NHC-Based Diazo Compounds: Pathways to N₂ Liberation or Dimerization.

Area of Science:

• Organometallic Chemistry
• Carbene Chemistry
• Computational Chemistry

Background:

• N-heterocyclic carbenes (NHCs) are versatile ligands in organometallic chemistry.
• Previous work reported C-H bond cleavage of silyl diazomethane by 1,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene (5-SIPr).
• The reactivity of electron-poor diamido carbenes with silyl diazomethane was unexplored.

Purpose of the Study:

• To investigate the reactivity of electron-poor diamido carbene (5-tBuDAC) with silyl diazomethane.
• To compare the reactivity of 5-tBuDAC with its congener 6-DippDAC and the previously studied 5-SIPr.
• To elucidate the mechanistic pathways governing the observed reactivity using DFT studies.

Main Methods:

• Synthesis and characterization of novel carbene-metal complexes.
• Reaction of silyl diazomethane with 5-tBuDAC and 6-DippDAC.
• Reaction of resulting complexes with HCl.
• Density Functional Theory (DFT) calculations.

Main Results:

• 5-tBuDAC cleaves the C-H bond of silyl diazomethane, forming complex 5.
• 6-DippDAC forms an N-heterocyclic methylene hydrazine.
• Reaction of complex 5 with HCl leads to N2 elimination, yielding products 7 and 8, contrasting with dimerization observed for the 5-SIPr analogue.
• DFT studies explain the divergence in reactivity and favor N2 elimination over dimerization for 5-tBuDAC.

Conclusions:

• The electronic properties of the NHC framework significantly influence the reactivity of silyl diazomethane.
• Electron-poor diamido carbenes offer a distinct reaction pathway compared to imidazolin-2-ylidenes.
• DFT calculations provide crucial insights into the mechanistic underpinnings of these transformations.