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-mu,eta2,eta2-(Nu-CH2C(triple bond)C-C(triple bond)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-mu,eta2,eta2-(HO-CH2C(triple bond)C-C(triple bond)CCH2-OH)] (1) are presented. Complex 1 crystallizes in the triclinic space group P1 with a = 14.722(2) A, b = 14.571(3) A, c = 14.722(2) A, alpha = 105.17(1) degrees, beta = 113.30(1) degrees, gamma = 99.20(1) degrees, and Z = 4. Complex 3 crystallizes in the monoclinic space group P2(1)/n with a = 12.758(3) A, b = 13.360(3) A, c = 20.494(3) A, beta = 91.44(1) degrees, and Z = 4, and compound 5 also crystallizes in the monoclinic space group P2(1)/n with a = 9.426(2) A, b = 21.739(5) A, c = 18.704(3) A, beta = 94.86(1) degrees, 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-mu,eta2,eta2-(Me2S-CH2C(triple bond)C-C(triple bond)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-mu,eta2,eta2-(Me2S-CH2-C(triple bond)C-CH2-SMe2)][BF4]2 (4).