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

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posted on 27.04.2009, 00:00 by Farman Ullah, Markus K. Kindermann, Peter G. Jones, Joachim Heinicke
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 NH4PF6 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 7b9b 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 13CII nuclei.