Koordinationsambivalenz und elektronenstruktur ein- und zweikerniger methylcyclopentadienyldicarbonylmangan-komplexe der cyanpyridine und terephthalsäuredinitrile

Abstract

The ambident cyanopyridine ligands form N(pyridine) and N′(nitrile) coordinated mono- and binuclear complexes with the (C 5H 4CH 3)(CO) 2Mn fragment. All three possible forms for 4-cyanopyridine could be isolated, whereas mononuclear compounds were obtained as most stable species in N 1-coordinated form with 3-cyanopyridine and in CN 2-coordinated form with the 2-isomer. IR, NMR, and UV/VIS spectroscopy as well as electrochemistry and ESR spectroscopy of the anion radicals demonstrate superior π back-bonding via the pyridine nitrogen centers, the isolation of nitrile coordinated complexes is attributed to the kinetic stability of the CNMn bond. While terephthalonitrile was found to form exclusively mononuclear neutral complexes, its anion radical prefers to coordinate to a second metal fragment, illustrating the excellent coordination properties of reduced nitriles. A neutral binuclear complex could be isolated with the stronger π-acceptor, tetrafluoroterephthalonitrile.