Synthesis, characterisation and natural abundance Os NMR spectroscopy of hydride bridged triosmium clusters with chiral diphosphine ligands

Treatment of [Os₃(μ-H)₂(CO)₁₀] with the chiral diphosphines BINAP, tolBINAP [(R)-2,2′-bis(di-4-tolylphosphino)-1,1′-binaphthyl], DIOP [(4R,5R)-(−)-O-isopropenylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane] affords [Os₃(μ-H)₂(CO)₈(μ-L)] (L = BINAP (1), tolBINAP (2), DIOP (4)) in high yield. The X-ray structures for 1, 2 and 4 are reported, and structural and spectroscopic comparisons are made between these clusters and [Os₃(μ-H)₂(CO)₈(μ-L)] (L = dppm (5), dppe (6), dppp (7)) which were synthesised similarly. Compounds 5 to 7 were previously synthesised by hydrogenation of 1,2-[Os₃(CO)₁₀(μ-L)] but the route from [Os₃(μ-H)₂(CO)₁₀] is preferable. The H-bridged Os?Os distances are similar in 1, 2 and 4 indicating that these species are formally unsaturated 46-electron clusters. The P?P distances vary from 4.24 to 4.30 Å in 1 and 2, respectively, to 4.53 Å in 4 and there are related changes in the angles associated with the ligand set around the H-bridged osmium atoms. Introduction of the diphosphine ligands completely suppresses the ability to add CO, to insert acetylene to form a μ-η¹,η²-vinyl compound, and to exchange hydride ligands with styrene-d₈, which are reactions characteristic of [Os₃(μ-H)₂(CO)₁₀]. Clusters 2 and 5-7 were also used to examine the potential of natural abundance ¹⁸⁷Os NMR spectroscopy through techniques based on inverse detection by HMQC, HSQC and HMBC spectroscopy.     

The first pincer-aryl [M-(NCN)] complexes {M = Pd(II); Pt(II)} with chiral pyridine donors: Synthesis and catalytic activity in C-C bond formation

The first chiral bis(pyridine) N-C(H)-N pincer ligand, (5S,7S)-1,3-bis(6,6-dimethyl-5,6,7,8-tetrahydro-5,7-methanquinolin-2-yl)benzene (HL) has been synthesized and characterized by a thorough ¹H NMR analysis. Reaction of HL with K₂[PtCl₄] in acetic acid gives [Pt(L)Cl] (1), where L acts as a tridentate N-C-N pincer ligand. The analogous palladium(II) derivatives [Pd(L)Cl] (2), and [Pd(L)(OAc)] (3), were first prepared through a transmetalation reaction between Pd(OAc)₂ and the organomercury compound [Hg(L)Cl] (4). The structures of compounds 1 (Pt) and 2 (Pd), as determined by X-ray diffraction, are reported and compared. Compound 2 can also be obtained from Na₂[PdCl₄] and HL in refluxing acetic acid, i.e., under the same conditions used for compound 1. Apparently, this is the first palladium pincer derivative of a 1,3-bis(pyridyl)benzene ligand synthesized by direct C-H activation.The neutral complexes 1-3 are catalysts of modest activity, but devoid of enantioselectivity in the Heck reaction between iodobenzene and methyl acrylate and in the aldol condensation of benzaldehyde with methyl isocyanoacetate.     

Zirconium and hafnium aqua complexes [(H2O)3M(P2W17O61)]: Synthesis, characterization and substitution of water by chiral ligand

The hydroxocomplexes [{(H₂O)M(μ₂-OH)(P₂W₁₇O₆₁)}₂]¹⁴⁻ (M = Zr, Hf) in HCl undergo cleavage of the hydroxo bridges with the formation of monomeric species [(H₂O)₃M(P₂W₁₇O₆₁)]⁶⁻. In the case of Hf single crystals of the composition (Me₂NH₂)_5.5(H)_1.5[(Hf(H₂O)₃)_0.9(WO)_0.1{P₂W₁₇O₆₁}]Cl·9.5H₂O (1), as the result of co-crystallization of [(H₂O)₃Hf(P₂W₁₇O₆₁)]⁶⁻ and [P₂W₁₈O₆₂]⁶⁻ salts, were isolated from these solutions and structurally characterized. Zr gives (Me₂NH₂)₂(H)₄[{(H₂O)₂ZrP₂W₁₇O₆₁}]·8.67H₂O (2), in whose structure chiral polymeric chains {[(H₂O)₂M(P₂W₁₇O₆₁)]}_n⁶ⁿ⁻ are present. Under hydrothermal conditions the water molecules in [(H₂O)₃M(P₂W₁₇O₆₁)]⁶⁻ are replaced by l-malic acid with the formation of stable chiral polyoxoanions, isolated as (NH₂Me₂)₈[M(L-ООССН(ОН)СН₂СОО)P₂W₁₇O₆₁]·7·9H₂O (M = Zr, 3; M = Hf, 4). The structures of 1, 2 and 3 were determined; 3 and 4 were found to be isostructural. The products were also characterized by elemental analysis, thermogravimetry and IR-spectroscopy.     

Restriction of apical coordination in the square-planar nickel(II) complexes of meso-1,5,8,12-tetramethyl-1,4,8,11-tetraazacyclotetradecane with axially oriented C-methyl groups

Crystal structures of nickel(II) complexes coordinated with cyclam-type macrocyclic tetraamine, meso-1,5,8,12-tetramethyl-1,4,8,11-tetraazacyclotetradecane (L) in two complex salts 1 and 2 have been determined by single-crystal X-ray crystallographic analysis. Complexes in both salts adopted trans-III structure, but the C-methyl groups of L adopted equatorial configuration in 1, while axial in 2. Complex 2 is the first example of complex of cyclam-type tetraamine with only axially oriented C-methyl groups. Complex in 1 adopted six-coordinated octahedral geometry with two water molecules occupying two apical sites, while in 2, apical sites were vacant resulting in four-coordinated square-planar geometry. UV-Vis spectra in various solutions also revealed the formation of octahedral six-coordinated complex for 1 but not for 2. Network of hydrogen bonds involving chloride ion, water, and N-H of L was present in crystals of both 1 and 2. Convenient synthetic paths for 1 and 2 are also presented.     

Synthesis of spiroannulated oligopyrrole macrocycles derived from lithocholic acid

Two new steroidal spiroannulated calix[4]pyrroles 5 and 10, derived from bile acids (lithocholate), were prepared by the acid catalyzed condensation of methyl-3,3-bis(pyrrol-2-yl)-5β-cholan-24-oate 3 with carbonyl compounds and with 2,2′-propane-2,2-diylbis(1H-pyrrole), respectively. The new compounds were fully characterized by physicochemical methods.     

Carboxymethylated cyclosophoraose as a novel chiral additive for the stereoisomeric separation of some flavonoids by capillary electrophoresis

A carboxymethylated cyclosophoraose (CM-Cys) was synthesized by the chemical modification of neutral Cys, which was isolated from Rhizobium trifolii TA-1. CM-Cys was successfully applied as a novel chiral selector for the separation of some flavonoids including catechin, 3,5,7,3′,4′-pentahydroxyflavanone, hesperidin, hesperetin, isosakuranetin, naringenin, naringin, and eriodictyol. The effects of pH, chiral additive concentration, and temperature on resolution and migration time were also studied.     

An experimental and theoretical study of the enantioselective deprotonation of cyclohexene oxide with isopinocampheyl-based chiral lithium amides

The mechanism of the enantioselective deprotonation of cyclohexene oxide with isopinocampheyl-based chiral lithium amide was studied by quantum chemical calculations. The transition states of eight molecules were fully optimized at the ab initio HF/3-21G and density functional B3LYP/3-21G levels with Gaussian 98. The activation energies were calculated at the B3LYP/6-31+G(3df,2p)//B3LYP/3-21G level. We found the theoretical evaluation to be consistent with the experimental data. At the best case, an enantiomeric excess of up to 95% for (R)-2-scyclohexen-1-ol was achieved with (−)-N, N-diisopinocampheyl lithium amide. Enantioselective deprotonation of cyclohexene oxide Electronic Supplementary Material Supplementary material is available for this article at Dedicated to Professor Dr. Paul von Ragué Schleyer on the occasion of his 75th birthday.     

Asymmetric syntheses of pipecolic acid and derivatives

Summary Results in the field of asymmetric synthesis of pipecolic acid derivatives are reviewed. Three sections describe the asymmetric syntheses of the title compounds (i) from the chiral pool (-amino acids or carbohydrates) (ii) using a chiral auxiliary either derived from terpenes,-amino acids, tartaric acid, an amine or-amino alcohols (iii) by means of asymmetric catalysis.     

How to build optically activeα-amino acids

Summary Various methodologies published in the literature dealing with-amino carboxylic acid asymmetric synthesis are presented in a digest form. In each case, only some recent or most typical works are mentioned.     

Determination of enantiomeric compositions of pharmaceutical products by near-infrared spectrometry

A new method for the determination of enantiomeric compositions of a variety of drugs including propranolol, atenolol, and ibuprofen has been developed. The method is based on the use of the near-infrared technique to measure diastereomeric interactions between an added carbohydrate compound and both enantiomeric forms of a drug followed by evaluation of the data by partial least square analysis. The fact that the method works well with all three macrocyclic carbohydrates with different cavity sizes (i.e., alpha-, beta-, and gamma-cyclodextrin) and with sucrose, which is a linear carbohydrate, clearly demonstrates that it is not necessary to have inclusion complex formation to produce effective diastereomeric interactions. Rather a simple adsorption of the drug onto a carbohydrate is sufficient. Since inclusion complex formation is not a requisite, this method is not limited to the three drugs evaluated in this study but is rather universal as it can, in principle, be used for the sensitive and accurate determination of enantiomeric compositions of many different types of drugs with only about 1.5mg/mL concentration and enantiomeric excess as low as 0.80%, in water or in a mixture of water with organic solvent. Furthermore, it does not rely on the use of rather expensive carbohydrates such as cyclodextrins but is equally as effective even with a simple and inexpensive carbohydrate such as sucrose.