Modulation of the coordination geometries of NCN and NCNC Rh complexes for ambidextrous chiral catalysts.

A chirality switch between novel NCN pincer Rh complexes and a related double cyclometalated NCNC Rh complex containing secondary amino groups is described. Their catalytic abilities were determined in asymmetric alkynylation of ethyl trifluoropyruvate, and the change in the coordination geometry of the Rh catalysts affected the stereochemistry of the products.

Design of bifunctional chiral phenanthroline ligand with Lewis basic site for palladium-catalyzed asymmetric allylic substitution.

Conceptually new bifunctional chiral ligands were developed. The axially chiral N,N-bidentate phenanthroline ligand (S)-1 was found to be effective for Pd-catalyzed asymmetric allylic substitution of allyl acetate and dialkyl malonate. The intramolecular Lewis basic group from the hydroxybinaphthyl structure of (S)-1 played a pivotal role in the high reactivity and enantioselectivity.

Co6 H8 (Pi Pr3 )6 : A Cobalt Octahedron with Face-Capping Hydrides.

A square-planar Co4 amide cluster, Co4 {N(SiMe3 )2 }4 (2), and an octahedral Co6 hydride cluster, Co6 H8 (Pi Pr3 )6 (4), were obtained from metathesis-type amide to hydride exchange reactions of a CoII amide complex with pinacolborane (HBpin) in the absence/presence of Pi Pr3 . The crystal structure of 4 revealed face-capping hydrides on each triangular [Co3 ] face, while the formal CoII2 CoI4 oxidation state of 4 indicated a reduction of the cobalt centers during the assembly process. Cluster 4 catalyzes the hydrosilylation of 2-cyclohexen-1-one favoring the conjugate reduction. Generation of the catalytically reactive Co cluster species was indicated by a trapping experiment with a chiral chelating agent.

Enantioselective Direct Alkynylation of Ketones Catalyzed by Chiral CCN Pincer RhIII Complexes.

A direct asymmetric alkynylation of ketones with new chiral CCN Rh catalysts containing N-heterocyclic carbene and oxazoline hybrid ligands is described. The catalytic reaction of fluoroalkyl-substituted ketones, ArCOCF2 X (X=F, Cl, H), with aromatic and aliphatic alkynes yielded the corresponding chiral propargyl alcohols with high enantioselectivity. Control and kinetic experiments suggested a bis(alkynyl) Rh intermediate as the active species for the C-C bond-forming step.

Renovation of Optically Active Phenanthrolines as Powerful Chiral Ligands for Versatile Asymmetric Metal Catalysis.

In the field of asymmetric synthesis, the development of new chiral ligands has been regarded as an attractive challenge for decades. Novel chiral ligands can often have a great impact on synthetic protocols. In this context, we are currently interested in the application of 1,10-phenanthroline (phen) as an entirely new class of chiral ligand. To handle this issue, we designed a chiral phen ligand that provides the N,N,O-tridentate coordination of the phen moiety and an additional phenolic hydroxyl group. As phen possesses greater coordination ability with various ions, our chiral phen ligand would be valuable as one of the "privileged" chiral ligands applied to a broad range of metal catalysts and new reactions. This account summarizes the results of the application of the chiral phen ligand to various kinds of metal catalysis.

Asymmetric Induction at Remote Quaternary Centers of Cyclohexadienones by Rhodium-Catalyzed Conjugate Hydrosilylation.

The enantioselective desymmetrizing conjugate hydrosilylation of prochiral differently γ,γ-disubstituted cyclohexadienone derivatives 2 to furnish the corresponding cyclohexenones 4 with a remote chiral all-carbon quaternary center at the γ position is described. Chiral rhodium-bis(oxazolinyl)phenyl complexes 1 were effective catalysts for this transformation. This catalytic system was extended to the asymmetric transformation of spirocarbocyclic cyclohexadienones 5 to give the corresponding products 6 with high enantiomeric ratios.

Asymmetric Three-Component Coupling Reaction of Alkyne, Enone, and Aldehyde Catalyzed by Chiral Phebox Ruthenium Catalysts.

Catalytic asymmetric three-component coupling reactions of terminal alkynes, α,ß-unsaturated ketones, and aldehydes were studied. The chiral ruthenium complexes containing bis(oxazolinyl)phenyl ligands were found to serve as efficient catalysts for a tandem reaction based on conjugate addition of terminal alkynes to α,ß-unsaturated ketones and subsequent aldol reaction with aldehydes, giving ß-hydroxyketone derivatives containing α-propargyl groups in high yields with moderate to good enantioselectivities. This method can produce various functional molecules from commercially available substrates in a one-pot procedure. The absolute configuration of the major product was determined by X-ray analysis. The control experiments suggested that a ruthenium enolate species generated in situ by conjugate addition could be involved as an intermediate for the aldol coupling with an aldehyde.

Cu(ii)-catalyzed enantioselective oxygen atom transfer from oxaziridine to oxindole derivatives with chiral phenanthroline.

In the presence of a Cu(ii) complex of axially chiral, N,N,O-tridentate phenanthroline ligand (S)-2, asymmetric oxygen atom transfer of oxindole derivatives (3) using Davis' oxaziridine (4) occurred to give the corresponding 3-aryl-3-hydroxy-2-oxindole derivatives (1) with excellent enantioselectivity (up to 96% ee). The X-ray crystallographic analysis of the isolated Cu(ii) complex disclosed its N,N,O-tridentate coordination, which is critical to realize effective catalytic activity.

Construction of a Chiral Silicon Center by Rhodium-Catalyzed Enantioselective Intramolecular Hydrosilylation.

Rhodium-catalyzed enantioselective desymmetrizing intramolecular hydrosilylation of symmetrically disubstituted hydrosilanes is described. The original axially chiral phenanthroline ligand (S)-BinThro (Binol-derived phenanthroline) was found to work as an effective chiral catalyst for this transformation. A chiral silicon stereogenic center is one of the chiral motifs gaining much attention in asymmetric syntheses and the present protocol provides cyclic five-membered organosilanes incorporating chiral silicon centers with high enantioselectivities (up to 91 % ee). The putative active Rh(I) catalyst takes the form of an N,N,O-tridentate coordination complex, as determined by several complementary experiments.

Design of novel chiral N,N,O-tridentate phenanthroline ligands and their application to enantioselective addition of organozinc reagents to aldehydes.

The novel N,N,O-tridentate phenanthroline ligand (BinThro) bearing an axially chiral binaphthyl backbone prepared from BINOL was found to be an effective chiral catalyst for enantioselective addition of diethylzinc to aromatic aldehydes with high enantioselectivity (up to 95% ee).

Asymmetric diboration of terminal alkenes with a rhodium catalyst and subsequent oxidation: enantioselective synthesis of optically active 1,2-diols.

Pin it down: A highly enantioselective diboration of terminal alkenes with chiral 1 and bis(pinacolato)diboron (B2 pin2 ) was realized. Subsequent oxidation of the diboron adducts with sodium peroxoborate readily gave the corresponding optically active 1,2-diols in high yields and high enantioselectivities.

Direct conjugate addition of alkynes with α,ß-unsaturated carbonyl compounds catalyzed by NCN-pincer Ru complexes.

NCN-pincer Ru-complexes containing bis(oxazolinyl)phenyl ligands serve as suitable catalysts in the direct conjugate additions of α,ß-unsaturated carbonyl compounds, including ketones, esters, and amides, as well as vinylphosphonates, giving various ß-alkynyl carbonyl and phosphonate compounds. A bis(oxazolinyl)phenyl (phebox)-Ru complex also catalyzes the asymmetric conjugate addition of an alkyne with a ß-substituted, α,ß-unsaturated ketone to produce a chiral ß-alkynyl ketone.

Enantioselective synthesis of optically active 3,3-diarylpropanoates by conjugate hydrosilylation with chiral Rh-bis(oxazolinyl)phenyl catalysts.

Conjugate hydrosilylation of 3,3-diarylacrylate derivatives catalyzed by chiral rhodium-bis(oxazolinyl)phenyl complexes (1 mol %) at 60 °C for 2 h was investigated to prepare optically active 3,3-diarylpropanoate derivatives in high yields up to 99% yield and high enantioselectivities up to 99%.

Ruthenium-catalyzed hydrophosphinylative cyclization of 1,6-diynes. Stereoselective synthesis of exocyclic 1,3-dienylphosphine oxides.

The first catalytic synthesis of exocyclic 1,3-dienylphosphine oxides was achieved by the ruthenium-catalyzed selective hydrophosphinylative cyclization of 1,6-diynes. A plausible mechanism involving a ruthenacyclopentatriene intermediate is proposed on the basis of the DFT calculations of model ruthenium complexes.

Ruthenium-catalyzed transfer oxygenative cyclization of α,ω-diynes: unprecedented [2 + 2 + 1] route to bicyclic furans via ruthenacyclopentatriene.

A novel oxygen-atom-transfer process enables the catalytic [2 + 2 + 1] synthesis of bicyclic furans from α,ω-diynes with DMSO. [CpRu(AN)(3)]PF(6) catalyzed the transfer oxygenative cyclization of diynes with aryl terminal groups, while those of diynes with alkyl terminal groups were effectively promoted by the corresponding Cp* complex. A mechanism for bicyclic furan formation via a ruthenacyclopentatriene was proposed on the basis of both experimental and theoretical studies.

Enhancement of enantioselectivity by alcohol additives in asymmetric hydrogenation with bis(oxazolinyl)phenyl ruthenium catalysts.

Bis(oxazolinyl)phenyl ruthenium(II) complexes were found to catalyze asymmetric hydrogenation of ketones, in which chiral bulky alcohol additives showed significant enhancement of enantioselectivity even in protic solvents.

Ruthenium-catalyzed cyclization/transfer hydrogenation of 1,6-diynes: unprecedented mode of alcohol activation via metallacyclopentatriene.

The first transfer-hydrogenative cyclization of 1,6-diynes that leads to exocyclic dienes was developed using a ruthenium catalyst and MeOH as a H(2) surrogate.

Enantioselective addition of allyltin reagents to amino aldehydes catalyzed with bis(oxazolinyl)phenylrhodium(III) aqua complexes.

Bis(oxazolinyl)phenylrhodium(III) aqua complexes, (Phebox)RhX2(H2O) [X = Cl, Br], were found to be efficient Lewis acid catalysts for the enantioselective addition of allyl- and methallyltributyltin reagents to amino aldehydes. The reactions proceed smoothly in the presence of 5-10 mol % of (Phebox)RhX2(H2O) complex at ambient temperature to give the corresponding amino alcohols with modest to good enantioselectivity (up to 94% ee).