Reduction of nitric oxide by tetramesityliridium(IV) and cobaltocene. Reactions of hyponitrite complexes and of the ether [Co(η5-C5H5)(η4-C5H5)](µ-O-exo) with nitroalkanes, acids and amines

Abstract

The interactions of either Ir(mes)₄(mes = C₆H₂Me₃-2,4,6) or Co(cp)₂(cp =η⁵-C₅H₅) with NO in light petroleum gave unstable solids the IR spectra of which allow them to be formulated as hyponitrite complexes, e.g.[Co(cp)₂]₂(N₂O₂)1; their reaction with MeNO₂ is described. The compound Co(cp)₂ with either NO or Ag₂N₂O₂ in toluene gave N₂O and the very reactive ether [Co(cp)(η⁴-C₅H₅)]₂(µ-O-exo)2. This reacts with nitroalkanes where the product depends on the nature of the nitroalkane. Nitromethane produced both Co(cp)₂⁺ CH₂NO₂^–·H₂O 3 and [Co(cp)(η⁴-C₅H₅)]₂[(µ-CH(NO₂)-exo]4, while Me₂CH(NO₂) gave Co(cp)[η⁴-C₅H₅(CMe₂NO₂)-exo] and EtNO₂ corresponding species to 3 and 4(i.e.6 and 7). Reactions of 2 with alcohols or phenylacetylene gave mononuclear species of the same type as 4; treatment with NH₂Ph or NHPh₂ also gave similar exo complexes 8 and 9 respectively. All these exo species reacted with CHCl₃ to give the exo-CCl₃ compound by facile C–C bond cleavage. Mechanisms for the various reactions are discussed. The structures of compounds 2–4, 8 and 9 have been confirmed by X-ray crystallography: 2 and 4 contain Co(cp)(η⁴-C₅H₅) moieties bridged by oxygen or CH(NO₂) groups while 8 and 9 are monomers with exo-NHPh or -NPh₂ groups. In all cases but one (2) there are near-eclipsed C₅CoC₅ geometries; for one of the cobalts in 2 there is a twist of ca. 16° from the eclipsed configuration. Compound 3 has Co(cp)₂⁺ and CH₂NO₂^– ions the latter being involved in strong hydrogen bonding with the H₂O molecule also present in the lattice. In both 8 and 9 there is structural evidence for π interaction between p lone pairs on the planar nitrogen atom and the π system of a phenyl ring.