Derivatives of Cp*Co(2,3-Et(2)C(2)B(4)H(4)) containing substituents at the apex boron atom [B(7)], the first examples of apically functionalized small metallacarborane clusters, have been prepared in good yield via boron insertion into the nido-Cp*Co(2,3-Et(2)C(2)B(3)H(3))(2-) dianion. Reaction of this substrate with BX(3) (X = Cl, Pr, I) or PhBCl(2) in toluene at room temperature gave the corresponding Cp*Co(2,3-Et(2)C(2)B(4)H(3)-7-X) derivatives (2a-c and 3 in which X = Cl, Pr, I, and Ph, respectively), all of which were isolated via column chromatography as air-stable yellow solids and characterized via H-1, B-11, and C-13 NMR, infrared, UV-visible, and mass spectra. Treatment of the same dianion with 1,4-(Br2B)(2)C6H4 afforded air-stable orange crystalline [Cp*Co(2,3-Et(2)C(2)B(4)H(3)-7)]2C6H4 (4). The structure of this compound was defined via spectroscopy and X-ray crystallography as a bis-(cobaltacarborane) complex linked at the apex borons via a 1,4-phenylene bridge. Crystal data for 4 : space group Pbca; a 15.056(7) Angstrom, b = 21.612 (8) Angstrom, c = 11.641 (3) Angstrom; Z = 4; R = 0.045 for 1582 independent reflections having I > 3 sigma(I).