Synthesis, structures, and reactivity of isomers of [RuCp*(1,4-(MeN)CH)].

[RuCp*(1,3,5-RCH)] {Cp* = η-pentamethylcyclopentadienyl, R = Me, Et} have previously been found to be moderately air stable, yet highly reducing, with estimated D/0.5D (where D and D represent the dimer and the corresponding monomeric cation, respectively) redox potentials of -2.0 V FeCp. These properties have led to their use as n-dopants for organic semiconductors. Use of arenes substituted with π-electron donors is anticipated to lead to even more strongly reducing dimers. [RuCp*(1-(MeN)-3,5-MeCH)]PF and [RuCp*(1,4-(MeN)CH)]PF have been synthesized and electrochemically and crystallographically characterized; both exhibit D/D potentials slightly more cathodic than [RuCp*(1,3,5-RCH)]. Reduction of [RuCp*(1,4-(MeN)CH)]PF using silica-supported sodium-potassium alloy leads to a mixture of isomers of [RuCp*(1,4-(MeN)CH)], two of which have been crystallographically characterized. One of these isomers has a similar molecular structure to [RuCp*(1,3,5-EtCH)]; the central C-C bond is ,, , on the opposite face of both six-membered rings from the metals. A D/0.5D potential of -2.4 V is estimated for this , dimer, more reducing than that of [RuCp*(1,3,5-RCH)] (-2.0 V). This isomer reacts much more rapidly with both air and electron acceptors than [RuCp*(1,3,5-RCH)] due to a much more cathodic D˙/D potential. The other isomer to be crystallographically characterized, along with a third isomer, are both dimerized in an , fashion, representing the first examples of such dimers. Density functional theory calculations and reactivity studies indicate that the central bonds of these two isomers are weaker than those of the , isomer, or of [RuCp*(1,3,5-RCH)], leading to estimated D/0.5D potentials of -2.5 and -2.6 V FeCp. At the same time the D˙/D potentials for the , dimers are anodically shifted relative to those of [RuCp*(1,3,5-RCH)], resulting in much greater air stability than for the , isomer.