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

The Fe n X n scaffold (X = p-block elements) occurs in many multimetallic metallaproteins 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 alpha,alpha-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 '-Me-3-C6H2)(2)-C6H3). In both cases, the fluoroalkoxide ligand selectively occupies the terminal position at the iron centers, while the amide (HMDS) or the nonfluorinated alkoxide (HMTO) donor is bridging 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.