Efforts Toward the Site-Selective Dehydrogenation of Saturated Fatty Acids

Studies toward the selective functionalization of saturated fatty acids using iridium carboxylate complexes are described. A variety of iridium complexes were developed bearing a coordinated carboxylate ligand. These complexes were submitted to known dehydrogenation conditions; however, dehydrogenation products were not observed. The bidentate binding of the carboxylate was thought to be responsible for the lack of reactivity observed in these complexes. The carboxylate ligands were therefore derivatized in an effort to favor monodentate coordination. Acylphosphine ligands, which are readily synthesized from fatty acids, were of particular interest due to the long phosphorus carbonyl bond distance relative to the oxygen carbonyl bond distance in carboxylates. Initial studies using acylphosphines resulted in the synthesis of a novel anionic complex. The structural characterization and reactivity of this complex is discussed. Continued work with acylphosphines led to the discovery of a unique site-selective dehydrogenation reaction. A plausible mechanism for this transformation is proposed based on the isolation of observed intermediates and computational studies.