3 years ago

Aromaticity of the chelate rings. The case of bis(ethylenediamine)nickel(II)

Aromaticity of the chelate rings. The case of bis(ethylenediamine)nickel(II)
The aromaticity of the chelate rings in [Ni(en)2]2+, [Ni(pn)2]2+, [Ni(bn)2]2+, [Zn(en)2]2+ and [Pd(en)2]2+ (en=1,2-diaminoethane, pn=1,3-diaminopropane and bn=1,4-diamino-butane) are studied by means of nucleus independent chemical shift (NICS) calculations. Comparing the data with those of benzene and cyclopropane, it is concluded that the chelate rings in [Ni(en)2]2+, [Ni(pn)2]2+ and [Ni(bn)2]2+ are σ-aromatic while the ones in [Zn(en)2]2+ and [Pd(en)2]2+ are non aromatic. The order of aromaticity is [Ni(en)2]2+ >[Ni(pn)2]2+ >[Ni(bn)2]2+. The trend is correlated with the ease of formation of Curtis macrocycle from bis diamine complexes of Ni(II). The aromaticity in [Zn(en)2]2+ is lost because of breaking of sigma conjugation at the metal. It seems that the sigma aromatic systems do not follow the 4n +2 rule.

Publisher URL: www.sciencedirect.com/science

DOI: S2210271X17303444

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