Remarkable features of the McMurry reaction conditions in dimerization of formyl- And 2-formylvinylpurpurinimides. electrochemistry of monomeric Ni(II) purpurinimide and the corresponding dyads

Lalit N. Goswami, Manivannan Ethirajan, Mahabeer P. Dobhal, Min Zhang, Joseph R. Missert, Masayuki Shibata, Karl M. Kadish, Ravindra K. Pandey

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33 Scopus citations

Abstract

To investigate the electrochemical properties of purpurinimide dyads and electron transfer sites for their reduction and oxidation, a series of dimers with variable C-C linkages were synthesized. For the preparation of these novel structures, the formyl and 2-formylvinyl substituents were regioselectively introduced at positions 3 and 20 of Ni(II) purpurinimides by the Vilsmeier reaction. The Ni(II) complexes were then subjected to the McMurry reaction under two different conditions with unexpected results. For example, the reaction of formyl purpurinimides with TiCl 3(DME) 1.5 failed to produce the desired C-C dimers, and the starting compounds were recovered almost quantitatively. Under similar reaction conditions, the 20-(2-formylvinyl) purpurinimide also did not dimerize but produced instead unexpected benzoisobacteriochlorins via an intramolecular cyclization. However, treatment of the 3-formyl- and 20- formylpurpurinimides with TiC1 4/Zn produced corresponding dimers linked with one double bond (trans) in modest yields. Under similar conditions, Ni(II) purpurinimides containing a 2-formylvinyl substituent either at position 3 or at position 20 afforded the respective C-C dimers, where the purpurinimide moieties were joined with a trans-trans-trans hexatriene linker. Molecular modeling data suggest that the nature of the conformational energy difference found in all trans vs trans-cis-trans conformers of the dimers connected by a hexatriene linker at the meso- or β-position of the macrocycle is not because of the intrinsic conformational energy difference of the linker region, which is identical for both dimers.

Original languageEnglish (US)
Pages (from-to)568-579
Number of pages12
JournalJournal of Organic Chemistry
Volume74
Issue number2
DOIs
StatePublished - Jan 16 2009

All Science Journal Classification (ASJC) codes

  • Organic Chemistry

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