Multiple Aromatic C–H Bond Activations by an Unsaturated Dirhenium Carbonyl Complex

Reactions of Re₂(CO)₈(μ-C₆H₅)­(μ-H), 1, with naphthalene and anthracene have yielded the first multiply-CH activated arene products through the reductive elimination of benzene from 1 and multiple oxidative-additions of the dirhenium octacarbonyl grouping to these polycyclic aromatic compounds under very mild conditions. In addition, compound 1 was found to react with itself to yield the bis-Re₂-metalated C₆H₄ bridged compound Re₂(CO)₈(μ-H)­(μ-1,μ-3-C₆H₄)­Re₂(CO)₈(μ-H), 3. Reaction of 1 with naphthalene yielded two doubly CH activated isomers, Re₂(CO)₈(μ-H)­(μ–η²-1,2-μ–η²-3,4-C₁₀H₆)­Re₂(CO)₈(μ-H), 4, 41% yield, and Re₂(CO)₈(μ-H)­(μ–η²-1,2-μ–η²-5,6-C₁₀H₆)­Re₂(CO)₈(μ-H), 5, via the mono CH activated intermediate Re₂(CO)₈(μ–η²-C₁₀H₇)­(μ-H), 2. Compound 4 contains two Re₂(CO)₈(μ-H) groups on one C₆ ring formed by CH activations at the 2- and 4-positions. Compound 5 contains two Re₂(CO)₈(μ-H) groups; one formed by CH activation at the 2-position on one C₆ ring and the other formed by CH activation at the 6-position (or centrosymmetrically related 2′-position) on the second C₆ ring. The Re₂(CO)₈(μ-H) groups are coordinated to the C₆ rings by binuclear σ + π coordination to two adjacent carbon atoms in the rings. Compound 1 reacts with anthracene to yield the mono-CH activated compound Re₂(CO)₈(μ–η²-1,2-C₁₄H₉)­(μ-H), 6, and two doubly CH activated compounds, Re₂(CO)₈(μ-H)­(μ–η²-1,2-μ–η²-3,4-C₁₄H₈)­Re₂(CO)₈(μ-H), 7, and Re₂(CO)₈(μ-H)­(μ–η²-1,2-μ–η²-5,6-C₁₄H₈)­Re₂(CO)₈(μ-H), 8. Compounds 7 and 8 are isomers that are structurally similar to 4 and 5. Compounds 7 and 8 can also be obtained in good yields from the reaction of 6 with 1. In the presence of a 5/1 ratio of 1/anthracene, a small amount (5% yield) of the tetra-substituted anthracene product [Re₂(CO)₈(μ-H)]₄(μ–η²-1,2-μ–η²-3,4-μ–η²-5,6-μ–η²-7,8-C₁₄H₆), 9, was formed. Compound 9 contains four σ + π coordinated Re₂(CO)₈(μ-H) groups formed by oxidative additions of the CH bonds of anthracene to the Re₂(CO)₈ groups at the 2, 4, 6, and 8 positions of the three ring system. Molecular orbital calculations have been performed for all new compounds in order to develop an understanding of the bonding of the ring systems to the Re₂(CO)₈(μ-H) groups. All new compounds were characterized by single-crystal X-ray diffraction analyses.