Dinuclear TiIV and TiIII complexes supported by calix[4]arene ligands. Binding alkali-metal cations inside and outside the cavity of calix[4]arenes

New dinuclear TiIV and TiIII complexes with the calix[4]arene ligand C28H20O4H4 (H4L) have been isolated from the reaction of Ti(NMe2)4, H4L, and Na (or KC8) in THF. X-ray analyses revealed a similar core structure for the two complexes Na4(THF)8[TiIV 2(μ-O)2L2] (1) and K4(THF)8[TiIII 2(μ-NMe2)2L2] (2). Two titanium atoms are bridged by two oxygen atoms in 1 and by two dimethylamido groups in 2 and are also supported by two deprotonated calix[4]arene ligands in a cone conformation. This resulted in a similar Ti⋯Ti separation of about 3.29 Å in 1 and 3.28 Å in 2 and in a distorted octahedral environment for each Ti center in both complexes. In contrast, in a novel complex 3, Na2(THF)6[TiIII 2L2], two TiIII atoms are supported only by two deprotonated ligands. This results in a five-coordinate environment for both titanium(III) centers with the separation between them being 3.133(1) Å.