Synthesis and characterization of the homoleptic aryloxides [M{O(2,4,6-tert-Bu3C6H2)}2]2 (M = manganese, iron), the adducts [Mn(OCPh3)2(py)2] and [Fe(OCPh3)2(THF)2], and the mixed complex [Fe{N(SiMe3)2}{.mu.-O(2,4,6-tert-Bu3C6H2)}]2: evidence for primarily ionic metal-oxygen bonding