Enantiodivergent asymmetric catalysis with the tropos BIPHEP ligand and a proline derivative as chiral selector

Oczipka, Philipp; Müller, Dirk; Leitner, Walter; Franciò, Giancarlo

doi:10.1039/c5sc03465e

Cited by 20 publications

(10 citation statements)

References 37 publications

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“…A search of the Cambridge Structural Database (v. 5.40 with February 2019 updates [26]) for {Cu(BINAP)(N^N)}-containing compounds, in which N^N is constrained to a chelating ligand, reveals only six entries [27,28,29,30] and for these, the range of P–Cu–P bond angles is 99.25–105.13°. Both BINAP and BIPHEP are expected to exhibit atropisomerism, but, at room temperature, interconversion of ( R )- and ( S )-BINAP is slow, whereas the atropisomers ( R )- and ( S )-BIPHEP (Scheme 1) interconvert rapidly in solution [31]. Coordination of BIPHEP to a metal centre can lead to chiral metal coordination compounds.…”

Section: Introductionmentioning

confidence: 99%

Hinged and Wide: A New P^P Ligand for Emissive [Cu(P^P)(N^N)][PF6] Complexes

et al. 2019

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Heteroleptic [Cu(BIPHEP)(N^N)][PF6] complexes (BIPHEP = 1,1′-biphenyl-2,2′-diylbis(diphenylphosphane)), in which N^N is 2,2′-bipyridine (bpy), 6-methyl-2,2′-bipyridine (6-Mebpy), 6-ethyl-2,2′-bipyridine (6-Etbpy), or 5,5′-dimethyl-2,2′-bipyridine (5,5′-Me2bpy), have been synthesized and characterized using multinuclear NMR spectroscopies and electrospray ionization mass spectrometry. The single crystal structures of [Cu(BIPHEP)(bpy)][PF6]∙CH2Cl2, [Cu(BIPHEP)(5,5′-Me2bpy)][PF6]∙CH2Cl2, [Cu(BIPHEP)(6-Mebpy)][PF6]∙Et2O∙0.5H2O and [Cu(BIPHEP)(6-Etbpy)][PF6] confirm distorted tetrahedral {Cu(P^P)(N^N)} coordination environments. Each compound shows a quasi-reversible Cu+/Cu2+ process. In deaerated solution, the compounds are weak emitters. Powdered samples are yellow emitters (λemmax in the range 558–583 nm) and [Cu(BIPHEP)(5,5′-Me2bpy)][PF6] exhibits the highest photoluminescence quantum yield (PLQY = 14%). On cooling to 77 K (frozen 2-methyloxolane), the emission maxima are red-shifted and the excited state lifetimes increase from τ1/2 < 8 μs, to τ1/2 values of up to 53 μs, consistent with the compounds with N^N = 6-Mebpy, 6-Etbpy and 5,5′-Me2bpy exhibiting thermally activated delayed fluorescence (TADF).

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Section: Introductionmentioning

confidence: 99%

Hinged and Wide: A New P^P Ligand for Emissive [Cu(P^P)(N^N)][PF6] Complexes

et al. 2019

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“…One major advantage of stereodynamic ligands is that there is no need for separate preparation of one ligand enantiomer as long as their chirality can be controlled by chiral additives or auxiliaries. In addition, the simultaneous presence of both axially chiral BIPHEP enantiomers can be beneficial as this allows bidirectional control of enantioselectivity depending on temperature [ 14 – 15 ]. In this approach, both product enantiomers of an enantioselective transformation can be addressed selectively by fine tuning of the conditions prior to and during catalysis.…”

Section: Introductionmentioning

confidence: 99%

Stereodynamic tetrahydrobiisoindole “NU-BIPHEP(O)”s: functionalization, rotational barriers and non-covalent interactions

Storch¹,

Pallmann²,

Röminger³

et al. 2016

Beilstein J. Org. Chem.

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SummaryStereodynamic ligands offer intriguing possibilities in enantioselective catalysis. “NU-BIPHEPs” are a class of stereodynamic diphosphine ligands which are easily accessible via rhodium-catalyzed double [2 + 2 + 2] cycloadditions. This study explores the preparation of differently functionalized “NU-BIPHEP(O)” compounds, the characterization of non-covalent adduct formation and the quantification of enantiomerization barriers. In order to explore the possibilities of functionalization, we studied modifications of the ligand backbone, e.g., with 3,5-dichlorobenzoyl chloride. Diastereomeric adducts with Okamoto-type cellulose derivatives and on-column deracemization were realized on the basis of non-covalent interactions. Enantioselective dynamic HPLC (DHPLC) allowed for the determination of rotational barriers of ΔG ‡ 298K = 92.2 ± 0.3 kJ mol−1 and 99.5 ± 0.1 kJ mol−1 underlining the stereodynamic properties of “NU-BIPHEPs” and “NU-BIPHEP(O)s”, respectively. These results make the preparation of tailor-made functionalized stereodynamic ligands possible and give an outline for possible applications in enantioselective catalysis.

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“…[5,6] In such adynamic system, the resolution into one of the diastereomers is dependent on transfer of chiral information from as tereoregulating unit. This transfer has been achieved by coordination of achiral co-ligand or anion, [7][8][9][10][11] or control of the backbone by acovalently bound chiral auxiliary (Scheme 1). [12][13][14][15][16] Recently,control of axial chirality in a tropos ligand was demonstrated by association of small chiral molecules through hydrogen bonding.…”

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confidence: 99%

Inducing Axial Chirality in a Supramolecular Catalyst

2018

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A new type of ligand, which is able to form axially chiral, supramolecular complexes was designed using DFT calculations. Two chiral monomers, each featuring a covalently bound chiral auxiliary, form a bidentate phosphine ligand with a twisted, hydrogen-bonded backbone upon coordination to a transition metal center which results in two diastereomeric, tropos complexes. The ratio of the diastereomers in solution is very temperature- and solvent-dependent. Rhodium and platinum complexes were analyzed through a combination of NMR studies, ESI-MS measurements, as well as UV-VIS and circular dichroism spectroscopy. The chiral self-organized ligands were evaluated in the rhodium-catalyzed asymmetric hydrogenation of α-dehydrogenated amino acids and resulted in good conversion and high enantioselectivity. This research opens the way for new ligand designs based on stereocontrol of supramolecular assemblies through stereodirecting chiral centers.

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Enantiodivergent asymmetric catalysis with the tropos BIPHEP ligand and a proline derivative as chiral selector

Abstract: Enantiomer on demand: tropos ligand BIPHEP and chiral selector (S)-proline methyl ester allow enantiodivergent Rh-catalysed hydrogenation and asymmetric styrene hydroboration.

Cited by 20 publications

References 37 publications

Hinged and Wide: A New P^P Ligand for Emissive [Cu(P^P)(N^N)][PF6] Complexes

Hinged and Wide: A New P^P Ligand for Emissive [Cu(P^P)(N^N)][PF6] Complexes

Stereodynamic tetrahydrobiisoindole “NU-BIPHEP(O)”s: functionalization, rotational barriers and non-covalent interactions

Inducing Axial Chirality in a Supramolecular Catalyst

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