Apically Linked Small Metallacarborane Clusters. Directed Synthesis and Structural Characterization of 7,7‘-[CpCo(2,3-Et2C2B4H3]2 and [CpCo(2,3-Et2C2B4H3-7)]2X Complexes (X = MeCH, HCCH, C⋮C) † ,1

A series of novel bis(cobaltacarboranyl) (CoC2B4)2X dicluster complexes whose B(7) (apex) atoms are linked by organic moieties involving sp-, sp2-, or sp3-hybridized carbon, or by a direct B(7)−B(7‘) bond, has been prepared by extension of the recently described “recapitation” method (Curtis, M. A.; et al. Inorg. Chem. 1996, 35, 6703) that entails treatment of 6-vertex nido-CoC2B3 dianions with monoboron reagents. Reactions of Li2[nido-Cp*Co(Et2C2B3H3)] in toluene with MeCH(BCl2)2 and with cis-(BCl2)C2H2 gave, respectively, [Cp*Co(2,3-Et2C2B4H3-7-)]2MeCH (5) and cis-[Cp*Co(2,3-Et2C2B4H3-7-)]2C2H2 (6a) following chromatographic separation. Ultraviolet irradiation of 6a induced partial conversion to the trans isomer 6b, affording a 46:54 trans/cis equilibrium mixture in 84 h. Reactions of the same cobaltacarborane dianion with bis(catecholboryl)acetylene and with bis(catecholdiboryl) gave [Cp*Co(2,3-Et2C2B4H3-7-)]2C2 (7) and [Cp*Co(2,3-Et2C2B4H3-7-)]2 (8), respectively. The new complexes were isolated as air-stable, crystalline orange solids and were characterized from their 1H, 11B, and 13C NMR, IR, UV−visible, and mass spectra, supported by X-ray crystallographic studies of 5, 6a, 7, and 8. Crystal data for 5: space group P21 ca (orthorhombic); a = 14.220(10) Å, b = 15.690(10) Å, c = 16.860(10) Å, Z = 4; R = 0.041 for 7485 independent reflections. Crystal data for 6a: space group C2/c (monoclinic); a = 12.849(6) Å, b = 11.435(6) Å, c = 25.619(13) Å, β = 96.230(10)°; Z = 4; R = 0.036 for 5440 independent reflections. Crystal data for 7: space group P21/n (monoclinic); a = 17.298(12) Å, b = 13.932(10) Å, c = 30.82(2) Å, β = 96.34(5)°; Z = 8; R = 0.070 for 9632 independent reflections. Crystal data for 8: space group P1̄ (triclinic); a = 9.150(10) Å, b = 10.270(10) Å, c = 10.340(10) Å, α = 84.52(5)°, β = 78.05(5)°, γ = 68.6(5)°; Z = 1; R = 0.056 for 5154 independent reflections.