High magnetic field induced charge density wave states in a quasi-one dimensional organic conductor

We have measured the high field magnetoresistence and magnetization of quasi-one- dimensional (Q1D) organic conductor (Per)2Pt(mnt)2 (where Per = perylene and mnt = maleonitriledithiolate), which has a charge density wave (CDW) ground state at zero magnetic field below 8 K. We find that the CDW ground state is suppressed with moderate magnetic fields of order 20 T, as expected from a mean field theory treatment of Pauli effects[W. Dieterich and P. Fulde, Z. Physik 265, 239 - 243 (1973)]. At higher magnetic fields, a new, density wave state with sub-phases is observed in the range 20 to 50 T, which is reminiscent of the cascade of field induced, quantized, spin density wave phases (FISDW) observed in the Bechgaard salts. The new density wave state, which we tenatively identify as a field induced charge density wave state (FICDW), is re-entrant to a low resistance state at even higher fields, of order 50 T and above. Unlike the FISDW ground state, the FICDW state is only weakly orbital, and appears for all directions of magnetic field. Our findings are substantiated by electrical resistivity, magnetization, thermoelectric, and Hall measurements. We discuss our results in light of theoretical work involving magnetic field dependent Q1D CDW ground states in high magnetic fields [D. Zanchi, A. Bjelis, and G. Montambaux, Phys. Rev. B 53, (1996)1240; A. Lebed, JETP Lett. 78,138(2003)].Comment: 16 pages, 5 figure

Ru-Catalyzed Carbonylative Murai Reaction: Directed C3-Acylation of Biomass-Derived 2-Formyl Heteroaromatics

The Murai reaction is a ruthenium-catalyzed transformation leading to alkylated arenes through the C 12C bond formation between an alkene and an arene bearing a directing group. Discovered in the nineties, this useful C 12H activation based coupling has been the object of intense study since its discovery. After having studied the Murai reaction on 2-formylfurans of biomass derivation, we describe here the carbonylative version applied to 2-formylfurans, 2-formylpyrrols and 2-formylthiophenes. This acylation reaction takes place regioselectively at C3 position of the heterocyclopentadienes thanks to the installation of removable imine directing groups. The transformation can be achieved by treating the two reaction partners with a catalytic amount of Ru3(CO)12, in toluene at 120\u2013150 \ub0C, after CO bubbling, at atmospheric pressure. DFT computations of the full catalytic cycle help in deciphering the mechanism of this transformation, and to rationalize the different behaviors depending on the nature of imine directing groups. (Figure presented.)

Redox-Neutral Ru(0)-Catalyzed Alkenylation of 2-Carboxaldimine-heterocyclopentadienes

A new Ru3(CO)12-catalyzed directed alkenylation of 2-carboxaldimine-heterocyclopentadienes has been accomplished. This process allows coupling of furan, pyrrole, indole, and thiophene 2-carboxaldimines with electron-poor alkenes such as acrylates, vinylsulfones, and styrenes. This regio- and chemoselective oxidative C-H coupling does not require the presence of an additional sacrificial oxidant. Density functional theory calculations allowed us to propose a mechanism and unveiled the nature of the H2 acceptor

Mechanism of the electrochemical reduction of Fe(eta(5)-C6H7)(CO)(3) PF6 - a theoretical approach to the intermediates

A mechanism is proposed for the electrochemical reduction of [Fe(eta (5)-C6H7)(CO)(3)][PF6] based on cyclic voltammetry and simulation techniques. In [NBu4][X]/CH3CN (X = BF4 or ClO4) but not in [NBu4][BF4]/CH2Cl2, a rapid equilibrium prior to the electron transfer process is identified between [Fe(eta (5)-C6H7)(CO)(3)][PF6] and a species formulated as [Fe(eta (3)-C6H7)(CO)(3)(NCMe)](+). The formation of the species under equilibrium involves solvent coordination and eta (5) to eta (3) ring slippage of the cyclohexadienyl ligand as the response of the system to the high electron count. Electrochemical electron transfer to [Fe(eta (3)-C6H7)(CO)(3)(NCMe)](+) affords a highly reactive 19-clectron intermediate exhibiting chemical reactivity (ECE mechanism) that leads to the formation of dimer-type species. A 'father-son' type mechanism is proposed for the formation of the products of the electrochemical reduction of [Fe(eta (5)-C6H7)(Co)(3)][PF6]. All the species involved in the mechanism were analysed by theoretical means and are proposed on the basis of calculations made with the B3LYP HF/DFT hybrid functional. (C) 2001 Elsevier Science B.V. All rights reserved

Cyclic(Alkyl)(Amino)Carbene (CAAC)-Supported Zn Alkyls: Synthesis, Structure and Reactivity in Hydrosilylation Catalysis

The reactivity of ZnII dialkyl species ZnMe2 with a cyclic(alkyl)(amino)carbene, 1-[2,6-bis(1-methylethyl)phenyl]-3,3,5,5-tetramethyl-2-pyrrolidinylidene (CAAC, 1), was studied and extended to the preparation of robust CAAC-supported ZnII Lewis acidic organocations. CAAC adduct of ZnMe2 (2), formed from a 1:1 mixture of 1 and ZnMe2, is unstable at room temperature and readily undergoes a CAAC carbene insertion into the Zn−Me bond to produce the ZnX2-type species (CAAC-Me)ZnMe (3), a reactivity further supported by DFT calculations. Despite its limited stability, adduct 2 was cleanly ionized to robust two-coordinate (CAAC)ZnMe+ cation (5+) and derived into (CAAC)ZnC6F5+ (7+), both isolated as B(C6F5)4− salts, showing the ability of CAAC for the stabilization of reactive [ZnMe]+ and [ZnC6F5]+ moieties. Due to the lability of the CAAC−ZnMe2 bond, the formation of bis(CAAC) adduct (CAAC)2ZnMe+ cation (6+) was also observed and the corresponding salt [6][B(C6F5)4] was structurally characterized. As estimated from experimental and calculations data, cations 5+ and 7+ are highly Lewis acidic species and the stronger Lewis acid 7+ effectively mediates alkene, alkyne and CO2 hydrosilylation catalysis. All supporting data hints at Lewis acid type activation–functionalization processes. Despite a lower energy LUMO in 5+ and 7+, their observed reactivity is comparable to those of N-heterocyclic carbene (NHC) analogues, in line with charge-controlled reactions for carbene-stabilized ZnII organocations

New Cu(I) and Ag(I) binuclear complexes containing the dppa ligand

New Cu(I) and Ag(I) binuclear complexes were prepared by reaction of [M(NCCH3)4][PF6] (M = Ag, Cu) with the bidentate phosphine ligands Ph2PNHPPh2 (dppa) and Ph2PCH2PPh2 (dppm). In the reaction of Cu(I) with dppa the phosphine is easily oxidized to give the octahedral species of [Cu(dppaO2)3][PF6], 1. In an inert atmosphere, the binuclear complexes [Cu2(dppa)2(NCCH3)3][PF6]2, 2, [Cu2(dppa)2(NCCH3)4][PF6]2, 3, [Ag2(dppa)2(NCCH3)2][PF6]2, 4, and [Ag2(dppm)2][PF6]2, 5, were formed and structurally characterized by X-ray diffraction (except for 5). The electrochemical studies showed that the most relevant property of the binuclear species was the ease of forming the metal upon reduction. EH and DFT calculations were performed in order to try and understand the structural features of the [M2(dppa)2(NCCH3)x]n+ complexes, including the 0.47 Å increase in MM distance upon going from 2 to 3

An Oligosilsesquioxane Cage Functionalized with Molybdenum(II) Organometallic Fragments

A silsesquioxane cage polymer functionalized with eight chloropropyl arms (1, T-8-PrCl) reacted with 2,2'-dipyridiylamine (DPA) to afford a new derivative with eight pendant linear chains (2, T-8-Pr-DPA). Further reaction with [Mo(eta(3)-C3H5)Br(CO)(2)(NCMe)(2)] afforded another derivative containing three molybdenum units (3, T-8-Pr-DPA-Mo), after substitution of the two nitrite ligands in each complex. These are the first silsesquioxane species containing DPA and the Mo(eta(3)-C3H5)Br(CO)(2) fragment. The three materials were characterized by H-1, C-13, Si-29, and Mo-95 NMR, FTIR, XRD, and elemental analysis, and T-8-PrCl (1) was also structurally characterized by single-crystal X-ray diffraction. It was identified as a low-temperature polymorph of this material. Elemental analysis indicated that all Cl atoms in the parent material T-8-PrCl (1) were substituted by the deprotonated DPA group in T-8-Pr-DPA (2). However, only three [Mo(eta(3)-C3H5)Br(CO)(2)(DPA)] units were detected in T-8-Pr-DPA-Mo (3). A comprehensive NMR study, complemented with DFT calculations, was carried out in order to detect the effect of Mo coordination on the cage silicon and on the protons and carbons of the propyl chain, but no significant effects were observed. Both H-1 and Si-29 chemical shifts vary upon introducing DPA but remain the same after reaction with the Mo(II) precursor. The Mo-95 NMR data reveal that the metal is not sensitive to the cage. The catalytic activity of 3 was tested as a precursor in the epoxidation of cyclooctene and styrene in the presence of TBHP. Despite the high selectivity toward the epoxides, the conversion and turnover frequencies were low, reflecting the behavior of the [Mo(eta(3)-C3H5)Br(CO),(DPA)] complex.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

An Oligosilsesquioxane Cage Functionalized with Molybdenum(II) Organometallic Fragments

A silsesquioxane cage polymer functionalized with eight chloropropyl arms (<b>1</b>, T₈-PrCl) reacted with 2,2′-dipyridiylamine (DPA) to afford a new derivative with eight pendant linear chains (<b>2</b>, T₈-Pr-DPA). Further reaction with [Mo­(η³-C₃H₅)­Br­(CO)₂(NCMe)₂] afforded another derivative containing three molybdenum units (<b>3</b>, T₈-Pr-DPA-Mo), after substitution of the two nitrile ligands in each complex. These are the first silsesquioxane species containing DPA and the Mo­(η³-C₃H₅)­Br­(CO)₂ fragment. The three materials were characterized by ¹H, ¹³C, ²⁹Si, and ⁹⁵Mo NMR, FTIR, XRD, and elemental analysis, and T₈-PrCl (<b>1</b>) was also structurally characterized by single-crystal X-ray diffraction. It was identified as a low-temperature polymorph of this material. Elemental analysis indicated that all Cl atoms in the parent material T₈-PrCl (<b>1</b>) were substituted by the deprotonated DPA group in T₈-Pr-DPA (<b>2</b>). However, only three [Mo­(η³-C₃H₅)­Br­(CO)₂(DPA)] units were detected in T₈-Pr-DPA-Mo (<b>3</b>). A comprehensive NMR study, complemented with DFT calculations, was carried out in order to detect the effect of Mo coordination on the cage silicon and on the protons and carbons of the propyl chain, but no significant effects were observed. Both ¹H and ²⁹Si chemical shifts vary upon introducing DPA but remain the same after reaction with the Mo­(II) precursor. The ⁹⁵Mo NMR data reveal that the metal is not sensitive to the cage. The catalytic activity of <b>3</b> was tested as a precursor in the epoxidation of cyclooctene and styrene in the presence of TBHP. Despite the high selectivity toward the epoxides, the conversion and turnover frequencies were low, reflecting the behavior of the [Mo­(η³-C₃H₅)­Br­(CO)₂(DPA)] complex

An Oligosilsesquioxane Cage Functionalized with Molybdenum(II) Organometallic Fragments

A silsesquioxane cage polymer functionalized with eight chloropropyl arms (<b>1</b>, T₈-PrCl) reacted with 2,2′-dipyridiylamine (DPA) to afford a new derivative with eight pendant linear chains (<b>2</b>, T₈-Pr-DPA). Further reaction with [Mo­(η³-C₃H₅)­Br­(CO)₂(NCMe)₂] afforded another derivative containing three molybdenum units (<b>3</b>, T₈-Pr-DPA-Mo), after substitution of the two nitrile ligands in each complex. These are the first silsesquioxane species containing DPA and the Mo­(η³-C₃H₅)­Br­(CO)₂ fragment. The three materials were characterized by ¹H, ¹³C, ²⁹Si, and ⁹⁵Mo NMR, FTIR, XRD, and elemental analysis, and T₈-PrCl (<b>1</b>) was also structurally characterized by single-crystal X-ray diffraction. It was identified as a low-temperature polymorph of this material. Elemental analysis indicated that all Cl atoms in the parent material T₈-PrCl (<b>1</b>) were substituted by the deprotonated DPA group in T₈-Pr-DPA (<b>2</b>). However, only three [Mo­(η³-C₃H₅)­Br­(CO)₂(DPA)] units were detected in T₈-Pr-DPA-Mo (<b>3</b>). A comprehensive NMR study, complemented with DFT calculations, was carried out in order to detect the effect of Mo coordination on the cage silicon and on the protons and carbons of the propyl chain, but no significant effects were observed. Both ¹H and ²⁹Si chemical shifts vary upon introducing DPA but remain the same after reaction with the Mo­(II) precursor. The ⁹⁵Mo NMR data reveal that the metal is not sensitive to the cage. The catalytic activity of <b>3</b> was tested as a precursor in the epoxidation of cyclooctene and styrene in the presence of TBHP. Despite the high selectivity toward the epoxides, the conversion and turnover frequencies were low, reflecting the behavior of the [Mo­(η³-C₃H₅)­Br­(CO)₂(DPA)] complex