Selective ring-opening metathesis polymerization (ROMP) of cyclobutenes. Unsymmetrical ladderphane containing polycyclobutene and polynorbornene strands.

At 0 °C in THF in the presence of Grubbs first generation catalyst, cyclobutene derivatives undergo ROMP readily, whereas norbornene derivatives remain intact. When the substrate contains both cyclobutene and norbornene moieties, the conditions using THF as the solvent at 0 °C offer a useful protocol for the selective ROMP of cyclobutene to give norbornene-appended polycyclobutene. Unsymmetrical ladderphane having polycyclobutene and polynorbornene as two strands is obtained by further ROMP of the norbornene appended polycyclobutene in the presence of Grubbs first generation catalyst in DCM at ambient temperature. Methanolysis of this unsymmetrical ladderphane gives polycyclobutene methyl ester and insoluble polynorbornene-amide-alcohol. The latter is converted into the corresponding soluble acetate. Both polymers are well characterized by spectroscopic means. No norbornene moiety is found to be incorporated into polycyclobutene strand at all. The double bonds in the polycyclobutene strand are mainly in cis configuration (ca 70%), whereas the E/Z ratio for polynorbornene strand is 8:1.

Majority-Rules-Type Helical Poly(quinoxaline-2,3-diyl)s as Highly Efficient Chirality-Amplification Systems for Asymmetric Catalysis.

A highly efficient majority-rules effect of poly(quinoxaline-2,3-diyl)s (PQXs) bearing 2-butoxymethyl chiral side chains at the 6- and 7-positions was established and attributed to large ΔG(h) values (0.22-0.41 kJ mol(-1)), which are defined as the energy difference between P- and M-helical conformations per chiral unit. A PQX copolymer prepared from a monomer derived from (R)-2-octanol (23% ee) and a monomer bearing a PPh2 group adopted a single-handed helical structure (>99%) and could be used as a highly enantioselective chiral ligand in palladium-catalyzed asymmetric reactions (products formed with up to 94% ee), in which the enantioselectivity could be switched by solvent-dependent inversion of the helical PQX backbone.

mer-Bis(1,4-dibenzoylthiosemicarbazidato-kappa3O,N,O')cobalt(II).

The title complex, [Co(C(15)H(12)N(3)O(2)S)(2)], consists of an octahedrally coordinated Co(II) ion, with two crystallographically independent 1,4-dibenzoylthiosemicarbazidate ligands in a tridentate mer coordination [Co-O = 2.064 (3)-2.132 (3) A and Co-N = 2.037 (3)-2.043 (3) A]. There are intermolecular N-H...S hydrogen bonds involving one ligand and strong pi-pi stacking interactions involving the other ligand, resulting in a three-dimensional supramolecular framework. The hydrogen bonds and pi-pi interactions, as well as different intramolecular aryl-benzamide H-C...H(-N) distances, give rise to a difference in conformation between the two ligands.