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 [(IPr[double bond, length as m-dash]E)2Cu]ClO4, IPr[double bond, length as m-dash]E, 1,3-bis(2,6-diisopropylphenyl)imidazoline-2-thione (1) and 1,3-bis(2,6-diisopropylphenyl)imidazoline-2-selone (2); [(IMes[double bond, length as m-dash]E)2Cu]ClO4, IMes[double bond, length as m-dash]E, 1,3-bis(2,4,6-trimethylphenyl)imidazole-2-thione (3) and 1,3-bis(2,4,6-trimethylphenyl)imidazole-2-selone (4); [(IPr[double bond, length as m-dash]E)2Cu]BF4, E = S (5); E = Se (6) and [(IMes[double bond, length as m-dash]E)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.