Bis(η⁶-hexamethylbenzene)(η⁶,η⁶-polycyclic aromatic)diruthenium(II, II) complexes and their two-electron reduction to cyclohexadienyl anion complexes

The bis(tj*-hexamethylbenzene)(η⁶,η⁶-polycyclicaromatic)diruthenium(II, II) complexes 10,14,16,18, 20, and 22, where the polycyclic aromatic ligands are phenanthrene, 9,10-dihydrophenanthrene, biphenyl, 3,3',5,5'-tetramethylbiphenyl, 4,5,9,10-tetrahydropyrene, and triphenylene, respectively, have been synthesized and their electrochemical properties measured. A two-electron chemical reduction of each of these 4+ diruthenium complexes has led to the isolation and characterization of each of their corresponding 2+ diruthenium complexes: 11,15, 17, 19, 21, and 23. On the basis of analyses of their and,³C NMR spectra, structural assignments have been made for all of these 2+ diruthenium complexes. Although the phenanthrene derivative 11 is a class II mixed-valence ion having a Ru(0) site and a Ru(II) site, all of the other 4+ diruthenium complexes undergo two-electron reduction by changing the biphenyl moiety of their polycyclic aromatic ligand into two cyclohexadienyl anions joined by a carbon-carbon double bond. That the bis(cyclohexadienyl anion) system present in these 2+ diruthenium complexes is subject to electrophilic attack was shown by the easy protonation of 17, leading to the formation of 37. The 4+ diruthenium complex of biphenylene 42 was prepared, and it undergoes a similar two-electron reduction to give 43. In contrast, though, the highly rigid 4+ diruthenium complex of pyrene 35 shows two separate one-electron reduction waves. The bis(t;*-biphenyl)ruthenium(II) bis(tetrafluoroborate) derivatives 49, 50, and 51 were prepared. A single-crystal X-ray analysis of 49 shows the molecule to have a syn conformation.