethylamine have been reduced with dilithiocyclooctatetraene to form the corresponding Pd0 cyclooctatetraene complexes. Their reactions with E-4-methoxy-2′-bromophenylethene, and then benzylmagnesium chloride at −60 to −30°C, provide information on the structure of intermediates in asymmetric cross-coupling. 相似文献