ORGANOTRANSITION-METAL METALLACARBORANES .40. REGIOSPECIFIC HALOGENATION OF TRANSITION-METAL SMALL CARBORANE COMPLEXES

Methods for efficient, controlled direct halogenation of C2B3 and C2B4 carborane ligands in neutral nido- and closo-metallacarborane sandwich complexes are described. In an extension of our earlier work in this area, reactions of nido-Cp'Co(2,3-Et(2)C(2)B(3)H(5)) (CP' = Cp*, Cp; Cp* = eta(5)-C(5)Me(5)) With N-halosuccinimides placed Cl, Br, or I substituents on B(4) and/or B(6) but not on the middle boron (B(5)). In contrast, similar treatment of closo-LM-(2,3-Et(2)C(2)B(4)H(4)) species in which LM is Cp'Co, Cp*FeH, (eta(6)-C8H10)Fe, or (eta(6)-MeC(6)H(4)CHMe(2))-Ru gave only B(5)-monohalogen products. However, the triple-decker sandwich complex CpCo(2,3-Et(2)C(2)B(3)H(5))CoCp was readily tribrominated by N-bromosuccinimide. Reactions of Cp'CO(Et(2)C(2)B(4)H(4)) with Cl-2 rapidly formed the respective B(5)-Cl derivatives, which in turn were converted to the B(4,5,6)-Cl-3 species; analogous reactions with Br-2 and I-2 were much slower and gave essentially only B(5)-monosubstituted products. The Cp'Co(Et(2)C(2)B(4)H(3)-5-X) derivatives (X = Cl, Br, I) were decapitated with TMEDA to give the corresponding nido-Cp'Co(Et(2)C(2)B(3)H(4)-5-X) products. The reaction of Cp*(FeH)-H-II(Et(2)C(2)B(4)H(4)) with TMEDA was found to both deprotonate and decapitate the complex, affording respectively Cp*Fe-III-(Et(2)C(2)B(4)H(4)) and the previously unknown nido-Cp*Fe-III-(Et(2)C(2)B(3)H(5)) complex. The new compounds were isolated via column chromatography and obtained in most cases as air-stable colored crystalline solids, characterized via multinuclear NMR, FTIR and mass spectroscopy.