Regio- and stereoselective lithiation of 2,3-diphenylaziridines: a multinuclear NMR investigation

The alpha-lithiation-trapping sequence of trans-N-alkyl-2,3-diphenylaziridines (s-BuLi or s-BuLi/TMEDA), taking place with a stereochemistry which dramatically depends on the solvent coordinating ability (inversion of configuration in THF and retention in toluene), has been carefully investigated. 1H,13C, and 7Li multinuclear NMR investigations at low temperature suggest that two differently configured lithiated aziridines (monomeric cis-1-Li in THF and dimeric trans-1-Li in toluene) are involved.     

Site selectivity in the protonation of a phosphinito bridged Pt(I)-Pt(I) complex: a combined NMR and density-functional theory mechanistic study

The protonation of the dinuclear phosphinito bridged complex [(PHCy2)Pt(mu-PCy2){kappa(2)P,O-mu-P(O)Cy2}Pt(PHCy2)] (Pt-Pt) (1) by Br?nsted acids affords hydrido bridged Pt-Pt species the structure of which depends on the nature and on the amount of the acid used. The addition of 1 equiv of HX (X = Cl, Br, I) gives products of formal protonation of the Pt-Pt bond of formula syn-[(PHCy2)(X)Pt(mu-PCy2)(mu-H)Pt(PHCy2){kappaP-P(O)Cy2}] (Pt-Pt) (5, X = Cl; 6, X = Br; 8, X = I), containing a Pt-X bond and a dangling kappa P-P(O)Cy2 ligand. Uptake of a second equivalent of HX results in the protonation of the P(O)Cy2 ligand with formation of the complexes [(PHCy2)(X)Pt(mu-PCy2)(mu-H)Pt(PHCy2){kappaP-P(OH)Cy2}]X (Pt-Pt) (3, X = Cl; 4, X = Br; 9, X = I). Each step of protonation is reversible, thus reactions of 3, 4, with NaOH give, first, the corresponding neutral complexes 5, 6, and then the parent compound 1. While the complexes 3 and 4 are indefinitely stable, the iodine analogue 9 transforms into anti-[(PHCy2)(I)Pt(mu-PCy2)(mu-H)Pt(PHCy2)(I)] (Pt-Pt) (7) deriving from substitution of an iodo group for the P(OH)Cy2 ligand. Complexes 3 and 4 are isomorphous crystallizing in the triclinic space group P1 and show an intramolecular hydrogen bond and an interaction between the halide counteranion and the POH hydrogen. The occurrence of such an interaction also in solution was ascertained for 3 by (35)Cl NMR. Multinuclear NMR spectroscopy (including (31)P-(1)H HOESY) and density-functional theory calculations indicate that the mechanism of the reaction starts with a prior protonation of the oxygen with formation of an intermediate (12) endowed with a six membered Pt(1)-X...H-O-P-Pt(2) ring that evolves into thermodynamically stable products featuring the hydride ligand bridging the Pt atoms. Energy profiles calculated for the various steps of the reaction between 1 and HCl showed very low barriers for the proton transfer and the subsequent rearrangement to 12, while a barrier of 29 kcal mol(-1) was found for the transformation of 12 into 5.     

Regio- and stereoselective lithiation and electrophilic substitution reactions of N-Alkyl-2,3-diphenylaziridines: solvent effect

[structure: see text]. The lithiation reaction of cis- and trans-N-alkyl-2,3-diphenylaziridines has been investigated. While cis-diphenylaziridines do not undergo any lithiation upon treatment with organolithiums, the lithiation reaction of the trans counterparts is completely alpha-regioselective and the stereochemical course of the lithiation-trapping sequence is solvent dependent: inversion of configuration in coordinating solvents (THF or toluene/crown ether) and retention in hexane, ether, or toluene. The preparation of stereodefined functionalized N-alkyl-2,3-diphenylaziridines is described.     

Investigation into the reactivity of the coordinatively unsaturated phosphonodithioato [Ni(MeOpdt)2] towards 2,4,6-tris(2-pyridyl)-1,3,5-triazine: goals and achievements

The reaction between the coordinatively unsaturated phosphonodithioato complex [Ni(MeOpdt)2] (1) [MeOpdt = (MeO)(4-MeOC(6)H(4))PS2-] and tptz [2,4,6-tris(2-pyridyl)-1,3,5-triazine] has been investigated. Spectrophotometric and conductometric titrations showed the formation of a neutral and an ionic species, i.e. [Ni(MeOdtp)2(tptz)] (2) and [Ni(tptz)2](MeOdtp)2 (3), in correspondence to 1 : 1 and 2 : 1 tptz : ratios, respectively. XRD studies confirmed the formation of both complexes isolated in the compounds 2.MeOH and 3.4H(2)O. In the neutral complex 2 the central Ni(II) ion features a distorted octahedral coordination, achieved through three N-atoms of tptz and three S-atoms belonging to two MeOpdt anions, one of which unexpectedly acts as a monodentate S-donor. In 3.4H(2)O, the two phosphonodithioato anions are non-coordinating and counterbalance the charge of the [Ni(tptz)2](2+) distorted octahedral complex. From the reaction 2 of with I2 and Br2, crystals of [Ni(tptz)2](I3)2 (5) and [Ni(tptz)Br(micro-Br)]2 (6) have been obtained. The dinuclear complex 6 features a structure showing tubular canals with openings of about 6 x 6 A.     

Synthesis and characterization of positively capped CdTe quantum wires that exhibit strong luminescence in aqueous media

The novelty of the current work lies in the versatile synthesis of highly luminescent water-soluble CdTe quantum rods (QR) which to the best of our knowledge are the first known water-soluble QR carrying positively charged stabilizer.     

Template Assembly of Polyiodide Networks at Complexed Metal Cations: Synthesis and Structures of [Pd2Cl2([18]aneN2S4)]1.5I5(I3)2 and [K([15]aneO5)2]I9

The cations [Pd ₂ Cl ₂ L] ²⁺ and [KL ₂ ^{′ +} (L = [18]aneN₂S₄, L′ =[15]aneO₅) have been used as templates for the synthesis of unique three-dimensional polyiodide networks. The metal cations in [Pd₂Cl₂L]_1.5I₅(I₃)₂ are linked into infinite chains by pairwise hydrogen bonding; the resulting cationic polymers run through channels formed by the extended polyiodide network. [KL₂^′]I₉ shows a three-dimensional network of puckered cubic cages of I₉⁻ ions whose cavities are occupied by the metal cations (section from the structure shown on the right).     

Bond-based peridynamic modelling of singular and nonsingular crack-tip fields

A static meshfree implementation of the bond-based peridynamics formulation for linearly elastic solids is applied to the study of the transition from local to nonlocal behavior of the stress and displacement fields in the vicinity of a crack front and other sources of stress concentration. The long-range nature of the interactions between material points that is intrinsic to and can be modulated within peridynamics enables the smooth transition from the square-root singular stress fields predicted by the classical (local) linear theory of elasticity, to the nonsingular fields associated with nonlocal theories. The accuracy of the peridynamics scheme and the transition from local to nonlocal behavior, which are dictated by the lattice spacing and micromodulus function, are assessed by performing an analysis of the boundary layer that surrounds the front of a two dimensional crack subjected to mode-I loading and of a cracked plate subjected to far-field tension.     

Intramolecular cyclization of 4,7‐bis(2‐bromo­acetyl)‐1‐thia‐4,7‐di­azacyclo­nonane

The reaction of 1‐thia‐4,7‐di­azacyclo­nonane with bromo­acetyl bromide in CHCl₃ affords the unexpected salt 4‐(2‐bromo­acetyl)‐8‐oxo‐1‐thionia‐4,7‐di­aza­bi­cyclo­[5.2.2]­un­decane bromide, C₁₀H₁₆BrN₂O₂S⁺·Br⁻. Two units of the salt are linked by S⋯Br contacts about a crystallographic inversion centre, thus forming dimers that are linked by Br⋯Br contacts into extended ribbons. S⋯O contacts between these ribbons generate a two‐dimensional sheet.     

An easy access to unsymmetrically substituted 4,4′-bi-1,2,3-triazoles

A convenient synthesis of 4-alkynyl-1,2,3-triazoles and novel unsymmetrically substituted 4,4′-bi-1,2,3-triazole derivatives has been devised starting from easily available 1-trimethylsilyl-1,3-butadiyne. The starting compound was reacted with several azides, leading to 4-(silylalkynyl)-1,2,3-triazoles, which were easily transformed into 4-arylalkynyl-1,2,3-triazoles by a Pd catalyzed coupling reaction with aryl halides, or into novel 4,4′-bi-1,2,3-triazole derivatives by a subsequent cyclization reaction with azides.