Aktivierung von CO 2 an übergangsmetallzentren: Zum ablauf der homogen-katalytischen Bildung von 2-Pyron aus Kohlendioxid und Hex-3-in an Nickel(0)-Fragmenten

Abstract

IR-investigations of the catalytic formation of tetraethyl-2-pyrone from hex-3-yne and CO 2 at (TMED)Ni 0- or (COD)Ni 0 centres show that in the first step of this reaction the nickel(0) complex reacts under oxidative coupling with both CO 2 and alkyne to afford the five-membered metallacycle A. The alternative route, the oxidative coupling of two alkynes at nickel(0), can be excluded. Complex A reacts in a second step with a further molecule alkyne to yield compound B, which undergoes a reductive elimination forming the 2-pyrone C. The insertion of CO 2 into A and the “reductive disproportionation of CO 2 at (TMED)Ni 0 are deactivation reactions of the catalytic cycle forming the trimeric carbonato complex D and the Ni 0 compound E bearing diethylmaleic anhydride. The structure of complex A was determined by X-ray analysis.