Evidence for Reactivity of Decamethylcobaltocene with Dichloromethane
Emily R. Mikeska, James D. Blakemore
Abstract
Decamethylcobaltocene (Cp* 2 Co) is commonly encountered in organometallic chemistry, where it is often used as a one-electron reductant under inert atmosphere and considered to be a stable metallocene in both its reduced [Co II ] and oxidized [Co III ] forms. Here, we report that Cp* 2 Co is not stable in dichloromethane (CH 2 Cl 2 ), a finding that contrasts markedly with the robustness of this compound in other solvents used for redox chemistry, such as neat acetonitrile (CH 3 CN). Parallel chemical and electrochemical studies show that when Cp* 2 Co comes into contact with CH 2 Cl 2, both [Cp* 2 Co] + ( A ) and Cp*Co(η 4 -C 5 Me 5 CH 2 Cl) ( B ), a species in which a chloromethyl group has been added to one Cp* ring, are generated. B subsequently undergoes a ring-expanding rearrangement if exposed to MeOH, yielding Cp*Co(η 5 -C 6 Me 5 CH 2 ) ( C ) that is detectable by mass spectrometry (MS). [Cp*Co] 3 (μ 3 -CH) 2 ( D ) could also be detected by MS, adding to the array of products arising from Cp* 2 Co that do not maintain the expected metallocene motif. Taken together, these findings suggest that Cp* 2 Co should be used with caution in CH 2 Cl 2, particularly in cases in which one-electron transfer and/or clean reactivity are desired.