Synthesis of Trithia-Borinane Complexes Stabilized in Diruthenium Core: [(Cp*Ru)₂(η¹-S)(η¹-CS){(CH₂)₂S₃BR}] (R = H or SMe)

The thermolysis of arachno-1 [(Cp*Ru)2(B3H8)(CS2H)] in the presence of tellurium powder yielded a series of ruthenium trithia-borinane complexes: [(Cp*Ru)2(η1-S)(η1-CS){(CH2)2S3BH}] 2, [(Cp*Ru)2(η1-S)(η1-CS){(CH2)2S3B(SMe)}] 3, and [(Cp*Ru)2(η1-S)(η1-CS){(CH2)2S3BH}] 4. Compounds 2⁻4 were considered as ruthenium trithia-borinane complexes, where the central six-membered ring {C2BS3} adopted a boat conformation. Compounds 2⁻4 were similar to our recently reported ruthenium diborinane complex [(Cp*Ru){(η2-SCHS)CH2S2(BH2)2}]. Unlike diborinane, where the central six-membered ring {CB2S3} adopted a chair conformation, compounds 2⁻4 adopted a boat conformation. In an attempt to convert arachno-1 into a closo or nido cluster, we pyrolyzed it in toluene. Interestingly, the reaction led to the isolation of a capped butterfly cluster, [(Cp*Ru)2(B3H5)(CS2H2)] 5. All the compounds were characterized by 1H, 11B{1H}, and 13C{1H} NMR spectroscopy and mass spectrometry. The molecular structures of complexes 2, 3, and 5 were also determined by single-crystal X-ray diffraction analysis

Metal rich metallaboranes of group 9 transition metals

We report the synthesis and structural characterization of moderately air stable metal rich metallaboranes of iridium. Treatment of [Cp*IrCl₂]₂ with BH₃·thf at high temperature led to the isolation of a trimetallic [nido-5-(Cp*Ir)₃B₇H₁₁], 1. Compound 1 is isoelectronic and isostructural with decaborane-14 where three BH units in [B₁₀H₁₄] have been replaced by Cp*Ir fragments. As far as we are aware, 1 is the first example of a iridadecaborane having three metals. In addition to the formation of 1, a change in the reaction conditions enabled us to isolate a 7 sep [(Cp*Ir)₃B₄H₄], 2. The geometry of 2 can be viewed as a condensed polyhedron composed of Ir₃B₃ octahedron capped by a BH unit. All the compounds have been characterized by IR and ¹H, ¹¹B, and ¹³C NMR spectroscopy in solution, and the solid-state structures were established by X-ray crystallographic analysis. Quantum-chemical calculations by DFT methods for compounds 1 and 2 showed reasonable agreement with the experimentally observed structural parameters. The large HOMO–LUMO gaps are consistent with the high stabilities of the iridium clusters compared to their known Rh and Co analogues

Benzoindolium–triarylborane conjugates: a ratiometric fluorescent chemodosimeter for the detection of cyanide ions in aqueous medium

Based on benzo[e]indolium and dimesitylborylbenzaldehyde a new ratiometric fluorescent chemodosimeter, C₄₁H₄₃BIN (3) has been synthesized and characterized by ¹H, ¹³C NMR spectroscopy, mass spectrometry and single crystal X-ray crystallography. Probe 3 was found to be highly selective and sensitive toward cyanide (CN⁻) ions in aqueous medium even in the presence of other competing anions like F⁻, Cl⁻, Br⁻, I⁻, H₂PO₄⁻, HCO₃⁻ and AcO⁻. The detection limit was calculated to be 7.1 × 10⁻⁹ M, which is much lower than the maximum permissable concentration in drinking water (1.9 μM) set by the World Health Organization (WHO). In addition, the response time of the probe for CN⁻ is less than 5 seconds. The mechanism is based on a nucleophilic addition reaction of cyanide ions at the polarized [>C=N<]⁺ bond of the benzoindolium group thereby blocking the pi-conjugation between the benzoindolium and triarylborane moiety. This was further confirmed by ¹H NMR titration, ESI-MS studies and DFT calculations

Ferrocene and Triazole-Appended Rhodamine Based Multisignaling Sensors for Hg²⁺ and Their Application in Live Cell Imaging

Two triazole-appended ferrocene–rhodamine conjugates, C₄₇H₄₅N₇O₃Fe (<b>2</b>) and C₄₉H₄₉N₇O₃Fe (<b>3</b>), have been synthesized, and their electrochemical, optical, and metal cation sensing properties have been explored in aqueous medium. The newly synthesized receptors are simple, easily synthesizable, and display very high “turn on” fluorescence response for Hg²⁺ as well as I^– in an aqueous environment. Quantification of the absorption titration analysis shows that the receptors <b>2</b> and <b>3</b> can detect the presence of Hg²⁺ even at very low concentrations (∼3 ppb). The mode of metal coordination has been studied by DFT calculations. Furthermore, the receptors <b>2</b> and <b>3</b> are less toxic toward MCF-7 cells and could detect intracellular Hg²⁺ by fluorescent imaging studies

Ferrocene and Triazole-Appended Rhodamine Based Multisignaling Sensors for Hg²⁺ and Their Application in Live Cell Imaging

Two triazole-appended ferrocene–rhodamine conjugates, C₄₇H₄₅N₇O₃Fe (<b>2</b>) and C₄₉H₄₉N₇O₃Fe (<b>3</b>), have been synthesized, and their electrochemical, optical, and metal cation sensing properties have been explored in aqueous medium. The newly synthesized receptors are simple, easily synthesizable, and display very high “turn on” fluorescence response for Hg²⁺ as well as I^– in an aqueous environment. Quantification of the absorption titration analysis shows that the receptors <b>2</b> and <b>3</b> can detect the presence of Hg²⁺ even at very low concentrations (∼3 ppb). The mode of metal coordination has been studied by DFT calculations. Furthermore, the receptors <b>2</b> and <b>3</b> are less toxic toward MCF-7 cells and could detect intracellular Hg²⁺ by fluorescent imaging studies

Borate-based ligands with soft heterocycles and their ruthenium complexes

In a quest for effective synthetic precursors for the preparation of B-agostic complexes of ruthenium, we have shown that the reaction of [Cp*RuCl₂]₂ (Cp* = η⁵-C₅Me₅) with [NaBt] or [NaBo] (Bt = dihydrobis(2-mercaptobenzthiazolyl)borate; Bo = dihydrobis(2-mercaptobenzoxazolyl)borate) led to the formation of B-agostic complexes [Cp*RuBH₂L₂], 1a,b (1a: L = 2-mercaptobenzthiazol, 1b: L = 2-mercaptobenzoxazol) and [Cp*RuBH₃L], 2a,b (2a: L = 2-mercaptobenzthiazol, 2b: L = 2-mercaptobenzoxazol) in good yields. In parallel to the formation of 1a,b and 2a,b, this method also allowed the formation of ruthenium hydrotrisborate complexes [Cp*RuBYL₃], 3a–c (3a: L = 2-mercaptobenzthiazol, Y = H; 3b: L = 2-mercaptobenzoxazol, Y = H; 3c: L = 2-mercaptobenzoxazol, Y = Cl). The key feature of complexes 3a–c is the coordination of one of the 2-mercaptobenzothiazole ligand that connects to the metal and the boron centre through a common sulfur atom. Upon heating, compounds 3a,b change into their corresponding S→N linkage isomers, in which the boron atom is bonded to three nitrogen atoms. The cyclic voltammetric studies on compounds 3a–c and 4a,b suggest that a deviation in coordination of the ligand change the oxidation potential of the metal centre. All the new compounds have been characterized in solution by ¹H, ¹¹B and ¹³C NMR spectroscopy, mass spectrometry and the structural types of 3a–c and 4b were unequivocally established by crystallographic analysis

Synthesis and characterization of bis(sigma)borate and bis-zwitterionic complexes of rhodium and iridium

Building upon the chemistry of Rh–N,S-heterocyclic carbene complex, [(Cp*Rh)(L2)(1-benzothiazol-2-ylidene)], 2 (Cp*=η5-C5Me5; L=C7H4NS2) with various monoboranes-Lewis adducts, we explored the chemistry of 2 with BH3⋅thf at elevated temperature. As a result, mild thermolysis of 2 with BH3⋅thf led to the formation of bis(sigma)borate [(η4-C5Me5H)Rh(η2-H3BL)], 3 and a bis-zwitterionic species [Cp*RhS(BH2L2)], 4 with the concomitant release of BH3⋅bt (bt=benzothiazole). The RhS3C2N2B2 atoms in 4 generates two six membered rings fused by a common Rh−S bond, which may be considered as a bicycle [4.4.0] cage at the rhodium center. In an effort to generate the iridium analogue of 3, reaction of [Cp*IrCl2]2 with Na[H3B(mbt)] (mbt=2-mercaptobenzothiazole) was carried out that produced bis(sigma)borate complex [(η4-C5Me5H)Ir(η2-H3BL)], 1. The solid state X-ray structures of 1 and 3 showed that the Cp*H ligand coordinated to the metal center in a η4-fashion. In compound 3, the methyl group is oriented towards rhodium center, whereas it is away from Ir center in 1. In addition, the DFT computations were performed to shed light on the bonding and electronic structures of these compounds

Synthesis, crystal structure and spectroscopic and electrochemical properties of bridged trisbenzoato copper-zinc heterobinuclear complex of 2,2 `-bipyridine

The synthesis of the heterobinuclear copper-zinc complex CuZn(bz)(3)(bpy)(2)]ClO4 (bz = benzoate) from benzoic acid and bipyridine is described. Single crystal X-ray diffraction studies of the heterobinuclear complex reveals the geometry of the benzoato bridged Cu(II)-Zn(II) centre. The copper or zinc atom is pentacoordinate, with two oxygen atoms from bridging benzoato groups and two nitrogen atoms from one bipyridine forming an approximate plane and a bridging oxygen atom from a monodentate benzoate group. The Cu-Zn distance is 3.345 angstrom. The complex is normal paramagnetic having mu(eff) value equal to 1.75 BM, ruling out the possibility of Cu-Cu interaction in the structural unit. The ESR spectrum of the complex in CH3CN at RT exhibit an isotropic four line spectrum centred at g = 2.142 and hyperfine coupling constants A(av) = 63 x 10(-4) cm(-1), characteristic of a mononuclear square-pyramidal copper(II) complexes. At LNT, the complex shows an isotropic spectrum with g(parallel to) = 2.254 and g(perpendicular to) =2.071 and A(parallel to) = 160 x 10(-4) cm(-1). The Hamiltonian parameters are characteristic of distorted square pyramidal geometry. Cyclic voltammetric studies of the complex have indicated quasi-reversible behaviour in acetonitrile solution. (C) 2014 Elsevier B.V. All rights reserved

Synthesis, Structures and Chemistry of the Metallaboranes of Group 4–9 with M₂B₅ Core Having a Cross Cluster M–M Bond

In an attempt to expand the library of M2B5 bicapped trigonal-bipyramidal clusters with different transition metals, we explored the chemistry of [Cp*WCl4] with metal carbonyls that enabled us to isolate a series of mixed-metal tungstaboranes with an M2{B4M&#8217;} {M = W; M&#8217; = Cr(CO)4, Mo(CO)4, W(CO)4} core. The reaction of in situ generated intermediate, obtained from the low temperature reaction of [Cp*WCl4] with an excess of [LiBH4&#183;thf], followed by thermolysis with [M(CO)5&#183;thf] (M = Cr, Mo and W) led to the isolation of the tungstaboranes [(Cp*W)2B4H8M(CO)4], 1&#8315;3 (1: M = Cr; 2: M = Mo; 3: M = W). In an attempt to replace one of the BH&#8212;vertices in M2B5 with other group metal carbonyls, we performed the reaction with [Fe2(CO)9] that led to the isolation of [(Cp*W)2B4H8Fe(CO)3], 4, where Fe(CO)3 replaces a {BH} core unit instead of the {BH} capped vertex. Further, the reaction of [Cp*MoCl4] and [Cr(CO)5&#183;thf] yielded the mixed-metal molybdaborane cluster [(Cp*Mo)2B4H8Cr(CO)4], 5, thereby completing the series with the missing chromium analogue. With 56 cluster valence electrons (cve), all the compounds obey the cluster electron counting rules. Compounds 1&#8315;5 are analogues to the parent [(Cp*M)2B5H9] (M= Mo and W) that seem to have generated by the replacement of one {BH} vertex from [(Cp*W)2B5H9] or [(Cp*Mo)2B5H9] (in case of 5). All of the compounds have been characterized by various spectroscopic analyses and single crystal X-ray diffraction studies

Hypoelectronic 8–11-Vertex Irida- and Rhodaboranes

A series of novel <i>isocloso</i>-diiridaboranes [(Cp*Ir)₂B₆H₆], <b>1</b>, <b>2</b>; [1,7-(Cp*Ir)₂B₈H₈], <b>4</b>; [1,4-(Cp*Ir)₂B₈H₈], <b>5</b>; [(Cp*Ir)₂B₉H₉], <b>8</b>; <i>isonido-</i>[(Cp*Ir)₂B₇H₇], <b>3</b>; and 10-vertex cluster [5,7-(Cp*Ir)₂B₈H₁₂], <b>6</b> (Cp* = η⁵-C₅Me₅) have been isolated and structurally characterized from the pyrolysis of [Cp*IrCl₂]₂ and BH₃·thf. On the other hand, the corresponding rhodium system afforded 10- and 11-vertices clusters [5-(Cp*Rh)­B₉H₁₃)], <b>7</b>, and [(Cp*Rh)₂B₉H₉], <b>9</b>, respectively. Clusters <b>1</b> and <b>2</b> are topological isomers. The geometry of <b>1</b> is dodecahedral, similar to that of its parent borane [B₈H₈]^2–, in which two of the [BH] vertices are replaced by two [Cp*Ir] fragments. The geometry of <b>2</b> can be derived from a nine-vertex tricapped trigonal prism by removing one of the capped vertices. Compounds <b>4</b> and <b>5</b> are 10-vertex <i>isocloso</i> clusters based on a 10-vertex bicapped square antiprism structure. The only difference between them is the presence of a metal–metal bond in <b>5</b>. The solid-state structures of <b>8</b> and <b>9</b> attain an 11-vertex geometry in which a unique six-membered B₆H₆ moiety is bonded to the metal center. In addition, quantum-chemical calculations have been used to provide further insight into the electronic structure and stability of the clusters. All the compounds have been characterized by IR and ¹H, ¹¹B, and ¹³C NMR spectroscopy in solution, and the solid-state structures were established by X-ray crystallographic analysis