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 = OCMe(2)CH(2)[1-C(NCHCHN(i)Pr)]) and HL(s) (L(s) = OCMe(2)CH(2)[1-C(NCH(2)CH(2)N(i)Pr)]) 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-HL(s))Ce(O'Bu)(3)] were isolated. However, the salt metathesis of cerium triflate with KL provided a simple route to [CeL(4)], 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 [CeL(4)].