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A Short Desymmetrization Protocol for the Coordination Environment in Bis-salphen Scaffolds

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posted on 01.07.2011, 00:00 by Eduardo C. Escudero-Adán, Marta Martínez Belmonte, Eddy Martin, Giovanni Salassa, Jordi Benet-Buchholz, Arjan W. Kleij
A remarkable short preparation of desymmetrized bis-salphen scaffolds is presented. The protocol consists of an hydroxide-mediated hydrolysis of Lewis acidic bis-Zn(salphen) complexes yielding Cs-symmetric diimine/amine salts that can be selectively transformed into bis-salphens with dissymmetric substitution patterns within each salphen unit under mild conditions. These isolated nonsymmetrical bis-salphen derivatives do not show signs of imine scrambling or decomposition due to a metal template effect. A possible rationale is provided for the formation and isolation of one of the intermediate bis-phenolate salts, and the hypothesis involves H-bond directed hydrolysis of the nearest located imine bond across the bis-salphen scaffold.