Synthesis and structures of the group 1 metal/germanium cage complexes [M(μ-OC6H3Ph2-2,6)3Ge] (M = Li, Na, K, Rb, Cs);: periodic trends and alkali metal dependent arene bonding

Reaction of three equivalents of the alkali salts of 2,6-diphenylphenoxide, [MOC6H3Ph2-2,6] (M = Li, Na, K, Rb, Cs) with GeI2 provides the corresponding cage complexes [M(mu-OC6H3Ph2-2,6)(3)Ge], all of which have been structurally characterized. These species contain a germanium(II) metal and an alkali metal connected by the oxygen atoms of the bridging aryloxide ligands. The two metal atoms are at the apices of a five-atom trigonal bipyramidal metal framework. The alkali cations are also bound to the carbon atoms of three of the 2,6-diphenyl substitutents of the aryloxide ligands. The number of bonds to these arene rings is strongly dependent on the identity of the alkali metal. This results in high formal coordination numbers for the group 1 metals K, Rb and Cs. The germanium and alkali metal form similar bonds to all three aryloxide oxygens except in the case of the caesium compound. In this case some localization of bonding occurs with structural parameters more consistent with a caesium aryloxide adduct of a germanium(II) bis(aryloxide).