Ludovic Vieille-Petit

Impact of NHC ligand conformation and solvent concentration on the ruthenium-catalyzed ring-closing metathesis reaction

Two saturated N-heterocyclic carbene ligands with substituted naphthyl side chains were used for the preparation of Blechert-type ruthenium metathesis precatalysts. The resulting conformers of the complexes were separated and unambiguously assigned by X-ray diffraction studies. All new complexes were compared in terms of activity to the original, SIMes-derived Blechert catalyst and were shown to be superior. A study on the impact of solvent concentration in RCM reactions using the most active of these new catalysts ultimately led to the ring closing of a variety of substrates at very low catalyst loadings.

Improving Grubbs' II type ruthenium catalysts by appropriately modifying the N-heterocyclic carbene ligand

The introduction of N-heterocyclic carbene ligands that incorporate correctly substituted naphthyl side chains leads to increased activity and stability in second generation ruthenium metathesis catalysts.

Isolation and single-crystal X-ray structure analysis of the catalyst–substrate host–guest complexes [C6H6⊂H3Ru3{C6H5(CH2)nOH}(C6Me6)2(O)]+ (n=2, 3)

The trinuclear arene-ruthenium cluster cations [H3Ru3{C6H5(CH2)nOH}(C6Me6)2(O)]+ (3: n=2, 4: n=3) have been synthesised from the dinuclear precursor [H3Ru2(C6Me6)2]+ and the mononuclear complexes [{C6H5(CH2)nOH}Ru(H2O)3]2+ in aqueous solution, isolated and characterised as the hexafluorophosphate or tetrafluoroborate salts. Both 3 and 4 are derivatives of the parent cluster cation [H3Ru3(C6H6)(C6Me6)2(O)]+ (1) which was found to catalyse the hydrogenation of benzene to give cyclohexane under biphasic conditions. The mechanism postulated for this catalytic reaction (‘supramolecular cluster catalysis’), involving the hydrophobic pocket spanned by the three arene ligands in 1, was based on the assumption that the substrate molecule benzene is hosted inside the hydrophobic pocket of the cluster molecule to form a catalyst–substrate host–guest complex in which the hydrogenation of the substrate takes place. With the analogous cluster cations 3 and 4, containing a (CH2)nOH side-arm (n=2, 3) as substituent at the benzene ligand, it was possible to isolate the cationic host–guest complexes as the hexafluorophosphate or tetrafluoroborate salts. The single-crystal X-ray structure analyses of [C6H6⊂3][PF6] and [C6H6⊂4][BF4], compared to that of [3][PF6] show that the substrate molecule benzene is indeed held inside the hydrophobic pocket of 3 and 4, the angle between the metal (Ru3) plane and the aromatic plane being 67° and 89°, respectively.

Synthesis of a trinuclear cation [H3Ru3(Fc-arene)(C6Me6)2(O)]+ containing a ferrocenyl group tethered to an arene ligand

Abstract Ferrocene carboxylic acid 2-cyclohexa-1,4-dienyl-ethyl ester ( 1 ) is prepared from ferrocene carboxylic acid and 2-cyclohexa-1,4-dienyl-ethanol. This diene reacts with RuCl 3 · n H 2 O in refluxing ethanol to afford quantitatively [Ru(Fc-arene)Cl 2 ] 2 ( 2 ) (Fc-arene=ferrocene carboxylic acid phenethyl ester). The dinuclear complex 2 reacts with triphenylphosphine to give the mononuclear complex [Ru(Fc-arene)(PPh 3 )Cl 2 ] ( 3 ). The trinuclear arene-ruthenium cluster cation [H 3 Ru 3 (Fc-arene)(C 6 Me 6 ) 2 (O)] + ( 4 ) is synthesised from the dinuclear precursor [H 3 Ru 2 (C 6 Me 6 ) 2 ] + and the mononuclear complex [Ru(Fc-arene)(H 2 O) 3 ] 2+ , accessible from 2 in aqueous solution. The water-soluble trinuclear cluster cation 4 catalyses the hydrogenation of benzene to give cyclohexane under biphasic conditions.

Synthesis and molecular structure of the trinuclear ruthenium cluster cations [H3Ru3(C6H6)(C6H2Me4)2(O)]+ and [H3Ru3{C6H5(CH2)2OH}(C6H2Me4)2(O)]+

Abstract The trinuclear arene–ruthenium cluster cations [H3Ru3(C6H6)(C6H2Me4)2(O)]+ (2) and [H3Ru3{C6H5(CH2)2OH}(C6H2Me4)2(O)]+ (3) have been synthesised from the dinuclear precursor [H3Ru2(C6H2Me4)2]+ (1) and the mononuclear complexes [Ru(C6H6)(H2O)3]2+ and [Ru{C6H5(CH2)2OH}(H2O)3]2+, isolated and characterised as the tetrafluoroborate salts. Cations 2 and 3 are analogues of the cluster cation [H3Ru3(C6H6)(C6Me6)2(O)]+ which was found to catalyse the hydrogenation of benzene to give cyclohexane under biphasic conditions (‘supramolecular cluster catalysis’). The single-crystal X-ray structure analyses of 2 and 3 have been determined. Unlike [2][BF4]·3H2O, [3][PF6]·H2O shows a dimeric structure in the solid state, thanks to hydrogen bonds between the hydroxo function of one molecule of 3, a water molecule and the oxo cap of an other molecule of 3.