Selective Radical Transfer in a Series of Nonheme Iron(III) Complexes.

A series of nonheme iron complexes, Fe(III)(BNPA(Ph2)O)(L(ax))(L(eq)) (L(ax/eq) = N(3)(-), NCS(-), NCO(-), and Cl(-)) have been synthesized using the previously reported BNPA(Ph2)O(-) ligand. The ferrous analogs Fe(II)(BNPA(Ph2)O)(L(ax)) (L(ax) = N(3)(-), NCS(-), and NCO(-)) were also prepared. The complexes were structurally characterized using single crystal X-ray diffraction, which shows that all the Fe(III) complexes are six-coordinate, with one anionic ligand (L(ax)) in the H-bonding axial site and the other anionic ligand (L(eq)) in the equatorial plane, cis to the L(ax) ligand. The reaction of Fe(III)(BNPA(Ph2)O(-))(L(ax))(L(eq)) with Ph(3)C(•) shows that one ligand is selectively transferred in each case. A selectivity trend emerges that shows (•)N(3) is the most favored for transfer in each case to the carbon radical, whereas Cl(•) is the least favored. The NCO and NCS ligands showed an intermediate propensity for radical transfer, with NCS > NCO. The overall order of selectivity is N(3) > NCS > NCO > Cl. In addition, we also demonstrated that H-bonding has a small effect on governing product selectivity by using a non-H-bonded ligand (DPA(Ph2)O(-)). This study demonstrates the inherent radical transfer selectivity of nonhydroxo-ligated nonheme iron(III) complexes, which could be useful for efforts in synthetic and (bio)catalytic C-H functionalization.