Silver and Copper Complexes with closo-Polyhedral Borane, Carborane and Metallacarborane Anions: Synthesis and X-ray Structure

Synthesis and Structures of Lead(II) Complexes with Substituted Derivatives of the Closo-Decaborate Anion with a Pendant N3 Group

In this work, we studied lead(II) and cobalt(II) complexation of derivatives [2-B10H9O(CH2)2O(CH2)2N3]2- and [2-B10H9O(CH2)5N3]2- of the closo-decaborate anion containing pendant azido groups in the presence of 1,10-phenanthroline and 2,2'-bipyridyl. Mononuclear [PbL2{An}] and binuclear [Pb2L4(NO3)2{An}] lead complexes (where {An} is the N3-substituted boron cluster) were isolated and studied by IR spectroscopy and elemental analysis. The mononuclear lead(II) complex [Pb(phen)2[B10H9O(CH2)2O(CH2)2N3] and the binuclear lead(II) complex [Pb2(phen)4(NO3)2[B10H9O(CH2)5)N3] were determined by single-crystal X-ray diffraction. In complex [Pb2(phen)4(NO3)2[B10H9O(CH2)5)N3], the boron cluster is coordinated by the metal atom only via the 3c2e MHB bonds. In complex [Pb(phen)2[B10H9O(CH2)2O(CH2)2N3], the coordination environment of the metal includes BH groups of the boron cluster and the oxygen atom of the exo-polyhedral substituent. When the reaction was performed in a CH3CN/water mixture, the binuclear lead(II) complex [(Pb(bipy)NO3)(Pb(bipy)2NO3)(B10H9O(CH2)2O(CH2)2N3)]·CH3CN·H2O was isolated, where the boron cluster acts as a bridging ligand between lead atoms coordinated by the boron cage via the O atoms of the substituent and/or the BH groups. In the course of cobalt(II) complexation, the starting compound (Ph4P)2[B10H9O(CH2)5N3] was isolated and its structure was also determined by X-ray diffraction. Although a number of lead(II) complexes with coordinated N3 are known from the literature, no complexes with the boron cluster coordinated by the pendant N3 group involved in the metal coordination have been isolated.

Effect of Nature of Substituents on Coordination Properties of Mono- and Disubstituted Derivatives of Boron Cluster Anions [BnHn]2– (n = 10, 12) and Carboranes with exo-Polyhedral B–X Bonds (X = N, O, S, Hal)

This review systematizes data on the coordination ability of mono- and disubstituted derivatives of boron cluster anions and carboranes in complexation with transition metals. Boron clusters anions [BnHn]2–, monocarborane anions [CBnHn–1]–, and dicarboranes [C2BnHn–2] (with non-functionalized carbon atoms) (n = 10, 12) containing the B–X exo-polyhedral bonds (X = N, O, S, Hal) are discussed. Synthesis and structural features of complexes known to date are described. The effect of complexing metal and substituent attached to the boron cage on the composition and structures of the final complexes is analyzed. It has been established that substituted derivatives of boron cluster anions and carboranes can act as both ligands and counterions. A complexing agent can coordinate substituted derivatives of the boron cluster anions due to three-center two-electron 3c2e MHB bonds, by the substituent functional groups, or a mixed type of coordination can be realized, through the BH groups of the boron cage and the substituent. As for B-substituted carboranes, complexes with coordinated substituents or salts with non-coordinated carborane derivatives have been isolated; compounds with MHB bonding are not characteristic of carboranes.

Spontaneous Isomerization [trans-B20H18]2– → [iso-B20H18]2– during Cobalt(II) Complexation with Phenanthroline

Abstract

In this work, the cobalt(II) complexation with 1,10-phenanthroline (Phen) in the presence of the [trans-B20H18]2– anion has been studied. At a Co : Phen = 1 : 2 ratio in acetonitrile, a binuclear cobalt(II) complex with bridging chlorine atoms and the boron cluster anion as a counterion [(Phen)2Co(µ-Cl)2Co(Phen)2][trans-B20H18] has been isolated. However, during slow crystallization (within a month), spontaneous isomerization of [trans-B20H18]2– into [iso-B20H18]2– is observed. It has been established by X-ray diffraction analysis that in the crystal of the final compound [(Phen)2Co(µ-Cl)2Co(Phen)2][trans-B20H18]1/3[iso-B20H18]2/3, co-crystallization of both isomeric forms of the octadecahydroeicosaborate anion is observed for the first time. The presence of the iso form of the boron cluster anion is also confirmed by IR spectroscopy data: the spectrum of the product shows a band of stretching vibrations of the BHB bridge groups at 1773 cm–1, which is absent in the trans-form of the boron cluster.

Gold(III) Complexation in the Presence of the Macropolyhedral Hydridoborate Cluster [B20H18]2−

Gold(III) complexation with the octadecahydrido-eicosaborate anion [B20H18]2− was studied for the first time. It was found that when gold(III) complexes [Au(L)Cl2]BF4 (L = bipy, phen) reacted with [B20H18]2−, complexes [Au(L)Cl2]2[B20H18] were isolated. The compounds consisted of a cationic gold(III) complex [Au(L)Cl2]+ and the hydridoborate cluster as a counterion. X-ray diffraction studies revealed weak B–H...Au interactions for both compounds. Note that more reactive anions [BnHn]2− (n = 10, 12) in similar reactions with gold(III) complexes resulted in gold mirror reactions.

Structurally rigidified cobalt bis(dicarbollide) derivatives, a chiral platform for labelling of biomolecules and new materials

We report the difunctional modification of an anionic cobalta bis(dicarbollide)(1-) cluster with a B(8,8')-oxygen bridging unit that provides structural rigidity and an organic alkylazide substituent(s) on the carbon atoms of the metallacarborane cage. These ions present a good binding motif for incorporation into organic molecules using Huisgen-Sharpless (2+3) cycloaddition reactions. In addition, the compounds are chiral, as verified by separation of enantiomers using HPLC on chiral stationary phases (CSPs) and provide a high electrochemical peak in the window located outside of typical signals of biomolecules.

The Crystal Structures of Two Hydro-closo-Borates with Divalent Tin in Comparison: Sn(H2O)3[B10H10] · 3 H2O and Sn(H2O)3[B12H12] · 4 H2O

Single crystals of Sn(H2O)3[B10H10] · 3 H2O and Sn(H2O)3[B12H12] · 4 H2O are easily accessible by reactions of aqueous solutions of the acids (H3O)2[B10H10] and (H3O)2[B12H12] with an excess of tin metal powder after isothermal evaporation of the clear brines. Both compounds crystallize with similar structures in the triclinic system with space group P$$\bar{1 }$$ 1 ¯ and Z = 2. The crystallographic main features are electroneutral $${}_{\infty }^{1} \{$$ ∞ 1 { Sn(H2O)3/1[B10H10]3/3} and $${}_{\infty }^{1} \{$$ ∞ 1 { Sn(H2O)3/1[B12H12]3/3} double chains running along the a-axes. Each Sn2+ cation is coordinated by three water molecules of hydration (d(Sn–O) = 221–225 pm for the B10 and d(Sn–O) = 222–227 pm for the B12 compound) and additionally by hydridic hydrogen atoms of the three nearest boron clusters (d(Sn–H) = 281–322 pm for the B10 and d(Sn–H) = 278–291 pm for the B12 compound), which complete the coordination sphere. Between these tin(II)-bonded water and the three or four interstitial crystal water molecules, classical bridging hydrogen bonds are found, connecting the double chains to each other. Furthermore, there is also non-classical hydrogen bonding between the anionic [BnHn]2− (n = 10 and 12) clusters and the crystal water molecules pursuant to B–Hδ−$$\cdots$$ ⋯ δ+H–O interactions often called dihydrogen bonds.

Synthesis of Perchlorinated Sulfonium Derivatives of closo-Decaborate Anion [2-B10Cl9SR2]- (R = i-C3H7, n-C3H7, n-C4H9, n-C8H17, n-C12H25, n-C18H37, CH2Ph, and cyclo-S(CH2)4)

A method for obtaining perchlorinated di-S,S-substituted derivatives of the closo-decaborate anion with various alkyl groups has been developed: [B₁₀Cl₉SR₂]^- (R= i-C₃H₇, n-C₃H₇, n-C₄H₉, n-C₈H₁₇, n-C₁₂H₂₅, n-C₁₈H₃₇, CH₂Ph, and cyclo-S(CH₂)₄). The method is based on the preparation of the sulfonium-substituted anion [B₁₀H₉SR₂]^- by alkylation of the anion [B₁₀H₉SH]^2- with bromoalkanes (i-C₃H₇Br, n-C₃H₇Br, n-C₄H₉Br, n-C₈H₁₇Br, n-C₁₂H₂₅Br, n-C₁₈H₃₇Br, PhCH₂Br, and BrCH₂(CH₂)₂CH₂Br) followed by the cluster chlorination with sulfuryl chloride SO₂Cl₂ in acetonitrile. The process proceeds until the hydrogen atoms in the boron cluster are completely replaced with chlorine and completes within 60 h. It has been found that the melting point of salts ((C₄H₉)₄N)[B₁₀Cl₉SR₂] (R= i-C₃H₇, n-C₃H₇, n-C₄H₉, n-C₈H₁₇, n-C₁₂H₂₅, and n-C₁₈H₃₇) strongly depends on the length of the hydrocarbon chain of the substituent R.

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.

Silver(I) and Copper(I) Complexation with Decachloro-Closo-Decaborate Anion

A series of complexation reactions of silver(I) and copper(I) in the presence of a polyhedral weakly coordinating [B10Cl10]2− anion has been carried out. The effect of the solvent and the presence of Ph3P on the composition and structure of the reaction product were studied. Eight novel complexes were obtained and characterized by 11B Nuclear magnetic resonance, Infra-Red, and Raman spectroscopies as well as powder and single-crystal X-ray diffraction techniques. The [B10Cl10]2− anion demonstrated weaker coordinating ability towards coinage metals than [B10H10]2− at similar reaction conditions. The [B10Cl10]2− anion remains unreacted in the copper(I) complexation reaction, while in the absence of competing ligands, we obtained the first complexes containing decachloro-closo-decaborate anion directly coordinated by the metal atom. The bonding between metal atoms and the boron cluster anions was studied using the atomic Hirshfeld surfaces. Besides edge and face coordination of the polyhedral anion, this method allowed us to reveal the Ag–Ag bond in crystal of {Ag2(DMF)2[B10Cl10]}n, the presence of which was additionally supported by the Raman spectroscopy data.

Dihydrogen Bonds in Salts of Boron Cluster Anions [BnHn]2− with Protonated Heterocyclic Organic Bases

Dihydrogen bonds attract much attention as unconventional hydrogen bonds between strong donors of H-bonding and polyhedral (car)borane cages with delocalized charge density. Salts of closo-borate anions [B10H10]2− and [B12H12]2− with protonated organic ligands 2,2’-dipyridylamine (BPA), 1,10-phenanthroline (Phen), and rhodamine 6G (Rh6G) were selectively synthesized to investigate N−H...H−B intermolecular bonding. It was found that the salts contain monoprotonated and/or diprotonated N-containing cations at different ratios. Protonation of the ligands can be implemented in an acidic medium or in water because of hydrolysis of metal cations resulting in the release of H3O+ cations into the reaction solution. Six novel compounds were characterized by X-ray diffraction and FT-IR spectroscopy. It was found that strong dihydrogen bonds manifest themselves in FT-IR spectra that allows one to use this technique even in the absence of crystallographic data.

Properties of perhalogenated {closo-B10} and {closo-B11} multiply charged anions and a critical comparison with {closo-B12} in the gas and the condensed phase

Dependence of electronic properties and reactivity of closo-borates with size and halogen substituent was investigated.