METAL TETRATHIOLENES .4. SYNTHESIS, CHARACTERIZATION, AND ELECTROCHEMISTRY OF NEW DISCRETE DIPLATINUM-TETRATHIOLENE COMPLEXES

Oxidative addition reactions of low-valent platinum complexes with the “tetrathiolene” (TTL) ligands “tetrathiotetracene” (TTT), “tetrathionaphthalene” (TTN), and “tetrachlorotetrathionaphthalene” (TCTTN) have been investigated. New diplatinum complexes (Ph3P)4Pt2(TTL) were prepared by reacting Pt(PPh3)4 with TTL (where TTL = TTT, TTN, and TCTTN). Characterizations of these complexes by chemical and spectroscopic means led to the conclusion that the most probable structure of these complexes involves two metal coordinations bridged by a TTL ligand. The quadridentate bridging nature of tetrathiolene ligands was confirmed by a three-dimensional single-crystal X-ray diffraction study (reported elsewhere) on (Ph3P)4Pt2(TTN). The (Ph3P)4Pt2(TTL) complexes exhibit unusually rich electrochemistry as established by cyclic voltammetry (in 0.1 M [(n-C4H9)4N] + [ClO4]- in CH2Cl2): namely, (Ph3P)4Pt2(TTT) oxidizes in two one-electron reversible steps (at ambient temperature) at -0.51 and -0.28 V, (Ph3P)4Pt2(TTN) exhibits four reversible one-electron oxidation waves (at ambient temperature) at -0.28, ~-0.05, ~0.01, and 0.31 V, and (Ph3P)4Pt2(TCTTN) undergoes two reversible one-electron oxidations (at dry ice/acetone temperature) at -0.02 and 0.21 V as well as two quasi-reversible waves at 0.58 and 0.94 V (vs. Ag/0.01 M AgNO3 in CH3CN). These potentials are shifted in the negative direction in comparison to, but can be correlated with, the oxidation potentials of the free tetrathiolene ligands which occur at -0.05 and 0.44 V for TTT, 0.27 and 0.65 V for TTN, and 0.64 and 0.97 V for TCTTN. This can be taken as an indication that there is a substantial buildup of negative charge on the bridging TTL ligand upon coordination and, conversely, that the oxidation waves involve removal of electron densities from molecular orbitals substantially bridging ligand in character. The unusually rich redox chemistries of the tetrathiolene ligands and complexes are rationalized in terms of molecular orbital energetics. © 1979, American Chemical Society. All rights reserved.