The supramolecular architectures of a fluorophore are controlled through the design of a conjugated polycatenar molecule, the self-assembly of which can be addressed toward a columnar liquid-crystalline phase and organogels. Thus, depending on the environmental conditions for self-assembly, compound CA9 organizes into an unprecedented hexagonal columnar mesophase in the condensed state, in which half a molecule constitutes the slice of the column, or into a rectangular mesomorphic-like organization in the presence of apolar solvents such as cyclohexane and dodecane, at a concentration in which fibers form and gelling conditions are fulfilled. In this Col(r)-type arrangement, the organization within the columns depends on the solvent. All of the materials prepared show luminescence, and moreover, a remarkable 3-fold increase in fluorescence intensity was observed in going from the solution to the gel state.

The evolution of organic chemistry has been marked by the incorporation of novel transformations and the development of new synthetic tools, many of which are based on the potential of transition metals in carbon-carbon and carbonheteroatom bond-forming reactions. A number of these synthetic processes mediated by heteroatom-stabilized carbene complexes-particularly chromium and tungsten complexes-have been reported in the last two decades.[1] For instance, the reactivity of unsaturated carbene complexes such as the alkynyl(alkoxy)carbene complexes 1 is determined by the strong electron-acceptor nature of the metalcarbene functionality, which makes these metal species useful substrates for cycloaddition reactions as well as for 1,2-and 1,4-nucleophilic addition reactions. Recent advances in this area have shown that the novel nonstabilized alkynylcarbene complexes 2 are also readily available, [2] thus making studies of their reactivity possible.It is well known that the metal alkynyl(alkoxy)carbenes 1 (Scheme 1) readily undergo conjugate nucleophilic addition to form substituted alkenyl(alkoxy)carbenes B via the allenylmetalate species A, [3] and that intermediates containing a metal-carbon single bond, such as metalates, have a high tendency to expel a neutral metal pentacarbonyl fragment.

No abstract

Heads or tails? Chemo‐, regio‐, and stereoselective access to cross‐ and linear conjugated poly‐ynene scaffolds from alkynyl‐derived group six metal carbenes is reported. The metal carbenes shown (M=Cr, W; TIPS=triisopropylsilyl) readily undergo low‐temperature, tail‐to‐tail dimerization in the presence of potassium tert‐butoxide by reaction at either of the Cβ atoms to provide E‐polyalkynylethenes.

Das einfache (oder wiederholte) Einschieben von Alkineinheiten in Metallcarbenkomplexe, das mit einem Alkoxy‐Austausch einhergeht, liefert unproblematisch schwer fassbare Alkinyl(alkoxy)carbene (siehe Schema) sowie Polyalkinyl(alkoxy)carbene. M = W, Cr, Mo; TMSOTf=Trimethylsilyltrifluormethansulfonat.