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.