Thermochemistry of pentacarbonyl(2-propenyl)manganese and tetracarbonyl(eta(3)-2-propenyl)manganese. Thermochemical considerations in alkenyl isomerisation reactions

Microcalorimetric measurements at elevated temperatures of the enthalpies of sublimation, thermal decomposition and iodination of [Mn(CO)(5)(eta(1)-C3H5)] and [Mn(CO)(4)(eta(3)-C3H5)] have been made to obtain the standard enthalpies of formation Delta(f)H(m) degrees(cr) and Delta(f)H(m) degrees(g) (in that order) as follows (values in kilojoules per mole): [Mn(CO)(5)(eta(1)-C3H5)] -(727 +/- 20), -(679 +/- 25); [Mn(CO)(4)(eta(3)-C3H5)] -(651 +/- 12), -(570 +/- 15). The values of Delta(f)H(m) degrees(g) are used to derive enthalpy contributions for the (propenyl-Mn) bonds in these molecules, and thus to provide thermochemical information on the irreversible eta(1) --> eta(3) isomerisation reaction involved. (C) 1997 Elsevier Science S.A.