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

2012-09-03T00:00:00Z (GMT) by Julia Kozhukh Stephen J. Lippard
The size-dependent reactivity of cobalt tropocoronands [TC-<i>n</i>,<i>n</i>]<sup>2–</sup> is manifest in the NO chemistry of the cobalt­(III) nitrite complexes [Co­(η<sup>2</sup>-NO<sub>2</sub>)­(TC-<i>n</i>,<i>n</i>)] (<i>n</i> = 4–6), the synthesis and characterization of which are reported for the first time. Complete conversion of [Co­(η<sup>2</sup>-NO<sub>2</sub>)­(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(η<sup>2</sup>-NO<sub>2</sub>)­(TC-5,5)] generates both cobalt mono- and dinitrosyl adducts, and addition of nitric oxide to [Co­(η<sup>2</sup>-NO<sub>2</sub>)­(TC-6,6)] converts this complex to the dicobalt tetranitrosyl species [Co<sub>2</sub>(NO)<sub>4</sub>(TC-6,6)]. In the latter complex, two tetrahedral cobalt dinitrosyl units are bound to the aminotroponeiminate poles of the [TC-6,6]<sup>2–</sup> ligand. These results significantly broaden the chemistry of cobalt tropocoronands with nitric oxide and the nitrite anion.