Organometallic Cerium Complexes from Tetravalent Coordination Complexes

The use of tetravalent cerium alkoxides, nitrates, and triflates was studied as a direct route to [Ce-IV(carbene)] complexes. Protonolysis reactions between 1H-imidazolium- or imidazoline (=4,5-dihydro-1H-imidazole)-containing alkoxide proligands HL (L = OCMe2CH2[1-C((NCHCHNPr)-Pr-i)]) and HLs (L-s = OCMe2CH2[1-C((NCH2CH2NPr)-Pr-i)]) and Ce-IV tert-butoxide, triflate, and nitrate compounds were studied to target [Ce-IV(N-heterocyclic carbene)] complexes (of unsaturated and saturated carbenes, resp.). Instead, tetravalent cerium imidazolium [(O'Bu)(3)Ce(mu-O'Bu)(2)(mu-HL)Ce(O'Bu)(3)], or imidazolinium adducts [(O'Bu)(3)Ce(mu-O'Bu)(2)(mu-HLs)Ce(O'Bu)(3)] were isolated. However, the salt metathesis of cerium triflate with KL provided a simple route to [CeL4], which was significantly improved if an external oxidant, benzoquinone, was included in the mixture to maintain oxidation-state integrity. Likewise, the salt metathesis of cerium triiodide with KL and added benzoquinone provided a straightforward route to [CeL4].