Angew.Chem.Int.Ed.http://doi.org/fz4psr(2012)

Credit: © 2012 WILEY

The reactivity of organometallic compounds with oxygen has been explored since the early days of organometallic chemistry. Peroxides — in which the metal centre bears an –OOR ligand (where R is an alkyl group) — are very reactive, rendering the insertion of dioxygen into metal–carbon bonds difficult to control, and intermediates and mechanisms difficult to identify. Studies on zinc complexes have shown that peroxides could be stabilized, and in turn isolated, with chelating ligands. But although the in situ generation of cadmium peroxides has also been suggested, their characterization has remained elusive.

Kieran Molloy and co-workers at the University of Bath have now obtained crystals of organo-cadmium peroxides, and unambiguously characterized them by X-ray diffraction. They relied on a tridentate ligand featuring two stabilizing dimethyl-amino groups and a hydroxyl moiety (bdmap), previously shown to support the formation of an organozinc peroxide.

The complex [{MeCd(bdmap)3}·CdMe2] was first produced by reaction of dimethyl cadmium and bdmap in a 4:3 ratio, and subsequently submitted to an atmosphere of dry oxygen at low temperature. This yielded a double peroxide in which two {MeCd(bdmap)}2 units are held together by a {Cd(OOMe)} moiety. This complex was in turn subjected to an O2-insertion step, this time at room temperature, which led to a triple peroxide complex in which the central cadmium ion adopts a {MeCdO5} coordination environment. Such a pentadentate peroxy unit has not been observed previously with zinc, presumably because it can't accommodate the higher coordination numbers that cadmium can.Both organo-cadmium peroxides rapidly decompose into oxo clusters.