Substituted diaryldiazomethanes and diazofluorenes: structure, reactivity and stability

Reactivity of Nickel Complexes Bearing P(C=X)P Ligands (X = O, N) Toward Diazoalkanes: Evidence for Phosphorus Ylide Intermediates

Nickel carbenes are attracting attention for the development of more sustainable catalysts, among others, for cyclopropanation. Intramolecular trapping of a nickel carbene intermediate with an olefin incorporated in a P(C=C)P Ni pincer complex had previously allowed the isolation of a nickelacyclobutane intermediate and a detailed characterization of its reactivity. Herein, we report the reactivity of related nickel pincer complexes bearing a ketone P(C=O)P or an imine P(C=N)P with diazoalkanes as the carbene precursor. The observed reactivity suggests, in both cases, the reaction of the transient nickel carbene with one of the phosphine arms to form phosphorus ylides that subsequently react with the unsaturated backbone. Density functional theory (DFT) calculations are used to shed light on the mechanisms of these reactions.

Coordination-directed self-assembly of molecular motors: towards a two-wheel drive nanocar

Designing and constructing hierarchical and stimuli-responsive motorized nanocar systems to perform useful tasks on-demand is highly imperative towards molecular nanotechnology. In this work, a most simplified two-wheel nanocar was successfully prepared through a facile strategy of coordination-directed self-assembly. The nanocar meso-AgL2 features a central pseudo square-planar Ag(I) which was bridged by two enantiomeric motors as the wheels that ensure the car moves in the same direction when observed externally. Thanks to the electronic push-pull characteristic of L and ³ILCT triplet sensitization, this nanocar can be driven by visible light up to 500 nm. Furthermore, it could be disassembled into individual motor elements through the addition of pyridine, thus allowing dynamic regulation over the function of the nanocar. Importantly, our STM imaging results showed very organized tilted layered structures for meso-AgL2 on highly oriented pyrolytic graphite (HOPG) that are quite similar to its crystalline ones, paving the way for future single molecule manipulations. The nanocar reported here represents the first example of integrating individual motors into a hierarchical motorized nanocar system via the facile coordination-directed self-assembly method and may offer a good starting point to realize its robotic functions, e.g., metal transportation and release.

A Mononuclear and High-Spin Tetrahedral TiII Complex

A high-spin, mononuclear TiII complex, [(TptBu,Me)TiCl] [TptBu,Me- = hydridotris(3-tert-butyl-5-methylpyrazol-1-yl)borate], confined to a tetrahedral ligand-field environment, has been prepared by reduction of the precursor [(TptBu,Me)TiCl2] with KC8. Complex [(TptBu,Me)TiCl] has a 3A2 ground state (assuming C3v symmetry based on structural studies), established via a combination of high-frequency and -field electron paramagnetic resonance (HFEPR) spectroscopy, solution and solid-state magnetic studies, Ti K-edge X-ray absorption spectroscopy (XAS), and both density functional theory and ab initio (complete-active-space self-consistent-field, CASSCF) calculations. The formally and physically defined TiII complex readily binds tetrahydrofuran (THF) to form the paramagnetic adduct [(TptBu,Me)TiCl(THF)], which is impervious to N2 binding. However, in the absence of THF, the TiII complex captures N2 to produce the diamagnetic complex [(TptBu,Me)TiCl]2(η1,η1;μ2-N2), with a linear Ti═N═N═Ti topology, established by single-crystal X-ray diffraction. The N2 complex was characterized using XAS as well as IR and Raman spectroscopies, thus establishing this complex to possess two TiIII centers covalently bridged by an N22- unit. A π acid such as CNAd (Ad = 1-adamantyl) coordinates to [(TptBu,Me)TiCl] without inducing spin pairing of the d electrons, thereby forming a unique high-spin and five-coordinate TiII complex, namely, [(TptBu,Me)TiCl(CNAd)]. The reducing power of the coordinatively unsaturated TiII-containing [(ΤptBu,Me)TiCl] species, quantified by electrochemistry, provides access to a family of mononuclear TiIV complexes of the type [(TptBu,Me)Ti═E(Cl)] (with E2- = NSiMe3, N2CPh2, O, and NH) by virtue of atom- or group-transfer reactions using various small molecules such as N3SiMe3, N2CPh2, N2O, and the bicyclic amine 2,3:5,6-dibenzo-7-azabicyclo[2.2.1]hepta-2,5-diene.

Enantioselective Si-H Insertion Reactions of Diarylcarbenes for the Synthesis of Silicon-Stereogenic Silanes

We report the first example of enantioselective, intermolecular diarylcarbene insertion into Si-H bonds for the synthesis of silicon-stereogenic silanes. Dirhodium(II) carboxylates catalyze an Si-H insertion using carbenes derived from diazo compounds where selective formation of an enantioenriched silicon center is achieved using prochiral silanes. Fourteen prochiral silanes were evaluated with symmetrical and prochiral diazo reactants to produce a total of 25 novel silanes. Adding an ortho substituent on one phenyl ring of a prochiral diazo enhances enantioselectivity up to 95:5 er with yields up to 98%. Using in situ IR spectroscopy, the impact of the off-cycle azine formation is supported based on the structural dependence for relative rates of diazo decomposition. A catalytic cycle is proposed with Si-H insertion as the rate-determining step, supported by kinetic isotope experiments. Transformations of an enantioenriched silane derived from this method, including selective synthesis of a novel sila-indane, are demonstrated.

Crystal structure of 4,4′-(hydrazonomethylene)diphenol dihydrate, C13H16N2O4

C13H16N2O4, monoclinic, P21/c (no. 14), a = 13.312(2) Å, b = 8.8222(13) Å, c = 12.4784(18) Å, β = 115.350(2)°, V = 1324.4(3) Å3, Z = 4, Rgt(F) = 0.0372, wRref(F2) = 0.0739, T = 293 K.

Discovery of a pyrimidine compound endowed with antitumor activity

Recently, some synthetic nitrogen-based heterocyclic molecules, such as PJ34, have shown pronounced antitumor activity. Therefore, we designed and synthesized new derivatives characterized by a nitrogen-containing scaffold and evaluated their antiproliferative properties in tumor cells. We herein report the effects of three newly synthesized compounds on cell lines from three different human cancers: triple-negative breast cancer, colon carcinoma and glioblastoma. We found that two of these compounds did not affect proliferation, while the third significantly inhibited replication of the three cell lines. Moreover, this third molecule at 20 μM led to the upregulation of p21 and p27 and blockage of the cell cycle at G0/G1; in addition, it induced apoptosis in all three cell lines when used at higher concentrations (30-50 μM). The results demonstrate that this compound is a potent inhibitor of replication, an inducer of apoptosis and a negative regulator of cell cycle progression for cancer cells of different histotypes. Our data suggest a potential role for this new molecule as an interesting and powerful tool for new approaches in treating various cancers.

Cobalt-catalyzed regioselective syntheses of indeno[2,1-c]pyridines from nitriles and diynes bearing propargyl fragments

A highly efficient CoI2/o-phenanthroline catalyzed cycloaddition reaction of diynes bearing TBS protected propargylic alcohol fragments with nitriles has been developed. This methodology offers regioselective access, with good functional group tolerance, to various indeno[2,1-c]pyridine derivatives in moderate to excellent yields. It was found that o-phenanthroline as a bidentate nitrogen ligand showed high efficacy in this cycloaddition reaction.

Surface modification using crosslinking of diamine and a bis(diarylcarbene): synthesis, characterization, and antibacterial activity via binding hydrogen peroxide

Modification of polymer beads with a functionalized bis(arylcarbene) provides access to materials with biocidal properties.

Efficient covalent modification of graphene by diazo chemistry

Functionalized graphene is prepared by an efficient and facile approach via diazo chemistry.

Uncatalysed diaryldiazo cyclopropanations on bicyclic lactams: access to annulated prolines

The uncatalysed cycloaddition of substituted diaryldiazo compounds onto bicyclic unsaturated lactams derived from pyroglutamic acid efficiently leads to highly functionalised azatricyclononanes.

Rh(iii)-catalyzed and alcohol-involved carbenoid C–H insertion into N-phenoxyacetamides using α-diazomalonates

Here a new, mild and efficient Rh(iii)-catalyzed and alcohol-involved carbenoid insertion (ortho-alkylation) intoN-phenoxyacetamides using α-diazomalonates has been developed.

Enantioselective intramolecular C-H insertion reactions of donor-donor metal carbenoids

The first asymmetric insertion reactions of donor–donor carbenoids, i.e., those with no pendant electron-withdrawing groups, are reported. This process enables the synthesis of densely substituted benzodihydrofurans with high levels of enantio- and diastereoselectivity. Preliminary results show similar efficiency in the preparation of indanes. This new method is used in the first enantioselective synthesis of an oligoresveratrol natural product (E-δ-viniferin).

Diarylmethyl Ethers for the Protection of Polyols

The paper discusses the use of diarylmethyl ethers for the protection of hydroxyl groups, in particular, carbohydrate hydroxyl groups. The formation of these ethers can be done nonselectively by the thermal reactions of diryldiazomethanes via a carbene mechanism or by tin(II) halide catalysis of the diazo compounds with diols. The catalyzed reactions give useful regioselectivities.