Synthesis and characterization of TADDOL-based chiral group six PNP pincer tricarbonyl complexes.

ABSTRACT: The new chiral PNP pincer ligand N 2,N 6-bis((3aR, 8aR)-2,2-dimethyl-4,4,8,8-tetraphenyltetrahydro[1,3]dioxolo[4,5-e][1,3,2]dioxaphosphepin-6-yl)pyridine-2,6-diamine (PNP-TADDOL) was synthesized in 80% isolated yield. Complexes of the type [M(PNP-TADDOL)(CO)3] (M = Cr, Mo, and W) were prepared via a solvothermal approach. This methodology constitutes a fast, simple, and practical synthetic method to obtain complexes of that type in high isolated yields. The X-ray structure of the molybdenum complex is presented.

Synthesis and characterization of cationic dicarbonyl Fe(II) PNP pincer complexes.

ABSTRACT: In the present work, we have prepared a series of octahedral Fe(II) complexes of the type trans-[Fe(PNP)(CO)2Cl]+-PNP are tridentate pincer-type ligands based on 2,6-diaminopyridine. These complexes are formed irrespective of the size of the substituents at the phosphorus sites and whether cis-[Fe(PNP)(Cl2)(CO)] or trans-[Fe(PNP)(Cl2)(CO)] are reacted with CO in the presence of 1 equiv of silver salts. X-ray structures of representative complexes are presented. Based on simple bonding considerations the selective formation of trans-dicarbonyl Fe(II) complexes is unexpected. In fact, DFT calculations confirm that trans-dicarbonyl complexes are indeed thermodynamically disfavored over the respective cis-dicarbonyl compounds, but are favored for kinetic reasons.

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

ABSTRACT: A new asymmetric chiral PNP ligand based on the 2,6-diaminopyridine scaffold featuring a R-BINEPINE moiety was prepared. Treatment of anhydrous FeX2 (X = Cl, Br) with 1 equiv of PNP-iPr,BIN at room temperature afforded the coordinatively unsaturated paramagnetic complexes [Fe(PNP-iPr,BIN)X2]. The structure of [Fe(PNP-iPr,BIN)Cl2] 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)X2] 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)Br2] with CO and subsequent reaction with Na[HBEt3]. 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 H2, room temperature) with yields up to >99 % within 18 h.