Shape-Selective Synthesis of Pentacene Macrocycles and the Effect of Geometry on Singlet Fission.

Pentacene's extraordinary photophysical and electronic properties are highly dependent on intermolecular through-space interactions. Macrocyclic arrangements of chromophores have been shown to provide a high level of control over these interactions, but few examples exist for pentacene due to inherent synthetic challenges. In this work, zirconocene-mediated alkyne coupling was used as a dynamic covalent C-C bond forming reaction to synthesize two geometrically distinct, pentacene-containing macrocycles on a gram scale and in four or fewer steps.

Siloxyaluminate and Siloxygallate Complexes as Models for Framework and Partially Hydrolyzed Framework Sites in Zeolites and Zeotypes.

Anionic molecular models for nonhydrolyzed and partially hydrolyzed aluminum and gallium framework sites on silica, M[OSi(OtBu) ] and HOM[OSi(OtBu) ] (where M=Al or Ga), were synthesized from anionic chlorides Li{M[OSi(OtBu) ] Cl} in salt metathesis reactions. Sequestration of lithium cations with [12]crown-4 afforded charge-separated ion pairs composed of monomeric anions M[OSi(OtBu) ] with outer-sphere [([12]crown-4) Li] cations, and hydroxides {HOM[OSi(OtBu) ] } with pendant [([12]crown-4)Li] cations. These molecular models were characterized by single-crystal X-ray diffraction, vibrational spectroscopy, mass spectrometry and NMR spectroscopy.

A two-coordinate Ni(i) silyl complex: CO insertion and oxidatively-induced silyl migrations.

The synthesis and reactivity of the first open-shell two-coordinate silyl complex, (IPr)Ni-Si(SiMe), (IPr = 1,3-di(2,6-di-iso-propylphenyl)imidazolin-2-ylidene) is reported. Reaction with CO results in a novel insertion product that possesses a distorted geometry. Oxidations of the Ni center, with [CpFe][B(CF)] and PhCCl, result in migratory rearrangements of the silyl ligand, apparently via related silylene intermediates.

Titanocene-Mediated Dinitrile Coupling: A Divergent Route to Nitrogen-Containing Polycyclic Aromatic Hydrocarbons.

A general synthetic strategy for the construction of large, nitrogen-containing polycyclic aromatic hydrocarbons (PAHs) is reported. The strategy involves two key steps: (1) a titanocene-mediated reductive cyclization of an oligo(dinitrile) precursor to form a PAH appended with di(aza)titanacyclopentadiene functionality; (2) a divergent titanocene transfer reaction, which allows final-step installation of one or more o-quinone, diazole, or pyrazine units into the PAH framework. The new methodology enables rational, late-stage control of HOMO and LUMO energy levels and thus photophysical and electrochemical properties, as revealed by UV/vis and fluorescence spectroscopy, cyclic voltammetry, and DFT calculations.

Meningiomas in a male fetus from a hormonally dysequilibrated mother.

Congenital multiple meningiomas in a male fetus of 37 cm length are reported. The tumor was histologically a highly vascular meningioma. An unbalanced level of hormones before and at the beginning of the mother's pregnancy could be ascertained, which resulted in gestational abnormality.