CLEAVAGE OF (OCTAETHYL-2,5-DIHYDROXYCHLORINATO)NICKEL(II) TO GIVE THENOVEL 2,3-DIOXO-2,3-SECOCHLORIN SYSTEM

Treatment of (octaethyl-2,3-dihydroxychlorinato)nickel(II) with lead t etraacetate in benzene causes cleavage of the 2-3 bond to give the nic kel(II) 2,3-secochlorin-2,3-dione system 7, a previously unknown struc tural type. The structure is established by elemental analysis and spe ctroscopic methods, and confirmed by X-ray analysis. The dione gives a bis(2,4-dinitrophenylhydrazone). Treatment with base causes an aldol- type condensation to occur to give the (2-oxo-2a-homoporphyrinato)nick el(II) 8. This substance is rather unreactive, and it has not been pos sible to prepare carbonyl derivatives. This lack of reactivity is rati onalised in terms of charge delocalisation which reduces carbonyl doub le-bond character. These novel pathways are discussed in relation to t he known (and different) pathways of chlorophyll catabolism which have recently been uncovered.