Metallosupramolecular chemistry with bis(benzene-o-dithiolato) ligands

The bis(benzene-o-dithiol) ligands H-4-1, H-4-2, and H-4-3 react with [Ti(OC2H5)(4)] to give dinuclear triple-stranded helicates [Ti2L3](4-) (L = 1(4-), 2(4-), 3(4-)). NMR spectroscopic investigations revealed that the complex anions possess C-3 symmetry in solution. A crystal structure analysis for (PNP)(4)[Ti-2(2)(3)] ((PNP)(4)-[14]) confirmed the C-3 symmetry for the complex anion in the solid state. The complex anion in Li(PNP)(3)[Ti-2(1)(3)] (Li(PNP)(3)[13]) does not exhibit C-3 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 Delta, Delta and Lambda, Lambda isomers. In contrast to that, complex (PNP)(4)[Ti-2(3)(3)] ((PNP)(4)[15]) with the enantiomerically pure chiral ligand 3(4-) 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 H-4-4 reacts with Ti4+ to give the dinuclear double-stranded complex Li-2[Ti-2(4)(2)(mu-OCH3)(2)] containing two bridging methoxy ligands between the metal centers. The crystal structure analysis and the H-1 NMR spectrum of (Ph4As)(2)[Ti-2(4)(2)(mu-OCH3)(2)] ((Ph4As)(2)[(16]) reveal C-2 symmetry for the anion [Ti-2(4)(2)(mu-OCH3)(2)](2-). For a comparative study the dicatechol ligand H-4-5, containing the same o-phenylene diamine bridging group as the bis(benzene-o-dithiol) ligands H-4-4, was prepared and reacted with [TiO(acac)(2)] to give the dinuclear complex anion [Ti-2(5)(2)(mu-OCH3)(2)](2-). The molecular structure of (PNP)(2)[Ti-2(5)(2)(mu-OCH3)(2)] ((PNP)(2)[17]) contains a complex anion which is similar to [16](2-), with the exception that strong N-H center dot center dot center dot O hydrogen bonds are formed in complex anion [17](2-), while N-H center dot center dot center dot S hydrogen bonds are absent in complex anion [16](2-).