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Issue 43, 2010
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Synthesis, structure, and reductive elimination in the series Tp′Rh(PR3)(ArF)H; Determination of rhodiumcarbon bond energies of fluoroaryl substituents

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Abstract

A series of complexes of the type Tp′Rh(PR3)(ArF)H, where PR3 = PMe3 (3) and PMe2Ph (9), ArF = C6F5 (a), 2,3,4,5-C6F4H (b), 2,3,5,6-C6F4H (c), 2,4,6-C6F3H2 (d), 2,3-C6F2H3 (e), 2,5-C6F2H3 (g), and 2-C6FH4 (h) and Tp′ = tris(3,5-dimethylpyrazolyl)borate, has been synthesized as stable crystalline compounds by the reactions of the [Tp′Rh(PR3)] fragment with the corresponding fluorinated aromatic hydrocarbons, and their structures were characterized by NMR spectroscopy and elemental analysis together with X-ray crystallography. The kinetics of the reductive eliminations of fluoroarenes from complexes 3a–h in benzene-d6 solutions at 140 °C were investigated, but were complicated by the formation of the rhodium(I) bisphosphine complex, Tp′Rh(PMe3)2 (4). On the other hand, thermal reactions of (9) in THF-d8 solutions at 120 °C resulted in the formation of an intramolecular C–H bond activated complex of the phenyl group on the phosphorus atom, Tp′Rh(κ2-C6H4-2-PMe2)H (7), which prevents the formation of the corresponding bisphosphine complex. The experimentally determined rates of the reductive eliminations of fluoroarenes from the complexes 9a–h and their kinetic selectivities for formation in competition with the metallacycle have been used to determine relative RhCArF bond energies. The RhCArF bond energy is found to be dependent on the number of ortho fluorines. A plot of Rh–CArFvs. C–H bond strengths resulted in a line with a slope RM–C/C–H of 2.15 that closely matches the DFT calculated value (slope = 2.05).

Graphical abstract: Synthesis, structure, and reductive elimination in the series Tp′Rh(PR3)(ArF)H; Determination of rhodium–carbon bond energies of fluoroaryl substituents

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Publication details

The article was received on 17 Mar 2010, accepted on 08 Jun 2010 and first published on 05 Oct 2010


Article type: Paper
DOI: 10.1039/C0DT00157K
Citation: Dalton Trans., 2010,39, 10495-10509

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    Synthesis, structure, and reductive elimination in the series Tp′Rh(PR3)(ArF)H; Determination of rhodiumcarbon bond energies of fluoroaryl substituents

    T. Tanabe, W. W. Brennessel, E. Clot, O. Eisenstein and W. D. Jones, Dalton Trans., 2010, 39, 10495
    DOI: 10.1039/C0DT00157K

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