2,6-Diphenylphenolates of calcium, strontium and barium exhibiting π-phenyl encapsulation of the partially naked cations

Solvent free 2,6-diphenylphenolates of calcium, strontium and barium have been prepared by direct reaction of the bulk metals with 2,6-diphenylphenol (HOdpp) at elevated temperatures in evacuated sealed tubes. Single-crystal X-ray diffraction studies of crystalline [Ca2(Odpp)2(μ-Odpp)2]·(PhMe) (1), [Sr2(Odpp)(μ-Odpp)3]·(PhMe) (2) or [Ba2(Odpp)(μ-Odpp)3] (3), obtained by toluene extraction of the reaction mixtures, revealed different binuclear structural frameworks. In 1, both Ca atoms have one terminal and two bridging aryloxide ligands in a pyramidal array with the coordination vacancies occupied by π-bonded pendant phenyl groups (an η3- and an η1-Ph on one Ca and an η6-Ph on the other). By contrast, 2 has unsymmetrical metal–oxygen coordination with one terminal and three bridging aryloxides attached to one metal and solely three bridging aryloxides bound to the other. There are additional intramolecular π-Ph–Sr interactions with three η1-Ph groups on the four coordinate Sr and three η2-Ph groups on the three coordinate Sr. In 3, the structure exhibits a similar metal–oxygen framework to 2, but there are an increased number of π-phenyl–M interactions (one η2-Ph and two η1-Ph on the four coordinate Ba and one η6-Ph, one η3-Ph and one η2-Ph on the three coordinate Ba).