Single-Step Access to Thiolate-Supported, Six-Iron Clusters with an Authentic Carbide: Synthesis of [Fe6(μ6-C)(μ2-Stol)(μ2-CO)2(CO)12]3 via Non-PSEPT, Redox Intermediates

Abstract

We report a general synthetic method to access iron-carbide(carbonyl) clusters ligated by thiolate. We previously established that multiple neutral ligand substitution (phosphine) was enabled by utilizing the conventional six-iron carbide cluster [Fe₆(μ₆-C)(μ₂-CO)₄(CO)₁₂]^2- and generating the 2 e^- oxidized, polyhedral skeletal electron pair theory (PSEPT) non-compliant cluster [Fe₆(μ₆-C)(μ₂-CO)₄(CO)₁₂]⁰. However, ligation of thiolate proved intractable via this route due to inherent thiolate-cluster redox processes, resulting simply in reformation of the dianionic cluster. Here, we extend the non-PSEPT in situ oxidation method by commencing with the "super-reduced" cluster [Fe₆(μ₆-C)(μ₂-CO)₄(CO)₁₁]^4- (2, [Bortoluzzi, M. Eur. J. Inorg. Chem. 2017, 2017(25), 3135-3143]): in situ oxidation of 2 generates the six-iron, non-PSEPT 84 e^- anionic intermediate [Fe₆(μ₆-C)(μ₂-CO)₄(CO)₁₁]^2- (3) that is redox inactive with thiolates but substitutionally active. By this method, we synthesized the novel phosphine-bound cluster (4) [Fe₆((μ₆-C)PMe₃(μ₂-CO)₄CO)₁₁]^2- and the novel thiolate-bound, intact six-iron carbide cluster [Fe₆(μ₆-C)(μ₂-Stol)(μ₂-CO)₂(CO)₁₁]^3- (5). A further synthetic route to 5 is achieved by the reduction of [Fe₅(μ₅-C)(μ₂-Stol)(CO)₁₃]^- (1) in the presence of Fe(CO)₅, or rather with Na₂[Fe(CO)₄]. This synthetic method expands the scope to functionalize iron-carbide(carbonyl) with biorelevant ligands.