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Dalton Transactions

The international journal for inorganic, organometallic and bioinorganic chemistry



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Dalton Trans., 2009, 5401 - 5405, DOI: 10.1039/b904647j

Reduction of terphenyl iron(II) or cobalt(II) halides in the presence of trimethylphosphine: an unusual triple dehydrogenation of an alkyl group

Chengbao Ni, Bobby D. Ellis, Troy A. Stich, James C. Fettinger, Gary J. Long, R. David Britt and Philip P. Power

The reduction of {ArFeBr}2 (Ar = terphenyl) with KC8 in the presence of excess PMe3 afforded the Fe(I) complex 3,5-Pri2-ArFe(PMe3) ( 1) (Ar-3,5-Pri2 = C6H-2,6-(C6H3-2,6-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-Pri2-Ar* = C6H-2,6-(C6H2–2,4,6-Pri3)2–3,5-Pri2) and features a strong Fe-6-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(3-{1-(H2C)2C-C6H3–2-(C6H2–2,4-Pri2–5-(C6H3–2,6-Pri2))-3-Pri})(PMe3)3 ( 4) and Co(3-{1-(H2C)2C-C6H3–2-(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-Pri2-ArCo(PMe3), which is similar in structure to 1, followed by 3,5-Pri2-ArCo(PMe3) 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.

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