Add time:08/05/2019         Source:sciencedirect.com

Chloro- and bromo-(alkene)iridium(I) complexes were prepared by the reaction of monoenes, acyclic conjugated dienes, and cyclic polyenes with the cyclooctene complexes IrX(C3H14)2 with X = Cl or Br.IrCl(C2H4)4 is an unstable penta-coordinated compound from which the planar chlorine-bridged dimer [IrCl(C2H4)2]2 is formed upon ethylene dissociation. From the absence of broadening of the ethylene PMR resonances in chloroform upon cooling to −60°C, low barriers to rotation of the ethylene ligands around the metal-alkene bond were concluded. In toluene the appearance at −60°C of the “frozen out”-situation for the equatorial ligands suggested a considerably higher barrier for these ligands in this solution. The equatorial ethylene ligands show slow exchange with free ethylene by an associative mechanism. No exchange with the axial ethylene ligand could be detected.Acyclic conjugated dienes formed penta-coordinated complexes of the type IrX(alk)2.1,5-Cyclooctadiene formed the dimer complexes [IrX(C8H12)]2 and the monomer complexes IrX(C8H12)2.The investigation of the bromo compounds was limited to their identification by elementary analysis and by their IR spectrum in the 4000–400 cm−1 region. Their far-IR spectra were used as an aid in the assignment of the ν(IrCl) in the corresponding chloro compounds.From the comparison of the far-IR spectra of corresponding chloro(alkene)-rhodium(I) and -iridium(I) complexes it was concluded that the metal-alkene as well as the metal-chlorine bonds are stronger in the iridium(I) compounds.

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