The redox chemistry between divalent lanthanide complexes bearing bulky amidinate ligands has been studied with 3d transition metal carbonyl complexes (iron and cobalt). The reaction of [(DippForm)2Smǁ(thf)2] (DippForm = N,N′-bis(2,6-diisopropylphenyl)formamidinate) with [Co2(CO)8] resulted in the formation of a tetranuclear Sm–Co complex, [{(DippForm)2Smǁǀ(thf)}2{(μ-CO)2Co(CO)2}2]. The product of the reaction of [(DippForm)2Ybǁ(thf)2] and [Co2(CO)8] gives the dinuclear Yb–Co complex [{(DippForm)2Ybǁǀ(thf)}{(μ-CO)Co(CO)3}] in toluene. The reaction of [(DippForm)2Smǁ(thf)2] was also carried with the neighbouring group 8 carbonyl complexes [Fe2(CO)9] and [Fe3(CO)12], resulting in a pentanuclear Smǁǀ–Fe complex, [{(DippForm)2Smǁǀ}2{(μ3-CO)2Fe2(CO)9}], featuring a triangular iron carbonyl cluster core