摘要:
In an application of Wurtz-type coupling reactions to metallacarborane chemistry, treatment of the B(5)-halogenated close complexes Cp*Co(2,3-Et(2)C(2)B(4)H(3)-5-X) (X = Cl, Br, I; Cp* = eta(5)-C(5)Me(5)) with sodium metal in THF gave a single red-orange, air-stable product in 20-34% isolated yield. This species was characterized via NMR, UV-visible and mass spectroscopy and X-ray crystallography as a B-B-linked dimer, 5,5'-[Cp*CO(Et(2)C(2)B(4)H(3))](2) (2). Reactions of the same halogenated monomers, as well. as the parent complex (X = H), with alkyllithium reagents in THF generated in 28-56% yield the orange, air-stable dimeric products [(-CH(2)C(5)Me(4))Co(Et(2)C(2)B(4)H(3)-5-X)](2) (3a-d; X = H, Cl, Br, I), which are linked via Cp*-Cp* connections. This geometry, apparently novel to metallacarborane chemistry, was established by an X-ray diffraction study on 3c and supported by spectroscopic data for the four species. Decapitation of these dimers in wet TMEDA gave in high yield the corresponding nido complexes [(-CH(2)C(5)Me(4))Co(Et(2)C(2)B(3)H(4)-5-X)]2 (4a-d; X = H, Cl, Br, I) as air-stable yellow solids. In contrast, 2 was unaffected by similar treatment. The reaction of nido-Cp*Co(Et(2)C(2)B(3)H(4)-5-Cl) with sodium in THF gave the yellow air-stable dimeric species [Cp*Co(Et(2)C(2)B(3)H(4))]2 (8) together with the unsubstituted monomer Cp*Co(Et(2)C(2)B(3)H(5)), a previously characterized complex. An X-ray crystal structure determination on 8 disclosed that the two CoC2B3 units are connected via a B-B-B three-center bond such that the two C2B3 rings are almost mutually perpendicular.