Structure cristalline et configuration relative d'un complexe du titanocene presentant une chiralite plane et une chiralite centree sur l'atome de titane

Lecomte, Claude; Dusausoy, Y.; Protas, J.; Tirouflet, J.; Dormond, A.

doi:10.1016/s0022-328x(00)80382-4

Cited by 136 publications

(60 citation statements)

References 8 publications

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“…[5] For the specification of the Ru configuration the priority sequence Cy > Cl > O > N was used. [6,7] As expected, the bond lengths and bond angles of the two diastereomers (R Ru ,S C )-1 and (S Ru ,S C )-1 are very similar (Table 1). Surprisingly, the intermolecular Ru···Ru distances in the crystal are very different.…”

supporting

confidence: 72%

“…In both 12 and 13, there are short intermolecular Ru···Ru contacts, however, there are no CÀ H···X/Y hydrogen bonds (Table 2) and, most importantly, the angles Cy1-Ru1-Ru2 (120.58) and Cy2-Ru2-Ru1 (118.08) for 12 and mesitylene1-Ru1-Ru2 (125.48) and mesitylene2-Ru2-Ru1 (122.18) for 13 are much greater than 908, whereas for 1-11 they are less than 908 ("lying Z" arrangement). In the complex [(Cy)Ru{chiraphos(O)}Cl]SbF 6 (14, chiraphos = 2,3-bis(diphenylphosphano)butane), [17] the {(Cy)Ru} fragment and the two electronegative substituents O PP and Cl could conceivably form inverted piano stool motifs, but instead, a structure is found in which the diastereomeric cations are separated by the large SbF 6 dbp = 1-phenylbenzodiphosphole) [20] both exhibit 1:1 cocrystallization of diastereomers. In both cases, however, the structural prerequisites are so different that the molecular recognition motif shown in Figure 2 cannot be applied.…”

mentioning

confidence: 99%

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Inverted Piano Stools: A Molecular Recognition Motif That Enforces 1:1 Cocrystallization of Two Diastereomers in the Same Single Crystal

Brunner¹,

Weber²,

Zabel³

et al. 2003

Angew Chem Int Ed

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Half‐sandwich complexes of the type [(Ar)MXY(NR*)] (see structure; X, Y=electronegative substituents; M=Ru, Os, Rh, Ir) tend to form inversion pairs in the solid state, which are characterized by short M⋅⋅⋅M separations and CH⋅⋅⋅X/Y hydrogen bonds between the pairs of molecules. As a consequence, two diastereomers with a given chirality in the Z substituent, usually an NR* substituent, and different metal configurations approach each other with their “racemic sides” resulting in an unusually preferred 1:1 diastereomer cocrystallization in the same single crystal.

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supporting

confidence: 72%

mentioning

confidence: 99%

Inverted Piano Stools: A Molecular Recognition Motif That Enforces 1:1 Cocrystallization of Two Diastereomers in the Same Single Crystal

Brunner¹,

Weber²,

Zabel³

et al. 2003

Angew Chem Int Ed

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“…If the amidinato ligand were to remain rigid [*I The R,S system proposed by Cuhn, Ingold, and helog 1741 makes no provision for inclusion of n-bonded ligands in the sequence rule. Tiroufef [72] and Buird [73] have suggested that polyhapto ligands be considered as pseudoatoms with atomic number equal to the sum of the atomic numbers of the n-bonded atoms. Thus, for example, q6-C6H6, q5-C5HS, and q2-C2H4 are classified as pseudoatoms having the atomic numbers 36,30, and 12, respectively.…”

mentioning

confidence: 99%

Rhodium Catalysts for Enantioselective Hydrosilylation—A New Concept in the Development of Asymmetric Catalysts

Brunner

1983

Angew. Chem. Int. Ed. Engl.

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Dedicated to Professor Ernst Otto Fischer on the occasion of his 65th birthdayFollowing a survey of the asymmetric hydrogenation of prochiral olefins with transition metal/phosphane catalysts, the problem of chirality transfer from the optically active ligands of the catalyst to the substrate is discussed. A new concept for this chirality transfer is introduced ; the conformational analysis of model compounds as well as the development of catalysts for enantioselective hydrosilylation demonstrate the usefulness of this concept.For every reaction in which a new asymmetric center is created there exists a transition metal catalyst which-when added in small amounts-leads stereospecijkally to one enantiomer. One onZy has to find it. Introductory RemarksEnzymes catalyze the synthesis of optically active compounds from prochiral precursors. The reactions are usually stereospecific. Since an enzyme molecule converts its substrate 10000 to 1000000 times per minute"], the optical activity contained in it is multiplied by this factor each minute. Enzyme reactions are thus prime examples for "asymmetric catalysis" in which large amounts of optically active products are formed from a small amount of "optically active information". However, enzyme reactions are often restricted to natural substrates, and reactivity as well as stereoselectivity rapidly decrease when the substrate is varied. This poses the following questions: How good are synthetic catalysts in asymmetric catalysis? Can they make a contribution to the increasing demand for enantiomerically pure optically active pharmaceuticals, foods, animal feeds, pesticides, organic chemicals, etc.? Enantioselective Catalysis with Transition MetaVPhosphane ComplexesIn 1968 Horner et a1.[" and Knowles et ~1 . '~' independently discovered that prochiral olefins can be hydrogenated enantioselectively using rhodium complexes similar to Wilkinson's catalystE4] but having optically active phosphane ligands. Scheme 1 shows this for one of the first asymmetric hydrogenations-the conversion of a-methoxystyrene 1 into a-methoxyethylbenzene 2a, b. sure) and the possibility of converting dehydroamino acids into amino acids['' soon resulted in world-wide attention for this area of research. Although the use of monodentate optically active phosphanes led to high optical inductions for some special substrates, it was only the switch to chelating phosphanes that brought decidedly better optical yields. 3Scheme 2 *a CbThe synthesis of N-acetylphenylalanine 4a, b from (aa-(N-acetamido)cinnamic acid 3 according to Scheme 2 may be quoted as an example. The catalyst is formed in situ from the precatalyst [Rh(cod)Cl], (cod = 1,s-cyclooctadiene) and the cocatalyst diop 5 (Scheme 3), and gives an optical induction of 81% ee. Thus (-)-diop, which is derived from naturally occurring tartaric acid, leads to N-acetylphenylalanine with an ( R ) : ( S ) ratio of 90.5 :9.5[91. These studies culminated several years ago in the development of an industrial process for the synthesis of L-Dopa, a drug used to...

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“…Single crystals of 2a were grown at Ϫ30°C from CH 2 Cl 2 /hexane using a 2a:2b ϭ 93:7 mixture. For the (ϩ) 578 diastereomer 2a the absolute configuration at the molybdenum was determined to be R Mo , the priority of the ligands being η 7 -C 7 H 7 > P > N > C [12,13]. The structure determination confirmed the S C configuration of the stereogenic carbon centre.…”

Section: Molecular Structures Of 2a and 2bmentioning

confidence: 75%

Optically Active Transition Metal Complexes. 128 [1] Synthesis, Characterization and Molecular Structures of Cycloheptatrienyl-Iminphos-Molybdenum Complexes Differing Only in the Metal Configuration

Brunner

Klankermayer

Zabel

2002

Z. anorg. allg. Chem.

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The chiral-at-metal cycloheptatrienyl-molybdenum complexes (R Mo ,S C )-[(η 7 -C 7 H 7 )Mo(iminphos)(CO)]BF 4 (2a) and (S Mo ,S C )-[(η 7 -C 7 H 7 )Mo(iminphos)(CO)]BF 4 (2b) (iminphos ϭ 2-[N-(S)-1-phenylethylcarbaldimino]phenyl(diphenyl)phosphane), which only differ in the molybdenum configuration, were prepared and separated by fractional crystallization. The absolute configuration Optisch aktive Übergangsmetall-Komplexe. 128 [1] Synthese, Charakterisierung und Molekülstrukturen von chiralen CycloheptatrienylIminphos-Molybdän-Komplexen mit unterschiedlicher Metallkonfiguration

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Structure cristalline et configuration relative d'un complexe du titanocene presentant une chiralite plane et une chiralite centree sur l'atome de titane

Cited by 136 publications

References 8 publications

Inverted Piano Stools: A Molecular Recognition Motif That Enforces 1:1 Cocrystallization of Two Diastereomers in the Same Single Crystal

Inverted Piano Stools: A Molecular Recognition Motif That Enforces 1:1 Cocrystallization of Two Diastereomers in the Same Single Crystal

Rhodium Catalysts for Enantioselective Hydrosilylation—A New Concept in the Development of Asymmetric Catalysts

Optically Active Transition Metal Complexes. 128 [1] Synthesis, Characterization and Molecular Structures of Cycloheptatrienyl-Iminphos-Molybdenum Complexes Differing Only in the Metal Configuration

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