Synthesis and Reactivity of an Iron-Tin Complex with Adjacent Stannylidyne and Ferriostannylene Units

Heavier transition metal carbyne analogs hold significant potential for cooperative activation of small molecules. However, complexes containing more than one heavier tetrylidyne ligand RE (E = Si, Ge, Sn, Pb) are rare due to the high oligomerization tendency of RE ligands. In this study, we describe the complex [Fe(SnAr')₂] (1; Ar' = 2,6-Dipp₂-C₆H₃, Dipp = 2,6-Pr₂-C₆H₃), which features adjacent Fe-Sn single and double bonds. Complex 1 exhibits versatile reactivity with transition metal and main group compounds. Treatment of complex 1 with Ni(COD)₂ (COD = 1,5-cyclooctadiene) yields the tetranuclear complex [Fe(μ-SnAr')₂Ni] (2), characterized by an unusual "push-pull" interaction between nickel(0) and the two coordinating Sn atoms, as revealed by quantum chemical studies. The reaction of complex 1 with AlBr₃ results in Al-Br bond cleavage and Ar' migration to aluminum. CH₃I adds oxidatively to the Sn atom that is singly bonded to Fe, while PMe₃ coordinates to Fe, inducing reversible cleavage of the Fe═Sn double bond. In addition, complex 1 activates inorganic molecules. CO₂ undergoes disproportionation to produce a carbonate-bridged Ar'Sn(μ-OCO₂)SnAr' ligand, whereas CS₂ is reductively coupled to form an ethylene tetrathiolate ligand ([C₂S₄]^4-). The reaction with white phosphorus (P₄) generates an unusual Ar'P₄Sn₂Ar' ligand. This multifaceted reactivity illustrates the behavior of the Fe and Sn sites in complex 1, suggesting that complexes of this type are promising reagents for small molecule activation.