Cyclic alkyl amino carbenes

In chemistry, cyclic alkyl amino carbenes (CAACs) are a type of cyclic carbene which contain a single nitrogen atom within the cyclic structure. CAACs were first developed by Guy Bertrand at UCSD as an alternative to traditional N-heterocyclic carbenes which contain two nitrogen atoms with in the structure typically derived from imidazole. Replacing a single nitrogen in the NHC to a quaternary carbon in the CAAC makes a difference to the electron donating abilities of the carbene hence making it a stronger σ-donor ligand.

Current research is investigating the use of these ligands in organometallic compounds as catalysts and into developing new derivatives of CAACs such as bicyclic CAACs.

Cyclic alkyl amino carbenes can be prepared from 2,6-disopropylaniline and 2-methylpropanal. The initial step involves the deprotonation of 2,6-disopropylaniline with lithium diisopropylamide to give a aza-allyl anion. The aza-allyl anion then induces the ring opening of 1,2-epoxy-2-methylpro-pane leading to a lithium alkoxide. The lithium alkoxide is then treated with triflic anhydride at -78 celsius, this is then warmed to room temperature to generate the aldiminium salt. The production of the aldiminium salt gives a yield of 58% with respect to 2,6-disopropylaniline. The final step in the synthesis uses lithium diisopropylamide to generate the carbene which is a white solid.

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