Synthesis of silver nanoprisms in formamide

Polygonal (mainly triangular) silver nanoprisms were prepared by reducing silver perchlorate in formamide in the presence of polyethylene glycol (PEG) at room temperature. The reduction of silver ions by formamide leads to the deposition of arrays of triangular shaped silver nanoparticles on the glass walls of the container, accompanied by evolution of CO2 gas. In the presence of poly(N-vinyl-2-pyrrolidone) (PVP) and PEG (1:1), both nanospheres and nanoprisms are formed.     

(RO)(2)Ta[tris(2-oxy-3,5-dimethylbenzyl)amine]: structure and lactide polymerization activities

The novel atrane-like six-coordinate (RO)(2)TaL complexes [where R = Me or Et and L = tris(2-oxy-3,5-dimethylbenzyl)amine] containing three six-membered rings have been synthesized and characterized. The R = Me complex is the first group 5 representative of this class of compounds structurally characterized by X-ray means. Somewhat surprisingly, these compounds failed to function as single-site initiators for the polymerization of l-LA to isotactic PLA and rac-LA to atactic PLA, whereas Ta(OEt)(5) and two titanium analogues ROTiL (where R = 2,6-di-i-PrC(6)H(3) and i-Pr) as well as Ti(O-i-Pr)(4) were effective catalysts for both polymerizations.     

An innovative synthesis of dibenzofurans through a carbanion-induced ring transformation reaction

An innovative route for the synthesis of substituted dibenzofurans has been delineated through a ring transformation reaction of suitably functionalized 2H-pyran-2-ones by reaction with 7-methoxybenzofuran-3-one, in high yield. The novelty of the procedure lies in the creation of an aromatic ring from a 2H-pyran-2-one involving the -COCH₂-moiety of the substrate.     

Complexes of 3,3′-Oxybis[(diphenylphosphino)methylbenzene] with Ni(II), Pd(II), Pt(II), Rh(I), and Ag(I). How Important is Backbone Rigidity in the Formation of trans-Spanning Bidenatate Chelates??

The bidentate diphosphine ligand, 3,3′-oxybis[(dipenylphosphino)methylbenzene] ( 1 ) forms monomeric, trans-square-planar complexes MX₂( 1 ) (M = Ni, Pd, Pt; X = Cl^?, Br^? I^?, and, in part, N, NCS^?, CN^?, NO) as well as Pt(H)Cl( 1 ), Pt(H)Br( 1 ), and RhCl(CO)( 1 ). Polymeric species have been observed with substitutionally inert metal centres: trans-[PtCl₂( 1 )]₂ and cis-[PtCl₂( 1 )]_n (mean value of n ≈ 4–5) ³¹P-NMR, and selected IR and UV/VIS parameters are reported. Ligand 1 shows a marked preference for trans-spanning and monomeric chelate formation, despite its various degrees of freedom of internal rotation in the lignad backbone. The readily available ligand 1 as well as analogues with other donor atoms, therefore, appear useful in most potential applications of trans-spanning chelate ligands. The crystal structure of AgCl( 1 )·0.5 (CH₃)₂C?O·0.39 C₆H₁₂ (space group C2/c,a = 21.02 Å, b = 14.57 Å, c = 24.79 Å, β = 99.77°, V = 7531.4 ų, Z = 8) confirms the presence of three-coordinate Ag( I ), with a coordination intermediate between a trigonal-planar and a T-shaped geometry (P-Ag-P = 145.61(8)°).     

ZrCl4 as a new and efficient catalyst for the opening of epoxide rings by amines

Zirconium(IV) chloride catalyses the nucleophilic opening of epoxide rings by amines leading to the efficient synthesis of β-amino alcohols. The reaction works well with aromatic and aliphatic amines in short times at room temperature in the absence of solvent. Exclusive trans stereoselectivity is observed for cyclic epoxides. Aromatic amines exhibit excellent regioselectivity for preferential nucleophilic attack at the sterically less hindered position during the reaction with unsymmetrical epoxides. However, in case of styrene oxide, selective formation of the benzylic amine was observed during the reactions with aromatic amines.     

Kinetics and mechanisms of oxidation by metalions. Part XI(1). Kinetics of the osmium(VIII)-catalysed oxidation of glycols by alkaline hexacyanoferrate(III)

Summary The kinetics of the Os^VIII-catalysed oxidation of glycols by alkaline hexacyanoferrate(III) ion exhibits zerothorder dependence in [Fe(CN) ₆ ^3– ] and first-order dependence in [OsO₄]. The order with respect to glycols is less than unity, whereas the rate dependence on [OH^–] is a combination of two rate constants; one independent of and the other first-order in [OH^–]. These observations are commensurate with a mechanism in which two complexes, [OsO₄(H₂O)G]^– and [OsO₄(OH)G]^2–, are formed either from [OsO₄(H₂O)(OH)]^– or [OsO₄(OH)₂]^2– and the glycol GH, or by [OsO₄(H₂O)₂] and [OsO₄(H₂O)(OH)]^– and the glycolate ion, G^–, which is in equilibrium with the glycol GH through the reaction between GH and OH^–. Hence there is an ambiguity about the true path for the formation of the two Os^VIII-glycol complexes. A reversal in the reactivity order of glycols in the two rate-determining steps, despite the common attack of OH^– ion on the two species of Os^VIII-complexes, indicates that the two complexes are structurally different because S changes from the negative (corresponding to k₁₁) to positive (related to k₂).     

Polarographic study of the reaction between cerium(IV) and thiocyanate

Summary Polarographic studies have been made of the reaction between Cerium(IV) and potassium thiocyanate in acidic medium. Ce^IVin the concentration range 2 · 10^–4 M to 5 · 10^–3 M was found to be reduced to Ce^III by thiocyanate ion. One equivalent of thiocyanate reduced 4–6 equivalents of Ce^IV in the concentration range studied.

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Zusammenfassung Die Reaktion zwischen Cer^IV und Kaliumthiocyanat wurde in saurem Medium polarographisch untersucht. Cer^III wurde im Bereich von 2 · 10^–4 m bis 5 · 10^–3 m von Thiocyanat zu Cer^III reduziert. In diesem Konzentrationsbereich entsprachen einem Äquivalent Thiocyanat 4–6 Äquivalente Cer^IV.

     

Electron transfer (oxidation) of complexes between bifunctional phenols and DMSO in non-polar surroundings

Pulse-radiolysis reactions were performed to study the effect of hydrogen bonding to dimethyl sulfoxide (DMSO) on the oxidation of dihydroxy benzene and biphenyl diols to phenoxyl radicals. It was observed that with DMSO as the hydrogen-bond acceptor, the oxidation process proceeds via proton-coupled electron transfer in the case of hydroquinone. For resorcinol, DMSO acts in a similar way as in the case of hydroquinone. For other biphenols, viz., 2,2′- and 4,4′-biphenyl diols, it was found that DMSO had no effect on the electron transfer. The results are explained based on the ionization potential and structure of the phenol derivatives which probably depends on the rotation of the OH bond causing different electron distribution in the transient conformation.     

Formation of spatially patterned colloidal photonic crystals through the control of capillary forces and template recognition

We report the formation of microscopic patterns of substrate-supported, 3D planar colloidal crystals using physical confinement in conjunction with surfaces displaying predetermined binary patterns of hydropholicity. The formation process involves a primary self-assembly wherein nano- and microscale colloids order into a photonic fcc lattice via capillary interactions followed by a secondary template-induced crystal cleavage step. Following this method, arbitrary arrays of pattern elements, which preserve structural and orientational properties of the parent crystal, can be easily obtained.