Carbon-rich Metallacarboranes 12

Alternative Title

Synthesis and structures of chromium(III) complexes with “nonconforming” cage geometries


The reaction of the (C2H5)4C4B8H 82- dianion with CrCl2 and NaC5H5 in cold tetrahydrofuran (THF) gave primarily red, paramagnetic (η5-C5H5)Cr(C2H 5)4C4B8H8 (I). Column chromatography of the product mixture under N2 gave also purple II, an unstable species isomeric with I. Air oxidation of solutions of I over prolonged periods gave yellow, unstable (η5-C5H5)Cr(C2H 5)4C4B7H7 (III); products II and III were characterized only from mass spectra. On workup of the product mixture in air, a small quantity of green IV, isomeric with III, was obtained together with I (the major product) and III. Compounds I and IV were structurally characterized by X-ray diffraction studies and were shown to have respectively 13-vertex nido and 12-vertex nido cage geometries; each of these structures is a formal (2n + 1)-electron system and appears to violate the Wade electron-count scheme, which requires 2n + 4 electrons for nido geometry. However, if the deficiency of three electrons is localized in the metal nonbonding orbitals (rendering chromium a 15-electron atom), then both I and IV can be viewed as (2n + 4)-electron cage systems in conformity with their observed structures. Crystal data for I: CrC17B8H33; mol wt 376.94; space group P1; Z = 2; a = 8.637 (8), b = 8.664 (5), c = 16.484 (8) Å; α = 99.19 (5), β = 92.06 (4), γ = 118.66 (7)°; V = 1059 Å3; R = 0.102 for 2101 independent reflections having Fo2 > 3σ(Ro2). Crystal data for IV: CrC17B7H32; mol wt 364.12; space group Pna21; Z = 4; a = 14.763 (8), b = 10.828 (4), c = 12.348 (2) Å; V = 1974 Å3; R = 0.026 for 1820 independent reflections having Fo2 > 3σ(Fo2). © 1983 American Chemical Society.



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© 1983 American Chemical Society (ACS), All rights reserved.