[1,3-Bis(ethoxycarbonyl)-2,4,5-trimethylcyclopentadien-1-yl]rhodium(III) Dichloride Dimer

To a 20 mL two-necked flask with a reflux condenser are added 2,2-diarylalkanoic acid (1, 0.5 mmol), [Cp^ERhCl₂]₂ (8.5 mg, 0.01 mmol), AgSbF₆ (14 mg, 0.04 mmol), Cu(OAc)₂·H₂O (200 mg, 1 mmol), K₂CO₃ (69 mg, 0.5 mmol), 1-methylnaphthalene (ca. 40 mg) as internal standard, and diglyme (3 mL). The resulting mixture is stirred under nitrogen at 100−120 °C for 20−48 h. After cooling, the reaction mixture is extracted with ethyl acetate (100 mL) and ethylenediamine (2 mL). The organic layer is washed with water (100 mL, three times), dried over Na₂SO₄ and concentrated under reduced pressure. The residue is purified by column chromatography on silica gel using hexane to give 2; yield: up to 65%.