Metallosupramolecular Chemistry with Bis(benzene-<i>o</i>-dithiolato) Ligands

The bis(benzene-o-dithiol) ligands H4-1, H4-2, and H4-3 react with [Ti(OC2H5)4] to give dinuclear triple-stranded helicates [Ti2L3]4- (L = 14-, 24-, 34-). NMR spectroscopic investigations revealed that the complex anions possess C3 symmetry in solution. A crystal structure analysis for (PNP)4[Ti2(2)3] ((PNP)4[14]) confirmed the C3 symmetry for the complex anion in the solid state. The complex anion in Li(PNP)3[Ti2(1)3] (Li(PNP)3[13]) does not exhibit C3 symmetry in the solid state due to the formation of polymeric chains of lithium bridged complex anions. Complexes [13]4- and [14] 4- were obtained as racemic mixtures of the Δ,Δ and Λ,Λ isomers. In contrast to that, complex (PNP)4[Ti2(3)3] ((PNP)4[15]) with the enantiomerically pure chiral ligand 34- shows a strong Cotton effect in the CD spectrum, indicating that the chirality of the ligands leads to the formation of chiral metal centers. The o-phenylene diamine bridged bis(benzene-o-dithiol) ligand H4-4 reacts with Ti4+ to give the dinuclear double-stranded complex Li2[Ti2(4)2(μ-OCH3)2] containing two bridging methoxy ligands between the metal centers. The crystal structure analysis and the 1H NMR spectrum of (Ph4As)2[Ti2(4)2(μ-OCH3)2] ((Ph4As)2[(16]) reveal C2 symmetry for the anion [Ti2(4)2(μ-OCH3)2]2-. For a comparative study the dicatechol ligand H4-5, containing the same o-phenylene diamine bridging group as the bis(benzene-o-dithiol) ligands H4-4, was prepared and reacted with [TiO(acac)2] to give the dinuclear complex anion [Ti2(5)2(μ-OCH3)2]2-. The molecular structure of (PNP)2[Ti2(5)2(μ-OCH3)2] ((PNP)2[17]) contains a complex anion which is similar to [16]2-, with the exception that strong N−H···O hydrogen bonds are formed in complex anion [17]2-, while N−H···S hydrogen bonds are absent in complex anion [16]2-.