Alkyne Coupling and Cyclization on Metal Cluster Complexes. Additions and Couplings of Dimethyl acetylenedicarboxylate to Ru6(μ6-C)(CO)14(μ3-η4-C4H4)

Abstract

Reactions of the hexaruthenium cluster complex Ru6(μ6-C)(CO)14(μ3−η4−C4H4), 2 with dimethyl acetylenedicarboxylate (DMAD) at 25 °C yielded five new compounds: Ru6(μ5-C)(CO)16(μ−η4−C4H4), 3; Ru6(μ6-C)(CO)14[η6-1,2-C6H4(CO2Me)2], 4; Ru6(μ5-C)(CO)14(μ−η4−C4H4)[μ3−C2(CO2Me)2], 5; Ru6(μ5-C)(CO)14(μ−η4−C4H4)[μ3−C2(CO2Me)2], 6 and Ru6(μ6-C)(CO)14[μ3−η6−1,2−C6H4(CO2Me)2], 7. Compounds 4 and 7 are isomers that contain the six-membered arene, dimethyl phthalate, 1,2−C6H4(CO2Me)2, as a ligand. Compound 3 was formed as a side product in low yield (6%) by the simple addition of CO to 2. The addition of CO to 2 causes the cluster to open to that of a spiked, square pyramid. Direct reaction of CO to 2 provided 3 in a good yield (72%). A DMAD ligand was added to the cluster of 2 as a simple triply-bridging ligand to form open Ru6 clusters in compounds 5 and 6. Addition of DMAD to 3 yielded the DMAD derivative Ru6(μ5-C)(CO)15(μ−η4−C4H4)[μ−C2(CO2Me)2], 8 which contains a DMAD ligand bridging a basal edge of an opened spiked-square pyramidal Ru6 cluster. Compound 5 was thermally converted to the new complex Ru6(μ5-C)(CO)14[μ4−η6−CHCHCHCC(CO2Me)C(CO2Me)](μ-H), 9 that contains a bridging CHCHCHCC(CO2Me)C(CO2Me) ligand formed by a coupling of the DMAD ligand to the bridging C4H4 ligand in 5 accompanied by a cleavage of one CH bond and formation of a bridging hydrido ligand. Decarbonylation of 3 with Me3NO yielded the NMe3 derivative Ru6(μ5-C)(CO)15(μ−η4−C4H4)(NMe3), 10 in which the NMe3 ligand is coordinated to the spiked metal atom on the square-pyramidal Ru5 cluster. Treatment of 4 and 7 with CO at 25 °C induced elimination of the 1,2−C6H4(CO2Me)2 ligand to yield free dimethyl phthalate, 11 and formation of the known parent carbonyl complex Ru6(μ6-C)(CO)17. All of the new cluster compounds were characterized by single-crystal X-ray diffraction analyses.