Non-innocen t"-Liganden in elekt8ronenreichen Komplexen der spaten d-Elemente
Egon UhligFriedrich-Schiller-UniversitBt J e m , Sektion Chemic, Jena, DDR-G90O Professor Ur. Ur. h.c. Lothar Kolditz mm 60. Geburtstug gewidmet Summary The coordination behaviour of p-quinones and p-quinone fragments in electron-rich complexes is variable. Considering primarily the nickel triade elements, p-quinones are bound to palladium( 0) or platinum(0) by the C=C-groups (rlz-or +interaction). With nickel(0) the behavior is more complicated. $(C=C)-wordination is found for Ni(Dch), and rj+oordination for (dipy)Ni(Nch). But because of the stronger oxophilic properties of this element, also a n q2(C=O)-coordination is possible, as was shown .for (Cy,P),Ni(Ach) . Et,O. I n complexes with a low wntent of phosphine the donors R-cum or Nch have the function of 773(C=C, 0)-bridging ligands. Chloranile with its high half-wave potential oxidises nickel(0) to nickel(II) and is simultaneously reduced to the dianion of the corresponding hydroquinone. I n another case -(Cy,P)"i(Ach?)the redox process stops at the state of nickel(I) and of the radical anion. It is a general rule, that both I , 5-cyclooctadiene as a simple diolefine and normal p-quinones can coordinate to nickel(0) or nickel(I) as n-acceptor ligands by the C=Cor in the cuse of Ach even by the C=O-group. This i s not possible with nickelflf) which is only a weak n-donor. Tertiary phosphines attack Bch, CA, NCh or MSA nucleophilicully forming phosphabetaines. Because of the lower nucleophilicity of the phosphine and the lower electrophilicity of the p-quinone in the coordination sphere of electron-rich central atoms this reaction does not proceed. The systems of (Cy,P),Ni(C,H,) with CA, Bch and MSA are exceptional. In these cases the formation of phosphabetaines is connected with a n one-electron transfer. The productsare nickel(If)species with radical anions as ligands. I n general the normal reactions of p-qninones are hindered in the coordination sphere of electron-rich complexes. But sometimes other pathways of synthetic use are opend.
EinleitungDie Konzeption der ,,uon-innocent"-Liganden wurde in den secliziger Jahren entwickelt und geht im wesentlichen auf C. K. Jorgensen zuruck. In Komplexen, in denen kovalente Wechselwirkungen dominiercn, konnen Liganden dieses Typs sowohl als n-Donatoren als auch als n-Akzeptoren wirken. Die Balance zwischen Donator? und Akzeptorbexiehungen und als Folge davon die effektive negative Ladung dieser Liganden hangen wesentlich von der Zahl drr verfiigbaren auBeren Elektronen ab. Wenn diese Zahl groD ist, wird es schwierig, wenn nicht gar unmoglich, die Oxidationsstufe des Zentralatoms verlaiBlich anzugeben. Das muD auch bei der Interpretation von Redoxprozessen beachtet werden [l]. Typische ,,non-innocent"-Liganden sind die Dithio-a-diketone, das Tetrathiooxolatanion [2], die 1,4-Diaza-l, 3-diene und mit EinschrBnkungen das a,a'-Dipyridyl (dipy) [3]. Alle diese Verbin-dungen bilden funfgliedrige Chelate. A19 Sauerstoffanaloga konnen die Komplc...
