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ChemInform Abstract The reaction of the thio-and selenobenzaldehyde complexes (I) with the alkyne (II) leads to substitution of four CO ligands by two molecules of (II) with formation of the title complexes (III). At room temp. (III) are present in solution as an isomeric mixture, at elevated temp. rapid isomerization is observed. From the X-ray analysis of (IIIb) (space group P212121, Z=4) it follows that the aldehyde ligand is η2-bonded and that the multiple bonds of the alkyne, the CO, and the aldehyde ligands are nearly parallel in the mode shown.

Pentacarbonyl(thioaldehyd)-, -(selenoaldehyd)-und -(selenoke-tonstereospecific. According to the NMR spectra and to an X-ray structure analysis of 3b, the E isomer (with respect to the C = C double bond) is formed. By applying CO pressure (105 bar) at elevated temperatures, the thio-and selenoacrylamide ligands can be cleaved off the metal unchanged. The compound Se = C(NEt2)C(Me)=CPhz (4c) was investigated by X-ray analysis.

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