Now showing 1 - 10 of 36
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    Combined Experimental and Theoretical Investigations of Group 6 Dimetallaboranes [(Cp∗M)2B4H10] (M = Mo and W)
    (13-08-2018)
    Mondal, Bijan
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    Bag, Ranjit
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    Thermolysis of mono metal carbonyl fragment, [M′(CO)5·thf, M′ = Mo and W, thf = tetrahydrofuran] with an in situ generated intermediate, obtained from the reaction of [Cp∗MCl4] (M = Mo and W, Cp∗ = 1,2,3,4,5-pentamethylcyclopentadienyl) with [LiBH4·thf], yielded dimetallaboranes, 1 and 2. Isolations of [{Cp∗M(CO)}2B4H6] (M = Mo (1) and W(2)) provide direct evidence for the existence of saturated molybdaborane and tungstaborane clusters, [(Cp∗M)2B4H10]. Our extensive theoretical studies together with the experimental observation suggests that the intermediate may be a saturated cluster [(Cp#M)2B4H10], not unsaturated [(Cp#M)2B4H8] (Cp# = Cp or Cp∗), which was proposed earlier by Fehlner. Furthermore, in order to concrete our findings, we isolated and structurally characterized analogous clusters [(Cp∗Mo)2(CO)(μ-Cl)B3H4W(CO)4] (3) and [(Cp∗WCO)2(μ-H)2B3H3W(CO)4] (4). All the compounds have been characterized by solution-state 1H, 11B, IR, and 13C NMR spectroscopy, mass spectrometry, and the structural architectures of 1, 3, and 4 were unequivocally established by X-ray crystallographic analysis. The density functional theory calculations yielded geometries that are in close agreement with the observed structures. Both the Fenske-Hall and Kohn-Sham molecular orbital analyses showed an increased thermodynamic stability for [(Cp#M)2B4H10] compared to [(Cp#M)2B4H8]. Furthermore, large HOMO-LUMO gap and significant cross cluster M-M bonding have been observed for clusters 1-4.
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    Homometallic Cubane Clusters: Participation of Three-Coordinated Hydrogen in 60-Valence Electron Cubane Core
    (08-09-2015)
    Yuvaraj, K.
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    Roy, Dipak Kumar
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    Mondal, Bijan
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    Varghese, Babu
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    This work describes the synthesis, structural characterizations, and electronic structures of a series of novel homometallic cubane clusters [(Cp∗Ru)2{Ru(CO)2}2BH(μ3-E)(μ-H)B(μ-H)3M], (2, M = Cp∗Ru, E = CO; 3, M = Ru(Cp∗Ru)2(μ-CO)3(μ-H)BH), E = BH), [(Cp∗Ru)3(μ3-CO)(BH)3(μ3-H)3], 4, and [(Cp∗Ru)2(μ3-CO){Ru(CO)3}2(BH)2(μ-H)B], 5 (Cp∗ = η5-C5Me5). These cubane clusters have been isolated from a thermally driven reaction of diruthenium analogue of pentaborane(9) [(Cp∗RuH)2B3H7], 1, and [Ru3(CO)12]. Structural and spectroscopic studies revealed the existence of triply bridged hydrogen (μ3-H) atoms that participate as a vertex in the cubane core formation for compounds 2, 3, and 4. In addition, the crystal structure of these clusters clearly confirms the presence of an electron precise borane ligand (borylene fragment) which is triply bridged to the trimetallic units. Bonding of these novel complexes has been studied computationally by DFT methods, and the studies demonstrate that the cubane clusters 2 and 3 possess 60 cluster valence electrons (cves) with six metal-metal bonds. All the new compounds have been characterized in solution by mass spectrometry; IR; and 1H, 11B, and 13C NMR studies, and the structural types were unequivocally established by crystallographic analysis of compounds 2-5. (Figure Presented).
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    Chemistry of diruthenium analogue of pentaborane(9) with heterocumulenes: Toward novel trimetallic cubane-type clusters
    (06-10-2014)
    Anju, R. S.
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    Saha, Koushik
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    Mondal, Bijan
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    Dorcet, Vincent
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    Roisnel, Thierry
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    Halet, Jean Francois
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    Reactions of the CS2 and CO2 heterocumulene ligands with nido-ruthenaborane cluster [1,2-(Cp∗Ru)2(μ-H)2B3H7], 1, were explored (Cp∗ = pentamethylcyclopentadienyl). Compound 1 when treated with CS2 underwent metal-assisted hydroboration to yield arachno-ruthenaborane [(Cp∗Ru)2(B3H8)(CS2H)], 2, with a dithioformato ligand attached to it. The chemistry of 2 was then explored with various transition metal carbonyl compounds under photolytic and thermolytic conditions. Thermolysis of 2 with [Mn2(CO)10] resulted in the formation of an unprecedented cubane-type cluster [(Cp∗Ru)2Mn(CO)3(CS2H2)B3H4], 3, with a rare [M3E5] formulation (E = B, S). On the other hand, when compound 2 was photolyzed in the presence of [Mn2(CO)10], it yielded an incomplete cubane-type cluster [(Cp∗Ru)2Mn(CO)3BH2(CS2H2)], 4. The room-temperature reaction of 2 with [Fe2(CO)9] yielded heterometallic arachno clusters [(Cp∗Ru)(CO)2{Fe(CO)3}2S2CH3], 6 and [(Cp∗Ru)2(B3H8)(CO){Fe(CO)3}2(CS2H)], 7. In contrast, photolysis of 2 with [Fe2(CO)9] yielded a tetrahedral cluster [(Cp∗Ru)(CO)2S(μ-H){Fe(CO)3}3], 8, tethered to an exo-polyhedral moiety [(Cp∗Ru)(CO)2]. Compound 6 provides an unusual bonding pattern by means of fusing the wing-tip vertex (S) of the [Fe2S2] butterfly core by an exo-polyhedral [(Cp∗Ru)(CO)2] unit. Density functional theory calculations were carried out to provide insight into the mechanistic pathway, electronic structure, and bonding properties.
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    (M = Zr or Hf): Early transition metal 'guarded' heptaborane with strong covalent and electrostatic bonding
    (21-02-2018)
    De, Anangsha
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    Zhang, Qian Fan
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    Mondal, Bijan
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    Cheung, Ling Fung
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    Kar, Sourav
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    Saha, Koushik
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    Varghese, Babu
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    Wang, Lai Sheng
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    Among the series of stable closo-borate dianions, [BnHn]2-, the X-ray crystallographic structure of [B7H7]2- was determined only in 2011. To explore its chemistry and stability, we have isolated and structurally characterized two new transition metal complexes of the heptaborane, [(Cp2M)2B9H11] (Cp = η5-C5H5; M = Zr or Hf). The structures of [(Cp2M)2B9H11] contain a pentagonal bipyramidal B7 core, coordinated by two {Cp2M} and two {BH2} units equatorially. Structural and spectroscopic characterizations and DFT calculations show that [(Cp2M)2B9H11] complexes are substantially more stable than the parent dianion, in either [B7H7]2- or (nBu4N)2[B7H7]. Our theoretical study and chemical bonding analyses reveal that the surprising stability of the two new heptaborane metal complexes is due to multi-center covalent bonds related to the two exo-{Cp2M} units, as well as electrostatic interactions between the {Cp2M} units and the B7 core. The facile syntheses of the heptaborane metal-complexes will allow further exploration of their chemistry.
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    Reactivity of diruthenium and dirhodium analogues of pentaborane(9): Agostic versus boratrane complexes
    (10-03-2014)
    Anju, R. S.
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    Roy, Dipak Kumar
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    Mondal, Bijan
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    Yuvaraj, K.
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    Arivazhagan, C.
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    Saha, Koushik
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    Varghese, Babu
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    A series of novel Cp*-based (Cp*=η5-C 5Me5) agostic, bis(σ-borate), and boratrane complexes have been synthesized from diruthenium and dirhodium analogues of pentaborane(9). The synthesis and structural characterization of the first neutral ruthenadiborane(6) analogue are also reported. This new route offers a very efficient method for the isolation of bis(σ-borate) and agostic complexes from diruthenapentaborane(9). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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    In search for new bonding modes of the methylenedithiolato ligand: novel tri- and tetra-metallic clusters
    (07-07-2015)
    Anju, R. S.
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    Saha, Koushik
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    Mondal, Bijan
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    Roisnel, Thierry
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    Halet, Jean François
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    Building upon our earlier results on the chemistry of diruthenium analogue of pentaborane (9) with heterocumulenes, we continued to investigate the reactivity of arachno-[(Cp∗Ru)2(B3H8)(CS2H)], 1, (Cp∗ = η5-C5Me5) towards group 7 and 8 transition metal carbonyl compounds under photolytic and thermolytic conditions. The metal carbonyl compounds show diverse reactivity pattern with arachno-1. For example, the photolysis of arachno-1 with [Re2(CO)10] yielded [(Cp∗Ru)2B3H5(CH2S2){Re(CO)4}2], 2, [(Cp∗RuCO)2(μ-H)2(CH2S2){Re(CO)4}{Re(CO)3}], 3 and [(Cp∗Ru)2(μ-CO)(μ-H)(CH2S2){Re(CO)3}], 4. The geometry of 2 with a nearly planar eight-membered ring containing heavier transition metals rhenium, ruthenium is unprecedented. Compounds 3 and 4 can be considered as M4-quadrilateral and M3-triangle with a methylenedithiolato ligand attached to the metal centres, respectively. [Mn2(CO)10], on the other hand, reacts with arachno-1 to yield heterometallic binuclear [(Cp∗RuCO){Mn(CO)4}(μ-H)(SCH3)], 5 and homocubane [(Cp∗Ru)2{Mn(CO)3}-(CS2H2)B3H4], 6. In an attempt to generate group 8 analogues of 2-5, we performed the reaction of arachno-1 with [Fe2(CO)9] and [Ru3(CO)12]. Although, the objective of isolating analogous compounds was not achieved, the reaction with [Fe2(CO)9] led to novel tetrahedral cluster [(Cp∗RuCO){(Fe(CO)3}2S(μ-H)], 7. [Ru3(CO)12], in contrast, yielded known compounds [{Cp∗Ru(CO)}2B2H6], 9 and [Cp∗Ru(CO)2]2, 10. All the cluster compounds have been characterized by mass spectrometry, IR, and 1H, 11B, and 13C NMR spectroscopy, and the geometric structures were unequivocally established by crystallographic analysis of 2-5 and 7.
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    Novel triple-decker sandwich complex with a six-membered [B 3Co2(μ4-Te)] ring as the middle deck
    (04-03-2013)
    Thakur, Arunabha
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    Chakrahari, Kiran Kumar Varma
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    Mondal, Bijan
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    Thermolysis of nido-[(Cp*Mo)2B4TeClH 5], with an excess of Co2(CO)8 at room temperature, afforded a triple-decker sandwich complex [(Cp*Mo) 2{μ-η6:η6-B3H 3TeCo2(CO)5}] (4), which represents an unsaturated 24-valence-electron sandwich cluster in which the middle deck is composed of B, Co, and a heavy group 16 element. © 2013 American Chemical Society.
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    Chemistry of diruthenium and dirhodium analogues of pentaborane(9): Synthesis and characterization of metal N,S-heterocyclic carbene and B-agostic complexes
    (23-12-2015)
    Roy, Dipak Kumar
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    Mondal, Bijan
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    Anju, R. S.
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    Building upon our earlier results on the synthesis of electron-precise transition-metal-boron complexes, we continue to investigate the reactivity of pentaborane(9) and tetraborane(10) analogues of ruthenium and rhodium towards thiazolyl and oxazolyl ligands. Thus, mild thermolysis of nido-[(Cp∗RuH)2B3H7] (1) with 2-mercaptobenzothiazole (2-mbtz) and 2-mercaptobenzoxazole (2-mboz) led to the isolation of Cp∗-based (Cp∗ = η5-C5Me5) borate complexes 5a, b [Cp∗RuBH3L] (5a: L = C7H4NS2; 5b: L = C7H4NOS)) and agostic complexes 7a,b [Cp∗RuBH2(L)2], (7a: L = C7H4NS2; 7b: L=C7H4NOS). In a similar fashion, a rhodium analogue of pentaborane(9), nido-[(Cp∗Rh)2B3H7] (2) yielded rhodaboratrane [Cp∗RhBH(L)2], 10 (L = C7H4NS2). Interestingly, when the reaction was performed with an excess of 2-mbtz, it led to the formation of the first structurally characterized N,S-heterocyclic rhodium-carbene complex [(Cp∗Rh)(L2)(1-benzothiazol-2-ylidene)] (11) (L = C7H4NS2). Furthermore, to evaluate the scope of this new route, we extended this chemistry towards the diruthenium analogue of tetraborane(10), arachno-[(Cp∗RuCO)2B2H6] (3), in which the metal center possesses different ancillary ligands.
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    A fine tuning of metallaborane to bridged-boryl complex, [(Cp*Ru)2(μ-H)(μ-CO)(μ-Bcat)] (cat = 1,2-O2C6H4; Cp* = η5-C5Me5)
    (20-08-2013)
    Anju, R. S.
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    Roy, Dipak Kumar
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    Geetharani, K.
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    Mondal, Bijan
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    Varghese, Babu
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    Room temperature photolysis of [(Cp*RuCO)2BH4(Bcat)], 3, generated from the reaction of arachno-[(Cp*RuCO)2B2H6], 1, with HBcat (cat = 1,2-O2C6H4), yielded a rare homodinuclear bridged-boryl complex, [(Cp*Ru)2(μ-H)(μ-CO)(μ-Bcat)], 4, confirmed by X-ray diffraction. © 2013 The Royal Society of Chemistry.
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    Synthesis, Structure, Bonding, and Reactivity of Metal Complexes Comprising Diborane(4) and Diborene(2): [{Cp*Mo(CO)2}2{μ-η2:η2-B2H4}] and [{Cp*M(CO)2}2B2H2M(CO)4], M=Mo,W
    (02-07-2018)
    Mondal, Bijan
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    Bag, Ranjit
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    Ghorai, Sagar
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    Bakthavachalam, K.
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    Jemmis, Eluvathingal D.
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    The reaction of [(Cp*Mo)2(μ-Cl)2B2H6] (1) with CO at room temperature led to the formation of the highly fluxional species [{Cp*Mo(CO)2}2{μ-η2:η2-B2H4}] (2). Compound 2, to the best of our knowledge, is the first example of a bimetallic diborane(4) conforming to a singly bridged Cs structure. Theoretical studies show that 2 mimics the Cotton dimolybdenum–alkyne complex [{CpMo(CO)2}2C2H2]. In an attempt to replace two hydrogen atoms of diborane(4) in 2 with a 2e [W(CO)4] fragment, [{Cp*Mo(CO)2}2 B2H2W(CO)4] (3) was isolated upon treatment with [W(CO)5⋅thf]. Compound 3 shows the intriguing presence of [B2H2] with a short B−B length of 1.624(4) Å. We isolated the tungsten analogues of 3, [{Cp*W(CO)2}2B2H2W(CO)4] (4) and [{Cp*W(CO)2}2B2H2Mo(CO)4] (5), which provided direct proof of the existence of the tungsten analogue of 2.