Chromium Tricarbonyl Facilitated Nucleophilic Aromatic Substitution by Metal Carbonyl Anions: The Synthesis and Molecular Structure of a New Class of Bimetallic π-Arene Complexes

Joseph A. Heppert, Mark A. Morgenstern, Devin M. Scherubel, Fusao Takusagawa, Mohammad R. Shaker

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Abstract

The highly nucleophilic metal carbonyl anions [CpFe(CO)2]- and [(C5Me5)Fe(CO)2]-(C5Me5≡ Cp*) react with (η-XRC6H4)Cr(CO)3 substrates in a previously unknown type of nucleophilic aromatic substitution to form (η6-{CpFe(CO)2}RC6H4)Cr(CO)3 products. A variety of less reactive metal nucleophiles, including [CpMo(CO)3]-, [CpNi(CO)]-, [Mn(CO)5]-, and [Co(CO)4]- fail to participate in the substitution reactions. The structure of (η-{CpFe(CO)2}ClC6H4)Cr(CO)3 has been determined by X-ray crystallography. The compound crystallizes in the space group P21/n with four molecules in the unit cell of dimensions a = 7.969 (2) Å, b = 18.982 (4) Å, c = 10.789 (2) Å, and β = 91.45 (3). Full-matrix least-squares refinement yielded R = 0.0353 for 2153 reflections. The structure shows that the conformation of the Cr(CO)3 fragment is determined by a cogging of the carbonyl ligands of the CpFe(CO)2 and Cr(CO)3 units to avoid steric interactions, although and 13C NMR studies failed to show a perceptible barrier to Cr(CO)3 rotation about the Cr-Phcentroidvector. Certain haloarene substrates react predominantly through an apparent electron-transfer pathway to produce [CpFe(CO)2]2 and (η-RC6H5)Cr(CO)3. The fraction of reduced products formed is dependent on (1) the reducing power of the anion ([Cp*Fe(CO)2]- >> [CpFe(CO)2]-), (2) the electron-donating ability of the R group (electron donor >> electron acceptor), (3) the substitution pattern of the arene (in general ortho >> meta ≅ para), and (4) the identity of the halogen leaving group (I >> Cl > F).

Original languageEnglish
Pages (from-to)1715-1723
Number of pages9
JournalOrganometallics
Volume7
Issue number8
DOIs
StatePublished - Aug 1988

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