Ferromagnetic Coupling through Spin Polarization in a Dinuclear Copper(II) Metallacyclophane

No Abstract     

TGSA: A molecular superposition program based on topo‐geometrical considerations

In this article, a new molecular alignment procedure to provide general‐purpose, fast, automatic, and user‐intuitive three‐dimensional molecular alignments is presented. This procedure, called Topo‐Geometrical Superposition Approach (TGSA), is only based on comparisons of atom types and interatomic distances; hence, the procedure can handle large molecular sets within affordable computational costs. The method is able to accurately align 3D structures using the common molecular substructures, as inferred by the bonding pattern (atom correspondences), where present. The algorithm has been implemented into a program named TGSA99, and it has been tested over eight different molecular sets: flavilium salts, amino acids, indole derivatives, AZT, steroids, anilide derivatives, poly‐aromatic‐hydrocarbons, and inhibitors of thrombine. The TGSA algorithm performance is evaluated by means of computational time, number of superposed atoms, and index of fit between the compared structures. © 2000 John Wiley & Sons, Inc. J Comput Chem 22: 255–263, 2001     

New POCOP-type pincer complexes of Nickel(II)

The pincer complex [(POCOP)Ni(NCMe)][OSO₂CF₃] (1: POCOP = {2,6-(i-Pr₂PO)₂C₆H₃}) undergoes an acetonitrile substitution reaction in the presence of CN(t-Bu), KCN, and KOCN to give the new complexes [(POCOP)Ni{CN(t-Bu)}][O₃SCF₃] and (POCOP)Ni(X) (X = CN and NCO). The Ni-CN derivative is also obtained from a gradual decomposition of the Ni-CN(t-Bu) derivative, while the aquo derivative [(POCOP)Ni(OH₂)][O₃SCF₃] was obtained from slow hydrolysis of (POCOP)Ni(OSO₂CF₃). All new complexes have been characterized spectroscopically and by X-ray crystallography. IR and solid state structural data indicate that Ni-L/X interactions are dominated by ligand-to-metal σ-donation; presence of little or no π-backbonding is consistent with the electrophilicity of the cationic fragment [(POCOP)Ni]⁺.     

Stereoselective organocatalytic one-pot α,α-bifunctionalization of acetaldehyde by a tandem Mannich reaction/electrophilic amination

The first asymmetric organocatalyzed one-pot α,α-bifunctionalization of acetaldehyde with two different electrophiles is described. A diarylprolinol silyl ether-catalyzed reaction of acetaldehyde with an imine and di-tert-butyl azodicarboxylate affords syn-2,3-diaminoalcohols with excellent ee values of up to 98%. This methodology was successfully applied to the synthesis of a chiral α,β-diaminocarboxylic acid.     

DFT Mechanistic Study on Diene Metathesis Catalyzed by Ru‐Based Grubbs–Hoveyda‐Type Carbenes: The Key Role of π‐Electron Density Delocalization in the Hoveyda Ligand

The catalytic activity and catalyst recovery of two heterogenized ruthenium‐based precatalysts ( H and NO₂(4) ) in diene ring‐closing metathesis have been studied by means of density functional calculations at the B3LYP level of theory. For comparison and rationalization of the key factors that lead to higher activities and higher catalyst recoveries, four other Grubbs–Hoveyda complexes have also been investigated. The full catalytic cycle (catalyst formation, propagation, and precatalyst regeneration) has been considered. DFT calculations suggest that either for the homogeneous and heterogenized systems the activity of the catalysts mainly depends on the ability of the precursor to generate the propagating carbene. This ability does not correlate with the traditionally identified key factor, the Ru???O interaction strength. In contrast, precatalysts with lower alkoxy‐dissociation energy barriers and lower stabilities compared with the propagating carbene also present larger C1? C2 bond length (i.e., lower π character of the C? C bond that exists between the metal–carbene (Ru?C) and the phenyl ring of the Hoveyda ligand). Catalyst recovery, regardless of whether a release–return mechanism occurs or not, is also mainly determined by the π delocalization. Therefore, future Grubbs–Hoveyda‐type catalyst development should be based on fine‐tuning the π‐electron density of the phenyl moiety, with the subsequent effect on the metalloaromaticity of the ruthenafurane ring, rather than considering the modification of the Ru???O interaction.