Catalysts containing (?5-C5Me5)-ruthenium(II) chloride [Cp*RuCl] mediate a variety of organic transformations including the azide alkyne cycloaddition (RuAAC), which provides 1,5-disubstituted 1,2,3-triazoles in a regioselective manner. The sterically less hindered and less electronically rich [CpRuCl] fragment (Cp = ?5-C5H5) is inactive in RuAAC processes except when 1-halogenated alkynes are used, at which point, incidentally, [Cp*RuCl] is no longer active. The ability of catalytic CpRuCl(cod) to engage 1-haloalkynes in cycloadditions with organic azides, as well as nitrile oxides, is a simple and practical means to access 5-halotriazoles and 4-haloisoxazoles, respectively. The lack of catalysis observed with Cp*RuCl(cod) in this reaction is attributed to the steric demands of the Cp* ligand in comparison to Cp. This hypothesis is supported by the poor reactivity of (?5-C5Me4CF3)RuCl(cod), which serves as a an isosteric mimic of Cp* and as an isoelectronic analog of Cp.

CpRuCl(cod) catalyzed cycloaddition of 1-haloalkynes with organic azides and nitrile oxides: Synthesis of 5-halotriazoles and 4-haloisoxazoles

248th National Meeting (2014)

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