Catalyst 1.
n-Butyllithium (1.6 M in hexanes; 2.1 mL, 3.4 mmol) was added to a solution of penta(3,5-dimethylphenyl)cyclopentadiene (2.00 g, 3.41 mmol) in dry THF (20 mL). A suspension of crushed FeCl2 (433 mg, 3.42 mmol) in dry THF (250 mL) was prepared in a 500-mL round-bottomed flask. The flask was fitted with a rubber septum, equipped with a nitrogen-inlet needle, and then cooled to 0 °C in an ice bath. Next, the cyclopentadienyllithium solution was added by cannula into the FeCl2 solution, and the resulting green mixture was stirred at 0 °C for 15 min. In a separate flask, 4-dimethylaminopyridine (0.529 g, 2.84 mmol) was dissolved in dry THF (15 mL) and then treated with n-butyllithium (1.6 M in hexanes; 1.8 mL, 2.9 mmol). The mixture was stirred at r.t. for 10 min, and then it was transferred by cannula into the cold mixture that contained the iron complex (previous paragraph). The resulting dark-yellow solution was placed into an oil bath preheated to 60 °C and stirred for 3 h. During that time, the solution turned dark red. The solvents were removed by rotary evaporation, and the residue was purified by flash chromatography (CH2Cl2 and then ethyl acetate). The dark-purple fractions were concentrated to provide the product as a glassy, dark-purple solid (1.68 mg, 72%).
Catalyst 1 is air-stable (for months).
1 H NMR (CDCl3, 400 MHz): δ 8.11 (d, J = 5.4 Hz, 1H), 6.72 (s, 5H), 6.57 (s, 10H), 5.73 (d, J = 5.4 Hz, 1H), 4.97-4.91 (m, 2H), 4.16 (t, J = 2.8 Hz, 1H), 3.53-3.42 (br, 4H), 2.09 (s, 30H), 1.94-1.88 (