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

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]

References

• 1 Feigl F. Krumholtz P. Monatsh. Chem.  1932,  59:  314 
• 2 Smith M. Bau R. J. Am. Chem. Soc.  1973,  95:  2388 
• 3 Boldrini GP. Umani-Ronchi A. Synthesis  1976,  596 
• 4 Periasamy M. Radhakrishnan U. Brunet J.-J. Chauvin R. El Zaizi AW. Chem. Commun.  1996,  1499 
• 5 Brunet J.-J. Chauvin R. Kindela F. Neibecker D. Tetrahedron Lett.  1994,  35:  8801 
• 6 Shim SC. Choi KN. Tetrahedron Lett.  1985,  26:  3277 
• 7a Boldrini GP. Panunzio M. Umani-Ronchi A. Synlett  1974,  733 
• 7b Nakagawa Y. Stevens RV. J. Org. Chem.  1988,  53:  1873 
• 8a Watanabe Y. Shim SC. Uchida H. Mitsudo T. Takegami Y. Tetrahedron  1979,  35:  1433 
• 8b Shim SC. Huh KT. Park WH. Tetrahedron  1986,  42:  259 
• 9a Yamashita M. Watanabe Y. Mitsudo T.-A. Takegami Y. Tetrahedron Lett.  1975,  31:  1867 
• 9b Noyori R. Umeda I. Ishigami T. J. Org. Chem.  1972,  1542 
• 10 Cainelli GF. Panuzio M. Umani-Rochi A. J. Chem. Soc., Perkin Trans. 1  1975,  1273 
• 11 Shim SC. Huh KT. Park WH. Synthesis  1987,  59 
• 12 Periasamy M. Rameshkumar U. Brunet J.-J. J. Org. Chem.  1998,  63:  4930 
• 13 Periasamy M. Radhakrishnan U. Rameshkumar C. Brunet J.-J. Tetrahedron Lett.  1997,  38:  1623