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

Article abstract of DOI:10.1016/0022-328X(88)87081-5

Pentacarbonyl-(-thio- and -seleno-aldehyde) complexes and pentacarbonyl(diphenylselenoketone) complexes, (CO)3M (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, Et2NCCNEt2 (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)5M (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/dt = k₂.The actvation enthalpy ΔH is small (27(2) kJ/mol), and the activation entropy ΔS 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 deg C and the selenoacrylamide Se=C(NEt2)C(NEt2)=CPh2 is isolated in almost quantitative yield.