INOR 122 |
| Despite their electronic similarity to N-heterocyclic carbenes (NHCs), acyclic diaminocarbenes (ADCs) have received little attention as ligands for catalysis. One likely reason for this is that NHC-based synthetic methods (e.g. deprotonation of amidinium salts) are not consistently effective for acyclic carbene derivatives. One potentially versatile synthetic route to ADC complexes is metal-templated addition of amines to coordinated isocyanides. We have investigated the use of chiral diamines to prepare new chiral ADC complexes in a single step using this strategy. Palladium complexes of arylisocyanides with a range of electron-donating or –withdrawing substituents undergo attack by readily available chiral secondary diamines to yield chelating chiral bis(ADC) complexes. Investigations of the donor properties of the new carbene ligands revealed a bite-angle dependence of donicity that can result in surprisingly electrophilic Pd centers. For example, bis(ADCs) that form 7-membered chelate rings apparently donate more weakly than bis(diphenylphosphino)ethane, in contrast to the conventional view of carbenes as stronger donors than phosphines. Pd-catalyzed aza-Claisen [3,3]-sigmatropic rearrangement reactions were utilized to test the ability of the new catalysts to act as electrophilic catalysts. Extensions of the ligand synthesis method to less costly metals (Cu, Ni) will also be presented. |
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Organometallic Synthesis
1:30 PM-5:20 PM, Sunday, August 19, 2007 BCEC -- 212, Oral
Division of Inorganic Chemistry |