[Fe3(μ3-Me)]-/0 Clusters: Masking a Methyl Radical.

We report the synthesis and characterization of an anionic triiron μ3-methyl cluster [(FtbsL)Fe3(μ3-CH3)]- and its one-electron oxidized neutral congener (FtbsL)Fe3(μ3-CH3). The anionic cluster [(FtbsL)Fe3(μ3-CH3)]- is a stable species in solution that exhibits methyl migration reactivity with unsaturated substrates (e.g., isocyanides, alkynes, and carbonyls). The oxidized neutral congener (FtbsL)Fe3(μ3-CH3) undergoes facile homolysis of the [Fe3]-CH3 bond in solution to generate ethane or undergo radical recombination with persistent radicals, transferring a methyl radical equivalent (•CH3). The anionic [(FtbsL)Fe3(μ3-CH3)]- and neutral (FtbsL)Fe3(μ3-CH3) clusters were characterized in the solid state by single crystal X-ray diffraction, and spectroscopically via 19F NMR, 1H NMR, and 57Fe Mössbauer spectroscopies. SQUID magnetometry measurements of the anionic [(FtbsL)Fe3(μ3-CH3)]- cluster revealed an isolated S = 6 ground state. Alternating current (ac) mode SQUID magnetometry measurements under a zero-applied field (H = 0 T) revealed that the anionic [(FtbsL)Fe3(μ3-CH3)]- cluster undergoes slow magnetic relaxation at low temperatures with an energy barrier for spin reversal of Ueff = 19.1(4) cm-1. The electronic structure of the neutral cluster (FtbsL)Fe3(μ3-CH3) was investigated by X-band EPR spectroscopy, revealing a non-isolated S = 5/2 spin state with an accessible thermal population of a higher spin state (S = 13/2), as suggested by calculations.