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

A series of solvent-free heteroleptic terminal rare-earth-metal alkyl complexes stabilized by a superbulky tris(pyrazolyl)borato ligand with the general formula [Tp LnMeR] have been synthesized and fully characterized. Treatment of the heterobimetallic mixed methyl/tetramethylaluminate compounds [Tp LnMe(AlMe )] (Ln=Y, Lu) with two equivalents of the mild halogenido transfer reagents SiMe X (X=Cl, I) gave [Tp LnX ] in high yields. The addition of only one equivalent of SiMe Cl to [Tp LuMe(AlMe )] selectively afforded the desired mixed methyl/chloride complex [Tp LuMeCl]. Further reactivity studies of [Tp LuMeCl] with LiR or KR (R=CH Ph, CH SiMe ) through salt metathesis led to the monomeric mixed-alkyl derivatives [Tp LuMe(CH SiMe )] and [Tp LuMe(CH Ph)], respectively, in good yields. The SiMe elimination protocols were also applicable when using SiMe X featuring more weakly coordinating moieties (here X=OTf, NTf ). X-ray structure analyses of this diverse set of new [Tp LnMeR/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.