“Recapitation” of nido-Metallacarboranes as a Synthetic Tool:  Preparation of Apically Substituted CoC₂B₄ Clusters via Boron Insertion¹

Abstract

Derivatives of CpCo(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-CpCo(2,3-Et(2)C(2)B(3)H(3))(2-) dianion. Reaction of this substrate with BX(3) (X = Cl, Br, I) or PhBCl(2) in toluene at room temperature gave the corresponding CpCo(2,3-Et(2)C(2)B(4)H(3)-7-X) derivatives (2a-c and 3 in which X = Cl, Br, I, and Ph, respectively), all of which were isolated via column chromatography as air-stable yellow solids and characterized via (1)H, (11)B, and (13)C NMR, infrared, UV-visible, and mass spectra. Treatment of the same dianion with 1,4-(Br(2)B)(2)C(6)H(4) afforded air-stable orange crystalline [CpCo(2,3-Et(2)C(2)B(4)H(3)-7)](2)C(6)H(4) (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) Å, b = 21.612 (8) Å, c = 11.641 (3) Å; Z = 4; R = 0.045 for 1582 independent reflections having I > 3sigma(I).

Metal-containing carboranes with antitumor activity

“…7 Bromo deriva tive 70 was prepared analogously by the reaction of 72a with BBr 3 (Scheme 26). 57 The reaction of compound 72 with butyllithium is accompanied by hydrogen abstraction to form com…”

Benzene-Centered Tri- and Tetrametallacarborane Sandwich Complexes

“…Although 1,3,5-tris(carboranyl)benzene derivatives incorporating icosahedral 1,2-or 1,12-C 2 B 10 polyhedra have been reported, [5] no corresponding metallaborane or metallacarborane species (i.e., having metal atoms in the polyhedral framework) have been described; to our knowledge, the closest known metal system is the dimetallic 1,4-bis-(7-cobaltacarboranyl)benzene complex 1 (B BH, B), which was recently prepared in one of our laboratories. [6] In contrast, a number of benzene-centered trinuclear organometallic compounds of the type 1,3,5-C 6 H 3 (XML n ) 3 have been synthesized, [7] in which transition metals M are linked to benzene through groups X (e.g. alkynyl).…”

“…[6,8] In the present work, we required a suitable trifunctional benzene derivative as a precursor to the desired metal complexes. Accordingly, 1,3,5-tris(diiodoboryl)benzene (3), previously prepared but not isolated, [9] was generated from the corresponding tris(trimethylsilyl)benzene as shown in Scheme 1 and isolated in 30 % yield as a colorless, air-Scheme 1.…”

“…A notable feature of the 1 H NMR spectrum of 5 is the strong upfield shift of the aromatic benzene resonances (d 5.92 in CDCl 3 versus 7.51 for benzene itself), reflecting the electron-donating character of the carborane ligand (for comparison, the corresponding signal in 1 appears at d 6.38, while those in the monocobalt species [Cp*Co(2,3-Et 2 C 2 B 4 H 3 -7-C 6 H 5 )] are found at d 6.75 ± 7.08). [6] A fourth metallacarborane unit was added to 5 by thermal displacement of cyclooctatriene from [(h 6 -C 8 H 10 )Fe-(Et 2 C 2 B 4 H 4 )] [11] to give the heterotetranuclear complex [{Cp*Co(Et 2 C 2 B 4 H 3 -7)} 3 {Fe(Et 2 C 2 B 4 H 4 )}C 6 H 3 ] (6, Scheme 2). This species was isolated as a yellow solid in 30 % yield and characterized by spectroscopy and X-ray crystallography ( Figure 2).…”

Benzene-Centered Tri- and Tetrametallacarborane Sandwich Complexes

“…[6,8] In the present work, we required a suitable trifunctional benzene derivative as a precursor to the desired metal complexes. [6,8] In the present work, we required a suitable trifunctional benzene derivative as a precursor to the desired metal complexes.…”