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Issue 1, 2015
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Iron(II) complexes featuring κ3- and κ2-bound PNP pincer ligands – the significance of sterics

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Abstract

Treatment of anhydrous FeX2 (X = Cl, Br) with 2 equiv. of the sterically little demanding N,N′-bisphosphino-2,6-diaminopyridine based PNP ligands – featuring Ph, biphenol (BIPOL), Me, Et, nPr, and nBu substituents at the phosphorus sites and H, Me, and Ph substituents at the N-linkers – afforded diamagnetic cationic octahedral complexes of the general formula [Fe(κ3-P,N,P-PNP)(κ2-P,N-PNP)X]+ featuring a κ2-P,N bound PNP ligand. With the sterically more encumbered N-methylated ligand PNPMe-Ph the related complex [Fe(κ3-P,N,P-PNPMe-Ph)(κ2-P,N-PNHMe-Ph)Cl]+ rather than [Fe(κ3-P,N,P-PNPMe-Ph)Cl2] was formed. This reaction was accompanied by P–N bond cleavage, thereby forming the κ2-P,N-bound N-diphenylphosphino-N,N′-methyl-2,6-diaminopyridine ligand. In contrast, with the N-phenylated ligands PNPPh-Et and PNPPh-nPr, despite small Et and nPr substituents at the phosphorus sites, complexes [Fe(κ3-P,N,P-PNPPh-Et)Cl2] and [Fe(κ3-P,N,P-PNPPh-nPr)Cl2] were formed, revealing that sterics can be also controlled by substituent variations at the amino N-sites. Depending on the solvent, complexes featuring κ2-P,N-bound ligands undergo facile rearrangement reactions to give dicationic complexes of the type [Fe(κ3-P,N,P-PNP)2]2+ where both PNP ligands are bound in a κ3-P,N,P-fashion. In the presence of either Ag+ or Na+ salts as halide scavengers this reaction takes place within a few minutes. The pendant PR2 arm of the κ32-complexes is readily oxidized to the corresponding phosphine sulfides upon treatment with elemental sulfur. This was exemplarily shown for [Fe(κ3-P,N,P-PNP-nPr)(κ2-P,N-PNS-nPr)Cl]+. Halide abstraction afforded the dicationic bis-chelated octahedral Fe(II) complex [Fe(κ3-P,N,P-PNP)2]2+ together with the free SNP ligand rather than [Fe(κ3-P,N,P-PNP-nPr)(κ3-S,P,N-PNS-nPr)]2+.

Graphical abstract: Iron(ii) complexes featuring κ3- and κ2-bound PNP pincer ligands – the significance of sterics

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The article was received on 17 Sep 2014, accepted on 17 Oct 2014 and first published on 22 Oct 2014


Article type: Paper
DOI: 10.1039/C4DT02866J
Author version available: Download Author version (PDF)
Citation: Dalton Trans., 2015,44, 281-294
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    Iron(II) complexes featuring κ3- and κ2-bound PNP pincer ligands – the significance of sterics

    M. Glatz, B. Bichler, M. Mastalir, B. Stöger, M. Weil, K. Mereiter, E. Pittenauer, G. Allmaier, L. F. Veiros and K. Kirchner, Dalton Trans., 2015, 44, 281
    DOI: 10.1039/C4DT02866J

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