Linear Cu(i) chalcogenones: synthesis and application in borylation of unsymmetrical alkynes

Abstract

The syntheses and structures of copper(I) chalcogenone complexes are described. The homoleptic mononuclear copper(I) complexes [(IPrE)₂Cu]ClO₄, IPrE, 1,3-bis(2,6-diisopropylphenyl)imidazoline-2-thione (1) and 1,3-bis(2,6-diisopropylphenyl)imidazoline-2-selone (2); [(IMesE)₂Cu]ClO₄, IMesE, 1,3-bis(2,4,6-trimethylphenyl)imidazole-2-thione (3) and 1,3-bis(2,4,6-trimethylphenyl)imidazole-2-selone (4); [(IPrE)₂Cu]BF₄, E = S (5); E = Se (6) and [(IMesE)₂Cu]BF₄, E = S (7); E = Se (8) are formed from the reduction of copper(II) to copper(I) with the corresponding imidazoline-2-chalcogenones. X-ray structure analyses of seven compounds (1–3 and 5–8) show that the copper(I) ion is in a perfect linear coordination, while 4 is in quasi-linear geometry. Molecules 2, 4, 6 and 8 are the first structurally characterized homoleptic copper(I) selone complexes. The optical and thermal properties of imidazoline-2-chalcogenones and their copper(I) derivatives are investigated. These complexes are able to act as catalysts in regioselective borylation of numerous unsymmetrical alkynes, yielding synthetically useful vinylboronates. Among catalysts 1–8, catalyst 4 is highly selective towards the regioselective boron addition of 1-phenyl-1-propyne.