Ligand Noninnocence In Manganese, Iron, and Cobalt Corroles

Abstract

In recent years, first-row metallocorroles have provided some of the most instructive examples of noninnocent ligands. This thesis presents a study of some 50 iron, manganese, and cobalt corrole complexes with different axial ligands (including approximately 30 new compounds and 6 new X-ray structures) with emphasis on their noninnocent/innocent character. UV-vis spectroscopy has for some time provided a convenient empirical probe of ligand noninnocence in transition metal meso-tris(para-X-phenyl)corrole (TpXPC) complexes. Redshifts of the Soret maxima with increasing electron-donating character of the para-substituent X have indicated noninnocent systems, while substituent-insensitive Soret maxima have indicated innocent corrole ligands. I have greatly expanded the scope of this optical probe of noninnocence and used it to identify new classes of noninnocent metallocorroles. The μ-oxo diiron corroles have long been thought of as true Fe(IV) complexes. However, as discussed in Paper A, a study of the optical spectra of {Fe[TpXPC]}2O derivatives along with DFT calculations have indicated a noninnocent description for these complexes. Iron-aryl corroles are classic examples of true Fe(IV) species. Several Fe-aryl corroles were synthesized and examined together with other Fe corrole derivatives by means of UV-vis and NMR spectroscopy and electrochemistry in a detailed study for ligand noninnocence in a wide range of Fe corroles (Paper B). Analogous studies of Mn-aryl corroles were also carried out (Chapter 3), but these have not yet been written up as a manuscript. A collaborative study with the Stanford Synchrotron Radiation Lightsource also provided the first X-ray absorption spectroscopic analysis of the question of ligand noninnocence in Fe corrole complexes. Cobalt-triphenylphosphine (Co-PPh3) corroles have also been thought of as classic low-spin Co(III) complexes until now. An examination of the UV-vis spectra of Co-PPh3 corroles and DFT calculations again indicated a partially noninnocent Co(II) corrole radical description for these complexes (Paper C). In contrast, an innocent description was indicated for Rh-PPh3 corroles. Finally, as discussed in Paper D, Co corrole pyridine adducts were likewise studied with a variety of spectroscopic techniques and the noninnocent behavior of the monopyridine adducts was elucidated in considerable detail.