A Tertiary Carbon–Iron Bond as an FeICl Synthon and the Reductive Alkylation of Diphosphine-Supported Iron(II) Chloride Complexes to Low-Valent Iron

Ligand-induced reduction of ferrous alkyl complexes via homolytic cleavage of the alkyl fragment was explored with simple chelating diphosphines. The reactivities of the sodium salts of diphenylmethane, phenyl­(trimethylsilyl)­methane, or diphenyl­(trimethylsilyl)­methane were explored in their reactivity with (py)4FeCl2. A series of monoalkylated salts of the type (py)2FeRCl were prepared and characterized from the addition of 1 equiv of the corresponding alkyl sodium species. These complexes are isostructural and have similar magnetic properties. The double alkylation of (py)4FeCl2 resulted in the formation of tetrahedral high-spin iron complexes with the sodium salts of diphenylmethane and phenyl­(trimethylsilyl)­methane that readily decomposed. A bis­(cyclohexadienyl) sandwich complex was formed with the addition of 2 equiv of the tertiary alkyl species sodium diphenyl­(trimethylsilyl)­methane. The addition of chelating phosphines to (py)2FeRCl resulted in the overall transfer of Fe­(I) chloride concurrent with loss of pyridine and alkyl radical. (dmpe)2FeCl was synthesized via addition of 1 equiv of sodium diphenyl­(trimethylsilyl)­methane, whereas the addition of 2 equiv of the sodium compound to (dmpe)2FeCl2 gave the reduced Fe(0) nitrogen complex (dmpe)2Fe­(N2). These results demonstrate that iron–alkyl homolysis can be used to afford clean, low-valent iron complexes without the use of alkali metals.