Synthesis of novel chiral phosphine-triazine ligand derived fromα-phenylethylamine for Pd-catalyzed asymmetric allylic alkylation

A novel chiral phosphine-triazine ligand was synthesized from chiralα-phenylethylamine through a three-step procedure.In a model reaction of Pd-catalyzed allylic alkylation of rac-1,3-diphenylprop-2-en-l-yl pivalate with dimethyl malonate,good enantioselectivity (90% e.e.) was obtained by using this ligand.     

Modular chiral β-selenium-, sulfur-, and tellurium amides: synthesis and application in the palladium-catalyzed asymmetric allylic alkylation

A series of modular chiral β-chalcogen amides have been efficiently synthesized from inexpensive and easily available 2-oxazolines. All the selenium, sulfur, and tellurium compounds were evaluated as chiral ligands in the palladium-catalyzed asymmetric allylic alkylation. The corresponding alkylated products were obtained in excellent enantiomeric excess, using BSA/CH₂Cl₂ as the base/solvent system.     

Synthesis and resolution of 2,2′-bis[di(p-tolyl)stibano]-1,1′-binaphthyl (BINASb); the first example of an optically active organoantimony ligand for asymmetric synthesis

Racemic 2,2′-bis[di(p-tolyl)stibano]-1,1′-binaphthyl (BINASb) (±)-2 has been prepared from 2,2′-dibromo-1,1′-binaphthyl 1 via 2,2′-dilithio-1,1′-binaphthyl intermediate, and has been resolved via the separation of a mixture of the diastereomeric Pd complexes 4A and 4B, derived from the reaction of (±)-2 with di-μ-chlorobis{(S)-2-[1-(dimethylamino)ethyl]phenyl-C,N}dipalladium(II) 3. The optically active BINASbs (S)-(+)-2 and (R)-(−)-2 have been shown to be effective chiral ligands for the rhodium-catalyzed asymmetric hydrosilylation of ketones.     

From tropos to atropos: 5,5′-bridged 2,2′-bis(diphenylphosphino)biphenyls as chiral ligands for highly enantioselective palladium-catalyzed hydrogenation of α-phthalimide ketones

A class of atropisomeric diphosphine ligands with a wide range of dihedral angles has been developed. X-ray study of the Pd(II) complexes of these ligands showed that as the bridge length increased, the dihedral angles and the ligand bite angles increased as well, while an excessive increase in bridge length had a reverse effect. It was found that there was a correlation between the ligand dihedral angles and the enantioselectivity in Pd-catalyzed asymmetric hydrogenation of α-phthalimide ketones, and excellent enantioselectivities of up to 99% ee were afforded.     

2,2′-Bis((di-tert-butylphosphino)methyl)-1,1′-biphenyl (ditbi): a bulky analogue of bisbi. The crystal structure of [Rh2Cl2(1,5-cod)2(μ-ditbi)]

Diphosphine 2,2′-bis(di-tert-butylphosphino)methyl)-1,1′-biphenyl (ditbi) is synthesised by the addition of to 2,2′-bis(bromomethyl)-1,1′-biphenyl, followed by deprotection with diethylamine. Treatment of [Rh₂Cl₂(1,5-cod)₂], with ditbi gives [Rh₂Cl₂(1,5-cod)₂(μ-ditbi)] (2) as confirmed by its X-ray crystal structure determination. Hydroformylation of 1-hexene using [Rh(acac)(CO)₂]/ditbi as catalyst gave n- and iso-heptanal in a ratio of 1:1.     

Studies on the rhodium- and ruthenium-catalyzed asymmetric hydrogenation of α-dehydroamino acids using a family of chiral dipyridylphosphine ligand (P-Phos)

The applications of the chiral dipyridylphosphine ligand P-Phos and its derivatives Tol-P-Phos and Xyl-P-Phos in Ru- and Rh-catalyzed hydrogenations of the methyl esters of a variety of (Z)-2-acetamido-3-arylacrylic acids have been studied systematically. The results show that the electronic and steric properties of these ligands have significant influences on the enantioselectivity of the reduction. Rh and Ru complexes of the same dipyridylphosphine ligand family exhibit different trends in enantioselectivity toward the same substrate.     

Electrocatalytic reductive dimerization of the 2,2′-bipyridyl tungsten alkylidyne complex [W(CC6H4NMe2-4)(NCMe)(CO)2{κ-2,2′-(NC5H4)2}]

Potentiometric measurements have shown that the cationic 2,2′-bipyridyl tungsten alkylidyne complex [W(CC₆H₄NMe₂-4)(NCMe)(CO)₂{κ²-2,2′-(NC₅H₄)₂}][PF₆] (2) is electroactive in MeCN solution with a reduction (E_pc ≈ −1.0 V vs. ferrocene) leading to complex dimerization, identified by a number of electrochemical markers. Multiple redox cycles have led to the partial deposition of the dimerized product on the electrode surface, which appears to electrocatalyze subsequent coupling cycles. Comparison with electrochemical measurements of related alkylidyne complexes, including the precursor complex [W(CC₆H₄NMe₂-4)(O₂CCF₃)(CO)₂{κ²-2,2′- (NC₅H₄)₂}] (1), has provided indirect evidence of intermolecular bond formation between κ²-2,2′-bipyridyl ligands. The cationic complex 2 has additionally been the subject of gamess computational analysis, revealing calculated ν_max(CO) stretching absorptions in good agreement with measured parameters. This study has also permitted a molecular orbital analysis, which has indicated an energy-accessible LUMO almost entirely located on the 2,2′-bipyridyl ligand of complex 2, the purported site for dimerization. It is believed that occupation of this orbital upon reduction of compound 2 leads to a short-lived metastable precursor to 2,2′-bipyridyl ring coupling. Furthermore, a very weak π-antibonding interaction of the metal-alkylidyne π-framework with the MeCN ligand in the occupied frontier molecular orbitals of complex 2 has been noted and compared with a surprisingly significant π interaction with the carboxylate group in complex 1.     

Determination of the absolute configuration and identity of chiral carboxylic acids using a Cu(II) complex of pyridine–benzimidazole-based ligand

We report a new achiral Cu host [Cu(bmb–bpy)(H₂O)(OTf)₂] (bmb–bpy = 6,6′-bis[((1-methylbenzimidazol-2-yl)thio)methyl]-2,2′-bipyridine) for the enantioselective and chemoselective recognition of chiral carboxylic acids. The binding of chiral carboxylic acids to [Cu(bmb–bpy)(H₂O)(OTf)₂] produced an exciton-coupled circular dichroism signal; the linear discriminant analysis allowed the assignment of the absolute configuration, enantiomeric excess, and identity of chiral carboxylic acids.     

Synthesis,crystal structure,and magnetism of a binuclear Cu(II) complex with double azido as asymmetric basal–apical end-on bridged ligand

A new binuclear copper(II) complex, [Cu₂(μ_1,1-N₃)₂(PP)₂)] ? 2ClO₄ (PP = 2,6-dipyrazol-1-yl-pyridine), was synthesized with double azide as asymmetric end-on bridge ligand and 2,6-dipyrazol-1-yl-pyridine as the terminal ligand. The crystal structure was determined by X-ray crystallography. Cu(II) is located in a distorted square pyramidal geometry, and azide bridges the equatorial-axial linking two Cu(II) atoms with a separation of 3.3595(11) Å. The fitting for the data of the variable-temperature (2–300 K) magnetic susceptibilities by using the Curie–Weiss law gives the Weiss temperature θ = ?7.830 K, indicating a very weak anti-ferromagnetic interaction between the bridging Cu(II) complexes.     

Synthesis,structure and spectroelectrochemical property of (2,2′-bipyridine)–metal (M = Pt,Pd) dichloride with 4,4′-bis(fluorous-ponytail) on bipyridine

The 4,4′-bis(R_fCH₂OCH₂)-2,2′-bpy ligands [R_f = n-C₃F₇ (1a), HCF₂(CF₂)₃ (1b)] were prepared and then treated with [MCl₂(CH₃CN)₂] (M = Pt or Pd) to result in the corresponding metal complexes, [MCl₂(4,4′-bis(R_fCH₂OCH₂)-2,2′-bpy)] (M = Pt 2a–b; Pd 3a–b). Both ligands and metal complexes were fully characterized by multi-nuclei NMR (¹H, ¹⁹F and ¹³C), FTIR, and mass (GC/MS or HR-FAB) methods. The X-ray structures of 2a–b and 3a–b were studied. With terminal CF₃, the structures of 2a and 3a exhibit disordered polyfluorinated regions in solid state. With terminal HCF₂, the structures of 2b and 3b show a π–π stacking of the bpy planes, five-membered C–H···O hydrogen bond and an unusual intramolecular blue-shifting C–H···F–C hydrogen bond system, whereas without terminal HCF₂, the structures of 2a and 3a show the similar π–π stacking, five-membered C–H···O hydrogen bond and typical orientation of polyfluorinated ponytails, but not the C–H···F–C hydrogen bond system. The CV and UV/Vis studies were also carried out.     

The imine (+)-pseudoephedrine glycinamide: a useful reagent for the asymmetric synthesis of (R)-α-amino acids

The new imine derived from Myers (+)-pseudoephedrine glycinamide can be diastereoselectively alkylated with alkyl halides at room temperature using NaOEt or LiO-tert-Bu as bases under phase transfer conditions. Hydrolysis to the corresponding alkylated products was easily achieved under mild conditions to afford (R)-α-amino acids.     

Synthesis and structure of the iron(<Emphasis Type="SmallCaps">iii</Emphasis>) tris-chelate complex based on 1,1´-ferrocenediylbis(phenylphosphinic acid)

The previously unknown isomorphous tris{µ²-[1,1´-ferrocenediylbis(phenylphosphinato)]}-iron(iii) complexes as solvates with methanol and DMSO were synthesized and characterized.     

Synthesis,crystal structure,and biological activity of 4′-chloro-2,2′ : 6′,2″-terpyridine (Cltpy) as tridentate ligand in a Cd(II) complex

A new Cd(II) complex with 4′-chloro-2,2′?:?6′,2″-terpyridine (Cltpy), [Cd(Cltpy)(NO₃)₂(H₂O)_0.45(CH₃OH)_0.55], has been synthesized and characterized by CHN elemental analysis, ¹H-NMR, ¹³C-NMR, IR spectroscopy, and structurally analyzed by X-ray single-crystal diffraction. The single-crystal X-ray analyses show that the coordination number is seven with three terpyridine (Cltpy) N-donors, three oxygen atoms of two nitrates and one oxygen atom of methoxy/water. The antibacterial activities of Cltpy and its Cd(II) complex are tested against different bacteria. The free ligand has considerable activity against Staphylococcus aureus, Bacillus anthracis, and Pseudomonas aeruginosa (inhibition zones?≥?20?mm), but has moderate activity against Escherichia coli and Streptococcus pyogenes (inhibition zones?≤?15?mm). In comparison with free Cltpy ligand, its complex has more activity against Klebsiella pneumonia, S. aureus, and B. anthracis (inhibition zones?≥?30?mm), but is inactive against P. aeruginosa and S. pyogenes. The quantitative assays gave minimal inhibitory concentration values in the range 6.25–100?mg?mL^?1 that confirmed the above results. Against K. pneumonia and S. aureus, antibacterial activity of the complex is higher than Cltpy ligand.     

Ruthenium cluster compounds containing 1,1′-bis(diphenylphosphino)ferrocene (dppf): an electrochemical analysis and the crystal structure of [Ru3(CO)11]2(μ-dppf)

The electrochemistry of 1,1′-bis(diphenylphosphino)ferrocene (dppf) derivatives of Ru₃(CO)₁₂ was investigated. Two known compounds [Ru₃(CO)₈(μ-dppf)₂ (1) and Ru₃(CO)₁₀dppf (2)] and a new compound [Ru₃(CO)₁₁(μ-dppf)Ru₃(CO)₁₁ (3)] were prepared. Compound 3 was characterized spectroscopically and an X-ray crystal structure was obtained. The reductive electrochemistry of 1 and 2 showed an irreversible reduction and a follow-up oxidation, similar to Ru₃(CO)₁₂. The electrochemistry of compound 3 showed two irreversible waves and a follow-up oxidation. A trend in the reduction potential vs. the number of coordinated phosphorus atoms was noted. The oxidative electrochemistry of 1-3 showed a dppf-based chemically reversible wave, and an irreversible wave similar to that of Ru₃(CO)₁₂. Trends were also noted between the oxidation potential and the number of coordinated phosphorus atoms.     

A Raman spectroscopic study of the XeOF4/XeF2 system and the X-ray crystal structure of α-XeOF4·XeF2

The mixed oxidation state complexes, α-XeOF₄·XeF₂ and β-XeOF₄·XeF₂, result from the interaction of XeF₂ with excess XeOF₄. The X-ray crystal structure of the more stable α-phase shows that the XeF₂ molecules are symmetrically coordinated through their fluorine ligands to the Xe(VI) atoms of the XeOF₄ molecules which are, in turn, coordinated to four XeF₂ molecules. The high-temperature phase, β-XeOF₄·XeF₂, was identified by low-temperature Raman spectroscopy in admixture with α-XeOF₄·XeF₂; however, the instability of the β-phase precluded its isolation and characterization by single-crystal X-ray diffraction. The Raman spectrum of β-XeOF₄·XeF₂ indicates that the oxygen atom of XeOF₄ interacts less strongly with the XeF₂ molecules in its crystal lattice than in α-XeOF₄·XeF₂. The ¹⁹F and ¹²⁹Xe NMR spectra of XeF₂ in liquid XeOF₄ at −35 °C indicate that any intermolecular interactions that exist between XeF₂ and XeOF₄ are weak and labile on the NMR time scale. Quantum-chemical calculations at the B3LYP and PBE1PBE levels of theory were used to obtain the gas-phase geometries and vibrational frequencies as well as the NBO bond orders, valencies, and NPA charges for the model compounds, 2XeOF₄·XeF₂, and XeOF₄·4XeF₂, which provide approximations of the local XeF₂ and XeOF₄ environments in the crystal structure of α-XeOF₄·XeF₂. The assignments of the Raman spectra (−150 °C) of α- and β-XeOF₄·XeF₂ have been aided by the calculated vibrational frequencies for the model compounds. The fluorine bridge interactions in α- and β-XeOF₄·XeF₂ are among the weakest for known compounds in which XeF₂ functions as a ligand, whereas such fluorine bridge interactions are considerably weaker in β-XeOF₄·XeF₂.     

Synthesis,structure and catalase activity of the [TPA2Mn2(μ-Cl)2] complex

The dinuclear Mn complex (Et₃NH)₂[TPA₂Mn₂(μ-Cl)₂](ClO₄)₄ (I) was synthesized and characterized. Complex I was obtained from the reaction between MnCl₂ and [H₃TPA](ClO₄)₃ in MeOH. Structural analysis of I showed the two Mn(II) atoms are bridged by two chloride ligands, forming a bis(μ-chloro)dimanganese core. The [Mn₂(μ-Cl)₂]²⁺ core, with a Mn–Mn distance of 3.521(2) Å, is similar to the active site found in chloride-inhibited Mn catalase. EPR and temperature-dependent magnetic susceptibility measurements of complex I showed an antiferromagnetic interaction between the two S = 5/2 Mn centers with an exchange parameter J = −8.8 cm⁻¹. Catalytic activity of H₂O₂ dismutation was measured for complex I and compared with other related complexes. Kinetic parameters of H₂O₂ dismutation were obtained and a possible catalytic mechanism of complex I, related to chloride-inhibited Mn catalase, was suggested.     

Synthesis of a chiral pyridylphosphine ligand and a comparison of its rhodium complex with the structurally similar arylphosphine rhodium catalysts in the asymmetric hydrogenation of 2-(6′-methoxy-2′-naphthyl)propenoic acid

A chiral pyridylphosphine ligand (2R,4R)-2,4-bis[di-3′-(2′,6′-dimethoxypyridyl)phosphino]pentane was synthesized. The rhodium catalyzed asymmetric hydrogenation of 2-(6′-methoxy-2′-naphthyl)propenoic acid was studied by using this ligand in comparison with the structurally similar Skewphos analogs.     

Soluble {[Rh2(μ-OOCCH3)2(dbbpy)2][BF4]}n molecular wire and [Rh2(μ-OOCCH3)2(dbbpy)2L2] complexes; dbbpy = 4,4′-di-tert-butyl-2,2′-bipyridine: Synthesis and physicochemical characterization

Binuclear Rh(II) compounds [Rh₂(μ-OOCCH₃)₂(dbbpy)₂(H₂O)₂](CH₃COO)₂ (1) (dbbpy = 4,4′-di-tert-butyl-2,2′-bipyridine), [Rh₂(μ-OOCCH₃)₂(dbbpy)₂(H₂O)₂](BF₄)₂·H₂O·CH₃CN (2), [Rh₂(CH₃COO)₂(C₁₈H₂₄N₂)₂(CH₃CN)₂](BF₄)₂·4CH₃CN (3) and {[Rh₂(μ-OOCCH₃)₂(dbbpy)₂][BF₄]}_n (4) have been synthesized and characterized with spectroscopic methods. Structure of complex 3 has been determined using X-ray crystallography. Rhodium atoms in compound 3 have distorted octahedral coordination with O and N atoms in equatorial positions and Rh atom and CH₃CN molecule in axial coordination sites. Reduction of rhodium(II) compounds with aqueous 2-propanol leads to the formation of polymetallic compound {[Rh₂(μ-OOCCH₃)₂(dbbpy)₂][BF₄]}_n (4) containing [Rh₂]³⁺ core. Compound 4 shows strong antiferromagnetic properties, μ = 0.18–1.73 M.B. in the range 1.8–300 K, J = −597 cm⁻¹. Electrochemistry of compounds 3 and 4 in CH₃CN has been investigated. Compound 4 exhibits a poorly reversible oxidation system at E_1/2 = −0.92 V (ΔE_p = 0.19 V) and in solution in DMF is slowly oxidized to 3 even in total absence of oxygen. Complex 3 is irreversibly oxidized to Rh(III) compound at E_pa = 1.48 V and irreversibly reduced at E_pc = −1.02 V to lead to the unstable polynuclear complex 4 in CH₃CN.