99829-87-5Relevant academic research and scientific papers
Aufbau von Heterocyclen durch -Cycloaddition von Uebergangsmetall-koordinierten Heteroolefinen mit Butadienen: zur Regioselektivitaet der Cycloaddition
Fischer, Helmut,Gerbing, Ulrike,Riede, Juergen
, p. 155 - 168 (2007/10/02)
The pentacarbonyl(thioaldehyde), -(selenoaldehyde), and -(selenoketone) complexes (CO)5M (I) (M = Cr: X = S, R = H (a); M = W: X = S, R = H (b); X = Se, R = H (c); X = Se, R = Ph (d)) react with 2,3-dimethyl-1,3-butadiene by -cycloaddition to give the metal-coordinated thia- and selenacycles, (CO)5M (IIIa-d).The Structure of IIId was established by an X-ray diffraction study.The reactions of Ia with 2-methyl-1,3-butadien (IV) and of Ia and Ib with trans-penta-1,3-diene (VI) are regioselective.The cycloaddition of IV to Ia yields the two isomers (CO)5Cr or (CO)5M in the ratio 2.4/1 (M = Cr) or 3/1 (M = W), respectively.The thiacycle can be cleaved from the metal intact by oxidation of IIIa with (NH4)2 in acetone.
Kinetische and mechanistische Untersuchungen von Uebergangsmetall-Komplex-Reaktionen; XXIV. Kinetische Untersuchungen zur -Cycloaddition von Diene an Uebergangsmetallkoordinierte Thioaldehyde, Selenoaldehyde und Selenoketone
Fischer, Helmut
, p. 65 - 78 (2007/10/02)
The pentacarbonyl(thioaldehyde), -(selenoaldehyde), and -(selenoketone) complexes (CO)5M (I) (M = Cr, X = Se, R = Ph; M = W, X = S, R = H; M = W, X = Se, R = H, Ph, C6H4Br-p, C6H4Me-p, C6H4OMe-p, C6H4NMe2-p) react with dienes such as cyclopentadiene, trans-1-methyl-1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, and 1,3-cyclohexadiene via -cycloaddition to give metal-coordinated thia- and selenacycles.The reaction follows second-order kinetics: -d/dt=k2*.The activation enthalpy ΔH is small (46 to 28.7 kJ/mol) and decreases along the series selenoketone, thioaldehyde, selenoaldehyde complex.The activation entropy ΔS is strongly negative (-144 to -147 J/(mol K)) and is indipendent of the type of complex.The rate constant k2 for the reaction with cyclopentadiene decreases clearly with increasing donor capacity of Y in (CO)5W.A good positive correlation is observed between k2 and the Hammett constants ρp of Y (ρ = 2.5).Exchange of R = Ph in (CO)5W for R = H accelerates the reaction with cyclopentadiene by a factor of 73500.In contrast the influences of X (k2(Se)=19.0*k2(S)), M (k2(W) = 1.87*k2(Cr)), and the solvent are small.The rate constant for the reaction of dienes with (CO)5W increases significantly along the series 1,3-cyclohexadiene ca. trans-1-methyl-1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, cyclopentadiene.A concerted biradicaloid mechanism is proposed.
