Variable Nitric Oxide Reactivity of Tropocoronand Cobalt(III) Nitrite Complexes as a Function of the Polymethylene Linker Chain Length

The size-dependent reactivity of cobalt tropocoronands [TC-n,n]^2– is manifest in the NO chemistry of the cobalt­(III) nitrite complexes [Co­(η²-NO₂)­(TC-n,n)] (n = 4–6), the synthesis and characterization of which are reported for the first time. Complete conversion of [Co­(η²-NO₂)­(TC-4,4)] to the cobalt mononitrosyl [Co­(NO)­(TC-4,4)] occurs upon exposure to NO­(g). In contrast, addition of NO­(g) to [Co­(η²-NO₂)­(TC-5,5)] generates both cobalt mono- and dinitrosyl adducts, and addition of nitric oxide to [Co­(η²-NO₂)­(TC-6,6)] converts this complex to the dicobalt tetranitrosyl species [Co₂(NO)₄(TC-6,6)]. In the latter complex, two tetrahedral cobalt dinitrosyl units are bound to the aminotroponeiminate poles of the [TC-6,6]^2– ligand. These results significantly broaden the chemistry of cobalt tropocoronands with nitric oxide and the nitrite anion.