Two triazole-appended ferrocene−rhodamine conjugates, C 47 H 45 N 7 O 3 Fe (2) and C 49 H 49 N 7 O 3 Fe (3), 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 Hg 2+ as well as I − in an aqueous environment. Quantification of the absorption titration analysis shows that the receptors 2 and 3 can detect the presence of Hg 2+ even at very low concentrations (∼3 ppb). The mode of metal coordination has been studied by DFT calculations. Furthermore, the receptors 2 and 3 are less toxic toward MCF-7 cells and could detect intracellular Hg 2+ by fluorescent imaging studies.

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A series of novel isocloso-diiridaboranes [(Cp*Ir)2B6H6], 1, 2; [1,7-(Cp*Ir)2B8H8], 4; [1,4-(Cp*Ir)2B8H8], 5; [(Cp*Ir)2B9H9], 8; isonido-[(Cp*Ir)2B7H7], 3; and 10-vertex cluster [5,7-(Cp*Ir)2B8H12], 6 (Cp* = η(5)-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)], 7, and [(Cp*Rh)2B9H9], 9, respectively. Clusters 1 and 2 are topological isomers. The geometry of 1 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 2 can be derived from a nine-vertex tricapped trigonal prism by removing one of the capped vertices. Compounds 4 and 5 are 10-vertex isocloso clusters based on a 10-vertex bicapped square antiprism structure. The only difference between them is the presence of a metal-metal bond in 5. The solid-state structures of 8 and 9 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 (1)H, (11)B, and (13)C NMR spectroscopy in solution, and the solid-state structures were established by X-ray crystallographic analysis.

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The development of catalysts for the oxygen reduction reaction is a coveted objective of relevance to energy research. This study describes a metal-free approach to catalyzing the reduction of O2 into H2O2, based on the use of redox-active carbenium species. The most active catalysts uncovered by these studies are the bifunctional dications 1,8-bis­(xanthylium)-biphenylene ([3]2+) and 4,5-bis­(xanthylium)-9,9-dimethylxanthene ([4]2+) which promote the reaction when in the presence of decamethylferrocene and methanesulfonic acid. Electrochemical studies carried out with [4]2+ suggest the intermediacy of an organic peroxide that, upon protonation, converts back into the starting dication while also releasing H2O2. Kinetic studies point to the second protonation event as being rate-determining.

In an effort to synthesize supraicosahedral iridaboranes, pyrolysis of [Cp*IrCl2]2 with excess [BH3·] was carried out, and this synthesis afforded the isomeric iridaborane [(Cp*Ir)2B6H6] clusters 1 and 2. The geometry of 1 was determined to be dodecahedral, i.e., similar to that of [B8H8](2-), whereas 2 was found to exhibit a cluster shape that can be derived from a nine-vertex tricapped trigonal prism by removing one of the capped vertices. The calculation of a large HOMO-LUMO gap further rationalized the isocloso structures for these isomers.

The chemistry of ruthenium-borane complex, [Cp*RuCO(µ-H)BH 2 L] (Cp* = η 5-C 5 Me 5 ; L = C 7 H 4 NS 2), 1 with various alkynes has been explored. Photolysis of 1 with alkynyl-Grignard, [HC≡CMgBr] in toluene led to the isolation of vinyl hydroborate complex [Cp*Ru(µ-H)BH{HC=CH 2 }L], 2a as a sole product. Compound 2a can be viewed as a ruthenium-borate complex with an ethylene moiety. Further, the chemistry of 1 with various internal and terminal alkynes has been performed in photolytic conditions. Photolysis of 1 with [RC≡CR] (R = CO 2 Me) yielded vinyl hydroborate complex [Cp*Ru(µ-H)BCl{RC=CR}L], 2b. Terminal alkynes [HC≡CR] (R = Ph or CO 2 Me) under the same reaction conditions led to the isolation of metal vinyl complexes [Cp*Ru(CO)(C 2 HR)(L)], 3a and 3b (3a: R = Ph; 3b: R = CO 2 Me). In addition, DFT calculations were carried out to analyze the bonding and electronic structures of these new compounds.

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’} {M = W; M’ = 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·thf], followed by thermolysis with [M(CO)5·thf] (M = Cr, Mo and W) led to the isolation of the tungstaboranes [(Cp*W)2B4H8M(CO)4], 1–3 (1: M = Cr; 2: M = Mo; 3: M = W). In an attempt to replace one of the BH—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·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 1–5 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.