Annulated N-Heterocyclic Carbenes: 1,3-Ditolylphenanthreno[9,10-d]imidazol-2-ylidene and Transition Metal Complexes Thereof

The N, N′ -bis(tolylamino)phenanthrenes 1a and 1b were synthesized by reductive cyclization of benzil-bis(tolylimines) and cyclized with triethyl orthoformate in the presence of NH 4 PF 6 to give the corresponding bis(tolyl)phenanthreno[9,10- d ]imidazolium hexafluorophosphates 2a, b . These were deprotonated with excess KH in THF. Whereas the p -tolyl-substituted phenanthrene-annulated imidazol-2-ylidene (phenimy) 3a proved to be unstable and dimerized to 4a, the bulkier o -tolyl derivative is isolable as the monomer carbene 3b . Cationic silver complexes were prepared by the method of Wang and Lin ( 6a, 6b ) or directly ( 6b ), rhodium and palladium complexes 7b − 9b by reaction of 3b and the respective metal precursors. Detailed structural information is given by X-ray crystal structure analyses of 6a and 7b and by HH- and CH-COSY NMR measurements of 1b, 2a, 2b, 3b, and 7b, representing the various compound types. The phenimy ligands are distinguished from benzo- or linear naphtho-annulated imidazol-2-ylidene ligands by higher basicity and free 3b by lower deshielding of the 13 C II nuclei.