Reduction of Terphenyl Iron(II) Or Cobalt(II)halides in the Presence of Trimethylphosphine: An Unusual Triple Dehydrogenation of an Alkyl Group

Abstract

The reduction of {ArFeBr}2 (Ar = terphenyl) with KC8 in the presence of excess PMe3 afforded the Fe(i) complex 3,5-Pr i2-Ar′Fe(PMe3) (1) (Ar′-3,5-Pr i2 = C6H-2,6-(C6H 3-2,6-Pri2)-3,5-Pri2), which has a structure very different from the previously reported, linear Cr(i) species 3,5-Pri2-Ar*Cr(PMe3) (3,5-Pr i2-Ar* = C6H-2,6-(C6H 2-2,4,6-Pri3)2-3,5-Pr i2) and features a strong Fe-η6-aryl interaction with the flanking aryl ring of the terphenyl ligand. In sharp contrast, the reduction of {ArCoCl}2 (Ar = 3,5-Pri2-Ar′ and Ar′) afforded the allyl complexes Co(η3-{1-(H2C)2C-C6H 3-2-(C6H2-2,4-Pri2-5-(C6H3-2,6-Pri2))-3-Pri})(PMe3)3 (4) and Co(η3-{1-(H2C)2C-C6H 3-2-(C6H4-3-(C6H3-2,6- Pri2))-3-Pri})(PMe3)3 (5) formed by an unusual triple dehydrogenation of an isopropyl group. It is proposed that the reduction initially generates an intermediate 3,5-Pr i2-Ar′Co(PMe3), which is similar in structure to 1, followed by 3,5-Pri2-Ar′Co(PMe 3) decomposition to a cobalt hydride intermediate and dehydrogenation of the isopropyl group via remote C-H activation induced by PMe3 complexation. Complexes 1, 4, and 5 were characterized by X-ray crystallography. In addition, 1 was studied by NMR and EPR spectroscopy; 4 and 5 were characterized by NMR spectroscopy.

Department(s)

Chemistry

Sponsor(s)

National Science Foundation (U.S.)

Keywords and Phrases

Cobalt compounds; Dehydrogenation; Nuclear magnetic resonance; X-ray crystallography

International Standard Serial Number (ISSN)

1477-9226

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2009 Royal Society of Chemistry, All rights reserved.

Publication Date

01 May 2009

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