RESUMO
A series of oxahelicenes composed of ortho/meta-annulated benzene/pyridine and 2H-pyran rings were synthesized on the basis of the cobalt(I)-mediated (or rhodium(I)- or nickel(0)-mediated) double, triple, or quadruple [2+2+2] cycloisomerization of branched aromatic hexa-, nona-, or dodecaynes, thus allowing the construction of 6, 9, or 12 rings in a single operation. The use of a flow reactor was found to be beneficial for the multicyclization reactions. The stereogenic centers present in some of the oligoynes steered the helical folding in such a way that the final oxa[9]-, [13]-, [17]- and [19]helicenes were obtained in both enantiomerically and diastereomerically pure form. Specifically, the oxa[19]helicenes beat the current record in the length of a helicene backbone. Single-molecule conductivity was studied by the mechanically controllable break-junction method with a pyridooxa[9]helicene.
RESUMO
[structure: see text] An unprecedented V-shape (2.1.2.1) expanded porphyrin incorporating an extended pi-conjugated system is described. Its efficient synthesis relied on the use of a new peralkyl tetrapyrrolylquinoxaline building block that constitutes the ideal intermediate for the versatile preparation of new quinoxaline-containing macrocycles.
RESUMO
Herein, we report the manganese complex with a novel trianionic ligand, the pentafluorophenyldipyrrinphenol ligand DPPH(3). The X-ray crystal structure reveals that the Mn(III) complex exists in a dimeric form in the solid state. Electrochemical studies indicate two quasi-reversible one electron oxidation processes. EPR data on the one electron oxidised species in solution support the formation of a monuclear Mn complex with an S = 3/2 spin system. Preliminary studies towards epoxidation reactions were tested in the presence of iodosylbenzene (PhIO) and are in favour of an oxygen-atom-transfer (OAT) reaction catalyzed by the Mn(III) complex.