Abstract
Despite the interest in them, easily isolable and thermally stable Cu^I^, Ag^I^, and Au^I^ complexes of ethylene are stilllimited and get increasingly sparse as one descends the group 11 triad towards gold. Recently, there have been some notable developments in this field, including the isolation of gold–ethylene complexes and coinage‐metal adducts with more than one ethylene molecule on a metal center. This article focuses on the chemistry of coinage‐metal–ethylene adducts that have been synthesized and characterized by X‐ray crystallography. Thus far, bidentate and tridentate donors based on nitrogen appear to be the ligands of choice forstabilizing species with an M–C~2~H~4~ (M = Cu^I^, Ag^I^, and Au^I^) moiety. Weakly donating ligands and anions are also commonly used, as they do not interfere with and displace the ethylene from the metal center. The ethylene ^13^C NMR chemical shift provides useful information about the nature of the metal–ethylene interaction. In some adducts (especially those with relatively weak M–C~2~H~4~ interactions), the change in the C=C bond length upon coordination to the metal site is difficult to discern because it falls within the errors associated with the crystallographically determined C=C bond length value. IR and Raman C=C stretching data would be useful but, probably due to the very weak nature of the IR band and the lack of convenient access to the Raman instruments, are often not reported. In this microreview, results from some computational and gas‐phase spectroscopic studies are also provided for comparison.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)