Synthesis, Structures, and Reactivities of Iron Complexes Bearing an Isoindoline‐Based, Polyprotic Pincer‐Type Pyrazole Ligand

Abstract

AbstractThe synthesis and properties of polyprotic NNN pincer‐type bis(pyrazole) iron complexes derived from a 1,3‐bis(pyrazol‐3‐ylimino)isoindoline 1 were investigated. When 1 was treated with iron(II) chloride, the paramagnetic, square‐pyramidal complex [FeCl2(LH3)] (2; LH3=3‐(5‐tert‐butylpyrazol‐3‐ylamino)‐1‐(5‐tert‐butylpyrazol‐3‐ylimino)‐1H‐isoindole) was obtained. Reaction of 2 with two equiv. of silver triflate followed by addition of two equiv. of trimethylphosphine yielded the diamagnetic, octahedral complex [Fe(OTf)(PMe3)2(LH3)]OTf (3), which was converted to the carbonyl complex [Fe(CO)(PMe3)2(LH3)](OTf)2 (4). Treatment of 4 with triethylamine led to deprotonation of the chelate backbone to give the isoindolin‐2‐yl complex [Fe(CO)(PMe3)2(LH2)]OTf (5). The structures of the LH3 and LH2 ligands were compared in details. The NH groups in the pincer ligand in 2–5 are accompanied by hydrogen bonds, showing their Brønsted acidic nature. In addition, 3 catalyzed disproportionation of hydrazine, although the catalytic activity was lower than that of a related pyridine‐based pincer complex 6 a.