Noble metals such as platinum are effective catalysts because they can switch reversibly between oxidation state zero and two. Redox activity in metals like iron on the other hand are 1 electron events with less appeal to organic chemistry. That so-called non-innocent ligands can alter the oxidation state of the central metal is well established but the key point made by Chirik & Wieghardt is that ligands (as radicals) can also assist metals in redox activity. As always nature provides inspiration: in the two-electron oxidation of an alcohol to an aldehyde by galactose oxidase , its copper atom gives up just one electron and the other is provided by the tyrosine ligand which in the active state is a free radical. In other scenarios the ligands change the oxidation state of the metal and it is even possible for the ligand to do al the redox action.
Some random examples: hydrazine oxidation (Blackmore et al. 2008 DOI) , manganese(IV)-monoradical complex (Mukherjee et al. 2009 DOI) , dihydrogen oxidation (Ringenberg et al. 2008 DOI)