Kinetische und mechanistische Untersuchungen von Uebergangsmetall-Komplex-Reaktionen XXIII*. Kinetik und Mechanismus der Reaktion von 1-Dimethylamino-1-propin mit uebergangsmetallkordinierten Selenoketonen

Article abstract of DOI:10.1016/0022-328X(87)85129-X

The pentacarbonyl(arylphenylselenoketone) complexes (CO)5M (M = Cr, R = H (Ia); M = W, R = H (Ib), Br (Ic), OMe (Id), NMe2 (Ie)) react with 1-diethylamino-1-propyne, Et2NC<*>CMe (II), via <2 + 2>-cycloaddition across the C<*>C triple bond of II to teh Se=C bond of I and electrocyclic ring-opening to give selenoacrylamido complexes, (CO)5M (III).The reaction follows second-order rate kinetics: -d/dt = k₂.For the reaction of I with II in toluene the activation enthalpy ΔH<*> is 29(1) kJ/mol for both Ia and Ib, the activation entropy Δ<*> is -152(5) J/(mol K) for Ia and -161(2) J/(mol K) for Ib.The rate constant k₂ decreases clearly with increasing donor caoacity of R in Ib-e.A good positive correlation is observed between k₂ and the Hammett constants ?_p of the R with ρ = 2.50.In contrast, the influence of the metal and the solvent is small.At 20.6 deg C, k₂(W) is only 3.48 k₂(Cr) (for R = H in toluene) and K₂ (nitrobenzene) = 6.8 k₂ (decane).A concerted biradicaloid mechanism with an early transition state is proposed.Reaction of the Se=C bond of I with 1-diethylamino-1-propyne is compared with the reaction of WW=C, O=C and S=C bonds with same alkyne.