Übergangsmetalkoordinierte Heteroolefine als Synthesebausteine : Einfluss des Alkins auf die Geschwindigkeit und die Stereoselektivität der Reaktion mit Heteroaldehyd- bzw. -keton-Komplexen

Abstract Pentacarbonyl-(-thio- and -seleno-aldehyde) complexes and pentacarbonyl(diphenylselenoketone) complexes, (CO) 5 M[XC(Ph)R] (M  W: X  S, R  H (Ia); X  Se, R  H (Ib); X  Se, R  Ph (Ic); M  Cr: X  Se, R  Ph (Id)), react with bis(diethylamino)acetylene, Et 2 NcCNEt 2 (II) by [2 + 2]-cycloaddition of the alkyne to the XC bond of I, and with electrocyclic ring opening to give the pentacarbonyl-(-thio- and -seleno-acrylamide) complexes, (CO) 5 M[XC(NEt 2 )C(NEt 2 )C(Ph)R] (III). If R  H, ring opening is stereospecific. According to the NMR spectra, only the E isomer (with respect to the CC double bond) is formed. Compounds IIIa and IIIb were studied by X-ray crystallography. The plane of the amido group, XC(N)C, is almost perpendicular to that of the olefin, C(N)CC. The reaction of Ic with II in 1,1,2-trichloroethane follows second-order kinetics: −d[Ic]/d t = k 2 [Ic][II]. The activation enthalpy Δ H * is small (27(2) kJ/mol), and the activation entropy Δ S * is strongly negative (−164(8) J/(mol K)). Cleavage of the CrSe Bond in IIId is achieved by applying a CO pressure (105 bar) at 70°C and the selenoacrylamide SeC(NEt 2 )C(NEt 2 )CPh 2 is isolated in almost quantitative yield.