Cobalt Complex of an N-Linked Carbacorrole Analog: Axial Ligand Effect on Electronic Structure

Corrole, recognized as a contracted tetrapyrrolic macrocycle featuring an α,α'-linked bipyrrole moiety, has garnered attention for its unique trianionic N4 donor environment at the inner core. This characteristic has prompted the exploration of various high-valent metal species for potential catalytic applications. In our pursuit of uncovering new reactivity in metallo-corroles, we have previously synthesized a distinct carbacorrole ligand known as N-confused/N-linked corrole analogs.1 The former variant incorporates an inverted pyrrole moiety connected at the α and β’-linking positions, while the latter exhibits a unique linkage between the α-pyrrole ring and the pyrrolic N site. The resulting NNNC coordination environment of carbacorroles stabilizes distinctive organometallic species, particularly with copper(III) ions.2 In this study, we synthesized novel cobalt complexes featuring an N-linked carbacorrole analog with a benzo annulation, referred to as benzonorrole. The electronic structure of the ensuing complex is notably influenced by the axial ligands. The monodentate pyridine axial coordination to the cobalt norrole complex revealed unique reactivity, resulting in an oxygenated product at the inner carbon site. The oxygenated cobalt norrole complex can be characterized as a singlet Co(II) ligand radical at the ground state, as evidenced by various spectroscopic methods and magnetic susceptibility measurements. Upon substitution with a triphenylphosphine ligand, the resulting five-coordinated cobalt norrole complex was found to be stable and considered a diamagnetic cobalt(III) species, devoid of redox noninnocent character. This talk will delve into the detailed structure and electrochemical properties of these intriguing complexes. 1 Fujino, K.; Hirata, Y.; Kawabe, Y.; Morimoto, T.; Srinivasan, A.; Toganoh, M.; Miseki, Y.; Kudo, A.; Furuta, H. Angew. Chem. Int. Ed. 2011 , 50 , 6855-6859; Toganoh, M.; Kawabe, Y.; Uno, H.; Furuta, H. Angew. Chem. Int. Ed. 2012 , 51 , 8753-8756. 2 Maurya, Y.; Noda, K.; Yamasumi, K.; Mori, S.; Uchiyama, T.; Kamitani, K.; Hirai, T.; Ninomiya, K.; Nishibori, M.; Hori, Y.; Shiota, Y.; Yoshizawa, K.; Ishida, M.; Furuta, H. J. Am. Chem. Soc . 2018 , 140 , 6883-6892.