High-spin iron(II) complexes with mono-phosphorylated 2,6-diaminopyridine ligands

ABSTRACT: Several new monophosphorylated 2,6-diaminopyridine ligands bearing PiPr(2) and PtBu(2) units (PN(NH2)-iPr, PN(NH2)-tBu, PN(NHMe)-iPr, and PN(NHEt)-iPr) are prepared by treatment of the respective 2,6-diaminopyridines with the chlorophosphines PiPr(2)Cl and PtBu(2)Cl in the presence of a base. Treatment of anhydrous FeCl(2) with 1 equiv of these afforded the tetracoordinated coordinatively unsaturated 14e(−) complexes [Fe(κ(2)P,N-PN(NH2)-iPr)Cl(2)] and [Fe(κ(2)P,N-PN(NH2)-tBu)Cl(2)], while with PN(NHMe)-iPr and PN(NHEt)-iPr a phosphine transfer reaction of a second PN ligand took place to yield the known PNP pincer complexes [Fe(κ(3)P,N,P-PNP(Me)-iPr)Cl(2)] and [Fe(κ(3)P,N,P-PNP(Et)-iPr)Cl(2)]. The four-coordinate complexes [Fe(κ(2)P,N-PN(NH2)-iPr)Cl(2)] and [Fe(κ(2)P,N-PN(NH2)-tBu)Cl(2)] did not react with CO and the formation of iron PNC pincer complexes was not observed. The reason for the reluctance to add CO was investigated in detail by DFT calculations. GRAPHICAL ABSTRACT: [Image: see text]