Synthesis and elaboration of the dinuclear iron-imide cluster core [Fe 2(μ-NR)2]2+

Article abstract of DOI:10.1021/ic061133+

The protolysis of mononuclear ferric amide precursors FeCl[N(SiMe ₃)₂]₂(THF) (1) or [FeCl₂{N(SiMe ₃)₂}₂]^- (2) by primary amines provides, under suitable conditions, an effective route to dinuclear weak-field ferric-imide clusters with [Fe₂(μ-NR)₂]²⁺ cores. In the synthesis of known arylimide clusters [Fe₂(μ-NAr) ₂Cl₄]^2- (Ar = Ph, p-Tol, Mes) from 2, the counterion has a major effect on selectivity and yield, and the use of quaternary ammonium salts affords a substantial improvement over earlier, Li⁺-based chemistry. The new tert-butylimide core is obtained by protolysis of 1 with excess ^tBuNH₂ to give crystalline cis-Fe₂(μ-N^tBu)₂Cl₂(NH ₂^tBu)₂ (9). Complex 9 can be transformed to other dinuclear species through substitution of the terminal amines by pyridines, PEt₃, or chloride, or through protolysis of bridging alkylimides by arylamines, allowing isolation of trans-Fe₂(μ- N^tBu)₂Cl₂(DMAP)₂ (DMAP = 4-dimethylaminopyridine), cis-Fe₂(μ-N^tBu) ₂Cl₂(PEt₃)₂, [Fe₂(μ- N^tBu)₂Cl₄]^-, and trans-Fe ₂(μ-NPh)₂Cl₂(NH₂Bu)₂. The susceptibility of alkyl substituents to β-elimination appears to limit the general applicability of protolytic cluster assembly using alkylamines. The dinuclear clusters have been characterized by X-ray, spectroscopic, and electrochemical analyses.