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

Mathias Glatz,Karl Kirchner,Christian Schröder-Holzhacker,Luis F Veiros,Berthold Stöger,Bernhard Bichler,Kurt Mereiter

doi:10.1007/s00706-016-1811-x

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.Graphical abstract

Highlights

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
DFT calculations confirm that trans-dicarbonyl complexes are thermodynamically disfavored over the respective cis-dicarbonyl compounds, but are favored for kinetic reasons
In continuation of our studies on iron PNP complexes, we report on the synthesis and reactivity of a series octahedral Fe(II) carbonyl complexes bearing both sterically little demanding as well as bulky PNP ligands in order to probe whether sterics influences the preference for a trans- over a cis-dicarbonyl arrangement

Summary

Introduction

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. DFT calculations confirm that trans-dicarbonyl complexes are thermodynamically disfavored over the respective cis-dicarbonyl compounds, but are favored for kinetic reasons. Salts (with SbF6-, BF4-, or CF3SO3- as counterions) in THF or acetone in the presence of CO at room temperature selectively afforded the cationic complexes trans-[Fe(j3P,N,P-PNP)(CO)2X]?

Results

Conclusion