Construction of Diiron Diamond-Core Complexes Influenced by a Fluoroalkoxide Ligand

The FenXn scaffold (X = p-block elements) occurs in many multimetallic metalloproteins and metalloenzymes. Studies on synthetic complexes with a Fe2X2 core are of great interest for understanding their electronic structures and intrinsic reactivities. Here is presented the use of α,α-bis(trifluoromethyl)benzyloxide as a ligand to support the assembly of two heteroleptic iron complexes featuring a core structure of the type Fe2X2 (X = HMDS, N(SiMe3)2; HMTO, O-2,6-(2’,4’,6’-Me3-C6H2)2-C6H3). In both cases, the fluoroalkoxide ligand selectively occupies the terminal position at the iron centers, while the amide (HMDS) or the non-fluorinated alkoxide (HMTO) donor bridges the iron atoms to constitute the Fe2X2-type scaffold. In solution, even at room temperature, the amido-bridged compound features a stable diamond-core structure, exhibiting low-coordinate iron centers and a strong intermetallic antiferromagnetic interaction, as supported by experimental data and theoretical calculations. In contrast, the HMTO-bridged compound features ferromagnetic coupling but is labile in solution.