Ruthenium-Catalyzed Metathesis Reactions of ortho- and meta-Dialkenyl-Carboranes: Efficient Ring-Closing and Acyclic Diene Polymerization Reactions

The ruthenium-catalyzed metathesis reactions of dialkenyl-substituted ortho- and meta-carboranes provide excellent routes to both cyclic-substituted o-carboranes and new types of main-chain m-carborane polymers. The adjacent positions of the two olefins in the 1,2-(alkenyl)₂-o-carboranes strongly favor the formation of ring-closed (RCM) products with the reactions of 1,2-(CH₂CHCH₂)₂-1,2-C₂B₁₀H₁₀ (1), 1,2-(CH₂CH(CH₂)₃CH₂)₂-1,2-C₂B₁₀H₁₀ (2), 1,2-(CH₂CHSiMe₂)₂-1,2-C₂B₁₀H₁₀ (3), 1,2-(CH₂CHCH₂SiMe₂)₂-1,2-C₂B₁₀H₁₀ (4), and 1,2-[CH₂CH(CH₂)₄SiMe₂]₂-1,2-C₂B₁₀H₁₀ (5) affording 1,2-(−CH₂CHCHCH₂−)-C₂B₁₀H₁₀ (10), 1,2-[−CH₂(CH₂)₃CHCH(CH₂)₃CH₂−]-1,2-C₂B₁₀H₁₀ (11), 1,2-[−SiMe₂CHCHSiMe₂−]-1,2-C₂B₁₀H₁₀ (12), 1,2-[−SiMe₂CH₂CHCHCH₂SMe₂−]-C₂B₁₀H₁₀ (13), and 1,2-[−SiMe₂(CH₂)₄CHCH(CH₂)₄SiMe₂−]-C₂B₁₀H₁₀ (14), respectively, in 72−97% yields. On the other hand, the reaction of 1,2-(CH₂CHCH₂OC(O))₂-1,2-C₂B₁₀H₁₀ (6) gave cyclo-[1,2-(1′,8′-C(O)OCH₂CHCHCH₂OC(O))-1,2-C₂B₁₀H₁₀]₂ (15a) and polymer 15b resulting from intermolecular metathesis reactions. The nonadjacent positions of the alkenyl groups in the 1,7-(alkenyl)₂-m-carboranes, 1,7-(CH₂CHCH₂)₂-1,7-C₂B₁₀H₁₀ (7), 1,7-(CH₂CH(CH₂)₃CH₂)₂-1,7-C₂B₁₀H₁₀ (8), and 1,7-(CH₂CHCH₂SiMe₂)₂-1,7-C₂B₁₀H₁₀ (9), disfavor the formation of RCM products, and in these cases, acyclic diene metathesis polymerizations (ADMET) produced new types of main chain m-carborane polymers. The structures of 3, 9, 11, 12, 13, and 15a were crystallographically confirmed.