Mixed Methyl Aryloxy Rare-Earth-Metal Complexes Stabilized by a Superbulky Tris(pyrazolyl)borato Ligand

Various mixed methyl aryloxide complexes TptBu,MeLnMe­(OAr) (Ln = Y, Lu) were obtained in moderate to high yields according to distinct synthesis protocols dependent on the metal size and sterics of the phenolic proligand. The reaction of TptBu,MeLuMe2 and TptBu,MeYMe­(AlMe4) via protonolysis with 1 or 2 equiv HOC6H2tBu2-2,6-Me-4 in n-hexane gave the desired complexes TptBu,MeLnMe­(OAr). Corresponding treatment of TptBu,MeLuMe2 with the sterically less demanding HOC6H3Me2-2,6, HOC6H3iPr2-2,6 and HOC6H3(CF3)2-3,5 led to the formation of the bis­(aryloxy) lutetium complexes TptBu,MeLu­(OAr)2. Application of a salt-metathesis protocol employing TptBu,MeLnMe­(AlMe4) and the potassium aryloxides KOAr made complexes TptBu,MeLnMe­(OAr) accessible for the smaller aryloxy ligands as well. All complexes were analyzed by X-ray crystallography to compare the terminal Ln–Me bond lengths and to evaluate the implication of the methyl/aryloxy coordination for the exact cone angles Θ° of the [TptBu,Me] ancillary ligand. Treatment of TptBu,MeLnMe­(AlMe4) (Ln = Lu, Y) with HOC6H2tBu2-2,6-Me-4 in the presence of 4-(dimethylamino)­pyridine (dmap) produced ion-separated complexes [TptBu,MeLnMe­(dmap)2]­[Me3AlOC6H2tBu2-2,6-Me-4)]. The thermal instability of TptBu,MeLuMe­(OC6H2tBu2-2,6-Me-4) was revealed by the formation of (Tp(tBu‑H)/(tBu)2,Me)­Lu­(OC6H2tBu2-2,6-Me-4) via intramolecular C–H-bond activation.