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.