Copper catalyst activation driven by photoinduced electron transfer: a prototype photolatent click catalyst

PET cat. While the copper(II) tren ketoprofenate precatalyst 1 (see picture) is inactive at room temperature in methanol, it is quantitatively and rapidly reduced to its cuprous state upon light irradiation to provide a highly reactive click catalyst. By simply introducing air into the reaction medium the catalysis can be switched off and then switched on again by bubbling argon followed by irradiation.     

New kinetic model for the rapid step of calcium oxide carbonation by carbon dioxide

Carbonation of solid calcium oxide by gaseous carbon dioxide was monitored by thermogravimetry. A kinetic model of CaO carbonation is proposed in order to interpret the first rapid step of the reaction. By taking into account, the existence of large induction period as well as the sigmoidal shape of the kinetic curves in this kinetic-controlled region, a surface nucleation and isotropic growth kinetic model based on a single nucleus per particle is proposed, and the expressions of the fractional conversion and the reaction rate versus time are detailed. The induction period is found to have a linear variation with respect to temperature and to follow a power law with respect to CO₂ partial pressure. The areic reactivity of growth decreases with temperature increase, and increases with CO₂ partial pressure increase. A mechanism of CaCO₃ growth is proposed to account for these results and to determine a dependence of the areic reactivity of growth on the temperature and the CO₂ partial pressure.     

Poly(Organophosphazenes): Use in the Improvement of Standard Materials. Application to the Modification of Surface Properties of Poly(Vinyl Alcohol)

Abstract

Modification of surface properties of poly(vinyl alcohol) by grafting of poly(organophosphazenes).     

New 4,4-oligophenylenevinylene functionalized-[2,2]-bipyridyl chromophores: synthesis, optical and thermal properties

The synthesis and characterization of new bipyridyl-based chromophores featuring extended oligophenylenevinylene π-conjugated backbones are reported. Their absorption and emission properties as well as their thermal stabilities are discussed in comparison to those of the parent ligand.     

Crystal Structure of a Non-Conductive Non-Stoichiometric Tetrathiafulvalenium Salt: (TTF)3(BF4)2

Abstract

(TTF)₃(BF₄)₂ crystallizes in the triclinic system, space group P1, a = 8.017(3), b = 8.601(1), c = 11.635(2) Å, α = 108.79(1), β = 100.96(2), γ = 99.09(2)°, Z = 1. The TTF entities are stacked in parallel columns arranged into parallel layers alternating with layers of BF₄ ^? anions. A TTF stack is constituted of (TTF⁺)₂ diads interspersed with TTF° monads; the TTF⁺-TTF⁺ overlap is of the ring-over-ring type while the TTF⁺-TTF⁺ overlap is of the bond-over-ring type. These features explain the low conductivity ([sgrave]_powdcr = 2 × 10^?5 Ω^?l cm^?1) of this apparently non-stoichiometric TTF salt.     

Charge‐Transfer State and Large First Hyperpolarizability Constant in a Highly Electronically Coupled Zinc and Gold Porphyrin Dyad

We report the synthesis and the characterizations of a novel dyad composed of a zinc porphyrin (ZnP) linked to a gold porphyrin (AuP) through an ethynyl spacer. The UV/Vis absorption spectrum and the electrochemical properties clearly reveal that this dyad exhibits a strong electronic coupling in the ground state as evidenced by shifted redox potentials and the appearance of an intense charge‐transfer band localized at λ=739 nm in dichloromethane. A spectroelectrochemical study of the dyad along with the parent homometallic system (i.e., ZnP–ZnP and AuP–AuP) was undertaken to determine the spectra of the reduced and oxidized porphyrin units. Femtosecond transient absorption spectroscopic analysis showed that the photoexcitation of the heterometallic dyad leads to an ultrafast formation of a charge‐separated state (⁺ZnP–AuP^.) that displays a particularly long lifetime (τ=4 ns in toluene) for such a short separation distance. The molecular orbitals of the dyad were determined by DFT quantum‐chemical calculations. This theoretical study confirms that the observed intense band at λ=739 nm corresponds to an interporphyrin charge‐transfer transition from the HOMO orbital localized on the zinc porphyrin to LUMO orbitals localized on the gold porphyrin. Finally, a Hyper–Rayleigh scattering study shows that the dyad possesses a large first molecular hyperpolarizability coefficient (β=2100×10^?30 esu at λ=1064 nm), thus highlighting the valuable nonlinear optical properties of this new type of push–pull porphyrin system.     

Cp2TiCH2Si(Me2)NSiMe3: A Single-Source Precursor to Titanium-based Ceramic Thin Films by Chemical Vapor Deposition

The four-membered-ring heterocyclic molecule Cp₂TiCH₂Si(Me₂)NSiMe₃ (1; Cp=η−C₅H₅) was studied as a single-source precursor to titanium-based ceramic thin films. Its decomposition was studied at atmospheric and low pressure under nitrogen, argon and helium by TG–DTA–MS. Thin films containing the four elements of the metallacycle and oxygen were deposited on silicon substrates by low-pressure (20 Torr) chemical vapor deposition (CVD) between 773 and 923 K. Films were characterized by SEM–EDS, XPS, EPMA–WDS and XRD analyses. © 1997 by John Wiley & Sons, Ltd.     

Huisgen click cycloadditions from a copper(II)-tren precatalyst without external sacrificial reductant

The copper(II) complex [Cu(C18₆tren)](Br)₂, 2, is an efficient precatalyst for the Huisgen ‘click’ cycloaddtion which can be used at low loading without the requirement of an external sacrificial reductant such as sodium ascorbate. EPR studies support the in situ reduction of 2 by the alkyne to generate a reactive copper(I) catalyst.