Stable N-Phosphanyl Acyclic Diaminocarbenes

The deprotonation of N‐di‐tert‐butylphosphanyl‐N‐aryl‐N′‐diisopropylformamidinium salts led to a new type of stable acyclic N‐phosphanyl‐diaminocarbene (PADC). Carbenes 8a–8d were separated as single compounds. The molecular structure of 8c was determined by X‐ray diffraction analysis. The PADC 8 possess an optimal substitution pattern at the nitrogen atoms, and the N–Ccarbene–N bond angle is 120.7°. Structural changes near the carbenic carbon atom, such as substitution of phenyl with mesityl, phosphanyl with selenophosphoryl, or the diisopropylamino group with 2,2,6,6‐tetramethylpiperidino, rendered them unstable. The PADCs underwent N,C‐phosphorus shifts to afford new C‐phosphanylformamidines. The deprotonation of PIII N‐substituted formamidinium salts afforded a new type of stable acyclic N‐phosphanyl‐diaminocarbene. The carbenes possess an optimal substitution pattern, deviations from which make them unstable. They transform into C‐phosphanylformamidines by a N,C‐phosphorus shift, which was studied by quantum chemistry calculations.