Potential Precursors for Terminal Methylidene Rare-Earth-Metal Complexes Supported by a Superbulky Tris(pyrazolyl)borato Ligand.

Abstract

A series of solvent‐free heteroleptic terminal rare‐earth‐metal alkyl complexes stabilized by a superbulky tris(pyrazolyl)borato ligand with the general formula [TptBu,MeLnMeR] have been synthesized and fully characterized. Treatment of the heterobimetallic mixed methyl/tetramethylaluminate compounds [TptBu,MeLnMe(AlMe4)] (Ln=Y, Lu) with two equivalents of the mild halogenido transfer reagents SiMe3X (X=Cl, I) gave [TptBu,MeLnX2] in high yields. The addition of only one equivalent of SiMe3Cl to [TptBu,MeLuMe(AlMe4)] selectively afforded the desired mixed methyl/chloride complex [TptBu,MeLuMeCl]. Further reactivity studies of [TptBu,MeLuMeCl] with LiR or KR (R=CH2Ph, CH2SiMe3) through salt metathesis led to the monomeric mixed‐alkyl derivatives [TptBu,MeLuMe(CH2SiMe3)] and [TptBu,MeLuMe(CH2Ph)], respectively, in good yields. The SiMe4 elimination protocols were also applicable when using SiMe3X featuring more weakly coordinating moieties (here X=OTf, NTf2). X‐ray structure analyses of this diverse set of new [TptBu,MeLnMeR/X] compounds were performed to reveal any electronic and steric effects of the varying monoanionic ligands R and X, including exact cone‐angle calculations of the tridentate tris(pyrazolyl)borato ligand. Deeper insights into the reactivity of these potential precursors for terminal alkylidene rare‐earth‐metal complexes were gained through NMR spectroscopic studies.