Organotransition-Metal Metallacarboranes. 11. Chromium Tricarbonyl Eta(6)-Complexes of nido-2,3-(PhCH2)2C2B4H6: Metal Complexation and Oxidative Fusion

摘要

The consequences of phenyl coordination of Cr(CO)3 groups on the chemistry of the C,C dibenzylcarborane nido-2,3-(PhCH2)2C2B4H6(1) were investigated. The monochromium species (CO)3Cr(PhCH2)C2B4H6 underwent bridge (B-H-B) deprotonation by NaH in THF, and the resulting anion, on treatment with FeCl2, formed (CO)3Cr(PhCH2)C2B4H4)2FeH2 (not isolated); subsequent oxidation with O2 gave two isomers of (CO)3Cr)2(PhCH2)4C4B8H8(7A,B), which were characterized spectroscopically. Reaction of the tetracarbon carborane (PhCH2)4C4B8H8(5) with Cr(CO)6 gave dichromium products identical with 7A, B but no other isomers. An attempted analogous sequence with (CO)3Cr)2(PhCH2)2C2B4H6(3) proceeded only as far as bridge deprotonation with KH; the resulting anion on treatment with FeCl2/O2 did not undergo fusion, nor was fusion observed with other transition metals. An attempted mixed-ligand fusion of the anions of 1 and 3 gave only 5 and the original substrate 3. Deprotonation of 3 was shown to proceed cleanly, via deuteriation of the anion to produce monodeuteriated 3. The resistance of 3 to oxidative fusion is discussed in terms of steric and electronic effects. Keywords: Chromium tricarbonyl complexes, Metallacarboranes, Ferracarboranes, Oxidative fusion, Tetracarbon carboranes.