A Versatile Ligand Platform that Supports Lewis Acid Promoted Migratory Insertion

A helping hand: Incorporation of Group 2 Lewis acids into a macrocycle appended to a phosphine ligand attached to a rhenium carbonyl complex promotes otherwise unfavorable transformations of coordinated CO (see scheme; M=Ca, Sr). These Lewis acids form relatively weak M-O bonds, thereby enabling release of organic products from the metal center

Palladium catalysed alylic-C-F bond formation and activation

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Reductive coupling of carbon monoxide in carbonyl complexes with pendant Lewis acids or bases

An approach to conversion of light alkanes to value added mols. involves conversion via steam reforming to syngas, a mixt. of carbon monoxide and dihydrogen, with subsequent conversion to chems. and liq. fuels. Heterogeneous Fischer-Tropsch synthesis of hydrocarbons and oxygenates is well established, but selectvity is poor and subsequent upgrading to useful products is required. Recent progress has been made aimed at developing a homogeneous, more selective catalyst system for converting syngas to Cn>1 products by an approach involving two metals: one to coordinate carbon monoxide and to promote C-C bond formation, another to activate H2 and deliver it to CO and its partially reduced fragments. Recent progress toward using transition metal carbonyls with appended Lewis acid or bases will be discussed

The rippled β-sheet layer configuration-a novel supramolecular architecture based on predictions by Pauling and Corey.

The rippled β-sheet is a peptidic structural motif related to but distinct from the pleated β-sheet. Both motifs were predicted in the 1950s by Pauling and Corey. The pleated β-sheet was since observed in countless proteins and peptides and is considered common textbook knowledge. Conversely, the rippled β-sheet only gained a meaningful experimental foundation in the past decade, and the first crystal structural study of rippled β-sheets was published as recently as this year. Noteworthy, the crystallized assembly stopped at the rippled β-dimer stage. It did not form the extended, periodic rippled β-sheet layer topography hypothesized by Pauling and Corey, thus calling the validity of their prediction into question. NMR work conducted since moreover shows that certain model peptides rather form pleated and not rippled β-sheets in solution. To determine whether the periodic rippled β-sheet layer configuration is viable, the field urgently needs crystal structures. Here we report on crystal structures of two racemic and one quasi-racemic aggregating peptide systems, all of which yield periodic rippled antiparallel β-sheet layers that are in excellent agreement with the predictions by Pauling and Corey. Our study establishes the rippled β-sheet layer configuration as a motif with general features and opens the road to structure-based design of unique supramolecular architectures

Development of Improved Amidoquinoline Polyolefin Catalysts with Ultrahigh Molecular Weight Capacity

A new synthetic route to amidoquinoline olefin polymerization catalysts has been developed involving significantly less expensive and more readily available starting materials. The new methodology was used to prepare <i>N</i>-mesityl-2-methylquinolin-8-amine, which in turn was converted into trialkyl complexes of Hf, Zr, and Ti. The new complexes were characterized by elemental analysis, 1D and 2D NMR spectroscopy, and X-ray crystallography. A batch reactor ethylene/1-octene copolymerization evaluation at 140 °C showed that the new Hf congener outperformed a series of previously reported molecular olefin polymerization catalysts. In particular, the new Hf catalyst exhibits excellent activity and a remarkable capacity to produce ultrahigh molecular weight copolymers at elevated reaction temperatures