Asymmetric 1, 3-dipolar cycloaddition reactions between methacrylonitrile and nitrones catalysed by well-defined M(diphosphane) (M=Rh, Ir) complexes

The cationic half-sandwich aqua-complexes (¿ 5-C5Me5)M(PP*)(H2O)]SbF6]2 M=Rh, Ir; PP* =(R)-Benphos, (R)-Cyphos, (2R, 4R)-Norphos] catalyse the 1, 3-dipolar cycloaddition reaction of nitrones with methacrylonitrile with perfect regioselectivity, low-to-perfect endo-selectivity and low-to-moderate enantioselectivity. The active species involved in the catalytic process, (¿ 5-C5Me5)M(PP*)(methacrylonitrile)]SbF6]2, have been isolated and characterised as mixtures of the (S)- and (R)-at-metal epimers. NMR measurements of these mixtures indicated that the (R M)-isomers epimerise to the corresponding (S M) counterparts. The molecular structure of the rhodium complex (S Rh, R C)-(¿ 5-C5Me5)Rh((R)-Benphos)(methacrylonitrile)]SbF6]2 has been determined by X-ray diffraction methods. Diastereomerically pure (S Rh, R C)-(¿ 5-C5Me5)Rh(PP*)(methacrylonitrile)]SbF6]2 compounds catalyse stoichiometrically the above mentioned dipolar cycloaddition reaction with up to 90% enantiomeric excess, thus indicating the influence of the metal handedness on the catalytic stereochemical outcome. Catalysts can be recycled up to three times without a significant loss of either activity or selectivity

Reacciones de cicloadición catalizadas por complejos de rodio e iridio con ligandos difosfano quirales

Durante los últimos años en nuestro grupo de investigación se está estudiando el empleo de compuestos de metales de transición como catalizadores en reacciones de cicloadición de Diels-Alder y 1,3-dipolar. Se han obtenido buenos resultados con complejos organometálicos de la estequiometría (SM,RC)-[(¿5-C5Me5)M(Profos)(H2O)]2+. Se trata de compuestos semisandwich con iones d6 de rodio(III) e iridio(III) con un ligando pentametilciclopenadienilo y una molécula de disolvente, sustrato fácilmente desplazable, que proporcionará una vacante de coordinación en la que deberá tener lugar el proceso catalítico. En la presente Memoria nos proponemos: 1) Aplicar compuestos previamente descritos de formulación [(¿5-C5Me5) M(Profos)(H2O)][SbF6]2 (M = Rh, Ir) a nuevas reacciones de Diels-Alder entre enales ó enonas y diversos dienos. 2) Preparar nuevos compuestos semisandwich de rodio e iridio de estequiometría [(¿5-C5Me5)M(PP*)(H2O)][SbF6]2 donde PP* representa un ligando difosfano quiral. Los difosfanos no son comerciales (excepto Norfos), por lo que tendrán que ser previamente sintetizados. 3) Estudiar el empleo de los complejos [(¿5-C5Me5)M(PP*)(H2O)][SbF6]2 descritos en el apartado anterior en reacciones de DA entre metacroleína y diversos dienos. 4) Estudiar el empleo de los nuevos complejos [(¿5-C5Me5) M(PP*)(H2O)][SbF6]2 en reacciones de cicloadición 1,3-dipolar entre enales o metacrilonitrilo y nitronas.Peer Reviewe

Asymmetric 1,3-dipolar cycloaddition reactions between methacrylonitrile and nitrones catalysed by well-defined M(diphosphane) (M = Rh, Ir) complexes

The cationic half-sandwich aqua-complexes [(η-CMe)M(PP∗)(HO)][SbF] [M = Rh, Ir; PP∗ = (R)-Benphos, (R)-Cyphos, (2R,4R)-Norphos] catalyse the 1,3-dipolar cycloaddition reaction of nitrones with methacrylonitrile with perfect regioselectivity, low-to-perfect endo-selectivity and low-to-moderate enantioselectivity. The active species involved in the catalytic process, [(η-CMe)M(PP∗)(methacrylonitrile)][SbF], have been isolated and characterised as mixtures of the (S)- and (R)-at-metal epimers. NMR measurements of these mixtures indicated that the (R)-isomers epimerise to the corresponding (S) counterparts. The molecular structure of the rhodium complex (S,R)-[(η-CMe)Rh{(R)-Benphos}(methacrylonitrile)][SbF] has been determined by X-ray diffraction methods. Diastereomerically pure (S,R)-[(η-CMe)Rh(PP∗)(methacrylonitrile)][SbF] compounds catalyse stoichiometrically the above mentioned dipolar cycloaddition reaction with up to 90% enantiomeric excess, thus indicating the influence of the metal handedness on the catalytic stereochemical outcome. Catalysts can be recycled up to three times without a significant loss of either activity or selectivity.We thank the Ministerio de Economía y Competitividad, Spain and European Social Fund (Grants CTQ2012-32095, CTQ2015-66079-P and CONSOLIDER INGENIO-2010 CSD2006-0015), European Union and Gobierno de Aragón and European Social Fund (Grupo Consolidado: Catalizadores Organometálicos Enantioselectivos), European Union for financial support. A.A. thanks the IUCH for a grant.Peer Reviewe

Asymmetric 1,3-dipolar cycloaddition reactions between enals and nitrones catalysed by half-sandwich rhodium or iridium diphosphane complexes

The aqua complexes [(η5-C5Me5)M(PP*)(H2O)][SbF6]2 (M = Rh, Ir; PP* = chiral diphosphane) have been tested as catalysts for the asymmetric 1,3-dipolar cycloaddition of nitrones to α,β-unsaturated aldehydes. Quantitative conversions with very high regioselectivity, perfect endo selectivity and excellent enantioselectivity (up to 99% ee) were achieved. The stereochemical outcome was analyzed on the basis of the stereoelectronic properties of the intermediate enal complexes of the formula [(η5-C5Me5)M(PP*)(enal)][SbF6]2.We thank the Ministerio de Economía y Competitividad of Spain (CTQ2012-32095) and Gobierno de Aragón (Grupo Consolidado: Catalizadores Organometálicos Enantioselectivos) for financial support. A. A. acknowledges IUCH for a grant. R. R. acknowledges CSIC and European Social Fund for a JAE grant. M. C. acknowledges Gobierno de Aragón and CSIC for a DGA grant.Peer Reviewe

Enantioselective catalytic diels-alder reactions with enones as dienophiles

The aqua complexes (S M,R C)-[(η 5-C 5Me 5)M(PROPHOS)(H 2O)][SbF 6] 2 [PROPHOS = (R)-propane-1,2-diylbis(diphenylphosphane); M = Rh (1), Ir (2)] are active catalysts for the asymmetric Diels-Alder reaction between ketones and dienes. At low temperatures, enantioselectivities of up to 89% ee are achieved. The intermediate Lewis acid-dienophile complexes (S M,R C)-[(η 5-C 5Me 5)M(PROPHOS)(MVK)][SbF 6] 2 (MVK = methyl vinyl ketone; M = Rh (3), Ir (4)) and (S Ir,R C)- [(η 5-C 5Me 5)Ir(PROPHOS)(EVK)][SbF 6] 2 (EVK = ethyl vinyl ketone (5)) have been isolated and characterized by analytical and spectroscopic means, including the determination of the crystal structure of the iridium complexes 4 and 5 by X-ray diffractometric methods. Structural parameters indicate that the dispositions of the coordinated dienophiles are controlled by the CH/π attractive interactions established between a phenyl group of the PROPHOS ligand and the α-vinyl proton of the ketones. Proton NMR parameters indicate that these interactions are maintained in solution. From these data, the stereoselectivity of the catalytic reaction is discussed. © 2012 American Chemical Society.We thank the Ministerio de Educación y Ciencia (Grant CTQ 2009-10303/BTQ) and Gobierno de Aragón and Fondo Social Europeo (Grupo Consolidado: Catalizadores Organometálicos Enantioselectivos) for financial support. This work was supported by the CONSOLIDER INGENIO-2010 program under the project Factoría de Cristalización (CSD2006-0015). A.A. thanks the Instituto Universitario de Catálisis Homogénea (IUCH) for a grant. P.G.-O. acknowledges financial support from the CSIC, “JAE-Doc” program, contract cofunded by the ESF.Peer Reviewe

Enantioselective catalysts based on the chiral fragment (η5-C5Me5)Ir(Prophos) for Diels-Alder reactions

The aqua complex (SIr,RC)-[(η5-C 5Me5)Ir(Prophos)(H2O)][SbF6] 2 [Prophos = (R)-propane-1,2-diyl-bis(diphenylphosphane)] is an active precursor for the asymmetric Diels-Alder reaction of acyclic enals with cyclopentadiene, 2,3-dimethylbutadiene and isoprene. Enantioselectivities up to 78% ee are achieved. The intermediate Lewis acid-dienophile complex (S Ir,RC)-[(η5-C5Me 5)Ir(Prophos)(ethyl acrolein)][SbF6]2 has been isolated and completely characterized, including the X-ray crystal structure determination. Structural parameters indicate that the disposition of the coordinated dienophile is controlled by CH/π attractive interactions established between a phenyl group of the Prophos ligand and the aldehyde proton of the coordinated enal. Proton NMR data indicate that these interactions are maintained in solution. From diffractometric and spectroscopic data, the origin of the enantioselectivity is discussed. © 2014 Elsevier B.V. All rights reserved.We thank the Ministerio de Educación y Ciencia (Grant CTQ 2009-10303/BTQ), the Ministerio de Economía y Competitividad (Grant CTQ 2012-32095), and Gobierno de Aragón (Grupo Consolidado: Catalizadores Organometálicos Enantioselectivos) for financial support. A. A. thanks the IUCH for a grant. P. G.-O. acknowledges the CSIC, “JAE-Doc” program (contract co-funded by the ESF) and the “Factoría de Cristalización” project (CONSOLIDER INGENIO-2010, CSD 2006-0015 program) for financial support.Peer Reviewe

Enantioselective Catalysts for the Diels–Alder Reaction between Methacrolein and Cyclopentadiene Based on the Chiral Fragment (η5-C5Me5)M(chiral diphosphane) (M = Rh, Ir)

The aqua complexes [(η 5-C 5Me 5) M(PP*)(H 2O)][SbF 6] 2 (M = Rh, Ir; PP* = chiral diphosphane) (1-10) are prepared and characterized. These complexes efficiently catalyze the Diels-Alder reaction between methacrolein and HCp with enantioselectivities of up to 96% e.e. The norphos complexes 9 and 10, which are obtained as diastereomeric mixtures of the two epimers at the metal, afford the highest e.e. values. The intermediate complexes [(η 5- C 5Me 5)M(PP*)(methacrolein)][SbF 6] 2 (11-20) are also isolated and characterized, including the molecular structure determination of the [(η 5-C 5Me 5)M(benphos)(methacrolein)][SbF 6] 2 (M = Rh (13), Ir (14)) derivatives. An NMR study of the reactivity of the metallic intermediates under catalytic conditions explains the high enantioselectivities achieved with the norphos systems. © 2011 American Chemical Society.We thank the Ministerio de Educación y Ciencia (Grant CTQ 2009-10303/BQU) and Gobierno de Aragón (Grupo Consolidado: Catalizadores Organometálicos Enantioselectivos) for financial support. A.A thanks the IUCH for a grant. P.G.-O. acknowledges financial support from the CSIC, ″JAE-Doc″ program, contract cofunded by the ESF.Peer Reviewe

Enantioselective Catalytic Diels–Alder Reactions with Enones As Dienophiles

The aqua complexes (<i>S</i>_M,<i>R</i>_C)-[(η⁵-C₅Me₅)­M­(PROPHOS)­(H₂O)]­[SbF₆]₂ [PROPHOS = (<i>R</i>)-propane-1,2-diylbis­(diphenylphosphane); M = Rh (<b>1</b>), Ir (<b>2</b>)] are active catalysts for the asymmetric Diels–Alder reaction between ketones and dienes. At low temperatures, enantioselectivities of up to 89% ee are achieved. The intermediate Lewis acid–dienophile complexes (<i>S</i>_M,<i>R</i>_C)-[(η⁵-C₅Me₅)­M­(PROPHOS)­(MVK)]­[SbF₆]₂ (MVK = methyl vinyl ketone; M = Rh (<b>3</b>), Ir (<b>4</b>)) and (<i>S</i>_Ir,<i>R</i>_C)-[(η⁵-C₅Me₅)­Ir­(PROPHOS)­(EVK)]­[SbF₆]₂ (EVK = ethyl vinyl ketone (<b>5</b>)) have been isolated and characterized by analytical and spectroscopic means, including the determination of the crystal structure of the iridium complexes <b>4</b> and <b>5</b> by X-ray diffractometric methods. Structural parameters indicate that the dispositions of the coordinated dienophiles are controlled by the CH/π attractive interactions established between a phenyl group of the PROPHOS ligand and the α-vinyl proton of the ketones. Proton NMR parameters indicate that these interactions are maintained in solution. From these data, the stereoselectivity of the catalytic reaction is discussed