Organotransition-metal Metallacarboranes. 10. π-Complexation of nido-(PhCH₂)₂C₂B₄H₆ at the C₂B3 and C₆ rings. Synthesis and crystal structures of nido-2,3-[(CO)3Cr(η6-C₆H₅)CH₂]₂-2,3-C₂B₄H₆ and (PhCH₂)₄C₄B₈H₈, a nonfluxional C₄B₈ cluster
Reaction of the C,C′-dibenzyl-nido-carborane (PhCH2)2C2B4H6 (1) with NaH in THF followed by FeCl2 forms a red complex, [(PhCH2)2C2B4H4]2FeH2 (2), which on treatment with O2 generates a tetrabenzyl tetracarbon carborane, (PhCH2)4C4B8H8 (3). Compound 3 is nonfluxional in solution, in contrast to previously studied R4C4B8H8 species where R = Me, Et, or n-Pr, and an X-ray diffraction study of 3 disclosed that the C4B8 cage is locked into an open-cage geometry as a consequence of severe intramolecular crowding of the benzyl groups. Reaction of 2 with CpCo(CO)2 generates [(PhCH2)2C2B4H4]4FeCoCp (4), for which a wedged structure is proposed. Treatment of 1 with Cr(CO)6 produces the mono- and dichromium complexes (CO)3Cr(PhCH2)2C2B4H6 (5) and (CO)6Cr2(PhCH2)2C2B4H6 (6) as moderately air-sensitive solids which were characterized from NMR, IR, and mass spectra and an X-ray crystallographic investigation of 6. Crystal data for 3: Mr 507, space group P21/c, Z = 4, a = 10.007 (2) Å, b = 22.681 (6) Å, c = 13.692 (2) Å, β = 110.18 (2)°, V = 2917 Å3, R = 0.053 for 3813 reflections having Fo 2 > 3σ(Fo)2. Crystal data for 6: Mr 521, space group Pnam, Z = 4, a = 11.914 (2) Å, b = 6.927 (1) Å, c = 28.729 (6) Å, V = 2371 Å3, R = 0.044 for 1678 reflections having Fo2 > 3σ(Fo)2.
J. T. Spencer et al., "Organotransition-metal Metallacarboranes. 10. π-Complexation of nido-(PhCH₂)₂C₂B₄H₆ at the C₂B3 and C₆ rings. Synthesis and crystal structures of nido-2,3-[(CO)3Cr(η6-C₆H₅)CH₂]₂-2,3-C₂B₄H₆ and (PhCH₂)₄C₄B₈H₈, a nonfluxional C₄B₈ cluster," Organometallics, American Chemical Society (ACS), Jan 1987.
The definitive version is available at http://dx.doi.org/10.1021/om00145a016
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