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 Ph3C center dot shows that one ligand is selectively transferred in each case. A selectivity trend emerges that shows N-center dot(3) is the most favored for transfer in each case to the carbon radical, whereas Cl-center dot 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.