The rhodium and iridium Lewis-acid cations [(eta(5)-C(5)Me(5))M{(R)-Prophos}(H(2)O)](2+) ((R)-Prophos = 1,2-bis(diphenylphosphino)propane) efficiently catalyze the enantioselective 1,3-dipolar cycloaddition of nitrones to methacrolein. Reactions occur with perfect endo selectivity and with enantiomeric excesses up to 96%. Intermediates [(eta(5)-C(5)Me(5))M{(R)-Prophos}(methacrolein)](SbF(6))(2) (M = Rh (3), Ir (4)) have been spectroscopically and crystallographically characterized. The nitrone complexes [(eta(5)-C(5)Me(5))M{(R)-Prophos}(nitrone)](SbF(6))(2) (M = Rh, nitrone = 1-pyrrolidine N-oxide (5), 2,3,4,5,-tetrahydropyridine N-oxide (6), 3,4-dihydroisoquinoline N-oxide (7); M = Ir, nitrone = 1-pyrrolidine N-oxide (8)) have been isolated and characterized including the X-ray crystal structure of compounds 6 and 8. The equilibrium between methacrolein and nitrone complexes is also studied. [Ir]-adduct complexes are detected by (31)P NMR spectroscopy. A catalytic cycle involving [M]-methacrolein, [M]-nitrone, as well as [M]-adduct species is proposed, the first complex being the true catalyst. The absolute configuration of the adduct 4-methyl-2-N,3-diphenyl-isoxazolidine-4-carbaldehyde (9) was determined through its (S)-(-)-alpha-methylbenzylamine derivative diastereomer. Structural parameters strongly suggest that the disposition of the methacrolein in 3 and 4 is fixed by CH/pi attractive interactions between the pro-S phenyl ring of the Ph(2)PCH(CH(3)) moiety of the (R)-Prophos ligand and the CHO aldehyde proton. Proton NMR data indicate that this conformation is maintained in solution. From the structural data and the results of catalysis the origin of the enantioselectivity is discussed.

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have equal configuration at the metal centre, were the only diastereomers detected. In solution, a diastereomerisation process between both isomers occurs, where the equilibrium constant depends on the solvent, amino acidate, and metal. The different localisation of the polar groups (NH or NH 2 moieties) on the molecular surface of the two diastereomers (1 and s) provides a qualitative explanation for the different diastereomer stability observed in solution. The new chiral trimers catalyse the reduction of unsaturated aldehydes to unsaturated alcohols by hydrogen transfer from aqueous sodium formate and the reduction of acetophenone by hydrogen transfer from 2-propanol with up to 75 % ee.

The preparation and characterization of optically active half-sandwich osmium(II) complexes with L-α-amino carboxylate ligands (Aa) of formula [(η 6 -p-MeC 6 H 4 iPr)Os(Aa)-Cl] are reported. Chloride abstraction renders the corresponding cationic trimers [{(η 6 -p-MeC 6 H 4 iPr)Os(Aa)} 3 ] 3+ , which were isolated as tetrafluoroborate salts. Trimerization most probably occurs through the chiral-at-metal mononuclear species [(η 6 -p-MeC 6 H 4 iPr)Os(Aa)(MeOH)] + and takes place with chiral self-recognition: i.e., only the equal configurations at metal R Os ,R Os ,R Os and S Os ,S Os ,S Os diastereomers are detected. The molecular structures of the mononuclear complexes [(η 6 -p-MeC 6 H 4 iPr)Os(Aa)Cl] (Aa = MePhe, Pip, MePro) as well as those of the trimers [{(η 6 -p-MeC 6 H 4 iPr)Os(Aa)} 3 ][BF 4 ] 3 (Aa = Pro, Pip) are also reported. The metal and, for amino carboxylates with secondary or tertiary amino moieties, also the nitrogen atom are stereogenic centers. Characterization of the new compounds includes determination of their absolute configuration. Assignment of the configurations in solution has been carried out by NOE and circular dichroism experiments. While both configurations are detected for the osmium, the configuration at nitrogen is induced by that of the carbon of the starting L-αamino acid. Both neutral mononuclear compounds and cationic trimers catalyze the asymmetric transfer hydrogenation from 2propanol to ketones with up to 82% ee. From stereochemical considerations, the enantiodifferentiation achieved can be accounted for by assuming that Noyori's bifunctional mechanism is operating.

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The synthesis and characterization of optically active phosphinooxazoline complexes (R Rh and S Rh)-[(η5-C5Me5)RhCl(PN)][A] (PN = (4S)-2-(2-diphenylphosphino)phenyl)-4-isopropyl-1,3-oxazoline (PN(iPr)), A = SbF6 (1a,1a‘), A = BF4 (1b,1b‘); PN = (4S)-2-(2-diphenylphosphino)phenyl)-4-methyl-1,3-oxazoline (PN(Me)), A = SbF6 (2a,2a‘), A = BF4 (2b,2b‘); PN = (3aS,8aR)-2-(2-diphenylphosphino)phenyl)-3a,8a-dihydroindane[1,2-d]oxazole] (PN(Ind)), A = SbF6 (3a,3a‘)), (S Rh and R Rh)-[(η5-C5Me5)RhI(PN(Me))][SbF6] (4a,4a‘) and (R Ir and S Ir)-[(η5-C5Me5)IrCl(PN)][A] (PN = PN(iPr), A = SbF6 (5a,5a‘), A = BF4 (5b,5b‘); PN = PN(Me), A = SbF6 (6a,6a‘), A = BF4 (6b,6b‘); PN = PN(Ind), A = SbF6 (7a,7a‘)), and the solvate complexes (S Rh and R Rh)-[(η5-C5Me5)Rh(PN)S][SbF6]2 (PN = PN(iPr) (8a,8a‘), PN(Me) (9a,9a‘), PN(Ind) (10a,10a‘); S = H2O, Me2CO) and (S Ir and R Ir)-[(η5-C5Me5)Ir(PN)S][A]2 (PN = PN(iPr), A = SbF6 (11a‘), A = BF4 (11b‘); PN = PN(Me), A = SbF6 (12a‘), A = BF4 (12b‘); PN = PN(Ind), A = SbF6 (13a,13a‘)) are reported. The crystal structures of the (R Rh)-1a, (S Rh)-1a‘, (R Rh)-2a, (S Rh)-2a‘, (R Rh)-2b, (R Rh)-3a, (S Rh)-4a, (R Ir)-5b, (R Ir)-6a, (S Ir)-6a‘, and (R Rh)-9a‘ epimers were determined by X-ray diffractometric methods. All the complexes show the chiral metal center in a pseudo-octahedral environment, being bonded to an η5-C5Me5 ring, to the nitrogen and phosphorus atoms of the phosphinooxazoline ligand in a chelate fashion, and to a terminal chlorine (1a, 1a‘, 2a, 2a‘, 2b, 3a, 5b, 6a, 6a‘) or iodine (4a), or to the oxygen of an acetone molecule (9a‘). Two conformations of the M−P−C−C−C−N metallacycle have been found in the crystals:  the 5S4 (unprimed complexes and 2a‘) and the 1S2 (primed complexes and 2a) screw-boat conformations. In solution, complexes 2, 4, 6, 8a‘, 9, 10, 12, and 13 exist as a mixture of conformers, most probably arising from the interconversion of the 1S2 and 5S4 conformations. This process was studied by 1H and 31P NMR spectroscopy. Dichloromethane solutions of the solvate complexes [(η5-C5Me5)M(PN)S][SbF6]2 are active catalysts for the Diels−Alder reaction between methacrolein and cyclopentadiene. The reaction occurs rapidly at room temperature with good exo:endo ratio (from 81:19 to 95:5) and moderate enantioselectivity (up to 67% (Rh compounds), 65% (Ir compounds)).

Reaction of the complexes (SM,RC)‐[(η5‐C5Me5)M{(R)‐Prophos}(H2O)](SbF6)2 (M=Rh, Ir) with α,β‐unsaturated aldehydes diastereoselectively gave complexes (SM,RC)‐[(η5‐C5Me5)M{(R)‐Prophos}(enal)](SbF6)2 which have been fully characterized, including an X‐ray molecular structure determination of the complex (SRh,RC)‐[(η5‐C5Me5)Rh{(R)‐Prophos}(trans‐2‐methyl‐2‐pentenal)](SbF6)2. These enal complexes efficiently catalyze the enantioselective 1,3‐dipolar cycloaddition of the nitrones N‐benzylideneaniline N‐oxide and 3,4‐dihydroisoquinoline N‐oxide to the corresponding enals. Reactions occur with excellent regioselectivity, perfect endo selectivity and with enantiomeric excesses up to 94 %. The absolute configuration of the adduct 5‐methyl‐2,3‐diphenylisoxazolidine‐4‐carboxaldehyde was determined through its (R)‐(−)‐α‐methylbenzylamine derivative.