Abstract:The straightforward synthesis of a new donor-stabilized phosphenium ligand 3d by addition of bromodifurylphosphine to 1,3-dimethylimidazolium-2-carboxylate 1 is described. The obtained ligand exhibits a very strong p-acceptor character, comparable to that of triphenyl phosphite [PA C H T U N G T R E N N U N G (OPh) 3 ] or of tris-halogenophosphines, with a n CO (A 1 ) at 2087 cm À1for its nickel tricarbonyl complex. This ligand, as well as the related 3a which was obtained from chloroA C H T U N G T R E N N U N G diphenylphosphine, were tested in palladiumcatalyzed aryl alkynylation and in the platinum-catalyzed selective hydrogenation of chloronitrobenzenes, both in an ionic liquid phase. In C À C bond cross-coupling we observed that the increase of the p-acceptor character in ligand 3d, due to the introduction of an additional electron-withdrawing group, provides a very efficient catalyst in the alkynylation reaction of aryl bromides with phenylacetylene, including the deactivated 4-bromoanisole or the sterically hindered 2-bromonaphthalene. The catalytic activity decreases with recycling due to the sensitiveness of ligands to protonation in the ionic phase.Conversely, a multiple recycling of the metal/ligand system in non-acidic media was achieved from platinum-catalyzed hydrogenation of m-chloronitrobenzene. The catalytic results obtained by employing the complex of platiA C H T U N G T R E N N U N G num(II) chloride with 3a [transPtCl 2 (3a) 2 ] in comparison with the non-ionic related trans-tris(triphenylphosphine)platinum dichloride [trans-PtCl 2 A C H T U N G T R E N N U N G (PPh 3 ) 2 ] complex clearly indicate that the simultaneous existence of a strong p-acceptor character and a positive charge within the ligand 3a significantly increases the life-time of the platinum catalyst. The selectivity of the reaction is also improved by decreasing the undesirable formation of dehalogenation products. This cationic platinum complex trans-PtCl 2 (3a) 2 is the first example of a highly selective catalyst for hydrogenation of chloronitroarenes immobilized in an ionic liquid phase. The system was recycled six times without noticeable metal leaching in the organic phase, and no loss of activity.

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Cyclohexanone monooxygenases (CHMO) consume molecular oxygen and NADPH to catalyze the valuable oxidation of cyclic ketones. However, CHMO usage is restricted by poor stability and stringent specificity for NADPH. Efforts to engineer CHMO have been limited by the sensitivity of the enzyme to perturbations in conformational dynamics and longrange interactions that cannot be predicted. We demonstrate an aerobic, high-throughput growth selection platform in Escherichia coli for oxygenase evolution based on NADH redox balance. We applied this NADH-dependent selection to alter the cofactor specificity of CHMO to accept NADH, a less expensive cofactor than NADPH. We first identified the variant CHMO DTNP (S208D-K326T-K349N-L143P) with a ∼1200-fold relative cofactor specificity switch from NADPH to NADH compared to the wild type through semirational design. Molecular modeling suggests CHMO DTNP activity is driven by cooperative fine-tuning of cofactor contacts. Additional evolution of CHMO DTNP through random mutagenesis yielded the variant CHMO DTNPY with a ∼2900-fold relative specificity switch compared to the wild type afforded by an additional distal mutation, H163Y. These results highlight the difficulty in engineering functionally innovative variants from static models and rational designs, and the need for high throughput selection methods. Our introduced tools for oxygenase engineering accelerate the advancements of characteristics essential for industrial feasibility.

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4 ] mixture. We discovered that the addition of an ionic liquid to methanol allowed not only to increase the activity of the palladium catalyst but also to provide a recyclable catalyst which can be reused several times with a weaker drop of activity. To complete these catalytic studies, we describe the synthesis of the first poor -electron-donating/strong -electron-acceptor linear Triphosphine which, after palladium coordination, led to a better selectivity compared to its Triphos analogue. The performances of recovered ionic liquid reaction mixtures show for the first time that P-tridentate ligands efficiently immobilize palladium catalysts and lead to selective catalytic systems benign for environment.

The efficient palladium-catalyzed alkynylation of electron-rich bromoheteroarenes, incorporating deactivating electrondonating methyl and methoxy groups, and the (hetero)arylation of diynes, take place in the imidazolium ionic liquid [BMIM][BF 4 ], as a highly polar non-volatile solvent. This method may constitute a sustainable alternative to classical solvents such as dioxane, DMF, NMP, or DMAc. New enynes are formed in the presence of a system encompassing a copper-free palladium catalyst, triphenylphosphine as ligand, and various inexpensive bases. The enyne molecules reported are selectively synthesized in high yields and are mostly unprecedented.

Double Arylation of Diynes and Alkynylation of Functionalized Heteroaryl Halides by a Practical Heck Reaction in an Ionic Liquid. -(SALEH, S.; PICQUET, M.; MEUNIER, P.; HIERSO*, J.-C.; Synlett 2011, 19, 2844-2848, http://dx.doi.org/10.1055/s-0031-1289861 ; Inst. Chim. Mol., Univ. Bourgogne, F-21078 Dijon, Fr.; Eng.) -Mais 15-051

Catalysis O 0020Donor-Stabilized Phosphenium Adducts as New Efficient and Immobilizing Ligands in Palladium-Catalyzed Alkynylation and Platinum-Catalyzed Hydrogenation in Ionic Liquids. -Donor-stabilized phosphenium salts are successfully applied as ligands in the Pd-catalyzed Heck arylation of terminal alkyne (II) with aryl bromides. Best results are achieved for the ligand (DFIP) bearing two electron-withdrawing furyl groups. The recyclability, however, is limited due to protonation of the C-P bond of the ligand under acidic conditions. In contrast, the complex formed from PtCl2 and the diphenylphosphenium ligand (DPIP) shows excellent stability and chemoselectivity in the hydrogenation of m-chloronitrobenzene (IV). It can be recycled and reused for at least seven runs without significant loss of activity or chemoselectivity. -(SALEH, S.; FAYAD, E.; AZOURI, M.; HIERSO*, J.-C.; ANDRIEU, J.; PICQUET, M.; Adv. Synth. Catal. 351 (2009) 10, 1621-1628; Inst. Chim. Mol., Univ. Bourgogne, F-21078 Dijon, Fr.; Eng.) -Mischke 49-025