Reaction of cobalt porphycene with hydride reagents: spectroscopic detection of Co–H porphycene species and formation of Co–SnR₃ porphycene species

Abstract

The reaction of tetrapropylporphycenatocobalt(III) with tributyltin hydride generates a cobalt(III)-hydride porphycene detectable by UVvis spectroscopy under diluted conditions, whereas it is impossible to characterize hydride species of cobalt porphyrins. One of the reasons for the stability of the porphycene hydride species is that the porphycene ring has a lower LUMO energy level due to the decrease in the symmetry of the ligand character. However, the hydride species in a highly concentrated solution of the complex is easily converted into the cobalt(II) species via dimerization or reaction of the hydride with excess tributyltin hydride through hemolysis of the Sn-H/Co-H bonds. When the Co(III) porphycene is reacted with LiBHEt 3 , the final product is the cobalt(III)-ethyl complex formed by brearrangement during the reaction of the hydride species and diethylborane in a solvent cage. In the reaction of tetrakistrifluoromethylporphycenatocobalt(III) with tributyltin hydride, the dominant reaction pathway includes oneelectron reduction of the porphycene ring together with radical coupling of the tin reagent rather than the net hydride transfer. This finding suggests that the delicate control of the LUMO energy level influences the stability of the hydride species. The tetrapropyl porphycenatocobalt(III) complex with tributyltin or triphenyltin hydride in the presence of AIBN produces the corresponding Co(III)-trialkyltin complex. This complex was characterized by 1 H NMR spectroscopy. isolable in air in air Co III Bu + Bu 2 Sn=O etc. 1-Co III -SnBu 3 1-Co III -SnPh 3 Scheme 4. Reaction of 1-Co(II) with trialkyltin hydride in the presence of AIBN J. Porphyrins Phthalocyanines 2012.16:616-625. Downloaded from www.worldscientific.com by UNIVERSITY OF SASKATCHEWAN on 02/05/15. For personal use only.

Spectroscopy and Tautomerization Studies of Porphycenes

“…Various cobalt complexes have been investigated for porphycenes 13 , ,,,− 19 , , 20 , and 21 . UV/vis spectroscopy served as a tool for identifying different redox species. , Stable cobalt­(III) hydride species were detected for complexes with 13 . Reversible binding of molecular oxygen to 13 -Co­(II) could be monitored by observing changes in the absorption spectra. , Similar absorption changes were observed when dioxygen was inserted into 13 -Co­(III)­(alkyl) complexes .…”

“…Various cobalt complexes have been investigated for porphycenes 13 , ,,,− 19 , , 20 , and 21 . UV/vis spectroscopy served as a tool for identifying different redox species. , Stable cobalt­(III) hydride species were detected for complexes with 13 .…”

“…143 An Scheme 28 extremely high rate was found, explained by a small value of the inner-sphere reorganization energy. Various cobalt complexes have been investigated for porphycenes 13, 15,128,135,146−149 148 UV/vis spectroscopy served as a tool for identifying different redox species. 124,135 Stable cobalt(III) hydride species were detected for complexes with 13.…”

“…124,135 Stable cobalt(III) hydride species were detected for complexes with 13. 148 Reversible binding of molecular oxygen to 13-Co(II) could be monitored by observing changes in the absorption spectra. 146,149 Similar absorption changes were observed when dioxygen was inserted into 13-Co(III)(alkyl) complexes.…”