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

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.

Synthesis of Bis(Carboranyl)amides 1,1'-μ-(CH2NH(O)C(CH2)n-1,2-C2B10H11)2 (n = 0, 1) and Attempt of Synthesis of Gadolinium Bis(Dicarbollide)

Bis(carboranyl)amides 1,1'-μ-(CH2NH(O)C(CH2)n-1,2-C2B10H11)2 (n = 0, 1) were prepared by the reactions of the corresponding carboranyl acyl chlorides with ethylenediamine. Crystal molecular structure of 1,1'-μ-(CH2NH(O)C-1,2-C2B10H11)2 was determined by single crystal X-ray diffraction. Treatment of bis(carboranyl)amides 1,1'-μ-(CH2NH(O)C(CH2)n-1,2-C2B10H11)2 with ammonium or cesium fluoride results in partial deboronation of the ortho-carborane cages to the nido-carborane ones with formation of [7,7'(8')-μ-(CH2NH(O)C(CH2)n-7,8-C2B9H11)2]2-. The attempted reaction of [7,7'(8')-μ-(CH2NH(O)CCH2-7,8-C2B9H11)2]2- with GdCl3 in 1,2-dimethoxy- ethane did not give the expected metallacarborane. The stability of different conformations of Gd-containing metallacarboranes has been estimated by quantum-chemical calculations using [3,3-μ-DME-3,3'-Gd(1,2-C2B9H11)2]- as a model. It was found that in the most stable conformation the CH groups of the dicarbollide ligands are in anti,anti-orientation with respect to the DME ligand, while any rotation of the dicarbollide ligand reduces the stability of the system. This makes it possible to rationalize the design of carborane ligands for the synthesis of gadolinium metallacarboranes on their base.

The unexpected reactivity of 9-iodo-nido-carborane: from nucleophilic substitution reactions to the synthesis of tricobalt tris(dicarbollide) Na[4,4',4''-(MeOCH2CH2O)3-3,3',3''-Co3(μ3-O)(μ3-S)(1,2-C2B9H10)3]

An unusual reactivity of 9-iodo-nido-carborane [9-I-7,8-C₂B₉H₁₁]^- towards nucleophiles under strong basic conditions was revealed. The nucleophilic substitution of iodine with O- and N-nucleophiles results in [9-RO-7,8-C₂B₉H₁₁]^- (R = H, CH₂CH₂OMe) and [9-L-7,8-C₂B₉H₁₁] (L = Py, NEt₃, Me₂NCH₂CH₂NMe₂), respectively. Reaction of [9-I-7,8-C₂B₉H₁₁]^- with CoCl₂ in 1,2-dimethoxyethane in the presence of t-BuOK, depending on the order of addition of the reagents, leads either to a diastereomeric mixture of diiodo derivatives cobalt bis(dicarbollide) rac-[4,4'-I₂-3,3'-Co(1,2-C₂B₉H₁₀)₂]^- and meso-[4,7'-I₂-3,3'-Co(1,2-C₂B₉H₁₀)₂]^- or to the corresponding mixture of 2-methoxyethoxy derivatives rac-[4,4'-(MeOCH₂CH₂O)₂-3,3'-Co(1,2-C₂B₉H₁₀)₂]^- and meso-[4,7'-(MeOCH₂CH₂O)₂-3,3'-Co(1,2-C₂B₉H₁₀)₂]^-. In the presence of accidental admixture of sodium thiosulfate, the reactions of 9-iodo-nido-carborane and 9-(2'-methoxyethoxy)-nido-carborane with CoCl₂ in 1,2-dimethoxyethane were found to produce additionally unprecedented tricobalt tris(dicarbollide) cluster Na[4,4',4''-(MeOCH₂CH₂O)₃-3,3',3''-Co₃(μ³-O)(μ³-S)(1,2-C₂B₉H₁₀)₃], the central fragment of which is a trigonal bipyramid with apical oxygen and sulfur atoms, and the base is formed by the Co₃ triangle flanked by three dicarbollide ligands. In addition, the 2-methoxyethoxy substituents of the dicarbollide ligands chelate the sodium cation in such a way that they form a helix whose rotation direction depends on the enantiomer of the parent ligand. Thus, in this case, induction of the helical chirality of the complex occurs due to the point chirality of the initial inorganic ligand. It is worth noting that in the case of symmetrically substituted 2-methoxyethoxy derivative of nido-carborane [10-MeOCH₂CH₂O-7,8-C₂B₉H₁₁]^- only formation of the corresponding cobalt bis(dicarbollide) complex [8,8'-(MeOCH₂CH₂O)₂-3,3'-Co(1,2-C₂B₉H₁₀)₂]^- was observed.

The First Nickelacarborane with closo-nido Structure

The first nickelacarborane with closo-nido structure [10′,11′-(Py)₂-3,9′-Ni(1,2-C₂B₉H₁₁)(7′,8′-C₂B₈H₈)] was isolated from the reaction of nickel(IV) bis(dicarbollide) with pyridine. The molecular structure of this complex was determined by single crystal X-ray diffraction. The nickel atom is a common vertex for the closo-NiC₂B₉ cluster and the nido-NC₂B₈ cluster where it is located together with carbon atoms in the open NiC₂B₂ pentagonal face. It is assumed that its formation proceeds through the nucleophile-induced removal of the B(6)H vertex followed by rearrangement of the forming 11-vertex cluster, which most likely proceeds through a sequence of closing and opening reactions.

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.