Paramagnetic adducts between manganese-centred radicals and nitro derivatives. A new class of manganese-containing radicals

The photolytic or thermal reaction of pentacarbonylmanganese radicals with either aromatic or aliphatic nitro compounds in the presence of PBu3, and in one case of pyridine, gives spin adducts which have been studied by ESR spectroscopy. On the basis of the spectral parameters these paramagnetic species, which represent the first example of a new class of transition-metal containing radicals, have been assigned a cyclic structure, with the manganese atom acting as a bridge between the two oxygens of the nitro group; this implies the loss of a CO unit during complexation. The role of the phosphine in stabilizing these radicals by replacing one or two CO moieties is critical; doubly-substituted species are much more persistent than their mono-substituted analogues. In the absence of PBu3 the corresponding paramagnetic adduct could be observed only with 2-methyl-2-nitropropane.