Terphenylthiolate-Ligated Lanthanide Terminal Methyl Complexes Form Crystallographically Characterizable Terminal Acyls and Trimethylcyclopropanetriolates from Carbon Monoxide

The sterically bulky terphenylthiolate ligand {S[C₆H₃-2,6-(C₆H₂-2,4,6-^<i>i</i>Pr₃)₂]}^1-, (SAr^<i>i</i>Pr6)^1-, has permitted the isolation of the terminal methyl complexes Ln(SAr^<i>i</i>Pr6)₂CH₃, <b>1-Ln</b>, Ln = La and Nd, from salt metathesis between Ln(SAr^<i>i</i>Pr6)₂I and methyllithium. These complexes react with carbon monoxide to afford the first structurally authenticated examples of terminal acyl complexes of the rare-earth elements, Ln(SAr^<i>i</i>Pr6)₂(η²-OCCH₃), <b>2-Ln</b>. However, in the presence of lithium iodide, the reaction between Ln(SAr^<i>i</i>Pr6)₂CH₃ and CO forms the unique trimethylcyclopropanetriolate trianion, [cyclo-(OCCH₃)₃]^3-, in the complex [Ln(SAr^<i>i</i>Pr6)(μ-I)(μ-OCCH₃)]₃, <b>3-Ln</b>. This CO insertion product arises from the formation of six C-C bonds, demonstrating the power of the (SAr^<i>i</i>Pr6)^1- ligand to generate new organometallic rare-earth metal reaction chemistry with CO.