Singlet diradicals are usually not energy minima. As observed by femtosecond spectroscopy, they readily couple to form final sigma bonds. Substituent effects allow lifetimes to increase into the microsecond range. Taking advantage of the properties of hetero-elements, a diradical has been prepared that is indefinitely stable at room temperature. The availability of diradicals that can be handled under standard laboratory conditions will lead to further insight into their chemical and physical properties, raising the likelihood of practical applications, especially in the field of molecular materials such as electrical conductors and ferromagnets.

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A (phosphanyl)(trifluoromethyl)carbene is shown to be stable for weeks in solution at temperatures up to -30 degrees C. Its chemical behavior exactly matches that of its transient congeners, even to the extent that subtle effects, such as the recently discovered weak pi interaction with aromatics, are observed. The influence of substituents on the structure of push-pull carbenes is demonstrated by a single-crystal x-ray diffraction study of a (phosphanyl)[2, 6-bis(trifluoromethyl)phenyl]carbene. The lifetime of these molecules makes them accessible to a wider range of standard techniques, allowing their chemical and physical behaviors to be studied in more detail than was previously possible.

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A stable diphosphorus analogue of Enders' N‐heterocyclic carbene has been prepared by taking advantage of the inherent π‐donor capabilities of phosphorus, which are as good as, or better than, those of nitrogen. The P‐heterocyclic carbene (see figure; C gray, N blue, P red) behaves as a strong donor ligand and forms transition‐metal complexes that are thermally and air stable.

Fourteen different ligands have been synthesized with two covalently linked 8-hydroxyquinoline motifs that favor metal complexation. These bis-chelators include different bridges at the C2 positions and different substituents to modulate their physicochemical properties. They can form metal complexes in a ratio of one ligand per metal ion with Cu II and Zn II, two metal ions involved in the formation of amyloid aggregates of the toxic Abeta-peptides in the Alzheimer disease. The apparent affinity of all bis-8-hydroxyquinoline ligands for Cu II and Zn II are similar with logK Cu II approximately 16 and logK Zn II approximately 13 and are 10,000 times more efficient than for the corresponding 8-hydroxyquinoline monomers. Their strong chelating capacities allow them to inhibit more efficiently than the corresponding monomers the precipitation of Abeta-peptides induced by Cu II and Zn II and also to inhibit the toxic formation of H2O2 due to copper complexes of Abeta. The best results were obtained with a one-atom linker between the two quinoline units. X-ray analyses of single-crystals of Cu II, Zn II or Ni II complexes of 2,2'-(2,2-propanediyl)-bis(8-hydroxyquinoline), including a one-atom linker, showed that all heteroatoms of the bis-8-hydroxyquinoline ligand chelate the same metal ion in a distorted square-planar geometry. The Cu II and Zn II complexes include a fifth axial ligand and are pentacoordinated.

Trioxaquines are dual molecules that contain a trioxane motif linked to an aminoquinoline entity. Among the different compounds of this series, trioxaquine cis-15 (DU1302 c), prepared from alpha-terpinene, a cheap natural product, showed efficient antimalarial activity in vitro on both sensitive and resistant strains of Plasmodium falciparum (IC(50)=5-19 nM). A stereochemical description of this stable, nontoxic, and non-genotoxic antimalarial agent is detailed. Mice infected with P. vinckei were successfully treated with cis-15 in a four-day suppressive test. The doses required to decrease parasitemia by 50 % (ED(50)) were 5 and 18 mg kg(-1) d(-1) after intraperitoneal and oral administration, respectively. Parasitemia clearance was complete without recrudescence at an intraperitoneal dose of 20 mg kg(-1) d(-1).

To and fro: Diphosphanylborane derivative 1 behaves as a tridentate, ambiphilic ligand towards rhodium(I) fragments (see picture). The presence of metal→borane interactions in the resulting square‐pyramidal complexes is highlighted by structural analyses and DFT calculations.