Experiments on a simulation of the photochemical A/D-secocorrin leads to corrin cyclo-isomerization by redox processes. Electrochemical oxidation of nickel(II)-1-methylidene-2,2,7,7,12,12-hexamethyl-15-cyano-1,19-secocorrinate perchlorate (author's transl)

Abstract

Experiments on a simulation of the photochemical A/D‐secocorrin → corrin cycloisomerization by redox processes. Electrochemical oxidation of nickel(II)‐1‐methylidene‐2,2,7,7,12,12‐hexamethyl‐15‐cyano‐1,19‐secocorrinate perchlorateCan the act of light excitation in the photochemical A/D‐secocorrin → corrin cycloisomerization be replaced by redox reactions in the dark? Electrochemical oxidation of nickel(II)‐A/D‐secocorrinate 4 in acetonitrile containing a trace of water produces the secocorrinoxide–nickel‐complex 5 (structure determined by X‐ray analysis) in almost quantitative yield. This two‐electron oxidation involves a hydrogen shift from the methylene group C(19) in ring D to the methylidene carbon atom at ring A in the radical cation intermediate. Since the same type of hydrogen shift occurs in the photochemical A/D‐secocorrin → corrin cycloisomerization, a close parallelism in their chemical reactivity seems to exist between electronically excited A/D‐secocorrins and corresponding radical cations. Formation of the corrin complex 2 (M = Ni+) could be achieved (so far only in modest yields) by electrochemical one‐electron oxidation of 4 in acetonitrile/acetanhydride/acetic acid 8:1:1 followed by one‐electron reduction. – The transformation of the oxide nickel complex 5 to the corrinoid complex 10 – a new member in the family of dehydrocorrins – is also recorded.