Monomeric and Dimeric Cyclooctyne-Stabilized Complexes of Copper(I)¹

The syntheses and structures of cyclooctyne halogeno copper(I) complexes are described. The dimeric compounds [CuX(cyclooctyne)]2 (5: 5a, X = Cl; 5b, X = Br; 5c, X = I) are formed by reaction of equimolar amounts of cyclooctyne and copper(I) halide. X-ray structure analyses of all three compounds 5 show the copper(I) ion in a trigonal-planar coordination with bridging halide ligands. The complexes 5 react with an excess of cyclooctyne to give the monomeric bis(alkyne) complexes [CuX(cyclooctyne)2] (7: 7a, X = Cl; 7b, X = Br; 7c, X = I). Here, the three X-ray structure determinations prove that two η2-coordinated alkyne ligands are bound to a monomeric copper(I) halide unit. The reaction of the bromo complex 5b with 3,3,6,6-tetramethyl-l-thia-4-cycloheptyne (S-alkyne) affords the first mixed-alkyne copper complex [(cyclooctyne)CuBr2Cu(S-alkyne)] (9). Compound 9 forms dinuclear molecules in solution but a polymeric bent chain in the solid state (X-ray structure determination), in which one copper remains in a trigonal-planar environment and the other copper has a tetracoordinated structure.