Platinum(II) Olefin Hydroarylation Catalysts: Tuning Selectivity for the anti‐Markovnikov Product

Pt^II complexes containing unsymmetrical (pyridyl)pyrrolide ligands are shown to catalyze the hydroarylation of unactivated alkenes with selectivity for the anti‐Markovnikov product. Substitution on the pyrrolide portion of the ligand allows effective tuning of the selectivity to anti‐Markovnikov alkylarene products, whereas substitution on the pyridyl portion can promote competitive alkenylarene production.     

Reactions of iridium hydride pincer complexes with dioxygen: new dioxygen complexes and reversible O2 binding

The reaction of molecular oxygen with iridium pincer hydride complexes, ((tBu)PCP)Ir(H)(X) [(tBu)PCP = kappa(3)-C(6)H(3)(CH(2)P(t)Bu(2))(2), X = Ph, H, CCPh], results in O(2) induced reductive elimination and formation of the novel dioxygen complexes ((tBu)PCP)Ir(O(2))(n) [n = 1 (), 2 ()].     

Properties of square-pyramidal alkyl-thiolate Fe(III) complexes, including an analogue of the unmodified form of nitrile hydratase

The syntheses and structures of three new coordinatively unsaturated, monomeric, square-pyramidal thiolate-ligated Fe(III) complexes are described, [Fe(III)((tame-N(3))S(2)(Me2))](+) (1), [Fe(III)(Et-N(2)S(2)(Me2))(py)](1-) (3), and [Fe(III)((tame-N(2)S)S(2)(Me2))](2-) (15). The anionic bis-carboxamide, tris-thiolate N(2)S(3) coordination sphere of 15 is potentially similar to that of the yet-to-be characterized unmodified form of NHase. Comparison of the magnetic and reactivity properties of these reveals how anionic charge build up (from cationic 1 to anionic 3 and dianionic 15) and spin-state influence apical ligand affinity. For all of the ligand-field combinations examined, an intermediate S = 3/2 spin state was shown to be favored by a strong N(2)S(2) basal plane ligand field, and this was found to reduce the affinity for apical ligands, even when they are built in. This is in contrast to the post-translationally modified NHase active site, which is low spin and displays a higher affinity for apical ligands. Cationic 1 and its reduced Fe(II) precursor are shown to bind NO and CO, respectively, to afford [Fe(III)((tame-N(3))S(2)(Me))(NO)](+) (18, nu(NuO) = 1865 cm(-1)), an analogue of NO-inactivated NHase, and [Fe(II)((tame-N(3))S(2)(Me))(CO)] (16; nu(CO) stretch (1895 cm(-1)). Anions (N(3)(-), CN(-)) are shown to be unreactive toward 1, 3, and 15 and neutral ligands unreactive toward 3 and 15, even when present in 100-fold excess and at low temperatures. The curtailed reactivity of 15, an analogue of the unmodified form of NHase, and its apical-oxygenated S = 3/2 derivative [Fe(III)((tame-N(2)SO(2))S(2)(Me2))](2-) (20) suggests that regioselective post-translational oxygenation of the basal plane NHase cysteinate sulfurs plays an important role in promoting substrate binding. This is supported by previously reported theoretical (DFT) calculations.     

Indium triflate and ionic liquid-mediated Friedländer synthesis of 2-acylquinolines

Friedländer synthesis of 2-acylquinolines from the reaction of symmetrical and unsymmetrical 1,2-diketones with 2-aminoarylketones in the presence of indium triflate (In(OTf)₃) and ionic liquid gives quantitative yields. Once the reaction was completed, the catalysts can be recovered and subsequently run for next cycles. Results obtained from theoretical studies have been more strengthened by FT-IR, FT-NMR chemical shifts, and structural parameters which were attained with B3LYP/6-31G(d,p) level of theory and the related results were demonstrated with the experimental interpretations.     

Aggregation induced emission (AIE) of trifluoromethyl substituted distyrylbenzenes

The AIE properties of two trifluoromethyl substituted distyrylbenzene model compounds were compared. The fluorescence quantum efficiency of these molecules can be modulated by tuning their subtle solid-state intermolecular interactions.     

Study of the plastic zone near a crack in an anisotropic body

The plastic zone at a crack tip in a finite anisotropic body is studied. A boundary-value problem is formulated in terms of the components of the covariant displacement vector for small strains. Particular attention is given to the case of plain strain. In this case, a numerical solution is found for a long rectangular body with a central crack under tension. As a result, conditions for the occurrence and development of a plastic zone at the crack tip are established. A plastic zone on the lateral surface of the body is discovered. How both zones extend and coalesce is elucidated. The effect of anisotropy on the occurrence of a plastic zone is evaluated __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 7, pp. 29–44, July 2006.     

Protonation and concerted proton-electron transfer reactivity of a bis-benzimidazolate ligated [2Fe-2S] model for Rieske clusters

A model system for biological Rieske clusters that incorporates bis-benzimidazolate ligands ((Pr)bbim)(2-) has been developed ((Pr)bbimH(2) = 4,4-bis(benzimidazol-2-yl)heptane). The diferric and mixed-valence clusters have been prepared and characterized in both their protonated and deprotonated states. The thermochemistry of interconversions of these species has been measured, and the effect of protonation on the reduction potential is in good agreement to that observed in the biological systems. The mixed-valence and protonated congener [Fe(2)S(2)((Pr)bbim)((Pr)bbimH)](Et(4)N)(2) (4) reacts rapidly with TEMPO or p-benzoquinones to generate diferric and deprotonated [Fe(2)S(2)((Pr)bbim)(2)](Et(4)N)(2) (1) and 1 equiv of TEMPOH or 0.5 equiv of p-benzohydroquinones, respectively. The reaction with TEMPO is the first well-defined example of concerted proton-electron transfer (CPET) at a synthetic ferric/ferrous [Fe-S] cluster.     

Short-wave sectioned free-electron masers with Bragg resonators based on the traveling and quasi-critical wave coupling

We consider the possibility of implementation of a free-electron maser with a two-mirror resonator composed of modified and conventional Bragg mirrors, operated in the short-wave part of the millimeter-wave range. The use of a modified Bragg mirror based on the traveling and quasicritical wave coupling at the input of the interaction space permits the transverse-index selection of modes. Amplification of the synchronous co-propagating wave by an electron beam is reached mainly in the regular part of the resonator. Even slight reflections from the conventional output Bragg cavity, which directly couples the co- and counter-propagating traveling waves, turn out to be sufficient for generation of self-excited oscillations. It is shown that the new scheme of a free electron maser ensures the oscillation frequency stabilization with respect to the electron-energy variation. With the optimal choice of the parameters, the oscillation frequency is close to the cutoff frequency of a quasi-critical wave excited in the modified Bragg structure.