A Seven-Membered <i>N,N</i>′-Diamidocarbene

Condensation of N,N′-dimesitylformamidine with phthaloyl chloride afforded 1·HCl, which, upon treatment with base, afforded 2,4-dimesitylbenzo[e][1,3]diazepin-1,5-dione-2-ylidene (1), a seven-membered N,N′-diamidocarbene (DAC), in high yield (85%). The free DAC was used to synthesize four new, late transition metal complexes: [Rh(cod)(1)Cl] (2a) (cod = 1,5-cyclooctadiene), [Ir(cod)(1)Cl] (2b), [Rh(CO)2(1)Cl] (3a), and [1−AuCl] (5). The Tolman electronic parameter (TEP) of 1 was calculated to be 2047 cm−1 from the IR spectrum of 3a. This TEP value is approximately 10 cm−1 lower than known DACs and 5 cm−1 lower than known imidazol-2-ylidenes, indicating that DAC 1 is a relatively strong electron donor. Additionally, electrochemical analyses of 2a and 2b corroborated the IR data obtained on 3a and revealed E1/2 values that were shifted cathodically by ca. 0.16 V when compared to analogous complexes supported by N-heterocyclic carbenes. The gold complex 5 was found to catalyze the hydration of phenylacetylene, affording acetophenone in yields up to 78% after 12 h at 80 °C at a catalyst loading of 2 mol %. Treatment of 1 with 2,6-dimethylphenylisocyanide afforded N,N′-diamidoketenimine 4 as a thermally robust, crystalline solid.