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The ruthenium complex RuH2(PPh3)4 is an excellent catalyst for the Michael addition of active methylene compounds lacking cyano groups when the reactions are performed in acetonitrile instead of THF. The reaction proceeds satisfactorily in acetonitrile under mild and neutral conditions with malonates, beta-ketoesters, 1,3-diketones, 1,1-disulfones, nitro compounds, Meldrum acid and anthrone as the Michael donors. Cyano acetates can also be ideal substrates for this reaction.

A study was conducted to demonstrate the efficiency of titanocene(III) aqua complexes as a unique class of hydrogen-atom donor (HAT) reagents based on two key features such as excellent binding capabilities of water toward titanocene(III) complexes and a low activation energy for the HAT step. The results provide insight into the remarkable hydrogen-atom donor characteristics of water in [Ti.sup.III]-mediated free-radical chemistry.

A novel procedure for the straightforward synthesis of seven-membered carbocycles through free-radical chemistry, based on titanocene(III)-catalyzed 7-endo-dig and 7-endo-trig cyclizations is described. This procedure is proved to be useful for the preparation of several natural products including mono-, sesqui-, and diterpenoids with different skeletons containing cycloheptane rings.

In recent years solid evidence of HAT reactions involving water as hydrogen atom source have been presented. In this work we demonstrate that the efficiency of titanocene(III) aqua complexes as an unique class of HAT reagents is based on two key features: (a) excellent binding capabilities of water toward titanocene(III) complexes and (b) a low activation energy for the HAT step. The theory has predictive capabilities fitting well with the experimental results and may aid to find more examples of this remarkable radical reaction. [ABSTRACT FROM AUTHOR]

Stereochemistry, usually associated with the three-dimensional arrangement of atoms in molecules, is crucial in processes like life functions, drug action, or molecular reactions. This three-dimensionality typically originates from sp 3 hybridization in organic molecules, but it is also present in out-of-plane sp 2 -based molecules as a consequence of helical structures, twisting processes, and/or the presence of nonbenzenoid rings, the latter significantly influencing their global stereochemistry and leading to the emergence of new exotic properties. In this sense, on-surface synthesis methodologies provide the perfect framework for the precise synthesis and characterization of organic systems at the atomic scale, allowing for the accurate assessment of the associated stereochemical effects. In this work, we demonstrate the importance of the initial diastereomeric configuration in the surface-induced skeletal rearrangement of a substituted cyclooctatetraene (COT) moiety-a historical landmark in the understanding of aromaticity-into a cyclopenta[ c , d ]azulene (CPA) one in a chevron-like graphene nanoribbon (GNR). These findings are evidenced by combining bond-resolved scanning tunneling microscopy with theoretical ab initio calculations. Interestingly, the major well-defined product, a CPA chevron-like GNR, exhibits the lowest bandgap reported to date for an all-carbon chevron-like GNR, as evidenced by scanning tunneling spectroscopy measurements. This work paves the way for the rational application of stereochemistry in the on-surface synthesis of novel graphene-based nanostructures.

The chiral resolution of a kinetically inert molecular ruby [Cr(dqp) 2 ] 3+ ( 1 , dqp = 2,6-di(quinolin-8-yl)pyridine) displaying strong dual light emission at room temperature has been achieved. The wrapped arrangement of the six-membered dqp chelating ligands around the Cr(III) provided nonplanar helical conformations leading to the diastereoselective assembly of chiral bis-tridentate monometallic Cr(III)-helix. The PP- (+)-[Cr(dqp) 2 ] 3+ and MM -(-)-[Cr(dqp) 2 ] 3+ enantiomers could be separated and isolated by using cation-exchange chromatography and subsequent salt-metathesis with KPF 6 . X-ray crystallographic analysis based on Flack parameters assigned the absolute configurations of the two enantiomers. Circularly polarized luminescence (CPL) spectra showed two polarized emission bands within the NIR region corresponding to the characteristic metal-centered spin-flip Cr( 2 E → 4 A 2 ) and Cr( 2 T 1 → 4 A 2 ) transitions with exceptionally high dissymmetry factors, | g lum |, of 0.2 and 0.1, respectively, which are comparable to those reported for rare-earth chiral complexes. Photophysical properties also revealed an extremely long excited-state lifetime of 1.2 ms and a high quantum yield of 5.2% at room temperature in water. These properties make [Cr(dqp) 2 ] 3+ an ideal sensitizer for the preparation of enantiopure luminescent supramolecular energy-converting devices and also open up the possibility of using chiral Cr(III) chromophores for the construction of NIR-CPL materials and polarized photonic devices based on earth-abundant metals.