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).