Synthesis and reactivity of BINEPINE-based chiral Fe(II) PNP pincer complexes

Abstract

Abstract

A new asymmetric chiral PNP ligand based on the 2,6-diaminopyridine scaffold featuring a R-BINEPINE moiety was prepared. Treatment of anhydrous FeX ₂ (X = Cl, Br) with 1 equiv of PNP- iPr,BIN at room temperature afforded the coordinatively unsaturated paramagnetic complexes [Fe(PNP- iPr,BIN)X ₂]. The structure of [Fe(PNP- iPr,BIN)Cl ₂] is described. Both complexes react readily with the strong π-acceptor ligand CO in solution to afford selectively the diamagnetic complexes trans-[Fe(PNP- iPr,BIN)(CO)X ₂] in quantitative yield. Due the lability of the CO ligand, these complexes are only stable under a CO atmosphere and isolation in pure form was not possible. The preparation of the carbonyl hydride complex [Fe(PNP- iPr,BIN)(H)(CO)Br] was achieved albeit in low yields via a one pot procedure by treatment of [Fe(PNP- iPr,BINEP)Br ₂] with CO and subsequent reaction with Na[HBEt ₃]. This complex was obtained as an inseparable mixture of two diastereomers in a ca. 1:1 ratio and was tested as catalyst for the hydrogenation of ketones. The catalyst showed acceptable activity under mild conditions (5 bar H ₂, room temperature) with yields up to >99 % within 18 h.

Graphical abstract

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