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

The syntheses and structures of copper(I) chalcogenone complexes are described. The homoleptic mononuclear copper(I) complexes [(IPrvE)(2)Cu]ClO4, IPr=E, 1,3-bis(2,6-diisopropylphenyl)imidazoline-2-thione (1) and 1,3-bis(2,6-diisopropylphenyl)imidazoline-2-selone (2); [(IMes=E)(2)Cu]ClO4, IMes=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=E)(2)Cu]BF4, E = S (5); E = Se (6) and [(IMes=E)(2)Cu]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.