An E.S.R. Study of Adducts of Organometallic Radicals with Some Quinones and Diketones

Abstract

Radical species resulting from the reaction of Mn₂(CO)₁₀ and [CO(CO)₃P(OEt)₃]₂ with o-benzo- quinone have been generated and their e.s.r. spectra recorded. The reactions of Mn₂(CO)_lo with several other quinones and diketones have been similarly examined. In most cases the radicals were produced after a short period of ultraviolet irradiation. The radicals derived from Mn₂(CO)₁₀ and o-quinones or α-diketones are formulated as six-coordinate complexes (CO)₄MnA^· in which the manganese atom is chelated by the dicarbonyl compound A. The cobalt radical is similarly formulated as a five-coordinate complex (CO)₂P(OEt)₃CoA^· (A = o-benzoquinone), The proton coupling constants in these adducts are very similar to those of the corresponding quinone or diketone radical anion; this indicates that the unpaired electron resides mainly on the quinone or diketone molecule. The radicals derived from the reaction of Mn₂(CO)_lo with p-quinones are much shorter lived than those of the corresponding o-quinones, but in the case of 2,3,5,6-tetrachlorobenzoquinone, a spectrum which might belong to the Mn(CO)₅ adduct of this molecule was recorded.