Asymmetric Pauson-Khand-type reaction mediated by Rh(I) catalyst at ambient temperature

An efficient asymmetric PKR mediated by Rh(I) catalyst at ambient temperature was developed. The reaction utilizing a Rh(I) catalyst bearing a (R)-3,5-diMeC4H4-BINAP ligand at 18-20 degrees C under a reduced partial pressure of CO (0.1 atm) provided PKR products in high chemical yield as well as high enantioselectivity.     

Diastereoselective alkylation of the ( + )-ketopinic acid ketimine derived from benzylamine

Alkylation of the ketimine 2 obtained from condensation of (+)-ketopinic acid and benzylamine with a variety of alkylating agents gives the products whose trends in diastereomeric excesses (1 — 100% O.P.) appear to correlate with the structure and reactivity of electrophilic agents. Using excess n-butyl lithium and allylic or benzylic halides, β-alkylation occured.     

Complexes of Cu(I) supported by a tris(ketimine) tripod

Arylation of tris(2-benzylnitrile)amine with PhLi, followed by aqueous work-up, results in the formation of a tripodal tris(ketimine) scaffold, N(ArCNHPh)(3). N(ArCNHPh)(3) readily coordinates a number of Cu(I) salts, generating complexes that exhibit trigonal pyramidal geometries in the solid-state.     

Chelation-assisted Rh(I)-catalyzed ortho-alkylation of aromatic ketimines or ketones with olefins

Described herein is the Rh(I)-catalyzed ortho-alkylation of aromatic ketimines or ketones with olefins. This method showed high reactivity and selectivity to monoalkylation for a variety of olefins including 1-alkenes with an allylic proton, alpha,omega-dienes, and internal olefins. For a mechanistic study, H/D exchange experiments were carried out, which demonstrated that the ortho C-H bond could be easily cleaved even at the low temperature of 45 degrees C. The key step of this reaction is the formation of a stable five-membered metallacycle by a chelation-assisted ortho C-H bond activation. Furthermore, the direct ortho-alkylation of aromatic ketones with the Rh(I) complex was successfully achieved by adding 50 mol % of benzylamine as a chelation-assistant tool.     

Asymmetric transfer hydrogenation of aromatic ketones by Rh(I)/bimorpholine complexes

The asymmetric hydride transfer reduction of aromatic ketones, using a [Rh(cod)Cl]₂ complex as a catalyst and (3S,3′S)-bimorpholine as a chiral ligand, was studied. By varying the amount of ligand, basic co-catalyst and temperature, high yields (>90%) and good enantiomeric excesses of the alcohols (ee up to 83%) were achieved.     

Chelation-assisted hydrative dimerization of 1-alkyne forming alpha,beta-enones by an Rh(I) catalyst

The intermolecular hydrative dimerization of 1-alkyne was developed through the chelation-assisted catalytic system with Rh(I)/2-amino-3-picoline. This novel transformation afforded branched and linear alpha,beta-enones directly from two 1-alkyne molecules and H2O. The results demonstrate that a branch/linear ratio can be controlled by the alkyl substituent of 1-alkyne.     

Reaction of alkene oxides with aromatic thionylimines

The oxides of ethylene and propene, and epichlorohydrin, react with thionylanilines (ArN=S=O) in the presence of tetraethylammonium bromide catalyst at 95°–100° C to give N-arylalkeneamidosulfites, whose structures are confirmed by retrosynthesis from the corresponding N-phenylamino alcohols, and thionyl chloride, as well as by their IR spectra.     

Rh(I)-catalyzed solvent-free ortho-alkylation of aromatic imines under microwave irradiation

The synthesis of ortho-alkylated ketones through a chelation-assisted Rh (I) catalyzed ortho-alkylation reaction of aromatic imines under microwave activated solvent-free conditions in monomode reactors was performed. These conditions have been also applied to hydroacylation and ortho-alkylation reactions with aldimines.     

Silica-alumina supported transition metal oxide catalyst for alkylation of aromatic compounds

Titanium oxide on silica-alumina support is described to be an efficient regenerable catalyst for alkylation of aromatic compounds with alkyl halides, alcohols and olefins, and the reaction is proposed to be initiated by the protonated metal active species present in the catalyst.     

Chiral Jacobsen's catalyst immobilized on zinc poly(styrene‐phenylvinylphosphonate)‐phosphate functionalized by diamine as highly efficient and reusable catalyst for alkene epoxidation

Chiral Jacobsen's catalyst anchored on zinc poly(styrene‐phenylvinylphosphonate)‐phosphate (ZnPS‐PVPA) functionalized by diamines shows superior catalytic activities (conversion up to 99%; enantiomeric excess up to 99%) in the enantioselective epoxidations of unfunctional olefins with m ‐chloroperoxybenzoic acid and NaIO₄ as oxidants. The whole chiral salen Mn(III) catalyst, including the ZnPS‐PVPA support and the linker as well as chiral salen Mn ligand together contribute to the chirality of products. The heterogeneous catalyst has the potential for use in industry owing to superior stability (recycling nine times) and activity in large‐scale reactions (such as 200 times).     

Selective alkylation of (hetero)aromatic amines with alcohols catalyzed by a ruthenium pincer complex

A readily available pincer ruthenium(II) complex catalyzes the selective monoalkylation of (hetero)aromatic amines with a wide range of primary alcohols (including pyridine-, furan-, and thiophene-substituted alcohols) with high efficiency when used in low catalyst loadings (1 mol %). Tertiary amine formation via polyalkylation does not occur, making this ruthenium system an excellent catalyst for the synthesis of sec-amines.     

Scope and mechanism of the intermolecular addition of aromatic aldehydes to olefins catalyzed by Rh(I) olefin complexes

Rhodium (I) bis-olefin complexes Cp*Rh(VTMS)(2) and CpRh(VTMS)(2) (Cp* = C(5)Me(5), Cp = C(5)Me(4)CF(3), VTMS = vinyl trimethylsilane) were found to catalyze the addition of aromatic aldehydes to olefins to form ketones. Use of the more electron-deficient catalyst CpRh(VTMS)(2) results in faster reaction rates, better selectivity for linear ketone products from alpha-olefins, and broader reaction scope. NMR studies of the hydroacylation of vinyltrimethylsilane showed that the starting Rh(I) bis-olefin complexes and the corresponding Cp*/Rh(CH(2)CH(2)SiMe(3))(CO)(Ar) complexes were catalyst resting states, with an equilibrium established between them prior to turnover. Mechanistic studies suggested that CpRh(VTMS)(2) displayed a faster turnover frequency (relative to Cp*Rh(VTMS)(2)) because of an increase in the rate of reductive elimination, the turnover-limiting step, from the more electron-deficient metal center of CpRh(VTMS)(2). Reaction of Cp*/Rh(CH(2)CH(2)SiMe(3))(CO)(Ar) with PMe(3) yields acyl complexes Cp*/Rh[C(O)CH(2)CH(2)SiMe(3)](PMe(3))(Ar); measured first-order rates of reductive elimination of ketone from these Rh(III) complexes established that the Cp ligand accelerates this process relative to the Cp* ligand.     

Thermodynamics of the hydrogenation of olefins catalyzed by Rh(I) and Ir(I) complexes

The homogeneous hydrogenation of cyclohexene catalyzed by Rh(I) and Ir(I) complexes of the terdentate ligands (L) HN(CH₂CH₂Aφ₂)₂ (A = P, As) was investigated in the temperature range 20 - 50°C. Thermodynamic parameters corresponding to the formation of the dihydrido complexes ML(H)₂Cl (M = Ir(I), Rh(I)) and the olefin complexes MLCl(olefin) were computed. The activation parameters corresponding to the rate constant were also calculated. An inverse relationship is found between the enthalpy of formation ΔH⁰ of the dihydrido complexes and the enthalpy of activation ΔH^≠ of the hydrogenation step. This relationship establishes the involvement of the dihydrido complexes as the active intermediates in olefin coordination and hydrogen transfer. The stereochemistry of the terdentate complexes in dihydride formation is discussed. It is concluded that the enthalpy of formation ΔH⁰ of the dihydrido complexes of terdentate ligands is very favourable, as there is no change in the configuration of the ligand in oxidative addition reaction. The significance of the steric factors in the hydrogenation step is discussed.     

Rh(i)- and Rh(ii)-catalyzed C–H alkylation of benzylamines with alkenes and its application in flow chemistry

The Rh-catalyzed C–H alkylation of benzylamines with alkenes using a picolinamide derivative as a directing group is reported. Both Rh(i) and Rh(ii) complexes can be used as active catalysts for this transformation. In addition, a flow set up was designed to successfully mimic this process under flow conditions. Several examples are presented under flow conditions and it was confirmed that a flow process is advantageous over a batch process. Deuterium labelling experiments were performed to elucidate the mechanism of the reaction, and the results indicated a possible carbene mechanism for this C–H alkylation process.

Rh(i)- and Rh(ii)-catalyzed C–H alkylation of benzylamines with alkenes using a picolinamide derivative as a directing group is reported under both batch and flow.     

Rh(I)-catalyzed direct ortho-alkenylation of aromatic ketimines with alkynes and its application to the synthesis of isoquinoline derivatives

[reaction: see text] Novel synthetic methods of both ortho-alkenylated aromatic ketones and isoquinoline derivatives have been developed through the Rh(I)-catalyzed direct ortho-alkenylation of common aromatic ketimines with alkynes. Furthermore, a highly efficient one-pot synthesis of isoquinoline derivatives was achieved by simply mixing aromatic ketone, benzylamine, and alkyne under a Rh(I) catalyst.     

NiN(2)S(2) complexes as metallodithiolate ligands to Rh(I), Rh(II) and Rh(III)

Three molecular structures are reported which utilize the NiN(2)S(2) ligands -, (bis(mercaptoethyl)diazacyclooctane)nickel and -', bis(mercaptoethyl)diazacycloheptane)nickel, as metallodithiolate ligands to rhodium in oxidation states i, ii and iii. For the Rh(I) complex, the NiN(2)S(2) unit behaves as a bidentate ligand to a square planar Rh(I)(CO)(PPh(3))(+) moiety with a hinge or dihedral angle (defined as the intersection of NiN(2)S(2) and S(2)Rh(C)(P) planes) of 115 degrees . Supported by -' ligands, the Rh(II) oxidation state occurs in a dirhodium C(4) paddlewheel complex wherein four NiN(2)S(2) units serve as bidentate bridging ligands to two singly-bonded Rh(II) ions at 2.893(8) A apart. A compilation of the remarkable range of M-M distances in paddlewheel complexes which use NiN(2)S(2) complexes as paddles is presented. The Rh(III) state is found as a tetrametallic [Rh(-')(3)](3+) cluster, roughly shaped like a boat propeller and structurally similar to tris(bipyridine)metal complexes.