Screening of N,N‐bidentate and N,N,N‐tridentate pyridine‐based ligands in the catalytic allylic oxidation of cyclic olefins

A variety of chiral N,N‐bidentate and N,N,N‐tridentate ligands based on the pyridine framework, namely C2‐symmetric dipyridylmethane and terpyridine, N‐(p‐toluensulfinyl)iminopyridines and two kinds of iminopyridines, has been assessed in the asymmetric copper(I)‐catalysed allylic oxidation of cyclic olefins. Catalytic activity and enantioselectivity were found to be highly dependent upon the framework of the ligands, which afforded cycloalkenyl benzoates in low to moderate yields and enantioselectivities. The best yields (up to 70%) and enantioselectivities (up to 53% enantiomeric excess) were obtained with an iminopyridine based on camphane and quinoline skeletons. Copyright © 2014 John Wiley & Sons, Ltd.     

Dual‐Functional Semithiobambusurils

Semithiobambusurils, which represent a new family of macrocyclic host molecules, have been prepared by a convenient, scalable synthesis. These new cavitands are double functional: they strongly bind a broad variety of anions in their interiors and metal ions at their sulfur‐edged portals. The solid‐state structure of semithiobambus[4]uril with HgCl₂ demonstrates the ability of these compounds to form linear chains of coordination polymers with thiophillic metal ions. The crystal structure of semithiobambus[6]uril with tetraphenylphosphonium bromide exhibits the unique anion‐binding properties of the host cavity and the characteristics of the binding site.     

Metal complexes of chiral pyridine ligands. X-ray structure of nitratobis {2-(2S)-2-pyrrolidinyl]pyridine} copper (II) nitrate

Cobalt(II), nickel(II), and copper(II) complexes of 2-[(2S)-2-pyrrolidinyllpyridine (L) have been synthesized and characterized. The crystal structure of the complex [Cu(L)₂(NO₃)]NO₃ has been determined by X-ray diffraction. Crystals are monoclinic, space groupP2+, witha=10.766(3).b=7.525(2),c=13.447(4) Å. =104.64(2)°. and Z=2. The structure consists of [Cu(L)₂(NO₃)]⁺ cations and NO ₃ ^t- anions. The copper atom has a distorted trigonal bipyramidal coordination geometry with the two pyrrolidine nitrogens and one nitrate oxygen occupying the equatorial positions and the two pyridine nitrogens at the apices. The crystalline cohesion is ensured by a network of hydrogen bonds involving the pyrrolidine groups as donors and both coordinate and uncoordinate nitrates as acceptors.     

Efficient P‐Chiral Biaryl Bisphosphorus Ligands for Palladium‐Catalyzed Asymmetric Hydrogenation

A series of structurally novel P‐chiral biaryl bisphosphorus ligands L1‐L5 (BABIBOPs) are developed, providing high efficiency for the first time in palladium‐catalyzed asymmetric hydrogenation of β‐aryl and β‐alkyl substituted β‐keto esters. With the Pd‐ L3 (iPr‐BABIBOP) catalyst, a series of chiral β‐hydroxyl carboxylic esters are formed in excellent enantioselectivities (up to>99% ee) and yields at catalyst loading as low as 0.01 mol%.     

Synthesis of ReI tricarbonyl complexes with various sulfur‐ and oxygen‐donating ligands: crystal structures of two ReI dinuclear structures bridged by S atoms

The synthesis and characterization of two dinuclear complexes, namely fac‐hexacarbonyl‐1κ³C,2κ³C‐(pyridine‐1κN)[μ‐2,2′‐sulfanediyldi(ethanethiolato)‐1κ²S¹,S³:2κ³S¹,S²,S³]dirhenium(I), [Re₂(C₄H₈S₃)(C₅H₅N)(CO)₆], ( 1 ), and tetraethylammonium fac‐tris(μ‐2‐methoxybenzenethiolato‐κ²S:S)bis[tricarbonylrhenium(I)], (C₈H₂₀N)[Re₂(C₇H₇OS)₃(CO)₆], ( 2 ), together with two mononuclear complexes, namely (2,2′‐bithiophene‐5‐carboxylic acid‐κ²S,S′)bromidotricarbonylrhenium(I), ( 3 ), and bromidotricarbonyl(methyl benzo[b]thiophene‐2‐carboxylate‐κ²O,S)rhenium(I), ( 4 ), are reported. Crystals of ( 1 ) and ( 2 ) were characterized by X‐ray diffraction. The crystal structure of ( 1 ) revealed two Re—S—Re bridges. The thioether S atom only bonds to one of the Re^I metal centres, while the geometry of the second Re^I metal centre is completed by a pyridine ligand. The structure of ( 2 ) is characterized by three S‐atom bridges and an Re…Re nonbonding distance of 3.4879 (5) Å, which is shorter than the distance found for ( 1 ) [3.7996 (6)/3.7963 (6) Å], but still clearly a nonbonding distance. Complex ( 1 ) is stabilized by six intermolecular hydrogen‐bond interactions and an O…O interaction, while ( 2 ) is stabilized by two intermolecular hydrogen‐bond interactions and two O…π interactions.     

Access to the Bis‐benzene Cobalt(I) Sandwich Cation and its Derivatives: Synthons for a “Naked” Cobalt(I) Source?

The synthesis and structural characterization of the hitherto unknown parent Co(bz)₂⁺ (bz=benzene) complex and several of its derivatives are described. Their synthesis starts either from a CoCO₅⁺ salt, or directly from Co₂(CO)₈ and a Ag⁺ salt. Stability and solubility of these complexes was achieved by using the weakly coordinating anions (WCAs) [Al(OR^F)₄]^? and [F{Al(OR^F)₃}₂]^? {R^F=C(CF₃)₃} and the solvent ortho‐difluorobenzene (o‐DFB). The magnetic properties of Co(bz)₂⁺ were measured and compared in the condensed and gas phases. The weakly bound Co(o‐dfb)₂⁺ salts are of particular interest for the preparation of further Co^I salts, for example, the structurally characterized low‐coordinate 12 valence electron Co(P^tBu₃)₂⁺ and Co(NHC)₂⁺ salts.     

A Redox‐Active Bridging Ligand to Promote Spin Delocalization,High‐Spin Complexes,and Magnetic Multi‐Switchability

A dinuclear Co^II complex, [Co₂(tphz)(tpy)₂]ⁿ⁺ (n=4, 3 or 2; tphz: tetrapyridophenazine; tpy: terpyridine), has been assembled using the redox‐active and strongly complexing tphz bridging ligand. The magnetic properties of this complex can be tuned from spin‐crossover with T_1/2≈470 K for the pristine compound (n=4) to single‐molecule magnet with an S_T=5/2 spin ground state when once reduced (n=3) to finally a diamagnetic species when twice reduced (n=2). The two successive and reversible reductions are concomitant with an increase of the spin delocalization within the complex, promoting remarkably large magnetic exchange couplings and high‐spin species even at room temperature.     

The β‐Agostic Structure in (C5Me5)2Sc(CH2CH3): Solid‐State NMR Studies of (C5Me5)2Sc−R (R=Me,Ph, Et)

Multinuclear solid‐state NMR studies of Cp*₂Sc?R (Cp*=pentamethylcyclopentadienyl; R=Me, Ph, Et) and DFT calculations show that the Sc?Et complex contains a β‐CH agostic interaction. The static central transition ⁴⁵Sc NMR spectra show that the quadrupolar coupling constants (C_q) follow the trend of Ph≈Me>Et, indicating that the Sc?R bond is different in Cp*₂Sc?Et compared to the methyl and phenyl complexes. Analysis of the chemical shift tensor (CST) shows that the deshielding experienced by Cβ in Sc?CH₂CH₃ is related to coupling between the filled σ_C‐C orbital and the vacant orbital.     

A Planar‐Chiral Rhodium(III) Catalyst with a Sterically Demanding Cyclopentadienyl Ligand and Its Application in the Enantioselective Synthesis of Dihydroisoquinolones

The rapid development of enantioselective C?H activation reactions has created a demand for new types of catalysts. Herein, we report the synthesis of a novel planar‐chiral rhodium catalyst [(C₅H₂^tBu₂CH₂^tBu)RhI₂]₂ in two steps from commercially available [(cod)RhCl]₂ and tert‐butylacetylene. Pure enantiomers of the catalyst were obtained through separation of its diastereomeric adducts with natural (S)‐proline. The catalyst promoted enantioselective reactions of aryl hydroxamic acids with strained alkenes to give dihydroisoquinolones in high yields (up to 97 %) and with good stereoselectivity (up to 95 % ee).