Distinct Electronic Effects on Reductive Eliminations of Symmetrical and Unsymmetrical Bis-Aryl Platinum Complexes

Symmetrical bis-aryl platinum complexes (DPPF)Pt(C6H4-4-R)2 (R = NMe2, OMe, CH3, H, Cl, CF3) and electronically unsymmetrical bis-aryl platinum complexes (DPPF)Pt(C6H4-4-R)(C6H4-4-X) (R = CH3, X = NMe2, OMe, H, Cl, F, CF3; R = OMe, X = NMe2, H, Cl, F, CF3; R = CF3, X = H, Cl, NMe2; and R = NMe2, X = H, Cl) were prepared, and the rates of reductive elimination of these complexes in the presence of excess PPh3 are reported. The platinum complexes reductively eliminated biaryl compounds in quantitative yields with first-order rate constants that were independent of the concentration of PPh3. Plots of Log(kobs/kobs(H)) vs Hammett substituent constants (σ) of the para substituents R and X showed that the rates of reductive elimination reactions depended on two different electronic properties. The reductive elimination from symmetrical bis-aryl platinum complexes occurred faster from complexes with more electron-donating para substituents R. However, reductive elimination from a series of electronically unsymmetrical bis-aryl complexes was not faster from complexes with the more electron-donating substituents. Instead, reductive elimination was faster from complexes with a larger difference in the electronic properties of the substituents on the two platinum-bound aryl groups. The two electronic effects can complement or cancel each other. Thus, this combination of electronic effects gives rise to complex, but now more interpretable, free energy relationships for reductive elimination

Effects of Bases and Halides on the Amination of Chloroarenes Catalyzed by Pd(P<i>t</i>Bu₃)₂

We report a detailed study of the effects of anions on the rates of the amination of aryl halides catalyzed by palladium complexes of the hindered alkylmonophosphine PtBu3. These reactions occur by turnover-limiting oxidative addition. The extent of the dependence of the rates on the concentration and identity of bases was found to depend on the electronic properties of the haloarenes. The rates of reactions of electron-rich and electron-neutral chloroarenes were independent of the concentration of the bulky alkoxide base OCEt3-, but they were dependent on the concentrations of the less hindered OtBu- and the softer 2,4,6-tri-tert-butylphenoxide bases. The reactions were fastest when 2,4,6-tri-tert-butylphenoxide was used as base and slowest when NaOCEt3 was used as base. A concurrent reaction pathway involving simultaneous oxidative addition of chloroarenes to [Pd(PtBu3)] and [(PtBu3)Pd(OR)]- may explain the dependence of the rates of reactions of electron-rich and electron-neutral chloroarenes on the identity and concentration of bases. The rates of reactions of electron-poor chloroarenes and the reactions of bromoarenes were independent of the concentration of OCEt3-, OtBu-, or 2,4,6-tri-tert-butylphenoxide bases but were dependent on the identity of bases, even though an adduct of the base did not accumulate in any observable amounts. Further, long induction periods were observed for the reactions of electron-poor chloroarenes. These long induction periods suggest that the complex kinetic behavior could result from the generation of several catalytically active species

Ultrahigh Density Alignment of Carbon Nanotube Arrays by Dielectrophoresis

We report ultrahigh density assembly of aligned single-walled carbon nanotube (SWNT) two-dimensional arrays via AC dielectrophoresis using high-quality surfactant-free and stable SWNT solutions. After optimization of frequency and trapping time, we can reproducibly control the linear density of the SWNT between prefabricated electrodes from 0.5 SWNT/μm to more than 30 SWNT/μm by tuning the concentration of the nanotubes in the solution. Our maximum density of 30 SWNT/μm is the highest for aligned arrays via any solution processing technique reported so far. Further increase of SWNT concentration results in a dense array with multiple layers. We discuss how the orientation and density of the nanotubes vary with concentrations and channel lengths. Electrical measurement data show that the densely packed aligned arrays have low sheet resistances. Selective removal of metallic SWNTs via controlled electrical breakdown produced field-effect transistors with high current on−off ratio. Ultrahigh density alignment reported here will have important implications in fabricating high-quality devices for digital and analog electronics

Oxidative Addition of Phenyl Bromide to Pd(BINAP) vs Pd(BINAP)(amine). Evidence for Addition to Pd(BINAP)

The rates of oxidative addition of phenyl bromide to [Pd(BINAP)2] have been measured in the presence and absence of added amine to assess a previous hypothesis that addition to [Pd(BINAP)(amine)] is faster than addition to [Pd(BINAP)]. These data show that addition to the amine complex is not faster than addition to [Pd(BINAP)]. Instead, they are consistent with oxidative addition, even in the presence of amine, to [Pd(BINAP)] as the major pathway. These data underscore the value of studying the stoichiometric reactions of isolated complexes when assessing the mechanism of a catalytic process

Cu-Catalyzed Couplings of Aryl Iodonium Salts with Sodium Trifluoromethanesulfinate

A convenient method for the preparation of aryl trifluoromethylsulfones from the reactions of diaryliodonium salts with sodium trifluoromethanesulfinate in the presence of copper catalysts is described. Cuprous oxide in DMF was found to be the optimal catalyst for the reaction. The reaction conditions are tolerant of various functional groups as well as of various counteranions of the iodonium salt. The synthetic utility of the process is demonstrated by performing the reaction on a preparative scale (88 g)

Semiconducting Enriched Carbon Nanotube Aligned Arrays of Tunable Density and Their Electrical Transport Properties

We demonstrate assembly of solution-processed semiconducting enriched (99%) single-walled carbon nanotubes (s-SWNTs) in an array with varying linear density via ac dielectrophoresis (DEP) and investigate detailed electronic transport properties of the fabricated devices. We show that (i) the quality of the alignment varies with frequency of the applied voltage and that (ii) by varying the frequency and concentration of the solution, we can control the linear density of the s-SWNTs in the array from 1/μm to 25/μm. The DEP assembled s-SWNT devices provide the opportunity to investigate the transport property of the arrays in the direct transport regime. Room temperature electron transport measurements of the fabricated devices show that with increasing nanotube density the device mobility increases while the current on–off ratio decreases dramatically. For the dense array, the device current density was 16 μA/μm, on-conductance was 390 μS, and sheet resistance was 30 kΩ/◻. These values are the best reported so far for any semiconducting nanotube array

Sequential Catalytic Isomerization and Allylic Substitution. Conversion of Racemic Branched Allylic Carbonates to Enantioenriched Allylic Substitution Products

A catalytic protocol for the conversion of readily accessible racemic, branched aromatic allylic esters to branched allylic amines, ethers, and alkyls has been developed. Palladium-catalyzed isomerization of branched allylic esters to terminal allylic esters, followed by sequential iridium-catalyzed allylic substitution, gave the branched allylic products in good yield with high regioisomeric and enantiomeric selectivity. Both electron-rich and electron-poor branched allylic esters gave products in >90% ee. High enantiomeric excesses were also observed for the products from the reactions of 2-thienyl acetates and dienyl carbonates

<i>In silico</i> structural analysis of secretory clusterin to assess pathogenicity of mutations identified in the evolutionarily conserved regions

Clusterin (CLU) is a secreted glycoprotein, heterodimeric in nature, and is expressed in a wide variety of tissues and body fluids such as serum and plasma. CLU has also been known to be a promising biomarker for cell death, malignancy, cancer progression, and resistance development. However, the lack of a CLU crystal structure obstructs understanding the possible role of reported mutations on the structure, and the subsequent effects on downstream signaling pathways and cancer progression. Considering the importance of crystal structure, a model structure of the pre-secretory isoform of CLU was built to predict the effect of mutations at the molecular level. Ab initio model was built using RaptorX, and loop refinement and energy minimization were carried out with ModLoop, ModRefiner, and GalaxyWeb servers. The cancer associated mutational spectra of CLU was retrieved from the cBioPortal server and 117 unique missense mutations were identified. Evolutionarily conserved regions and pathogenicity of mutations identified in CLU were analyzed using ConSurf and Rhapsody, respectively. Furthermore, sequence and structure-based mutational analysis were carried out with iSTABLE, DynaMut and PremPS servers. Molecular dynamics simulations were carried out with GROMACS for 50 ns to determine the stability of the wild type and mutant protein structures. A dynamically stable model structure of pre-secretory CLU (psCLU) which has high concurrence with the sequence based secondary structure predictions has been explored. Changes in the intra-atomic interactions and folding pattern between wild type and mutant structures were observed. To our conclusion, eleven mutations with the highest structural and functional significance have been predicted to have pathogenic and deleterious effects. Communicated by Ramaswamy H. Sarma</p

2-Substituted <i>m</i>-Xylylene-Bridged Dicobaloximes: Structure−Property Relationship Using Variable-Temperature ¹H NMR Study^†

m-Xylylene-bridged dicobaloximes with a substituent at the 2-position having varying electronic and steric properties have been synthesized and characterized by 1H and 13C NMR spectroscopy. The variable-temperature 1H NMR study of these complexes shows that the electronic cis influence is an important phenomenon for the Co−C bond rotation. The coalescence temperature of the dioxime protons correlates well with the ortho substituent constant. The crystal structure of a 2-nitro-m-xylylene-bridged dicobaloxime, Py(dmgH)2Co-CH2-(2-NO2-1,3-C6H3)-CH2-Co(dmgH)2Py, is reported. The X-ray structural data support the 1H NMR findings

2-Substituted <i>m</i>-Xylylene-Bridged Dicobaloximes: Structure−Property Relationship Using Variable-Temperature ¹H NMR Study^†

m-Xylylene-bridged dicobaloximes with a substituent at the 2-position having varying electronic and steric properties have been synthesized and characterized by 1H and 13C NMR spectroscopy. The variable-temperature 1H NMR study of these complexes shows that the electronic cis influence is an important phenomenon for the Co−C bond rotation. The coalescence temperature of the dioxime protons correlates well with the ortho substituent constant. The crystal structure of a 2-nitro-m-xylylene-bridged dicobaloxime, Py(dmgH)2Co-CH2-(2-NO2-1,3-C6H3)-CH2-Co(dmgH)2Py, is reported. The X-ray structural data support the 1H NMR findings