Biferrocene

Biferrocene
Names
	IUPAC name 1,1"-Biferrocene
Identifiers
CAS Number	1287-38-3;
3D model (JSmol)	Interactive image;
ChemSpider	10157133;
PubChem CID	11984633;
	InChI InChI=1S/C10H8.2C5H5.2Fe/c1-2-6-9(5-1)10-7-3-4-8-10;21-2-4-5-3-1;;/h1-8H;21-5H;;/q-6;2*-1;; Key: CEMHVYUXQJEPPO-UHFFFAOYSA-N;
	SMILES C1=C[CH-]C=C1.[Fe+2].C2=C[C-](C=C2)[C-](C=C3)C=C3.[Fe+2].C1=C[CH-]C=C1;
Properties
Chemical formula	C20H18Fe2
Molar mass	370.054 g·mol−1
Appearance	dark orange solid
Melting point	239–240 °C (462–464 °F; 512–513 K)
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Biferrocene is the organometallic compound with the formula [(C₅H₅)Fe(C₅H₄)]₂. It is the product of the formal dehydrocoupling of ferrocene, analogous the relationship between biphenyl and benzene. It is an orange, air-stable solid that is soluble in nonpolar organic solvents.

Biferrocene can be prepared by the Ullmann coupling of iodoferrocene.^[1] Its one-electron oxidized derivative [(C₅H₅)Fe(C₅H₄)]₂⁺ attracted attention as a prototypical mixed-valence compound.^[2]

A related compound is biferrocenylene, [Fe(C₅H₄)₂]₂ wherein all cyclopentadienyl rings are coupled. Formally, biferrocene is derived from one fulvalene ligand, and biferrocenylene is derived from two.

Reactions

Biferrocene can easily be converted into a mixed-valence complex, which is called biferrocenium. This [Fe(II)-Fe(III)] cation is a class II type (0.707 > α > 0) mixed-valence complex according to the Robin-Day classification.^[2]

Derivatives

Aminophosphine ligands with biferroceno substituents have been prepared as catalysts for asymmetric allylic substitution^[3] and asymmetric hydrogenation of alkenes.^[4]

Related compounds

Bis(fulvalene)diiron

References

^ M. D. Rausch (1961). "Ferrocene and Related Organometallic π-Complexes. IV. Some Ullmann Reactions of Haloferrocenes". J. Org. Chem. 26 (6): 1802–1805. doi:10.1021/jo01065a026.
^ ^a ^b Cowan, D. O.; LeVanda, C.; Park, J.; Kaufman, F. (1973). "Organic Solid State. VIII. Mixed-Valence Ferrocene Chemistry". Acc. Chem. Res. 6: 1–7. doi:10.1021/ar50061a001.
^ Xiao, Li; Weissensteiner, Walter; Mereiter, Kurt; Widhalm, Michael (2002-03-08). "Novel Chiral Biferrocene Ligands for Palladium-Catalyzed Allylic Substitution Reactions". The Journal of Organic Chemistry. 67 (7): 2206–2214. doi:10.1021/jo016249w. ISSN 0022-3263. PMID 11925230.
^ Zirakzadeh, Afrooz; Groß, Manuela A.; Wang, Yaping; Mereiter, Kurt; Weissensteiner, Walter (2014-04-09). "Walphos versus Biferrocene-Based Walphos Analogues in the Asymmetric Hydrogenation of Alkenes and Ketones". Organometallics. 33 (8): 1945–1952. doi:10.1021/om401074a. ISSN 0276-7333. PMC 4006446. PMID 24795493.

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[:0-1] M. D. Rausch (1961). "Ferrocene and Related Organometallic π-Complexes. IV. Some Ullmann Reactions of Haloferrocenes". J. Org. Chem. 26 (6): 1802–1805. doi:10.1021/jo01065a026.

[:1-2] Cowan, D. O.; LeVanda, C.; Park, J.; Kaufman, F. (1973). "Organic Solid State. VIII. Mixed-Valence Ferrocene Chemistry". Acc. Chem. Res. 6: 1–7. doi:10.1021/ar50061a001.

[3] Xiao, Li; Weissensteiner, Walter; Mereiter, Kurt; Widhalm, Michael (2002-03-08). "Novel Chiral Biferrocene Ligands for Palladium-Catalyzed Allylic Substitution Reactions". The Journal of Organic Chemistry. 67 (7): 2206–2214. doi:10.1021/jo016249w. ISSN 0022-3263. PMID 11925230.

[4] Zirakzadeh, Afrooz; Groß, Manuela A.; Wang, Yaping; Mereiter, Kurt; Weissensteiner, Walter (2014-04-09). "Walphos versus Biferrocene-Based Walphos Analogues in the Asymmetric Hydrogenation of Alkenes and Ketones". Organometallics. 33 (8): 1945–1952. doi:10.1021/om401074a. ISSN 0276-7333. PMC 4006446. PMID 24795493.

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