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 Rh–CArF bond energies. The Rh–CArF 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).