Oxidative Coupling of Anionic Abnormal N‐Heterocyclic Carbenes: Efficient Access to Janus‐Type 4,4′‐Bis(2H‐imidazol‐2‐ylidene)s

The oxidative coupling of anionic imidazol‐4‐ylidenes protected at the C2 position with [MnCp(CO)₂] or BH₃ led to the corresponding 4,4′‐bis(2H‐imidazol‐2‐ylidene) complexes or adducts, in which the two carbene moieties are connected through a single C?C bond. Subsequent acidic treatment of the later species led to the corresponding 4,4′‐bis(imidazolium) salts in good yields. The overall procedure offers practical access to a novel class of Janus‐type bis(NHC)s. Strikingly, the coplanarity of the two NHC rings within the mesityl derivative 4,4′‐bis(IMes), favored by steric hindrance along with stabilizing intramolecular C?H???π aryl interactions, allows the alignment of the π‐systems and, as a direct consequence, significant electron communication through the bis(carbene) scaffold.     

Catalytic Oxo/Imido Heterometathesis by a Well‐Defined Silica‐Supported Titanium Imido Complex

Grafting Ti(=NtBu)(Me₂Pyr)₂(py)₂ (Me₂Pyr= 2,5‐dimethylpyrrolyl, py=pyridine) onto the surface of silica partially dehydroxylated at 700 °C gives the well‐defined silica‐supported Ti imido complex (≡SiO)Ti(=NtBu)(Me₂Pyr)(py)₂, which is fully characterized by IR and solid‐state NMR spectroscopy as well as elemental and mass balance analyses. While stoichiometric imido‐transfer reactivity is typical for Ti imides, the obtained surface complex is unique in that it enables catalytic transformations involving Ti imido and oxo intermediates. In particular, it efficiently catalyzes imidation of carbonyl compounds with N‐sulfinylamines by oxo/imido heterometathesis.     

α‐Sila‐Dipeptides: Synthesis and Characterization

The first two α‐sila‐dipeptides, 7 and cyclo‐sila‐dipeptide 8 , were synthesized and characterized by several methods, including X‐ray crystallography. Bulky t‐BuMe₂Si substituents provide some kinetic stabilization to the synthesized molecules. 7 and 8 are the first examples of a “Si for C switch” in the central α‐position of an amino acid or a peptide, in which silicon is bonded to both the amino and the carbonyl groups.     

Dearomatization of oxa- or selenadiazolopyridines with neutral nucleophiles as an efficient approach to pharmacologically relevant nitrogen compounds

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CF3-Carbenoid functionalization of N-(pyrimidin-2-yl)indole catalyzed by cobalt complexes: Ligand control of selectivity

The carbonyl cobalt complex Cp*Co(CO)I₂ catalyzes carbenoid Co alkylation of N-(pyrimidin-2-yl)indole with methyl 3,3,3-trifluoro-2-diazopropionate regioselectively giving 2-substituted indole, while the N,N’-ligated cations [CpCo(L)I]⁺ (L = bipy, phen) provide 3-substitution exclusively. The structure of [CpCo(phen)I]PF₆ was investigated by X-ray diffraction.

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Bohr's power series theorem in several variables

Generalizing a classical one-variable theorem of Bohr, we show that if an -variable power series has modulus less than in the unit polydisc, then the sum of the moduli of the terms is less than in the polydisc of radius .

     

Oracle Complexity Separation in Convex Optimization

Journal of Optimization Theory and Applications - Many convex optimization problems have structured objective functions written as a sum of functions with different oracle types (e.g., full...     

On generalized subreducts of Tarski’s algebras of relations with the operation of bi-directional intersection

In the paper, the systems of axioms for classes of groupoids and partially ordered groupoids of relations with the operation of bi-directional intersection are found.