On the acceptor properties of a Al-Nacnac carbene analogue, a density functional investigation

• Is :Al(NacNac) isolobal to the N-heterocyclic carbene?
• Donor complex formation of :Al(NacNac) with NHC and phosphines.
• Triplet enhancement of Al-carbene analogues.
• Biradicaloid formation of adducts.
• Induction of facile hydrogen shift reaction to tetravalent aluminium.

The Al-Nacnac compound is isolobal to the imidazol-2-ylidene (NHC) and forms donor complexes with phosphines and NHCs. These structural types were studied by density functional calculations. They reveal a strong biradical character, since donor addition to the Al-Nacnac reduces the singlet stability of the free carbene-analogue. This facilitates further biradical reactions, such as a subsequent hydrogen shift to the final corresponding tetravalent aluminium product. The latter is determined by maximum singlet stability, i.e. a large singlet-triplet energy separation. Relevance to the analogues Wittig ylids is drawn; these are constituted formally by addition of a phosphine to a carbene, and are well-known as stable synthons in organic chemistry.

The Al-Nacnac compound forms donor complexes with phosphines and NHCs. These structural types were studied by density functional calculations. They reveal a strong biradical character.Figure optionsDownload as PowerPoint slide