N,N’-Bis-(2,6-diisopropylphenylamine)ethane dihydrochloride (see Page 30)
Triethyl orthoformate (Aldrich, distilled from sieves onto sieves)
Formic acid (Aldrich)

N,N’-Bis-(2,6-diisopropylphenylamine)ethane dihydrochloride (37.33g, 0.082 mol) was placed in a round bottom flask with a stirbar. Triethyl orthoformate (463 mL) and formic acid (4 drops) were added. The flask was fitted with a condenser and the mixture was heated at reflux for 48h open to the air. After cooling to ambient temperature a white crystalline solid formed. The solid was collected by filtration and placed in a round bottomed flask. The excess triethyl orthoformate was removed by heating the solid at 70^oC under vacuum (1x10^-2mbar) for 8h to yield 28g of the product (80% yield).

The reaction mixture reaches reflux at a temperature of 125^oC (cf triethyl orthoformate bp=146^oC). If the reaction is carried out in a sealed ampoule heated at 146^oC the yield drops to 30%. The excess triethyl orthoformate is easily removed by heating under vacuum rather than repeated recrystallizations. The Cl^- counterion can be exchanged for BF₄^- by dissolving the imidazolinium salt (1mmol) in water (20mL) with ammonium tetrafuoroborate (1mmol). A white solid precipitates which when dried under vacuum yields the BF₄ salt (95% yield).

¹H NMR (D₆-DMSO): 1.14 (d, 12H, ⁱPrCH₃, ³J(HH) = 6.9 Hz), 1.30 (d, 12H, ⁱPrCH₃, ³J(HH) = 6.9 Hz), 3.03 (sept, 4H, ⁱPrCH, ³J(HH) = 6.9 Hz), 4.49 (s, 4H, CH2), 7.3-7.5 (m, 6H, aryl-CH), 9.52 (s, 1H, NCHN).

Arduengo, A. J.; Krafczyk, R.; Schmuter, R. Tetrahedron, 1999, 55, 14523.

For next stage in carbene prep see Page 34