Nickel-Catalyzed Reactions of Benzo[1,2:4,5]bis(1,1,2,2-tetraethyl-1,2-disilacyclobut-3-ene) with Alkynes and Ketones

Heating a benzene solution of benzo[1,2:4,5]bis(1,1,2,2-tetraethyl-1,2-disilacyclobut-3-ene) (1) with a catalytic amount of tetrakis(triethylphosphine)nickel(0) gave two regioisomers, 2 and 3, arising from C-H bond activation of benzene in 81% combined yield. The reaction of 1 with diphenylacetylene in the presence of the nickel catalyst afforded benzo[1,2:4,5]bis-(1,1,4,4-tetraethyl-2,3-diphenyl-1,4-disilacyclohexa-2,5- diene) in 91% yield, while with 3-hexyne, 1 yielded benzo[1,2:4,5]bis(1,1,2,3,4,4-hexaethyl-1,4-disilacyclohexa-2,5-diene) and its isomer (7) in 64% and 25% yields, respectively. The nickel-catalyzed reaction of 1 with benzophenone gave benzo[1,2](1,1,3,3-tetraethyl-2-oxa-1,3-disilacyclopent-4-ene)[4,5](1,1,3,3- tetraethyl-2,2-diphenyl-1,3-disilacyclopent-4-ene) and siloxane (8) in 40% and 50% yields. Similarly, with 4,4′-dimethylbenzophenone, 1 produced benzo[1,2](1,1,3,3-tetraethyl-2-oxa-1,3-disilacyclopent-4-ene)[4,5](1,1,3,3- tetraethyl-2,2-(p-tolyl)-1,3-disilacyclopent-4-ene)in 19% yield, together with a 50% yield of 8. When the similar treatment of 1 with benzophenone was carried out in cyclohexene, 7,7-diphenylnorcarane was obtained in 14% yield, along with a 54% yield of 8.