New Stable and Persistent Acyclic Diaminocarbenes.

Area of Science:

• Organometallic Chemistry
• Carbene Chemistry

Background:

• Acyclic diaminocarbenes (ADACs) are versatile ligands in organometallic chemistry.
• Expanding the library of ADAC precursors is crucial for exploring their reactivity and applications.

Purpose of the Study:

• To synthesize and characterize novel formamidinium salts as precursors to acyclic diaminocarbenes (ADACs).
• To investigate the stability and reactivity of newly synthesized ADACs.
• To compare the electronic properties of ADACs with N-heterocyclic carbenes (NHCs).

Main Methods:

• Synthesis of eleven new formamidinium salts.
• Isolation and in situ trapping of ADACs.
• Reaction of ADACs with elemental selenium and a rhodium complex.
• Characterization using (77)Se NMR spectroscopy.
• Density Functional Theory (DFT) calculations.

Main Results:

• Successful synthesis of eleven new formamidinium salts, expanding the ADAC precursor portfolio.
• Isolation of several ADACs, while others required in situ trapping due to stability.
• Efficient trapping with elemental selenium to form selenourea derivatives.
• ADACs demonstrated significantly higher electrophilicity and π-accepting ability than NHCs, indicated by (77)Se NMR shifts.
• DFT calculations explained the high electrophilicity of a specific ADAC due to its conformation.

Conclusions:

• The study significantly expanded the range of accessible acyclic diaminocarbenes (ADACs).
• The synthesized ADACs exhibit unique electronic properties, including high electrophilicity and π-accepting capabilities, surpassing those of NHCs.
• Conformational effects play a critical role in tuning the electronic properties and reactivity of ADACs.