| The synthesis and characterization of ruthenium complexes of phenanthrene and 9,10-dihydrophenanthrene are described. Electrochemical studies (cyclic voltammetry and coulometry) provided information regarding the stability and possibility of isolation of mixed-valence ions.;The detailed study of the mixed-valence complexes bis((eta)('6)-hexamethylbenzene)((eta)('6),(eta)('6)-phenanthrene)dirutherium(0,II) bis(tetrafluoroborate), 45, and bis((eta)('6)-hexamethylbenzene)(9,10-dihydrophenanthrene)diruthenium bis(tetrafluoroborate), 48, comprise the main interest of this investigation.;These studies revealed that the phenanthrene derivative, 45, is an example of a nonpolymeric mixed-valence ion Class II exhibiting a net two-electron transfer. It was not possible to determine kinetic or thermodynamic parameters of this molecule.;The 9,10-dihydrophenanthrene derivative, 48, however, is an unusual mixed-valence ion. It is the first discrete, nonpolymeric organometallic complex described to exhibit a net two-electron transfer with such extensive delocalization. The thermal energy barrier for electron transfer must be extremely low and it has not been possible to measure it by any of the methods employed thus far. Highly interesting is also its unique magnetic behavior. Temperature independent paramagnetism was found. Again, no energy barrier for presumed conformational changes could be observed.;The bis-capped compounds bis((eta)('6)-hexamethylbenzene)((eta)('6),(eta)('6)-phenanthrene)diruthenium(II,II) tetrakis(tetrafluoroborate), 44, and bis((eta)('6)-hexamethylbenzene) ((eta)('6),(eta)('6)-9,10-dihydrophenanthrene)diruthenium(II,II) tetrakis(tetrafluoroborate), 47, showed two reversible, net, two-electron waves each under cyclic voltammetry conditions in propylene carbonate. Their electrochemical potentials are: E(, 1/2)('I)(SCE) = -.0.185 (+OR-) 0.005 V and E(, 1/2)('II)(SCE) = -0.677 (+OR-) 0.005 V for 44, and E(, 1/2)('I)(SCE) = -0.195 (+OR-) 0.005 V and E(, 1/2)('II)(SCE) (DBLTURN) -1.177 (+OR-) 0.010 V for 47, respectively. The comproportionation constant K(,c) for the equilibrium between the fully oxidized species, the fully reduced species, and the corresponding mixed-valence ions are: 4.38 x 10('16) for 44 and > 10('30) in the case of 47. These large values of K(,c) indicate significant interaction between the two ruthenium atoms in their corresponding mixed-valence compounds.;At present it is not possible to deduce whether 48 is a Class III mixed-valence ion or a Class II, with very fast electron transfer and an extremely low energy barrier for this intervalence transfer. |
