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- PublicationAccès libreTri- and Tetranuclear Mixed-Metal Clusters Containing Alkyne Ligands : Synthesis and Structure of [Ru3Ir(CO)11(RCCR’)]-, [Ru2Ir(CO)9(RCCR’)]-, and [HRu2Ir(CO)9(RCCR’)]The tetrahedral cluster anion [Ru3Ir(CO)13]- (1) reacts with internal alkynes RCCR to afford the alkyne derivatives [Ru3Ir(CO)11(RCCR)]- (2: R = R’ = Ph; 3: R = R’ = Et; 4: R = Ph; R’ = Me; 5: R = R’ = Me) which have a butterfly arrangement of the Ru3Ir skeleton in which the alkyne is coordinated in a μ4-η2 fashion. Under CO pressure they undergo fragmentation to give the trinuclear cluster anions [Ru2Ir(CO)9 (RCCR)]- (6: R = R’ = Ph; 7: R = R’ = Et; 8: R’ = Ph; R’ = Me; 9: R = R’ = Me), in which the alkyne ligand is coordinated in a μ3-η2 parallel fashion. Protonation of these trinuclear anions leads to the formation of the corresponding neutral hydrido clusters [HRu2Ir(CO)9 (RCCR)] (10: R = R’ = Ph; 11: R = R’ = Et; 12: R = Ph; R’ = Me; 13: R = R’ = Me). The protonation of the butterfly anions 2 and 3, however, gives rise to the formation of the neutral tetrahedral clusters [HRu3Ir(CO)11(RCCR)] (14: R = R’ = Ph and 15: R = R’ = Et), respectively. The analogous clusters [HRu3Ir(CO)11(PhCCCH3)] (16) and [HRu3Ir(CO)11(CH3CCCH3)] (17) are only accessible from the reaction of the neutral cluster [HRu3Ir(CO)13] with the corresponding alkynes. The complexes 2, 4, 5, 6, 10, 12 and 15 are characterised by X-ray structure analysis.
- PublicationAccès libreTriruthenium–iridium clusters containing alkyne ligands : synthesis, structure, and catalytic implications of [(µ-H)IrRu3(CO)11(µ3-η2-PhC≡CPh)] and [IrRu3(CO)10(µ4-η2-PhC≡CPh)(µ-η2-PhC=CHPh)]The mixed-metal cluster [HIrRu3(CO)13] 1 reacts with one equivalent of disubstituted alkynes RC≡CR to give [HIrRu3(CO)11(µ3-η2-RC≡CR)] (R = Ph 2; R = Me 3), with a second equivalent of the alkyne the clusters [IrRu3(CO)10(µ4-η2-RC≡CR)(µ-η2-RC=CHR)] (R = Ph 4; R = Me 5) are obtained. The single-crystal X-ray structure analyses of 2 and 3 show these clusters to have a tetrahedral Ru3Ir framework containing the alkyne ligand coordinated in a parallel fashion over the Ru3 face of the metal skeleton. In contrast, the clusters 4 and 5 consist of a butterfly arrangement of the Ru3Ir framework with the alkyne ligand coordinated to all four metal atoms, giving an overall octahedral Ru3IrC2 skeleton, as demonstrated by the single-crystal structure analysis of 4. Cluster 1 is an excellent catalyst for the hydrogenation of diphenylacetylene to give stilbene (catalytic turnover number 990 within 15 min), clusters 2 and 4 are also catalytically active but seem to represent side-channels of the catalytic cycle.
- PublicationAccès libreApplication of the Novel Tandem Process Diels-Alder Reaction/Ireland-Claisen Rearrangement to the Synthesis of rac-Juvabione and rac-EpijuvabioneThe novel tandem process Diels-Alder reaction/Ireland-Claisen rearrangement shows a high diastereoselectivity for the Ireland-Claisen rearrangement starting from the endo-product of the Diels-Alder reaction. Based on this mechanistic knowledge, the novel tandem process could be applied to the synthesis of rac-juvabione.
- PublicationAccès libreMono and oligonuclear vanadium complexes as catalysts for alkane oxidation : synthesis, molecular structure, and catalytic potentialA series of mono- and oligonuclear vanadium(V) and vanadium(IV) complexes containing various chelating N,O-, N3-, and O2-ligands have been prepared. The biphasic reaction of an aqueous solution of ammonium vanadate and a dichloromethane solution of hexamethylphosphoramide (hmpa) and pyrazine-2-carboxylic acid (pcaH) or pyrazine-2,5-dicarboxylic acid (pdcaH2) or pyridine-2,5-dicarboxylic acid (pycaH2) yields yellow crystals of [VO2 (pca)(hmpa)] (1), [(VO2)2(pdca)(hmpa)2] (2), and [VO2(pycaH)(hmpa)] (3), respectively. The single-crystal X-ray structure analyses reveal 1 and 3 to be mononuclear vanadium(V) complexes, in which a VO2 unit coordinates to one nitrogen and one oxygen atom of a pca or pycaH chelating ligand, and 2 to be a dinuclear vanadium(V) complex, in which two VO2 units are coordinated through one nitrogen and one oxygen atom of a pdca bridging ligand; in the three complexes the vanadium atoms also coordinate to the oxygen atom of a hmpa ligand. The reaction of N,N,N′,N′-tetrakis(2-benzimidazolylmethyl)-2-hydroxo-1,3-diaminopropane (hptbH) and VOSO4 in methanol gives the cationic complex [(VO)4(hptb) 2(μ-O)]4+ (4), which can be crystallized as the perchlorate salt. In this tetranuclear complex, two dinuclear vanadium(IV) units are held together by a μ-oxo bridge. The known complex [VOCl2 (tmtacn)] (5) was synthesized from the reaction of 1,4,7-trimethyl-1,4,7-triazacyclononane (tmtacn) and VCl3 in acetonitrile; the reaction of tetrabutylammonium vanadate with pyro-cathecol (catH2) in acetonitrile gives the known anionic complex [V(cat)3]− (6), in which the vanadium(V) center is bonded to three cat chelating ligands through the oxygen atoms, obtained as the tetrabutylammonium salt. All compounds synthesized are highly efficient oxidation catalysts for the reaction of cyclohexane with air and hydrogen peroxide in the presence of four equivalents of pcaH per vanadium, although the catalytic activity of the complexes containing bulky chelating ligands 4 and 5 is somewhat lower in the initial period of the reaction. During this period the active species are formed from the complexes and final turnover numbers are high. The catecholate ligands of complex 6 may reduce from V(V) to V(IV) in the beginning of the process, thus providing very high initial oxidation rates.
- PublicationAccès libreThe mixed-metal carbonyl cluster anion [Ru3Ir(CO)13]– : synthesis, molecular structure, fluxionality, reactivityThe new cluster anion [Ru3Ir(CO)13]–1 was synthesized in high yield from [Ru3(CO)12] and [Ir(CO)4]–. The single-crystal X-ray structure analysis of the bis(triphenylphosphoranylidene)ammonium salt revealed the presence of two isomers, [Ru3Ir(CO)11(µ-CO)2]–1a and Ru3Ir(CO)9(µ-CO)4]–1b in the same crystal. Both 1a and 1b present a tetrahedral Ru3Ir framework, differing only by the number of bridging carbonyl ligands. Variable-temperature 13C NMR spectroscopic studies of 1 revealed the fluxionality of the carbonyl ligands and the interconversion of both isomers in solution. Protonation of 1 gave the neutral cluster [HRu3Ir(CO)13] 2, whereas reaction of 1 with molecular hydrogen yielded the anion [H2Ru3Ir(CO)12]–3. Either hydrogenation of 2 or protonation of 3 gave [H3Ru3Ir(CO)12] 4. The tetrahedral structure of the hydrido derivatives was confirmed by a single-crystal X-ray structure analysis of the bis(triphenylphosphoranylidene)ammonium salt of 3.
- PublicationAccès libre4,4-Bis(1H-pyrrol-2-yl)pentanolThe title achiral compound, C13H18N2O, crystallized in the chiral monoclinic space group P21. The pyrrole rings are inclined to one another by 62.30 (11)°, and the propanol chain is in an extended conformation. In the crystal, the two pyrrole NH groups are involved in intermolecular N-H ··· O hydrogen bonds, leading to the formation of a helical arrangement propagating along the b axis. An interesting feature of the crystal structure is the absence of any conventional hydrogen bonds involving the hydroxy H atom. There is, however, a weak intermolecular O-H ··· π interaction involving one of the pyrrole rings.
- PublicationAccès libreWater-Soluble Arene Ruthenium Complexes Containing a trans-1,2-Diaminocyclohexane Ligand as Enantioselective Transfer Hydrogenation Catalysts in Aqueous SolutionThe cationic chloro complexes [(arene)Ru(H2N∩NH2)Cl]+ (1: arene = C6H6; 2: arene = p-MeC6H4iPr; 3: arene = C6Me6) have been synthesised from the corresponding arene ruthenium dichloride dimers and enantiopure (R,R or S,S) trans-1,2-diaminocyclohexane (H2N∩NH2) and isolated as the chloride salts. The compounds are all water-soluble and, in the case of the hexamethylbenzene derivative 3, the aqua complex formed upon hydrolysis [(C6Me6)Ru(H2N∩NH2)OH2]2+ (4) could be isolated as the tetrafluoroborate salt. The molecular structures of 3 and 4 have been determined by single-crystal X-ray diffraction analyses of [(C6Me6)Ru(H2N∩NH2)Cl]Cl and [(C6Me6)Ru(H2N∩NH2)OH2][BF4]2. Treatment of [Ru2 (arene) 2Cl4] with the monotosylated trans-1,2-diaminocyclohexane derivative (TsHN∩NH2) does not yield the expected cationic complexes, analogous to 1-3 but the neutral deprotonated complexes [(arene)Ru(TsN∩NH2)Cl] (5: arene = C6H6; 6: arene = p-MeC6H4iPr; 7: arene = C6Me6; 8: arene = C6H5COOMe). Hydrolysis of the chloro complex 7 in aqueous solution gave, upon precipitation of silver chloride, the corresponding monocationic aqua complex [(C6Me6)Ru(TsHN∩NH2)(OH2)]+ (9) which was isolated and characterised as its tetrafluoroborate salt. The enantiopure complexes 1-9 have been employed as catalysts for the transfer hydrogenation of acetophenone in aqueous solution using sodium formate and water as a hydrogen source. The best results were obtained (60 °C) with 7, giving a catalytic turnover frequency of 43 h-1 and an enantiomeric excess of 93 %.
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- PublicationAccès libreSynthesis, Structure, and Complexation Properties of Partially and Completely Reduced meso-Octamethylporphyrinogens (Calixpyrroles)
- PublicationAccès libreOptically active liquid-crystalline fullerodendrimers from enantiomerically pure fulleropyrrolidinesA synthetic methodology based on the 1,3-dipolar cycloaddition reaction was developed to design enantiomerically pure liquid-crystalline fullerodendrimers.