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Synthesis of a Ruthenium(II) Complex Containing an [11]ane-P2CNHC (NHC = Imidazolidin-2-ylidene) Macrocycle

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posted on 09.11.2009, 00:00 by Aarón Flores-Figueroa, Oliver Kaufhold, Alexander Hepp, Roland Fröhlich, F. Ekkehardt Hahn
Reaction of [RuCl(Cp)(PPh3)2] with bis[di(2-fluorophenyl)phosphino]benzene, 3, yields complex [RuCl(Cp)(3)], [4]. The chloro ligand in [4] can be exchanged for the 2-azidoethyl isocyanide ligand 2, giving complex [Ru(Cp)(2)(3)]Cl, [5]Cl, which reacts with NH4BF4 to give [5]BF4. The azido group of the coordinated isocyanide ligand in [5]Cl or [5]BF4 can be reduced with Zn/NH4Cl/H2O to give the complex with the 2-aminoethyl isocyanide ligand. This ligand is not stable but cyclizes by an intramolecular nucleophilic attack of the amino group at the isocyanide carbon atom to give an NH,NH-stabilized NHC ligand in complexes [6]X (X = Cl, [6]Cl; X = 0.5 ZnCl4, [6]2(ZnCl4); X = BF4, [6]BF4). Deprotonation of the NH,NH-stabilized NHC ligands in cations of type [6]+ leads to an intramolecular nucleophilic attack of the amido nitrogen atoms at the fluorinated phenyl groups of the diphosphine ligand under formation of the complex with the facially coordinated macrocyclic [11]ane-P2CNHC ligand [1]X (X = Cl, [1]Cl; X = 0.5 ZnCl4, [1]2(ZnCl4); X = BF4, [1]BF4). Formation of the macrocycle is facilitated by the steric pressure excerted by the cyclopentadienyl ligand. The molecular structures of [4], [5]BF4, [6]BF4·CH2Cl2, and [1]Cl·CH2Cl2·0.5H2O have been determined by X-ray diffraction.