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

Abstract

Treatment of dimethylmalonyl dichloride with N,N'-bis(2,6-diisopropylphenyl)-N-trimethylsilylformamidine followed by trimethylsilyl triflate (TMS center dot OTf) afforded the pyrimidinium salt. [I H][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 degrees C; Delta H degrees = -35.33 kJ mol(-1) and Delta S degrees = -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)(2)Cl]. 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.