Cobalt-Complexed Conjugated Diyne Salts: A Family of Rigid Masked Dielectrophiles. Syntheses, Structures, and Double Nucleophilic Substitutions

A family of dicationic diyne salts of the general formula [(Co2(CO)6)2-μ,η2,η2-(Nu-CH2C⋮C−C⋮CCH2−Nu)][BF4]2 {Nu = SMe2 (3); Nu = NC6H7, 3-picoline, (5); Nu = NC9H7, quinoline (7)} were prepared and fully
characterized. Three X-ray molecular structures of 3, 5, and the neutral starting material 2,4-hexadiyne-1,6-diol
complex [(Co2(CO)6)2-μ,η2,η2-(HO−CH2C⋮C−C⋮CCH2−OH)] (1) are presented. Complex 1 crystallizes in the
triclinic space group P1̄ with a = 14.722(2) Å, b = 14.571(3) Å, c = 14.722(2) Å, α = 105.17(1)°, β = 113.30(1)°,
γ = 99.20(1)°, and Z = 4. Complex 3 crystallizes in the monoclinic space group P21/n with a = 12. 758(3) Å,
b = 13.360(3) Å, c = 20.494(3) Å, β = 91.44(1)°, and Z = 4, and compound 5 also crystallizes in the monoclinic
space group P21/n with a = 9. 426(2) Å, b = 21.739(5) Å, c = 18.704(3) Å, β = 94.86(1)°, and
Z = 4. The X-ray structures provide us with valuable information on the arrangement of the Co2−alkyne units,
which have a cis geometry and are in sharp contrast to that observed generally for diyne−tetracobalt compounds.
Complex [(Co2(CO)6)2-μ,η2,η2-(Me2S−CH2C⋮C−C⋮CCH2−SMe2)][BF4]2 (3) reacts with N-, S-, and P-centered
nucleophiles and affords the related substituted complexes in high yields. The stability and reactivity of the
disulfonium diyne complex 3 toward nucleophiles are compared to those of the analogous disulfonium-yne complex
[(Co2(CO)6)2-μ,η2,η2-(Me2S−CH2−C⋮C−CH2−SMe2)][BF4]2 (4).