Zwei die zusammenpassen: Ausgezeichnete Regio‐, endo/exo‐, Diastereo‐, und/oder Enantioselektivitäten sind das Markenzeichen einer Cu‐katalysierten Cycloaddition von Nitronen an α′‐Hydroxyenone (siehe Schema). Die Addukte können in die entsprechenden Isoxazolidin‐Aldehyde, ‐Ketone und ‐Carbonsäuren umgewandelt werden.

The N-heterocyclic carbenes (NHCs) 1,3-dialkyl-4,5-dimethylimidazol-2-ylidene (alkyl = ethyl, IEt2Me2; isopropyl, IiPr2Me2) and 1,3-di-isopropylimidazol-2-ylidene (IiPr2) cleave Ru3(CO)12 at room temperature to give the mononuclear complexes Ru(NHC)2(CO)3 (NHC = IEt2Me2 1; IiPr2Me2 2; IiPr2, 3 ). X-ray crystallography reveals that 1 contains trans-NHC ligands whereas 2 and 3 have an unexpected cis arrangement of carbenes. Exposure of 1−3 to air in the solid state or upon reaction with O2 in solution yields the carbonato complexes Ru(NHC)2(CO)2(CO3) (NHC = IEt2Me2 4, IiPr2Me2 5, IiPr2, 6).

The first examples of abnormal coordination of Ardeungo's carbene, 1,3-bis-adamantylimidazol-2-ylidene, have been isolated and structurally characterised following reaction of the free carbene with the trinuclear clusters M(3)(CO)(12) (M = Ru, Os).

Thermolysis of [Ru(AsPh3)3(CO)H2] with the N-aryl heterocyclic carbenes (NHCs) IMes (1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), IPr (1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) or the adduct SIPr.(C6F5)H (SIPr=1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene), followed by addition of CH2Cl2, affords the coordinatively unsaturated ruthenium hydride chloride complexes [Ru(NHC)2(CO)HCl] (NHC=IMes , IPr , SIPr ). These react with CO at room temperature to yield the corresponding 18-electron dicarbonyl complexes . Reduction of and [Ru(IMes)(PPh3)(CO)HCl] () with NaBH4 yields the isolable borohydride complexes [Ru(NHC)(L)(CO)H(eta2-BH4)] (, L=NHC, PPh3). Both the bis-IMes complex and the IMes-PPh3 species react with CO at low temperature to give the eta1-borohydride species [Ru(IMes)(L)(CO)2H(eta1-BH4)] (L=IMes , PPh3), which can be spectroscopically characterised. Upon warming to room temperature, further reaction with CO takes place to afford initially [Ru(IMes)(L)(CO)2H2] (L=IMes, L=PPh3) and, ultimately, [Ru(IMes)(L)(CO)3] (L=IMes , L=PPh3). Both and lose BH3 on addition of PMe2Ph to give [Ru(IMes)(L)(L')(CO)H2](L=L'=PMe2Ph; L=PPh3, L'=PMe2Ph). Compounds and have been tested as catalysts for the hydrogenation of aromatic ketones in the presence of (i)PrOH and H2. For the reduction of acetophenone, catalytic activity varies with the NHC present, decreasing in the order IPr>IMes>>SIMes.

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Protonation of the N-heterocyclic carbene (NHC) complex Ru(IPr)2(CO)H(OH) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with HBF4·OEt2 in thf affords the cationic aqua hydride complex [Ru(IPr)2(CO)H(OH2)](BF4), whereas if the solvent is changed to benzene, loss of imidazolium salt and H2O occurs to leave the 12e fragment [Ru(IPr)(CO)H] + , which is isolated as the cationic arene species [Ru(IPr)(η6-C6H6)(CO)H](BF4).