An N,N′-Diamidocarbene: Studies in C−H Insertion, Reversible Carbonylation, and Transition-Metal Coordination Chemistry

Treatment of dimethylmalonyl dichloride with N,N′-bis(2,6-diisopropylphenyl)-N-trimethylsilylformamidine followed by trimethylsilyl triflate (TMS·OTf) afforded the pyrimidinium salt [1H][OTf] in >99% yield. Subsequent deprotonation of this salt led to the formation of the corresponding free N-heterocyclic carbene (NHC) 1. Exhibiting a reactivity profile that is characteristic of traditional electrophilic carbenes, 1 was found to insert into a tertiary C−H bond and reversibly fix carbon monoxide (CO) under mild conditions to afford the first example of a diamidoketene. Remarkably, the aforementioned carbonylation reaction was found to be thermally reversible (K eq = 2.62 M−1 at 30 °C; ΔH° = −35.33 kJ mol−1 and ΔS° = −109.5 J mol−1 K−1). NHC 1 also displayed nucleophilic characteristics. Treatment of 1 with [Ir(COD)Cl]2 (COD = 1,5-cyclooctadiene) afforded 1−[Ir(COD)Cl], a complex with bond lengths and angles that were in accord with known NHC analogues. Treatment of 1−[Ir(COD)Cl] with CO afforded the carbonyl complex 1−[Ir(CO)2Cl]. IR studies of this complex revealed a Tolman Electronic Parameter of 2057 cm−1, a value similar to those for analogous metal complexes containing tricyclohexylphosphine.