Synthesis of cobalt bis(8-methylthio-1,2-dicarbollide)- pentacarbonyltungsten complexes

Bis(Dicarbollide) Complexes of Transition Metals: How Substituents in Dicarbollide Ligands Affect the Geometry and Properties of the Complexes

The interaction between different types of substituents in dicarbollide ligands and their influence on the stabilization of various rotational conformers (rotamers) of transition metal bis(dicarbollide) complexes [3,3'-M(1,2-C2B9H11)2]- are considered. It has been shown that the formation of intramolecular CH···X hydrogen bonds between dicarbollide ligands is determined by the size of the proton acceptor atom X rather than its electronegativity. Due to the stabilization of rotamers with different dipole moments, intramolecular hydrogen bonds between ligands in transition metal bis(dicarbollide) complexes can have a significant impact on the biological properties of their derivatives. In the presence of external complexing metals, weak intramolecular CH···X hydrogen bonds can be broken to form stronger X->M donor-acceptor bonds. This process is accompanied by the mutual rotation of dicarbollide ligands and can be used in sensors and molecular switches based on transition metal bis(dicarbollide) complexes.

Chemistry of Carbon-Substituted Derivatives of Cobalt Bis(dicarbollide)(1-) Ion and Recent Progress in Boron Substitution

The cobalt bis(dicarbollide)(1-) anion (1-), [(1,2-C2B9H11)2-3,3'-Co(III)](1-), plays an increasingly important role in material science and medicine due to its high chemical stability, 3D shape, aromaticity, diamagnetic character, ability to penetrate cells, and low cytotoxicity. A key factor enabling the incorporation of this ion into larger organic molecules, biomolecules, and materials, as well as its capacity for "tuning" interactions with therapeutic targets, is the availability of synthetic routes that enable easy modifications with a wide selection of functional groups. Regarding the modification of the dicarbollide cage, syntheses leading to substitutions on boron atoms are better established. These methods primarily involve ring cleavage of the ether rings in species containing an oxonium oxygen atom connected to the B(8) site. These pathways are accessible with a broad range of nucleophiles. In contrast, the chemistry on carbon vertices has remained less elaborated over the previous decades due to a lack of reliable methods that permit direct and straightforward cage modifications. In this review, we present a survey of methods based on metalation reactions on the acidic C-H vertices, followed by reactions with electrophiles, which have gained importance in only the last decade. These methods now represent the primary trends in the modifications of cage carbon atoms. We discuss the scope of currently available approaches, along with the stereochemistry of reactions, chirality of some products, available types of functional groups, and their applications in designing unconventional drugs. This content is complemented with a report of the progress in physicochemical and biological studies on the parent cobalt bis(dicarbollide) ion and also includes an overview of recent syntheses and emerging applications of boron-substituted compounds.

Bis(dicarbollide) Complexes of Transition Metals as a Platform for Molecular Switches. Study of Complexation of 8,8'-Bis(methylsulfanyl) Derivatives of Cobalt and Iron Bis(dicarbollides)

Complexation of the 8,8'-bis(methylsulfanyl) derivatives of cobalt and iron bis(dicarbollides) [8,8'-(MeS)₂-3,3'-M(1,2-C₂B₉H₁₀)₂]^- (M = Co, Fe) with copper, silver, palladium and rhodium leads to the formation of the corresponding chelate complexes, which is accompanied by a transition from the transoid to the cisoid conformation of the bis(dicarbollide) complex. This transition is reversible and can be used in design of coordination-driven molecular switches based on transition metal bis(dicarbollide) complexes. The solid-state structures of {(Ph₃P)ClPd[8,8'- (MeS)₂-3,3'-Co(1,2-C₂B₉H₁₀)₂-κ²-S,S']} and {(COD)Rh[8,8'-(MeS)₂-3,3'-Co(1,2-C₂B₉H₁₀)₂-κ²-S,S']} were determined by single crystal X-ray diffraction.

Synthesis and study ofC-substituted methylthio derivatives of cobalt bis(dicarbollide)

The C-methylthio derivatives of cobalt bis(dicarbollide) were synthesized by reaction of anhydrous CoCl₂ with nido-carborane [7-MeS-7,8-C₂B₉H₁₁]⁻ and isolated as a mixture of rac-[1,1′-(MeS)₂-3,3′-Co(1,2-C₂B₉H₁₀)₂]⁻ and meso-[1,2′-(MeS)₂-3,3′-Co(1,2-C₂B₉H₁₀)₂]⁻ isomers. The structures of both isomers were studied using DFT quantum chemical calculations. The most preferable geometry of rotamers and the stabilization energy of C-methylthio derivatives of cobalt bis(dicarbolide) were calculated. The (BEDT-TTF)[1,1′-(MeS)₂-3,3′-Co(1,2-C₂B₉H₁₀)₂] salt was prepared and its structure was determined by single crystal X-ray diffraction. The cisoid conformation of the rac-[1,1′-(MeS)₂-3,3′-Co(1,2-C₂B₉H₁₀)₂]⁻ anion is stabilized by short intramolecular CH⋯S hydrogen and BH⋯S chalcogen bonds between the dicarbollide ligands, that is in good agreement with the data of quantum chemical calculations.

The C-methylthio derivatives of cobalt bis(dicarbollide) rac-[1,1′-(MeS)₂-3,3′-Co(1,2-C₂B₉H₁₀)₂]⁻ and meso-[1,2′-(MeS)₂-3,3′-Co(1,2-C₂B₉H₁₀)₂]⁻ were synthesized and studied by DFT calculations and X-ray diffraction.

Synthesis and Structure of Methylsulfanyl Derivatives of Nickel Bis(Dicarbollide)

Symmetrically and unsymmetrically substituted methylsulfanyl derivatives of nickel(III) bis(dicarbollide) (Bu₄N)[8,8'-(MeS)₂-3,3'-Ni(1,2-C₂B₉H₁₀)₂], (Bu₄N)[4,4'-(MeS)₂-3,3'-Ni(1,2-C₂B₉H₁₀)₂], and (Bu₄N)[4,7'-(MeS)₂-3,3'-Ni(1,2-C₂B₉H₁₀)₂] were synthesized, starting from [Ni(acac)₂]₃ and the corresponding methylsulfanyl derivatives of nido-carborane (Bu₄N)[10-MeS-7,8-C₂B₉H₁₁] and (Bu₄N)[10-MeS-7,8-C₂B₉H₁₁]. Structures of the synthesized metallacarboranes were studied by single-crystal X-ray diffraction and quantum chemical calculations. The symmetrically substituted 8,8'-isomer adopts transoid conformation stabilized by two pairs of intramolecular C-H···S hydrogen bonds between the dicarbollide ligands. The unsymmetrically substituted 4,7'-isomer adopts gauche conformation, which is stabilized by two nonequivalent C-H···S hydrogen bonds and one short chalcogen B-H···S bond (2.53 Å, -1.4 kcal/mol). The gauche conformation was found to be also preferred for the 4,7'-isomer.