Metallacarboranes derived from 1,1′-bis(o-carborane)

Chapter one gives an overview of single cage heteroborane chemistry, particularly the areas of 12- and 13-vertex metallacarboranes and their isomerisations. Also included is the chemistry of bis(carboranes), with recent developments on chelating derivatives of 1,1'-bis(o-carborane), as well as reduction/metallation of bis(o-carborane). Chapter two describes metallation of the [7-(1′-1′,2′-closo-C2B10H11)-7,8-nido- C2B9H10]2– dianion with various {NiPP}2+, {PdNN}2+ or {NiP2}2+ fragments (PP = chelating diphosphine; NN = chelating diamine; P = monodentate phosphine or phosphite) and which leads either to unisomerised 3,1,2-MC2B9 species or to isomerised 4,1,2-MC2B9 or 2,1,8-MC2B9 species, all with a pendant C2B10 substituent. The products were fully characterised spectroscopically and crystallographically as appropriate. Overall the results suggest that an important factor in a 3,1,2 to 4,1,2 isomerisation is the relief gained from steric crowding, whereas a 3,1,2 to 2,1,8 isomerisation appears to be favoured by strongly electron-donating ligands on the metal. Chapter three describes capitation of the [7-(7′-7′,8′-nido-C2B9H10)-7,8-nido-C2B9H10]4– tetraanion with {NiPP}2+ and {BX}2+ fragments (PP = chelating diphosphine; X = Br, I, Ph). This results in examples of MC2B9-MC2B9 architectures (3′,1′,2′-3,1,2; 4′,1′,2′-3,1,2) or bis(carborane) derivatives. Thermal isomerisation of the bis(nickelacarboranes) is studied. Unexpected interconversion is observed between bis(nickelacarborane) diastereoisomers (rac and meso isomers of 3′,1′,2′-NiC2B9-3,1,2-NiC2B9) ligated by dmpe and the mechanism of this interconvesion is considered. A stereospecific product was observed in the nickelacarborane ligated by dppe and this is rationalised by DHB. Formation of 4′,1′,2′-NiC2B9-4,1,2-NiC2B9 and 2′,1′,8′-NiC2B9-4,1,2-NiC2B9 isomers on thermolysis of 3′,1′,2′-3,1,2 or 4′,1′,2′-3,1,2 MC2B9-MC2B9 precursors is elucidated in terms of DHB. Finally a new naming convention is introduced for these 12-vertex/12- vertex bis(nickelacarboranes) to distinguish the chirality between cages. Chapter four elaborates the thermolysis of a rac/meso mixture of the species [1-(1′-4′-Cp- 4′,1′,6′-closo-CoC2B10H11)-4-Cp-4,1,6-closo-CoC2B10H11] to yield a rac/meso mixture of [1-(1′-4′-Cp-4′,1′,12′-closo-CoC2B10H11)-4-Cp-4,1,12-closo-CoC2B10H11]. Cage carbonatom identification is accomplished by both the VCD and BHD methods. Polyhedral expansion of the rac and meso isomers of 4′,1′,12′-CoC2B10-4,1,12-CoC2B10 was also attempted targeting 14-vertex metallacarborane/14-vertex metallacarborane derivatives. Chapter five contains the experimental procedures leading to, and characterisation details for, all new compounds reported herein. Crystallographic data is listed in the Appendix together with structure solution and refinement details

Steric <i>versus</i> electronic factors in metallacarborane isomerisation: nickelacarboranes with 3,1,2-, 4,1,2- and 2,1,8-NiC₂B₉ architectures and pendant carborane groups, derived from 1,1′-bis(o-carborane)

Nickelacarborane derivatives of 1,1′-bis(o-carborane) allow comment on the factors important in the isomerisation of metallacarboranes.</p

Double deboronation and homometalation of 1,1'-bis(ortho-carborane)

Diastereomeric diruthenium and dicobalt species derived from double deboronation and metalation of 1,1′-bis(ortho-carborane) have been prepared and characterised.</p

Exploration of bis(Nickelation) of 1,1^′-bis(o-carborane)

The metalation of [Tl]2[1-(1&prime;-3&prime;,1&prime;,2&prime;-closo-TlC2B9H10)-3,1,2-closo-TlC2B9H10], with the smaller {Ni(dmpe)} fragment sourced from [Ni(dmpe)Cl2], is explored. The bis(metalated) products are obtained as a diastereoisomeric mixture. These isomers were separated, fully characterised spectroscopically and crystallographically and identified as rac-[1-(1&prime;-3&prime;-(dmpe)-3&prime;,1&prime;,2&prime;-closo-NiC2B9H10)-3-(dmpe)-3,1,2-closo-NiC2B9H10] (1) and meso-[1-(1&prime;-3&prime;-(dmpe)-3&prime;,1&prime;,2&prime;-closo-NiC2B9H10)-3-(dmpe)-3,1,2-closo-NiC2B9H10] (2). Previously, these 3,1,2-NiC2B9-3&prime;,1&prime;,2&prime;-NiC2B9 architectures (where both cages are not isomerised), were inaccessible, and thus new structures can be achieved during bis(nickelation) with {Ni(dmpe)}. Further, the metalation of the tetra-thallium salt with the bulky {Ni(dppe)} fragment sourced from [Ni(dppe)Cl2] was also studied. These bis(nickelated) products were also fully characterised and are afforded as the stereospecific species rac-[1-(1&prime;-3&prime;-(dppe)-3&prime;,1&prime;,2&prime;-closo-NiC2B9H10)-3-(dppe)-3,1,2-closo-NiC2B9H10] (3) and [1-(2&prime;-4&prime;-(dppe)-4&prime;,1&prime;,2&prime;-closo-NiC2B9H10)-3-(dppe)-3,1,2-closo-NiC2B9H10] (4&alpha;). In the latter metalation, compound 3 shows intramolecular dihydrogen bonding, contributing to the stereospecificity, whereas isomerisation from 3,1,2 to 4,1,2- in the 4&alpha; is related to steric relief

A triazole tethered triferrocene derivative as a selective chemosensor for mercury(II) in aqueous environment

The synthesis, electrochemical, optical and cation-sensing properties of two triazole tethered ferrocene derivatives, C₂₅H₂₅ON₃Fe₂, 2 and C₄₀H₄₀O₂N₆Fe₃, 3 are presented. The solid state structure of compound 2 has been established by X-ray diffraction analysis which reveals that the unit cell of molecule 2 consists of 3-D helical chain formed via CH⋯N interaction and π⋯π stacking. The complexation properties of the receptors can be inferred either from redox shift or visual output response (colorimetric) for Hg²⁺ and Cu²⁺ cations. The common structural feature of these ligands is the presence of other ferrocene moiety as redox unit. Interestingly, the redox and colorimetric responses, towards Hg²⁺ are preserved in the presence of water (CH₃CN/H₂O, 2/8), which can be used for the selective colorimetric detection of Hg²⁺ in aqueous environment over other competitor cations. The changes in the absorption spectra are accompanied by the appearance of a new low energy (LE) peak at ca. 626 nm for 2 and 632 nm for 3 (2: ε = 669 M⁻¹ cm⁻¹ and 3: ε = 1150 M⁻¹ cm⁻¹), due to the change in color from yellow to purple for Hg2+ cations in CH₃CN/H₂O (2:8)

A triazole based triferrocene derivative as a multiresponsive chemosensor for Hg(II) ion and a redox chemosensor for H₂PO₄⁻ ion

A triazole tethered triferrocene receptor, C₄₀H₄₀O₂N₆Fe₃ 3, has been synthesized from the reaction of mono-alkynyl substituted ferrocene, 1 and 1,1′-bis-(azidomethyl)ferrocene, 2. Consequently the cation and anion sensing properties of 3 have been examined. The receptor 3 was found to be highly selective electrochemical [Math Processing Error], optical and chromogenic chemosensor for Hg²⁺ ion in aqueous environment. The substantial changes in its absorption spectra are accompanied by the appearance of a new low-energy peak at 631 nm (ɛ = 3400 M⁻¹ cm⁻¹). This is also accompanied by a strong color change from yellow to purple, that allows a prospective for the “naked eye” detection of Hg²⁺ ion over other competitor cations such as Pb²⁺, Cd²⁺, Zn²⁺, etc. In addition, among various anions, 3 shows a distinct electrochemical recognition of dihydrogen phosphate anion by its multiple H-bonding (C–H⋯O), which is supported by electrochemical (large cathodic shift ΔE_1/2 = −175 mV) and ¹H NMR titration results

Multi-stimuli-responsive organometallic gels based on ferrocene-linked poly(aryl ether) dendrons: reversible redox switching and Pb²⁺-ion sensing

We describe the design, synthesis, and “stimuli-responsive” study of ferrocene-linked Fréchet-type [poly(aryl ether)]-dendron-based organometallic gels, in which the ferrocene moiety is attached to the dendron framework through an acyl hydrazone linkage. The low-molecular-weight gelators (LMWGs) form robust gels in both polar and non-polar solvent/solvent mixtures. The organometallic gels undergo stimuli-responsive behavior through 1) thermal, 2) chemical, and 3) electrochemical methods. Among them, conditions 1 and 3 lead to seamlessly reversible with repeated cycles of identical efficiency. Results indicate that the flexible nature of the poly(aryl ether) dendron framework plays a key role in retaining the reversible electrochemical behavior of ferrocene moiety in the LMWGs. Further, the organometallic gelators have exhibited unique selectivity towards Pb²⁺ ions (detection limit ≈10⁻⁸M). The metal ion-sensing results in a gel–sol phase transition associated with a color change visible to the naked eye. Most importantly, decomplexing the metal ion from the system leads to the regeneration of the initial gel morphology, indicating the restoring ability of the organometallic gel. The metal–ligand binding nature has been analyzed by using ¹H NMR spectroscopy, mass spectrometry, and DFT calculations

A Frustrated Lewis Pair Solution to a Frustrating Problem: Mono-Selective Functionalization of C–F Bonds in Di- and Trifluoromethyl Groups

10.1055/s-0039-1690811Synlettcompletedcomplete

Catecholboryl-functionalized ferrocene based Lewis acid system: a selective probe for fluoride ion through multiple channels

The design and synthesis of two new receptors, C₂₀H₁₉O₃BFe and C₂₀H₂₁O₃BFe and their anion sensing properties through multiple channels are reported. Both the receptors, having chelating boronic ester Lewis acidic centre as the sole binding site, selectively bind fluoride ion in micromolar concentration. The binding constant of C₂₀H₁₉O₃BFe with the fluoride ion has been found to be quite high [K = 106 M⁻¹], whereas it displays a negligible affinity towards other effective competitors, for example acetate and cyanide (K = 10 M₋₁) and no sensitivity towards other halide ions. Upon selective recognition of F⁻ in acetonitrile, the redox potential of C₂₀H₁₉O₃BFe shifted by ΔE = 200 mV and the fluorescence emission was quenched drastically. The considerable changes in their absorption spectra are accompanied by the appearance of a new low energy (LE) peak at 566 nm and by a strong colour change from yellow to deep green which allows the prospective for “naked eye” detection of F⁻ anion

Frustrated Lewis pair meditated selective single fluoride substitution in trifluoromethyl groups

10.1021/jacs.9b12167Journal of the American Chemical Societ