Organotransition-Metal Metallacarboranes. 9. Nido-2,3-dibenzyl-2,3-dicarbahexaborane(8) [(PhCH₂)₂C₂B₄H₆], A Versatile Multifunctional Nido-carborane: Iron-polyarene Sandwich Compounds and Chromium Tricarbonyl π-complexes

The title carborane 1, a nearly nonvolatile air- and water-stable liquid, has been prepared in multigram quantities from dibenzylacetylene (l,4-diphenyl-2-butyne) and B₆H₉in the presence of triethylamine. The multifunctional reactivity of 1 has been systematically explored via the preparation of a variety of mixed iron-carborane-polyarene complexes in which one or more of the three bonding rings in 1 (C₂B₃and two C₆) are coordinated to metals. Thus, 1 was bridge-deprotonated to give the (PhCH₂)₂C₂B₄H₅- anion which in turn was treated with FeCl₂and C₈H₈^2- ion to form the cyclooctatriene complex (η⁶-C₈H₁₀)Fe-[(PhCH₂)₂C₂B₄H₄] (2). The C₈H₁₀ligand in 2 is readily displaced by arenes on heating, affording sandwich complexes of general formula (arene)Fe[(PhCH₂)₂C₂B4H₄] where the arene is [2.2]paracyclophane (3), 9,10-dihydroanthracene (4), or fluorene (o,o'-diphenylenemethane) (6). The reaction of 4 with 2 at elevated temperature yielded the staggered triple-decker diiron species (η⁶,η⁶-C₁₄H₁₂)Fe₂[(PhCH₂)₂C₂B₄H₄]₂(5). Complexes 2–6 are air-stable orange crystalline solids. Treatment of 2 with chromium hexacarbonyl in refluxing butyl ether/tetrahydrofuran resulted in complexation of one phenyl ring with a Cr(CO)₃group, forming (2-[(CO)₃Cr(η⁶-C₆H₅)CH₂]-3-PhCH₂-2,3-C₂B₄H₄)Fe(η⁶-C₈H₁₀) (7); reaction of 7 with Cr(CO)₆gave the dichromium species (2,3-[(CO)₃Cr(η⁶-C₆H₅)CH₂]₂-2,3-C₂B₄H₄)Fe(η⁶-C₈H₁₀) (8) in which both of the phenyl rings and the carborane face are coordinated to metals. Complexes 7 and 8 are yellow, moderately air-and light-stable solids. Characterization of compounds 1–8 was achieved via¹¹B and¹H NMR, IR, and mass spectroscopy, supported by an X-ray diffraction analysis of a dichromium complex of 1 which is reported in the following paper.