Search

A square-planar Co4 amide cluster, Co4{N(SiMe3)2}4 ( 2), and an octahedral Co6 hydride cluster, Co6H8(P iPr3)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 P iPr3. The crystal structure of 4 revealed face-capping hydrides on each triangular [Co3] face, while the formal CoII2CoI4 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. [ABSTRACT FROM AUTHOR]

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, ArCOCF2X (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. [ABSTRACT FROM AUTHOR]

A square-planar Co 4 amide cluster, Co 4 {N(SiMe 3 ) 2 } 4 (2), and an octahedral Co 6 hydride cluster, Co 6 H 8 (P i Pr 3 ) 6 (4), were obtained from metathesis-type amide to hydride exchange reactions of a Co II amide complex with pinacolborane (HBpin) in the absence/presence of P i Pr 3 . The crystal structure of 4 revealed face-capping hydrides on each triangular [Co 3 ] face, while the formal Co II 2 Co I 4 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., (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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, ArCOCF 2 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., (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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.

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., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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).