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Planar Chirality (planar + chirality)

Distribution by Scientific Domains

Chemistry	88%

Selected Abstracts

ChemInform Abstract: 2-Phospha[3]ferrocenophanes with Planar Chirality: Synthesis and Use in Enantioselective Organocatalytic [3 + 2] Cyclizations.

CHEMINFORM, Issue 9 2009
Arnaud Voituriez
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Synthesis of Novel P-Ketimine Bidentate Ferrocenyl Ligands with Central and Planar Chirality and Comparison in the Catalytic Activity Between P-Ketimine and P-Aldimine.

CHEMINFORM, Issue 11 2004
Xiangping Hu
Abstract For Abstract see ChemInform Abstract in Full Text. [source]

New Macrocycles with Planar Chirality,Synthesis and Determination of Absolute Configurations

CHEMISTRY - A EUROPEAN JOURNAL, Issue 16 2006
Jaros, aw Kalisiak Dr.
Abstract A versatile system for preparing macrocyclic compounds with planar chirality is presented. In this system chiral diazacoronands are synthesized readily from lariat-type diesters 13 and 14 and unsymmetrical diamines 7, 8, 12, 15, and 16 under non-high-dilution conditions. The title compounds were subjected to structural analysis by X-ray crystallography and circular dichroism spectroscopy, and absolute configurations for two representative examples (compounds 2 and 3) were assigned by molecular modeling. The correctness of the theoretical approach was verified by the crystallographic results obtained experimentally. [source]

Expanding the Range of "Daniphos"-Type P,P- and P,N-Ligands: Synthesis and Structural Characterisation of New [(,6 -arene)Cr(CO)3] Complexes

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 31 2007
Elisabetta Alberico
Abstract New P,P- and P,N-ligands have been synthesised whose core structure is an [(,6 -arene)Cr(CO)3] unit. These new ligands, which extend the range of "Daniphos" ligands, are endowed with central and planar chirality and have been prepared through a stereoselective synthetic strategy from optically pure benzylamines bearing a second substituent on the arene other than the benzyldimethylamino group. Because the two faces of unsymmetrically 1,2- and 1,3-disubstituted benzylamine are diastereotopic, which means that diastereomeric complexes arise upon coordination of theCr(CO)3 fragment to either of these two faces, the synthetic plan has been adjusted by exploiting the trimethylsilyl group as a temporary steric modulator in order to access both complexes with high diastereoselectivity. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

Pirouetting in chiral [2]catenanes,

ISRAEL JOURNAL OF CHEMISTRY, Issue 2 2007
Seogshin Kang
One of the best known classes of mechanically interlocked molecules is the category of [2]catenanes, which exhibit donor-acceptor interactions between the 1,5-dioxynaphthalene (DNP) units in a crown ether and the bipyridinium units in the tetracationic cyclophane, cyclobis(paraquat- p -phenylene) (CBPQT4+). In order to gain an in-depth understanding and appreciation of the stereochemistry and dynamic behavior of these [2]catenanes, chiral analogues,having both the DNP ring, which is capable of displaying planar chirality, and the axially chiral binaphthol (BINAP) moiety (as both enantiomers and as the racemic modification), in a crown ether, in addition to the CBPQT4+ cyclophane,have been synthesized using a template-directed protocol. Dynamic 1H NMR spectroscopy shows that (i) the presence of immutable axial chirality, arising from the BINAP moiety in the crown ether component, leads to no induction of diastereoselectivity,the chiral catenanes exist as a mixture of diastereoisomers in solution at low temperatures in the approximate ratio of 1:1, (ii) the barrier (,GcD,) to the interconversion between these two diastereoisomers is 7.9 ± 0.1 kcal mol,1 at 171 K, and (iii) no induction of diastereoselectivity is observed upon the addition of a chiral solvating agent to the chrial catenanes. The pattern of behavior in the variable temperature 1H NMR spectra and the low ,TGcD, value indicates that the dynamic process involving the interconversion between these two diastereoisomers is one of a pirouetting nature. Of the four possible diastereoisomers, only two, (R)-(pR/pS) or (S)-(pR/pS), are shown to exist in solution. [source]

Studies of ethylene,styrene copolymerization with dinuclear constrained geometry complexes with methyl substitution at the five-membered ring in indenyl of [Ti(,5:,1 -C9H5SiMe2NCMe3)]2 [CH2]n

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 7 2004
Seok Kyun Noh
Abstract The new dinuclear half-sandwich CGC (constrained geometry catalyst) with methyl substitution in indenyl, [Ti(,5:,1 -2-methylindenyl)SiMe2NCMe3]2 [(CH2)n] [n = 6 (10), n = 9 (11), n = 12 (12)], have been synthesized, and structure of these complexes has been characterized by 1H and 13C NMR. The most important feature is that two protons of methylene directly bonded to the indenyl ring become inequivalent to be shown as two separated resonances at 2.9 and 3.0 ppm, probably due to the formation of planar chirality caused by a titanium complex formation. It has been found that the dinuclear CGCs with methyl substitution at an indenyl ring were very active catalysts for ethylene and styrene copolymerization. The activity increases in the order of 10 < 11 < 12, which indicates that the presence of a longer bridge between two active sites contributes to facilitate the polymerization activity of the dinuclear CGC more effectively. This result might be understood by the implication that the steric factor rather than the electronic factor may play a major role to direct the polymerization behavior of the dinuclear CGC. It is found that the dinuclear catalysts are very efficient to incorporate styrene in the polyethylene backbone. The styrene contents in the formed copolymers ranged from 5 to 40% according to the polymerization conditions. One can observe strong signals at 29.7 ppm of the polyethylene sequences, and, in addition, peaks at 27.5, 36.9, and 46. 2ppm (S,,, S,,, and T,,, respectively) of sequences of EESEE. Weak peak at 25.3 ppm are attributed to S,,, which represents SES sequence. The absence of a signal for T,, at 41.3 ppm and for S,, at 43.6 ppm shows there is no styrene,styrene sequences in copolymers. This result indicates that the dinuclear CGC are very effective to generate well-distributed poly(ethylene- co -styrene)s. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1712,1723, 2004 [source]

A commonly used spin label: S -(2,2,5,5-tetramethyl-1-oxyl-,3 -pyrrolin-3-ylmethyl) methanethiosulfonate

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 11 2008
Vitali Zielke
The title compound, C10H18NO3S2, which finds application as a spin label, has triclinic (P) symmetry at 100,(2),K with two independent molecules in the asymmetric unit. Both molecules are very similar with respect to bond lengths and angles, but molecule 2 shows disordering of its side chain. The pyrroline rings differ slightly with respect to the position of the NO group, which in both cases are sterically shielded by the surrounding methyl groups. The crystal structure of the title compound represents the first example of a 2,2,5,5-tetramethyl-1-oxyl-,3 -pyrroline derivative with a side chain at the double bond which is linked to it through an sp3 -hybridized C atom. In the solid state, the side chain adopts a conformation with the methyl group above/below the pyrroline ring and a H atom directed towards a C atom of the double bond. The disordered side chain of molecule 2 represents a second conformation with low potential energy. Both molecules exhibit planar chirality, but in the solid state both pairs of stereoisomers are present. These four stereoisomers are stacked one behind the other in four different columns, denoted A, A,, B and B,, the angle between the vectors of the N,O bonds in columns A and B being 80.38,(8)°. [source]

(R,R)-Tricarbonyl{,6 -1-(diphenylphosphino)-2-[1-(diphenylphosphino)ethyl]benzene}chromium(0), (R,R)-tricarbonyl-1,3C -{,-1(,6):2,2P,P,-1-(diphenylphosphino)-2-[1-(diphenylphosphino)ethyl]benzene}[2(,4)-norbornadiene]chromium(0)rhodium(I) tetrafluoroborate methanol 0.75-solvate and (R,R)-tricarbonyl-1,3C -{,-1(,6):2,2P,P,-1-(diphenylphosphino)-2-[1-(diphenylphosphino)ethyl]benzene}[2(,4)-(Z,Z)-cycloocta-1,5-diene]chromium(0)rhodium(I) tetrafluoroborate methanol 1.5-solvate

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2004
Wolfgang Braun
The title mononuclear chromium compound, [Cr(C32H28P2)(CO)3], (I), and its rhodium complexes [CrRh(C7H8)(C32H28P2)(CO)3]BF4·0.75CH4O, (II), and [CrRh(C8H12)(C32H28P2)(CO)3]BF4·1.5CH4O, (III), prepared as a ligand and precatalysts, respectively, for application in asymmetric homogeneous hydrogenation, have been studied by single-crystal X-ray diffraction. The structures of the free and complexed ligand are compared. It was found that the backbone of the ligand remains rigid on coordination, while only minor conformational changes of its side chains are observed. Both elements of central and planar chirality seem to build a well defined chiral environment for stereoselective catalysis. [source]