On the path to multi-electron redox chemistry with bimetallic systems

The following study is presented in two sections, in the first, a novel digold (II) complex with semi-bridging chlorides supported by two bulky formamidinates was synthesized for the purpose of studying late-transition metal multi-electron redox chemistry. Electrochemical analysis shows one non-reversible reduction. Although the electrochemistry of this complex is restricted, the compound shows interesting electronic properties. The crystal structure reveals a geometry distortion of the Au2?-Cl2 core. The coupling of an unoccupied orbital and an occupied orbital through a vibrational mode, causes a distortion in the geometry of the molecule lowering the D2h symmetry to C2h. This is an example of a second order Jahn-Teller distortion. In the second section, we show the tuning of the oxidation potential on a series of dimolybdenum systems by systematically probing the effects of ligands of different basicities. We have synthesized bimetallic compounds with different ratios of two different ligands, namely guanidinates and formamidinates in four different combinations of Mo2(DAniF)x(hpp)4-x, (where DAniF is the anion of N,N\u27-di-p-anisylformamidine and hpp is the anion of hexahydro-2H-pyrimido[1,2-a]pyrimidine), and Mo2(OAc)x(DAniF)4-x, and we measured the redox potentials, and Raman shifts of the respective Mo-Mo bonds. We have observed that the oxidation potentials shift to negative potentials with the addition of more guanidine ligands. The difference in redox potentials between Mo2(DAniF)4 (the fully formamidinate substituted compound) and Mo2(DAniF)3(hpp) (the first in the series of Mo2(DAniF)x(hpp)4-x) is in the order of half a volt in the negative direction. The difference in redox potentials between Mo2(DAniF)3(hpp) and t-Mo2(DAniF)2(hpp)2 is about 0.35 volts in the cathodic direction and it displays multi-electron redox processes. Lastly, Mo2(hpp)2(DAniF) shifted 0.07 volts as well. We have also study the electronics of these systems by DFT