Isolation of a Terminal Co(III)-Oxo Complex

Late
transition metal oxo complexes with high d-electron counts
have been implicated as intermediates in a wide variety of important
catalytic reactions; however, their reactive nature has often significantly
limited their study. While some examples of these species have been
isolated and characterized, complexes with d-electron counts >4
are
exceedingly rare. Here we report that use of a strongly donating tris­(imidazol-2-ylidene)­borate
scaffold enables the isolation of two highly unusual CoIII-oxo complexes which have been thoroughly characterized by a suite
of physical techniques including single crystal X-ray diffraction.
These complexes display O atom and H atom transfer reactivity and
demonstrate that terminal metal oxo complexes with six d-electrons
can display strong metal–oxygen bonding and sufficient stability
to enable their characterization. The unambiguous assignment of these
complexes supports the viability of related species that are frequently
invoked, but rarely observed, in the types of catalytic reactions
mentioned above. The studies described here change our understanding
of the reactivity and bonding in late transition metal oxo complexes
and open the door to further study of the properties of this class
of elusive and important intermediates.