title: Half-sandwich rhodium (and iridium) complexes as enantioselective catalysts for the 1,3-dipolar cycloaddition of 3,4-dihydroisoquinoline N-oxide to methacrylonitrile.
abstract: Cationic half-sandwich complexes containing the [(eta(5)-C(5)Me(5))M(Diphos*)] moiety (M=Rh, Ir; Diphos*=chiral diphosphine ligand) catalyze the cycloaddition of the nitrone 3,4-dihydroisoquinoline N-oxide (A) to methacrylonitrile (B) with excellent regio and endo selectivity and low-to-moderate enantioselectivity. The most active and selective catalyst, (S(Rh),R(C))-[(eta(5)-C(5)Me(5))Rh{(R)-Prophos)} (NC(Me)C==CH(2))](SbF(6))(2), has been isolated and fully characterized including the determination of the molecular structure by X-ray diffraction. The R-at-metal epimers of the complexes [(eta(5)-C(5)Me(5))M{(R)-Prophos)}(NC(Me)C==CH(2))](SbF(6))(2) (M=Rh, Ir) isomerize to the corresponding S-at-metal diastereomers. The stoichiometric cycloaddition of A with B is catalyzed by diastereopure (S(M),R(C))-[(eta(5)-C(5)Me(5))M{(R)-Prophos)}(NC(Me)C==CH(2))](SbF(6))(2) with perfect regio and endo selectivity and very good (up to 95 %) ee. The catalyst can be recycled up to nine times without significant loss of either activity or selectivity.
authors.affiliation: Departamento de Química Inorgánica, Instituto Universitario de Catálisis Homogénea, Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza-Consejo Superior de Investigaciones Científicas, Zaragoza, Spain. dcarmona@unizar.es
authors.forename: Daniel
authors.initials: D
authors.lastname: Carmona
authors.forename: M Pilar
authors.initials: MP
authors.lastname: Lamata
authors.forename: Fernando
authors.initials: F
authors.lastname: Viguri
authors.forename: Ricardo
authors.initials: R
authors.lastname: Rodríguez
authors.forename: Fernando J
authors.initials: FJ
authors.lastname: Lahoz
authors.forename: Luis A
authors.initials: LA
authors.lastname: Oro