Ring-expanded N-heterocyclic carbene complexes of rhodium with bifluoride, fluoride, and fluoroaryl ligands

Thermolysis of Rh(PPh)H in the presence of the six-membered N-heterocyclic carbene 1,3-bis(2-propyl)-3,4,5,6- tetrahydropyrimidin-2-ylidine (6-Pr) gave the monocarbene complex Rh(6-Pr)(PPh)H as a 1:2 mixture of the cis- and trans-phosphine isomers 1a and 1b. This same isomeric mixture was formed as the ultimate product from treating Rh(PPh)(CO)H with 6-Pr at room temperature, although pathways involving both CO and PPh loss were observed at initial times. Treatment of 1a/1b with EtN·3HF generated the bifluoride complex cis-Rh(6- Pr)(PPh)(FHF) (2a), which upon stirring with anhydrous MeNF was converted to the rhodium fluoride complex cis-Rh(6-Pr)(PPh)F (3a). Thermolysis of 1a/1b with CF resulted in C-F bond activation to afford a mixture of 3a and the pentafluorophenyl complex trans-Rh(6- Pr)(PPh)(CF) (5b). Complexes 1b, 2a, 3a, and 5b were structurally characterized.