Iridium | EPFL Graph Search

L'iridium est l'élément chimique de numéro atomique 77, de symbole Ir. Généralité sur l'élément et histoire L'élément est considéré, du fait de son corps simple, comme un platinoïde, dans la famille des métaux de transition. gauche|vignette|Deux ampoules scellées, l'une en haut contenant le corps simple métal iridium (blanc argenté jaunâtre) et l'autre en bas l'osmium (gris bleuté). L'iridium a été découvert en 1803 par Smithson Tennant à Londres, Angleterre, en même temps que l'osmium dans les résidus (osmiure d'iridium) de la dissolution du platine et des minerais de platine dans de l'eau régale. Pour récupérer le platinoïde osmium, le procédé de l'époque avait utilisé l'oxydation au creuset de grand feu, de façon à obtenir une matière pulvérulente, attaquable par l'eau régale à l'ébullition, puis l'addition d'ammoniaque avait permis de libérer par évaporation jusqu'à sec l'acide osmique ou le tétroxyde d'osmium. Le dernier résidu expurgé de l'essentiel de l'osmium c

Cooperative Effects between Chiral Cp-x-Iridium(III) Catalysts and Chiral Carboxylic Acids in Enantioselective C-H Amidations of Phosphine Oxides

Nicolai Cramer, Michael Christian Dieckmann, Yun-Suk Jang

An enantioselective C-H amidation of phosphine oxides by using an iridium(III) catalyst bearing an atropchiral cyclopentadienyl (Cp-x) ligand is reported. A very strong cooperative effect between the chiral Cp-x ligand and a phthaloyl tert-leucine enabled the transformation. Matched-mismatched cases of the different acid enantiomers are shown. The amidated P-chiral arylphosphine oxides are formed in yields of up to 95% and with excellent enantioselectivities of up to 99:1 er. Enantiospecific reduction provides access to valuable P-chiral phosphorus(III) compounds.

Wiley-Blackwell2017

Time-resolved X-ray and Optical Studies of Metalloproteins and Iridium Complexes

Mahsa Silatani

A wide variety of physicochemical processes at a molecular level, in particular charge or energy transfer, electronic and vibrational relaxation, are at the origin of biological functionality of proteins and organometallic compounds. The work reported in this thesis is devoted to the study of these molecular dynamics in selected organometallic systems. In particular, it focuses on the role of these dynamics in the ultrafast photophysics and photochemistry of Myoglobin and iridium complexes having a transition metal active center of d6 configuration. The nature of ligand recombination to the active centre has a strong impact on the reactivity and activation of heme proteins. Using picosecond (ps) Fe K-edge X-ray absorption spectroscopy (XAS) we probed the NO-heme recombination with direct sensitivity to the Fe-NO binding in physiological solution. The transient XAS at 70 ps and 300 ps are identical, but they deviate from the difference between the static spectra of deoxyMb and nitrosyl myoglobin demonstrating the formation of an intermediate species, supposedly the 6-coordinated domed form that is populated on a time scale of ~200 ps and relaxes in ~30 ps. A broadband femtosecond (fs) luminescence study of Ir(ppy)3 (Ir1), Ir(ppy)2(pic) (Ir2), [Ir(ppy)2(bpy)]+ (Ir3) and Ir(ppz)3 (Ir4) provides the first extensive picture of their ligand dependence. After excitation to a ligand-centered state (266 nm), we directly clock the relaxation cascade of Ir1 leading to the lowest metal-to-ligand charge transfer (3MLCT) state. The cascade proceeds within â€ 10 fs, being faster than some of the high-frequency modes of the system. In Ir4 the 3MLCT state decays (530 fs) by non-radiative channels. For Ir1-3, the early emission (100s ps the emission evolves to the steady-state showing evidence of dual emission for Ir1,2 due to a double-well minimum of the lowest 3MLCT state. For Ir3, the final emission stems from a ppy to bpy inter-ligand CT state. The studies of the electronic and geometric structure of Ir1-4 by Ir L3 XAS in solution reveals overall identical above-edge multiple scattering resonances and EXAFS indicating similar bond lengths and angles. Simulation of the XAS using TDDFT and FEFF9 shows good overall agreement with the experiment. The near-edge region of the spectra shows distinct differences among the studied complexes. Ir4 has stronger WL intensity than Ir1, indicating weaker Ï-back donation. The XAS spectra of Ir2,3 indicate larger 5d-electron density on the iridium. The XAS spectra of Ir1 and Ir4 show weak pre-edge resonance due to metal (2p3/2)-to-ligand charge transfer excitations. The absence of the pre-edge in Ir2,3 is due to the reduced covalency of the bonds. However, the existence of such transitions remains open for debate since Ir+3 has only occupied t2g orbitals in the low spin configuration. Using ps XAS, we have successfully captured the transient spectrum at the Ir L3-edge of both Ir1 and Ir4 probed 150 ps after laser excitation in solution. Upon excitation of a MLCT band (355 nm), we observed oxidation state change of Ir from +3 to +4. In DCM, the transient spectra are almost identical for both Ir1,4. The only significant changes in the transient spectra are those observed around the WL. The calculations reproduce the blue shift of the absorption spectrum due to the reduced electron density on the Ir, consistent with the MLCT excitation.

EPFL2015

Catalytic Enantioselective Functionalizations of C-H Bonds by Chiral Iridium Complexes

Nicolai Cramer, Adrien Jules Louis Madron Du Vigné, Qui-Hien Nguyen, Jin Fay Tan, Lukasz Piotr Wozniak

The development of catalytic enantioselective transformations, enabling the construction of complex molecular scaffolds from simple precursors, has been a long-standing challenge in organic synthesis. Recent achievements in transition-metal catalyzed enantioselective functionalizations of carbon-hydrogen (C-H) bonds represent a promising pathway toward this goal. Over the last two decades, iridium catalysis has evolved as a valuable tool enabling the stereocontrolled synthesis of chiral molecules via C-H activation. The development of iridium-based systems with various chiral ligand classes, as well as studies of their reaction mechanisms, has resulted in dynamic progress in this area. This review aims to present a comprehensive picture of the enantioselective functionalizations of C-H bonds by chiral iridium complexes with emphasis on the mechanisms of the C-H activation step.

2020

Time-resolved X-ray and Optical Studies of Metalloproteins and Iridium Complexes

Mahsa Silatani

EPFL2015