Force-modulated reductive elimination from platinum(ii) diaryl complexes

Coupled mechanical forces are known to drive a range of covalent chemical reactions, but the effect of mechanical force applied to a spectator ligand on transition metal reactivity is relatively unexplored. Here we quantify the rate of C(sp(2))–C(sp(2)) reductive elimination from platinum(ii) diaryl complexes containing macrocyclic bis(phosphine) ligands as a function of mechanical force applied to these ligands. DFT computations reveal complex dependence of mechanochemical kinetics on the structure of the force-transducing ligand. We validated experimentally the computational finding for the most sensitive of the ligand designs, based on MeOBiphep, by coupling it to a macrocyclic force probe ligand. Consistent with the computations, compressive forces decreased the rate of reductive elimination whereas extension forces increased the rate relative to the strain-free MeOBiphep complex with a 3.4-fold change in rate over a ∼290 pN range of restoring forces. The calculated natural bite angle of the free macrocyclic ligand changes with force, but (31)P NMR analysis and calculations strongly suggest no significant force-induced perturbation of ground state geometry within the first coordination sphere of the (P–P)PtAr(2) complexes. Rather, the force/rate behavior observed across this range of forces is attributed to the coupling of force to the elongation of the O⋯O distance in the transition state for reductive elimination. The results suggest opportunities to experimentally map geometry changes associated with reactions in transition metal complexes and potential strategies for force-modulated catalysis

Mechanistic Analysis of Gold(I)-Catalyzed Intramolecular Allene Hydroalkoxylation Reveals an Off-Cycle Bis(gold) Vinyl Species and Reversible C–O Bond Formation

Mechanistic investigation of gold(I)-catalyzed intramolecular allene hydroalkoxylation established a mechanism involving rapid and reversible C–O bond formation followed by turnover-limiting protodeauration from a mono(gold) vinyl complex. This on-cycle pathway competes with catalyst aggregation and formation of an off-cycle bis(gold) vinyl complex

Mechanochemical Regulation of Oxidative Addition to a Palladium(0) Bisphosphine Complex.

Here, we report the effect of force applied to the biaryl backbone of a bisphosphine ligand on the rate of oxidative addition of bromobenzene to a ligand-coordinated palladium center. Local compressive and tensile forces on the or-der of 100 pN were generated using a stiff stilbene force probe. A compressive force increases the rate of oxidative addition, whereas a tensile force decreases the rate, relative to that of the parent complex of strain-free ligand. Rates vary by a factor of ~6 across ~340 pN of force applied to the complexes. The crystal structures and DFT calculations support that force-induced perturbation of the geometry of the reactant is negligible. The force-rate relationship ob-served is mainly attributed to the coupling of force to nuclear motion comprising the reaction coordinate. These observations inform the development of catalysts whose activity can be tuned by an external force that is adjusted within a catalytic cycle

Aerobic oxidation of thiols to disulfides by heterogeneous gold catalysts

Thiols are smoothly and efficiently oxidized to disulfides (RSSR) with air in the presence of gold nanoparticles supported on CeO2 in absence of solvent, as well as in aqueous solutions and neutral pH. It is shown that the reaction can occur through the coupling of two sulphur radicals on the metal surface. The sulphur radicals are formed from thiols by one-electron oxidation with the metal. This reaction mechanism strongly resembles that found for sulfhydryl oxidases, a class of enzymes which are involved in the oxidative protein folding through de novo formation of disulfides from thiols.lFinancial support by Consolider-Ingenio 2010 (project MULTICAT), Spanish MICINN (Projects MAT2006-14274-C02-01 and MAT2011-28009), Generalitat Valenciana (Project PROMETEO/2008/130) and Fundacion Areces are gratefully acknowledged. T.R. expresses her gratitude to Consejo Superior de Investigaciones Cientificas for an I3-P fellowship.Corma Canós, A.; Ródenas Torralba, T.; Sabater Picot, MJ. (2012). 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Chirality transfer in metal-­‐catalysed intermolecular addition reactions involving allenes

Allene chemistry in the presence of transition metal complexes is nowadays a very important topic that underpins many challenges and advances in organic synthesis. The amount of research articles covering new transformations of allenes is vast and the development of enantioselective reactions involving allenes has flourished in the last 10-15 years. In this review we cover three important topics in allene chemistry that we feel are timely appropriate for this special issue celebrating the work of Prof Trost: the metal-catalysed reactions involving chirality transfer from chiral allenes to products; the analysis of the possible racemization processes that have been observed in the interaction of some metals with allenes; and the chirality transfer using racemic allenes in reactions catalysed by metal complexes bearing chiral ligands to produce enantioriched products. We have focussed the review on intermolecular addition reactions as they are still much less explored than the intramolecular version

Mechanistic Studies of Ethylene Hydrophenylation Catalyzed by Bipyridyl Pt(II) Complexes

This article discusses mechanistic studies of ethylene hydrophenylation catalyzed by bipyridyl Pt(II) complexes

Strong Electronic and Counterion Effects on Geminal Digold Formation and Reactivity as Revealed by Gold(I)-Aryl Model Complexes

Die geminale Diaurierung von [Ph3PAu(Aryl)]‐Komplexen wurde als Modell untersucht, um Einblick in die intermediäre Bildung von geminalen diaurierten Gold(I)‐Vinylkomplexen in der Katalyse zu gewinnen (siehe Schema). Die Ergebnisse tragen zum Verständnis der Faktoren bei, die die Stabilität, Reaktivität und Dynamik dieser metallorganischen Zwischenstufen bestimmen

Transmetalation between Au(I) and Sn(IV) complexes. The reaction mechanism in non-coordinating and coordinating polar solvents.

Some novel gold(I) derivatives of the type [LAuCl] (L = DIC, PPh3, NHCs) have been synthesized and characterized. The products of the transmetalation reaction between these species and tributyl-phenylethynylstannane have been isolated and characterized. An exhaustive kinetic study on the transmetalation reaction has also been carried out in CHCl3 and CH3CN. The experimental results were discussed in terms of the electronic and steric characteristics of the ligands and an interpretation of the peculiar influence of different solvents on the reaction rates was propose