Rhenium, Palladium, and Copper Pyridylalkoxide Complexes: Synthesis, Structural Characterization, and Catalytic Application in Epoxidation Reactions

Stereoisomers and functional groups in oxidorhenium(v) complexes: effects on catalytic activity

The syntheses of oxidorhenium(v) complexes [ReOCl(L1a-c)₂] (3a-c), equipped with the bidentate, mono-anionic phenol-dimethyloxazoline ligands HL1a-c are described. Ligands HL1b-c contain functional groups on the phenol ring, compared to parent ligand 2-(4,4-dimethyl-4,5-dihydro-1,3-oxazol-2-yl)-phenol H1a; namely a methoxy group ortho to the hydroxyl position (2-(4,4-dimethyl-4,5-dihydro-1,3-oxazol-2-yl)-6-methoxyphenol, H1b), or a nitro group para to the hydroxyl position (2-(4,4-dimethyl-4,5-dihydro-1,3-oxazol-2-yl)-4-nitrophenol, H1c). Furthermore, oxidorhenate(v) complexes (NBu₄)[ReOCl₃(L1a-b)] (2a-b) were synthesized for solid state structural comparisons to 3a-b. All novel complexes are fully characterized including NMR, IR and UV-Vis spectroscopy, MS spectrometry, X-ray crystallography, elemental analysis as well as cyclic voltammetry. The influence of functional groups (R = -H, -OMe and -NO₂) on the catalytic activity of 3a-c was investigated in two benchmark catalytic reactions, namely cyclooctene epoxidation and perchlorate reduction. In addition, the previously described oxidorhenium(v) complex [ReOCl(oz)₂] (4), employing the phenol-oxazoline ligand 2-(4,5-dihydro-2-oxazolyl)phenol Hoz, was included in these catalysis studies. Complex 4 is a rare case in oxidorhenium(v) chemistry where two stereoisomers could be separated and fully characterized. With respect to the position of the oxazoline nitrogen atoms on the rhenium atom, these two stereoisomers are referred to as N,N-cis and N,N-trans isomer. A potential correlation between spectroscopic and structural data to catalytic activity was evaluated.

Ruthenium carbonyl complexes with pyridine-alkoxide ligands: synthesis, characterization and catalytic application in dehydrogenative oxidation of alcohols

Dehydrogenative oxidation of secondary alcohols catalyzed by several new trinuclear ruthenium carbonyl complexes under mild conditions was proposed.

One-pot synthesis of benzoxaborole derivatives from the palladium-catalyzed cross-coupling reaction of alkoxydiboron with unprotected o-bromobenzylalcohols

Under very mild conditions, functionalized benzoxaborole derivatives were prepared in good to excellent yields via a palladium-catalyzed Miyaura borylation reaction of readily available unprotected o-bromobenzylalcohols, and bis(pinacolato)diboron (B₂pin₂) without the assistance of an acid.

Oxorhenium(V) complexes of quinoline and isoquinoline carboxylic acids--synthesis, structural characterization and catalytic application in epoxidation reactions

Six novel oxorhenium(V) complexes incorporating quinoline and isoquinoline carboxylic acid derivatives were prepared in good yields. Relying on the experimental conditions, compounds with two chelate ligands [ReOCl(iqc)2]·MeOH (1), [ReO(OMe)(iqc)2] (2), [ReO(OMe)(mqc)2] (3) and [ReO(OMe)(8-qc)2] (4) and compounds incorporating one bidentate ligand [ReOCl2(iqc)(PPh3)] (5) and [ReOCl2(mqc)(PPh3)] (6) were synthesized (iqcH = isoquinoline-1-carboxylic acid, mqcH = 4-methoxy-2-quinolinecarboxylic acid and 8-qcH = 8-quinolinecarboxylic acid). The reported compounds were characterized by spectroscopic methods and single crystal X-ray diffraction analysis. In compounds 1 and 2, one chelate ligand occupies an axial and an equatorial position, while the other one occupies two equatorial positions, forming a cis-(N,N) isomer. In turn, complexes 3 and 4 show a rare ligand arrangement with two trans-N, trans-O chelate ligands in the equatorial plane and a linear axial [O=Re-OMe] unit. The complexes with one chelate ligand 5 and 6 are cis-(Cl,Cl)-isomers. All compounds were tested as potential catalysts in the epoxidation of cyclooctene with 3 equiv. of tert-butylhydroperoxide. The yield of cyclooctane oxide varies between 16 and 68% (50 °C, 24 h), and the catalytic competency of compounds 1-6 was discussed with regard to the structure of each complex.

Chichibabin-type direct alkylation of pyridyl alcohols with alkyl lithium reagents

Direct C(6) alkylation of pyridyl alcohols can be achieved following an initial deprotonation of the hydroxy group. This transformation, which is believed to occur by a Chichibabin-type alkylation, avoids lateral deprotonation prior to pyridine ring alkylation and gives increased regioselectivity for C(6) over C(4) alkylation.

Imidazo[1,5-a]pyridine-1-ylalkylalcohols: synthesis via intramolecular cyclization of N-thioacyl 1,2-aminoalcohols and their silyl ethers and molecular structures

Iodine-mediated cyclization of N-thioacyl 1,2-aminoalcohols derived from aromatic aldehydes and ketones mainly produced bis(1-imidazo[1,5-a]pyridyl)arylmethanes, whereas the reaction of N-thioacyl 1,2-aminoalcohols derived from aliphatic aldehydes and N-thioacyl 1,2-aminoalcohols protected with a silyl group with iodine gave imidazo[1,5-a]pyridine-1-ylalkylalcohols as a major product.