Bidentate iminophosphorane-NHC ligand derived from the imidazo[1,5- a ]pyridin-3-ylidene scaffold

Karim Azouzi (1) , Carine Guyard-Duhayon (1) , Idir Benaissa (1) , Noël Lugan (1) , Yves Canac (1) , Stéphanie Bastin (1) , Vincent César (1)

1 LCC - Laboratoire de chimie de coordination

The synthesis of the bifunctional iminophosphorane-NHC (1) based on the imidazo[1,5-a]pyridin-3-ylidene (IPy) platform is reported. Its imidazo[1,5-a]pyridinium salt precursor [1·H](X) was readily obtained by an efficient three-component coupling reaction between 5-bromoimidazo[1,5-a]pyridinium bromide, sodium azide, and triphenylphosphine according to a SNAr/Staudinger reaction sequence. The stable free carbene 1 was generated by deprotonation of [1·H](X) with potassium bis(trimethylsilyl)amide, and its coordination ability toward various transition-metals was evaluated, either upon direct metalation of the free carbene or by transmetalation from a silver(I) NHC complex. While the ligand 1 is singly bounded through the carbene carbon atom in the latter complex, it behaves as a chelating bidentate ligand in all other complexes that were prepared, including the cationic and neutral palladium(II) complexes [Pd(allyl)(κ2C,N-1)](OTf) ([5](OTf)) and [PdCl2(κ2C,N-1)] (7), and the cationic rhodium(I) complexes [Rh(cod)(κ2C,N-1)](OTf) ([8](OTf)) and [Rh(CO)2(κ2C,N-1)](OTf) ([9](OTf)), generating stable 5-membered metallacycles. IR νCO measurements carried out on the complex [Rh(CO)2(κ2C,N-1)](OTf) ([9](OTf)) show evidence of the strong donating character of the iminophosphorane-NHC ligand 1.

Mots clés: Carbene compounds; Anions; Metals; Ligands; Carbon

Domaines: Chimie de coordination

Karim Azouzi, Carine Guyard-Duhayon, Idir Benaissa, Noël Lugan, Yves Canac, et al.. Bidentate iminophosphorane-NHC ligand derived from the imidazo[1,5- a ]pyridin-3-ylidene scaffold. Organometallics, 2018, 37 (24), pp.4726-4735. ⟨10.1021/acs.organomet.8b00733⟩. ⟨hal-02128330⟩