Synlett 2005(16): 2543-2544  
DOI: 10.1055/s-2005-872682
SPOTLIGHT
© Georg Thieme Verlag Stuttgart · New York

Tetracarbonylhydridoferrate Salts: NaHFe(CO)4 and KHFe(CO)4

Jiří Pospíšil*
Université catholique de Louvain, Département de Chimie, ­Bâtiment Lavoisier, Place Louis Pasteur 1, 1348 Louvain-la-Neuve, Belgium
e-Mail: pospisil@chim.ucl.ac.be;
Further Information

Publication History

Publication Date:
06 September 2005 (online)

Introduction

The HFe(CO)4 anion was first prepared by Feigl and Krumholtz in 1932 [1] in its sodium form and the structure was unambiguously established by X-ray diffraction ­analysis of an appropriate bis(triphenylphosphoranyl­idene)ammonium salt nearly 50 years later. [2] This monohydride iron complex is a source of hydride anion that behaves as an extremely soft reducing reagent. Therefore, this hydride complex is highly suitable for the reduction of, for example, unactivated olefins in the presence of a wide variety of other functional groups. Moreover, all the reactions mediated by NaHFe(CO)4 or KHFe(CO)4 ­proceed under extremely mild and essentially neutral ­conditions.

The second main property of NaHFe(CO)4 or KHFe(CO)4 is their high affinity for alkynes, with which they form various iron complexes. These complexes are not only ­interesting for their structure, but also for their chemical reactivity.

Preparation

The preparation of NaHFe(CO)4 and KHFe(CO)4 is easy and efficient, but the reagents cannot be stored for a long period of time, and they are light sensitive (formation of nonreactive dimer).

KHFe(CO)4 is generally prepared in situ, prior to the reaction, from Fe(CO)5 (1 equiv) and KOH (3 equiv) in MeOH, under an inert atmosphere. [3] THF solutions of NaHFe(CO)4 can be prepared from sodium amalgam and Fe(CO)5 in anhydrous THF.

NaHFe(CO)4 or KHFe(CO)4 can be also generated by careful acidification of Na2Fe(CO)4 or K2Fe(CO)4. [4]