Metallosupramolecular chemistry combines versatile polydentate organic ligands and transition metals in the design and synthesis of sophisticated assemblies of noncovalently attached components. [1] Various supramolecular architectures, such as helicates, [1e, 2] boxes, [3] grids, [4] squares, [5] molecular containers, [6] and others, [7] have been obtained from metal-directed spontaneous self-assembly reactions. Among these, metallohelicates [1e, 2] have gathered special interest due to the presence of the helical structure in nature. The DNA motif has been transferred to metallosupramolecular dinuclear double-and triple-stranded helical complexes by using ligands with amine or catecholato [2, 8] donor groups. Recently, we prepared the first dinuclear triple-stranded helicates based on bis(benzene-o-dithiolato) [9] and mixed benzene-o-dithiolato/catecholato ligands. [10] Raymond et al. introduced a 1,5-naphthalene-bridged dicatechol ligand H 4 -L, [6d, 11] which was designed to prevent the formation of a dinuclear triple-standed helicate [M 2 (L) 3 ] nÀ and thus reacted with metal ions to yield tetranuclear tetrahedral clusters of type [M 4 (L) 6 ] 2nÀ in which the dicatecholato ligands bridge the vertices of the tetrahedron. [6d, 11] We showed that the analogous bis(benzene-o-dithiol) ligand, against our expectations, reacts with Ti 4 + to yield a dinuclear triple-standed helicate. [12] Since linear bis(benzene-odithiol) ligands appear unsuitable for the generation of a tetrahedral tetranuclear cluster, we turned to tripodal tris-(benzene-o-dithiol) ligands. Raymond et al. [6c, 11] and Albrecht et al. [13] have shown that tripodal tricatechol ligands like H 6 -A are capable of forming tetranuclear tetrahedral clusters of type [M 4 (A) 4 ] mÀ . We have transferred this design principle to tris(benzene-o-dithiol) ligands. Ligand H 6 -B, however, is flexible enough to react with Ti 4 + to yield the mononuclear siderophor analogue [14] complex anion [Ti(B)] 2À . [15] Reduction of the lengths of the ligand arms by one methylene group each leads to the essentially planar ligand H 6 -1, which like H 6 -A is incapable of forming mononuclear chelate complexes. We report here on the preparation of ligand H 6 -1, its reaction with Ti 4 + , and on the unusual structural properties of the tetranuclear pseudo-tetrahedral cluster [Ti 4 (1) 4 ] 8À obtained in this reaction (Scheme 1).
The synthesis of the C 3 -symmetric ligand H 6 -1 was achieved by following a previously published procedure (Scheme 1). 1,3,5-Triaminobenzene (2), [6c] obtained by reduction of 3,5-dinitroaniline with Raney-Ni, was reacted with 2,3-di(isopropylmercapto)benzoic acid chloride (3) [16] to produce the S-alkylated ligand precursor 4. Elimination of the isopropyl groups with sodium/naphthalene provided ligand H 6 -1 in a yield of 82 % (see Supporting Information). [16] Reaction of ligand H 6 -1 with [TiA C H T U N G T R E N N U N G (OPr) 4 ] in methanol, in the presence of Li 2 CO 3 /K 2 CO 3 , led to the formation of a dark red solution (l max = 542 nm), indicating the formation of the {TiS 6 } 2À chromophore (Scheme 1). [17] Complex Li x K 8Àx A C H T U N G T R E N N U N G [Ti 4 (1) 4 ] was not isolated. Instead the alkali metal [a] Dr.