Christian Bruneau

Direct Arylation of Arene C−H Bonds by Cooperative Action of NHCarbene−Ruthenium(II) Catalyst and Carbonate via Proton Abstraction Mechanism

Direct functionalization of sp2 C−H bonds via ortho diarylation of 2-pyridyl benzene with arylbromides was achieved using ruthenium(II) catalysts containing a RuCl2(NHC) unit and generated from [RuCl2(arene)]2 and two types of NHC precursors, pyrimidinium and benzimidazolium salts, in the presence of Cs2CO3. DFT calculations from RuCl2(NHC)(2-pyridylbenzene) show that a proton abstraction mechanism, on cooperative actions of both the coordinated base and the Ru(II) center, is favored via a 13.7 kcal·mol-1 exothermic process affording an orthometalated intermediate with a 2.009 A Ru−C bond.

Transition metal catalyzed nucleophilic allylic substitution: activation of allylic alcohols via π-allylic species.

Modern organic synthesis now requires efficient atom economical synthetic methods operating under greener pathways to achieve C-C and C-heteroatom bond formation. Direct activation of allylic alcohols in the presence of transition metal catalysts leading to electrophilic π-allyl metal intermediates represents such a promising target in the field of nucleophilic allylation reactions. During the last decade, this topic of recognized importance has become an emerging area, and selected transition metals, sometimes associated with alcohol activators, have brought elegant solutions for performing allylic substitution directly from alcohols in a regio, stereo and enantioselective manner.

Renewable materials as precursors of linear nitrile-acid derivatives via cross-metathesis of fatty esters and acids with acrylonitrile and fumaronitrile

The cross-metathesis of fatty acids and esters, as renewable raw materials, with acrylonitrile and fumaronitrile is presented. The cross-metathesis reactions of both terminal and internal double bond containing compounds were performed using a ruthenium catalyst and led to bifunctional nitrile-esters or nitrile-acids with high conversions. The tandem ruthenium catalysed cross-metathesis and hydrogenation provide precursors of aminoacid monomers for the production of polyamides from renewable resources.

First ring-opening metathesis polymerization in an ionic liquid. Efficient recycling of a catalyst generated from a cationic ruthenium allenylidene complex

Ring-opening metathesis polymerization (ROMP) of norbornene was carried out in a biphasic medium consisting of the ionic liquid [bdmim][PF6] and toluene with a cationic ruthenium allenylidene precatalyst. The ionic liquid contained the ruthenium allenylidene complex and toluene dissolved the formed polymer. Both the catalyst and the ionic liquid were reused several times and led to very good polymer yields.

sp3 C-H bond activation with ruthenium(II) catalysts and C(3)-alkylation of cyclic amines.

A selective C(3)-alkylation via activation/functionalization of sp(3) C-H bond of saturated cyclic amines was promoted by (arene)ruthenium(II) complexes featuring a bidentate phosphino-sulfonate ligand upon reaction with aldehydes. This highly regioselective sustainable transformation takes place via initial dehydrogenation of cyclic amines and hydrogen autotransfer processes.

Diethyl carbonate as a solvent for ruthenium catalysed C–H bond functionalisation

The ruthenium catalysed direct functionalisation of arene C–H bonds by aryl halides is reported. Reactions were performed in diethyl carbonate (DEC) instead of N-methylpyrrolidone (NMP), the solvent of choice used in most ruthenium catalysed C–H bond transformations. The use of diethyl carbonate facilitates the workup procedure thus reducing the amount of waste water. The slight loss of activity due to the use of diethyl carbonate is counterbalanced by the improvement of the catalyst efficiency achieved by a judicious choice of additives. Several arenes containing an N-heterocycle as a directing group have been diarylated.

First ruthenium complexes with a chelating arene carbene ligand as catalytic precursors for alkene metathesis and cycloisomerisation

Electron-rich carbene precursors 2 and 3, containing the imidazolidin-2-ylidene moiety with one (2) and two (3) pendent N-(2,4,6-trimethylbenzyl) groups, on reaction with [RuCl2(arene)]2 lead to ruthenium(II) complexes 5 and 6 containing the chelating 8-electron mixed arene–carbene ligand; the X-ray diffraction crystal structure of RuCl2{η1-CN[CH2( η6-2,4,6-Me3C6H2)]CH2CH2N(CH2CH2OMe)} 6, was established. These complexes are precursors of the unstable ruthenium-allenylidene intermediates 7 and 8, but are active catalysts either for selective catalytic alkene metathesis or cycloisomerization, depending on the nature of the 1,6-diene.

Ruthenium–alkylidene catalysed cross-metathesis of fatty acid derivatives with acrylonitrile and methyl acrylate: a key step toward long-chain bifunctional and amino acid compounds

The ruthenium catalysed cross-metathesis of fatty-esters arising from plant oils with acrylonitrile is presented. The resulting linear nitrile ester products have potential as new intermediates for polyamides synthesis. A series of commercially available catalysts are able to promote the transformation of methyl 10-undecenoate 1, dimethyl octadec-9-en-1,18-dioate 5 and methyl ricinoleate 9 with acrylonitrile and a protocol based on the slow addition of catalyst allowed TONs as high as 1900 (92% yield) to be reached for cross-metathesis with acrylonitrile. These cross-metathesis conditions have been applied to methyl acrylate and TONs up to 7600 were obtained.

Ruthenium(IV) Complexes Featuring P,O‐Chelating Ligands: Regioselective Substitution Directly from Allylic Alcohols

Branching out: A new ruthenium(IV) complex (1), containing a P,O-chelating ligand, is an efficient precatalyst for regioselective allylations starting from various allylic alcohol derivatives.

Ruthenium catalysts and fine chemistry

S. Derien, F. Monnier and P.H. Dixneuf: Ruthenium-Catalyzed C-C Bond Formation.- F. Kakiuchi, N. Chatani: Activation of Inert C-H Bonds.- H. Nishiyama: Cyclopropanation with Ruthenium Catalysts.- S.J. Connon, S. Blechert: Recent Advances in Alkene Metathesis.- C. Bruneau: Ruthenium Vinylidenes and Allenylidenes in Catalysis.- L. Delaude, A. Demonceau and A.F. Noels: Ruthenium-Promoted Radical Processes Toward Fine Chemistry.- N. Chatani: Selective Carbonylations with Ruthenium Catalysts.- B. Marciniec, C. Pretraszuk: Synthesis of Silicon Derivatives with Ruthenium Catalysts.- Y. Yamamoto, K. Itoh: Ruthenium-Catalyzed Synthesis of Heterocyclic Compounds.- I.W.C.E. Arends, T. Kodama and R.A. Sheldon: Oxidations Using Ruthenium Catalysts.- M. Wang, C.-J. Li: Ruthenium-Catalyzed Organic Synthesis in Aqueous Media