Ionic 4,4 '-biphenylene-bridged bis-ruthenium complexes [Ru-2(4,4 '-(C6H2(CH2NMe2)(2)-2,6}(2))(terpy)(2)](n+) (n = 2 and 4) and their reversible redox interconversion: A molecular switch
P. Steenwinkel et al., Ionic 4,4 '-biphenylene-bridged bis-ruthenium complexes [Ru-2(4,4 '-(C6H2(CH2NMe2)(2)-2,6}(2))(terpy)(2)](n+) (n = 2 and 4) and their reversible redox interconversion: A molecular switch, ORGANOMETAL, 17(26), 1998, pp. 5647-5655
Copper(II)-mediated oxidative coupling of the blue, 18-electron mononuclear
complex [Ru-II{C6H3(CH2NMe2)(2)-2,6}(terpy)]Cl, 3 (terpy = 2,2';6',2 "-ter
pyridine), affords the unique diamagnetic, binuclear 34-electron complex [(
Ru-III)(2)(4,4'-{C6H2(CH2NMe2)(2)-2,6}(2))(terpy)(2)](CuCl2)(4), 5a. This i
ntensely green complex has been the subject of an X-ray crystal structure d
etermination, and the molecular geometry of the tetracation shows the C4-C4
'-coupled bridging biphenylene dianion to be planar. Two-electron reduction
of this tetracation as its PF6- salt, 5b, with N2H4. H2O affords the corre
sponding dicationic intensely blue, 36-electron complex [(Ru-II)(2)(4,4'-{C
6H2(CH2NMe2)(2)-2,6}(2))(terpy)(2)](PF6)(2), 8. An X-ray crystal structure
determination of 8 shows a molecular geometry in which the bridging bipheny
lene dianion is nonplanar, with the metal coordination planes twisted by ca
. 36 degrees relative to each other. Cyclic voltammetry data show that the
reduction of 5b(4+) to 8 (2+), i.e., [Ru-III-Ru-III] to [Ru-II-Ru-II], is r
eversible. This reduction proceeds through the mixed valence 35-electron [R
u-II-Ru-III] complex [(Ru-II)(Ru-III)(4,4'-{C6H2(CH2NMe2)(2)-2,6}(2))(terpy
)(2)](3+), 9 (3+), which is intensely purple and which can be independently
prepared by mixing acetonitrile solutions of equimolar amounts of 5 (4+) a
nd 8 (2+).