Rare Earth Complexes of Bulky 2,6-Diphenylphenolates Containing Additional, Potentially Buttressing 3,5-Substituents

The rare earth aryloxide complexes, [Yb(OArtBu)3(THF)]·THF, [Sc(OArtBu)3(THF)]·THF, [Yb(OArMe)3(THF)], and [Sm(OArPh)3(THF)2] (OArR = 2,6-diphenyl-3,5-di-R-phenolate), have been prepared by redox transmetallation/ligand exchange between the rare earth metal, bis(pentafluorophenyl)mercury, and HOArR in tetrahydrofuran. This reaction also provided [Yb(OArPh)3(DME)]·3/2THF by incorporation of adventitious 1,2-dimethoxyethane. A similar reaction between Yb metal, diphenylmercury, and HOArMe gave [Yb(OArMe)2(THF)3]. The homoleptic complexes [Yb(OArPh)3] and [Sc(OArH)3] have been prepared by direct reaction of the rare earth element with HOArR in a sealed tube in the presence of mercury at elevated temperatures (200−250 °C) and the latter was converted into [Sc(OArH)3(THF)] by treatment with THF. X-ray crystal structure determinations of [Yb(OArtBu)3(THF)]·THF, [Sc(OArtBu)3(THF)]·THF, and [Yb(OArMe)3(THF)] show the complexes to be monomeric and four coordinate with a trigonal pyramidal stereochemistry. These structures provide clear evidence that groups meta to the phenolate donor can modify the coordination behaviour of the 2,6-diphenylphenolate ligand. In [Yb(OArPh)3(DME)]·3/2THF a distorted square pyramidal stereochemistry is observed. The divalent complex [Yb(OArMe)2(THF)3] exhibits a distorted trigonal bipyramidal arrangement of the oxygen donor atoms with apical THF ligands. The homoleptic scandium 2,6-diphenylphenolate has three oxygen atoms in a triangular array with additional π-η1-Ph···Sc interactions above and below the ScO3 plane [C−Sc−C = 154.2(8)°], providing a new type of binding of this aryloxide ligand.