Hydrogen Radical Chemistry at High-Symmetry {2Fe2S} Centers Probed Using a Muonium Surrogate

Redox-active metal hydrides are of central importance in the development of novel hydrogen generation catalysts. Direct insight into open-shell hydrides is, however, difficult to obtain. One approach to gain this information is to use muonium (Mu^• = μ⁺ e^-) as a surrogate for the hydrogen radical. The chemistry of Mu^• is analogous to H^•; however, the species provides a highly sensitive probe through detection of the positrons arising from the muon decay (with a lifetime of ∼2.2 μs) and can therefore provide unique information about hyperfine couplings and thus molecular structure. Using this approach, we demonstrate here that the high-symmetry {2Fe2S} systems Fe₂(edt)(CO)₄L₂ (edt = ethane-1,2-dithiolato; L = CO, PMe₃, CN^-) form bridging radicals directly on the time scale of the muon experiment. We also extend our computational approach to detail all of the possible addition sites in solid state samples.