Remarkable Activation of an Alkyne [2+2+2]-Cycloaddition Catalyst, 2-Iminomethylpyridine (dipimp)/CoCl₂·6H₂O/Zn, by a Phthalate Additive

Abstract

A catalyst for alkyne [2+2+2]-cycloaddition reactions, 2-(2,6-diisopropylphenyl)iminomethylpyridine (dipimp)/CoCl₂·6H₂O/Zn, can be effectively activated by addition of a catalytic amount of dialkyl phthalate to enable reactions that cannot proceed under un­activated conditions. The activation by adding phthalate was ligand- and solvent-dependent, and it was unique to dipimp and N-methyl-2-pyrrolidone (NMP). With use of diphosphine ligand instead of dipimp or with use of tetrahydrofuran (THF) instead of NMP, no activation by a phthalate additive was observed. This simple method of catalyst activation with use of inexpensive, commercially available compounds is highly practical and may find many applications.

Key words

cycloaddition - homogeneous catalysis - alkynes - esters - ligands - phthalate - catalyst activation

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