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=OCMe₂CH₂1‐C(NCHCHNⁱPr)]) and HL^S (L^S=OCMe₂CH₂1‐C(NCH₂CH₂NⁱPr)]) 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^tBu)₃Ce(μ‐O^tBu)₂(μ‐HL)Ce(O^tBu)₃], or imidazolinium adducts (O^tBu)₃Ce(μ‐O^tBu)₂(μ‐HL^S)Ce(O^tBu)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].