title: Heterolytic Cleavage of Dihydrogen by an Iron(II) PNP Pincer Complex via Metal-Ligand Cooperation.
abstract: The bis-carbonyl Fe(II) complextrans-[Fe(PNP-iPr)(CO)2Cl]+reacts with Zn as reducing agent under a dihydrogen atmosphere to give the Fe(II) hydride complexcis-[Fe(PNP-iPr)(CO)2H]+in 97% isolated yield. A crucial step in this reaction seems to be the reduction of the acidic NH protons of the PNP-iPr ligand to afford H2and the coordinatively unsaturated intermediate [Fe(PNPH-iPr)(CO)2]+bearing a dearomatized pyridine moiety. This species is able to bind and heterolytically cleave H2to givecis-[Fe(PNP-iPr)(CO)2H]+. The mechanism of this reaction has been studied by DFT calculations. The proposed mechanism was supported by deuterium labeling experiments using D2and the N-deuterated isotopologue oftrans-[Fe(PNP-iPr)(CO)2Cl]+. While in the first case deuterium was partially incorporated into both N and Fe sites, in the latter case no reaction took place. In addition, the N-methylated complextrans-[Fe(PNPMe-iPr)(CO)2Cl]+was prepared, showing no reactions with Zn and H2under the same reaction conditions. An alternative synthesis ofcis-[Fe(PNP-iPr)(CO)2H]+was developed utilizing the Fe(0) complex [Fe(PNP-iPr)(CO)2]. This compound is obtained in high yield by treatment of eithertrans-[Fe(PNP-iPr)(CO)2Cl]+or [Fe(PNP-iPr)Cl2] with an excess of NaHg or a stoichiometric amount of KC8in the presence of carbon monoxide. Protonation of [Fe(PNP-iPr)(CO)2] with HBF4gave the hydride complexcis-[Fe(PNP-iPr)(CO)2H]+. X-ray structures of bothcis-[Fe(PNP-iPr)(CO)2H]+and [Fe(PNP-iPr)(CO)2] are presented.
authors.affiliation: Institute of Applied Synthetic Chemistry, Institute of Materials Chemistry, and Institute of Chemical Technologies and Analytics, Vienna University of Technology , Getreidemarkt 9, A-1060 Vienna, Austria.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Bichler
authors.forename: Christian
authors.initials: C
authors.lastname: Holzhacker
authors.forename: Berthold
authors.initials: B
authors.lastname: Stöger
authors.forename: Michael
authors.initials: M
authors.lastname: Puchberger
authors.forename: Luis F
authors.initials: LF
authors.lastname: Veiros
authors.forename: Karl
authors.initials: K
authors.lastname: Kirchner