Search Results (9)

The synthesis and structural characterization of a series of heterotrimetallic ruthenaborane clusters are reported. The photolytic reaction of nido-[(Cp*Ru)₂(µ-H)₂B₃H₇] (nido-1) (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl) with [M(CO)₅·THF] (THF = tetrahydrofuran, M = Mo and W) yielded the heterotrimetallic clusters pileo-[(Cp*Ru)₂{M(CO)₃}(µ-CO)(µ-H)(µ₃-BH)B₂H₅], M = Mo (2), W (3) and the known arachno ruthenaboranes [1,2-(Cp*Ru)(Cp*RuCO)(µ-H)B₃H₈] (I) and [{Cp*Ru(CO)}₂B₂H₆] (II). In an attempt to synthesize the Mn-analog of 2 and 3, we performed a similar reaction of nido-1 with [Mn₂(CO)₁₀], which afforded the heterotrimetallic pileo-[(Cp*Ru){Mn(CO)₃}(µ-H)₂(µ₃-BH)B₂H₅] (4) cluster along with the reported trimetallic hydrido(hydroborylene) species [(Cp*Ru)₂{Mn(CO)₃}(µ-H)(µ-CO)₃(µ-BH)] (III). Ruthenaboranes 2, 3 and 4 are isoelectronic and isostructural. The geometry of 2–4 can be viewed as a triangle face-fused square pyramidal and tetrahedral geometry, in which the apical vertex of the tetrahedron is occupied by a µ₃–BH moiety. All of these pileo ruthenaborane clusters obey Mingos’ fusion formalism. Clusters 2–4 were characterized using multinuclear NMR, IR spectroscopies and electrospray ionization mass spectrometry. The single-crystal X-ray diffraction studies of clusters 2 and 4 confirmed their structures. Further, density functional theory (DFT) studies of these pileo ruthenaboranes have been carried out to investigate the nature of bonding, fusion and electronic structures. Full article

The synthesis of the first conjugates of acridine with cobalt bis(dicarbollide) are reported. A novel 9-azido derivative of acridine was prepared through the reaction of 9-methoxyacridine with N₃CH₂CH₂NH₂, and its solid-state molecular structure was determined via single-crystal X-ray diffraction. The azidoacridine was used in a copper (I)-catalyzed azide-alkyne cycloaddition reaction with cobalt bis(dicarbollide)-based terminal alkynes to give the target 1,2,3-triazoles. DNA interaction studies via absorbance spectroscopy showed the weak binding of the obtained conjugates with DNA. The antiproliferative activity (IC₅₀) of the boronated conjugates against a series of human cell lines was evaluated through an MTT assay. The results suggested that acridine derivatives of cobalt bis(dicarbollide) might serve as a novel scaffold for the future development of new agents for boron neutron capture therapy (BNCT). Full article

The octahydridotriborate anion plays a crucial role in the field of polyhedral boron chemistry, facilitating the synthesis of higher boranes and the preparation of diverse transition metal complexes. Among the stable forms of this anion, CsB₃H₈ (or (n-C₄H₉)₄N)[B₃H₈] have been identified. These salts serve as valuable precursors for the synthesis of metallaboranes, wherein the triborate anion acts as a ligand coordinating to the metal center. In this study, we have successfully synthesized a novel rhodatetraborane dihydride, [Rh(η²-B₃H₈)(H)₂(PPh₃)₂] (1), which represents a Rh(III) complex featuring a bidentate chelate ligand fasormed by B₃H₈⁻. Extensive characterization of this rhodatetraborane complex has been performed using NMR spectroscopy in solution and X-ray diffraction analysis in the solid state. Notably, the complex exhibits intriguing fluxional behavior, which has been investigated using NMR techniques. Moreover, we have explored the reactivity of complex 1 towards pyridine (py) and dimethylphenylphosphine (PMe₂Ph). Our findings highlight the labile nature of this four-vertex rhodatetraborane as it undergoes disassembly upon attack from the corresponding Lewis base, resulting in the formation of borane adducts, LBH₃, where L = py, PMe₂Ph. Furthermore, in these reactions, we report the characterization of new cationic hydride complexes, such as [Rh(H)₂(PPh₃)₂ (py)]⁺ (2) and [Rh(H)₂(PMe₂Ph)₄]⁺. Notably, the latter complex has been characterized as the octahydridotriborate salt [Rh(H)₂(PMe₂Ph)₄][B₃H₈] (3), which extends the scope of rhodatetraborane derivatives. Full article

The structure and bonding of two novel tungstaboranes which were synthesized using diverse synthetic methods are described. (i) The room-temperature photolysis of [Cp*W(CO)₃Me] with [BH₃·SMe₂] led to the isolation of the hydrogen-rich tungstaborane [Cp*W(CO)₂B₃H₈] (1). Its geometry consists of an arachno butterfly core similar to tetraborane(10) and obeys the Wade-Mingos electron counting rules (n vertices, n + 3 skeletal electron pairs (seps)). (ii) Further, the tungstaborane [(Cp*W)₃(μ-H)₂(μ₃-H)(μ-CO)₂B₄H₄] (4) was isolated by thermolysis reaction of a tungsten intermediate, obtained by low temperature reaction of [Cp*WCl₄] and [LiBH₄·THF] with [Cr(CO)₅·THF]. Compound 4 which seems to have formed by replacement of a BH unit in [(Cp*W)₂B₅H₉] by the isoelectronic fragment {Cp*W(CO)₂}, adopts an oblato-nido hexagonal-bipyramidal core (n vertices, n–1 seps). Both compounds were characterized using multinuclear NMR, IR spectroscopy, mass spectrometry as well as single crystal X-ray diffraction analysis. In addition, density functional theory (DFT) calculations were performed in order to elucidate their bonding and electronic structures. Full article

Synthesis, isolation, and structural characterization of unique metal rich diamagnetic cobaltaborane clusters are reported. They were obtained from reactions of monoborane as well as modified borohydride reagents with cobalt sources. For example, the reaction of [Cp*CoCl]₂ with [LiBH₄·THF] and subsequent photolysis with excess [BH₃·THF] (THF = tetrahydrofuran) at room temperature afforded the 11-vertex tricobaltaborane nido-[(Cp*Co)₃B₈H₁₀] (1, Cp* = η⁵-C₅Me₅). The reaction of Li[BH₂S₃] with the dicobaltaoctaborane(12) [(Cp*Co)₂B₆H₁₀] yielded the 10-vertex nido-2,4-[(Cp*Co)₂B₈H₁₂] cluster (2), extending the library of dicobaltadecaborane(14) analogues. Although cluster 1 adopts a classical 11-vertex-nido-geometry with one cobalt center and four boron atoms forming the open pentagonal face, it disobeys the Polyhedral Skeletal Electron Pair Theory (PSEPT). Compound 2 adopts a perfectly symmetrical 10-vertex-nido framework with a plane of symmetry bisecting the basal boron plane resulting in two {CoB₃} units bridged at the base by two boron atoms and possesses the expected electron count. Both compounds were characterized in solution by multinuclear NMR and IR spectroscopies and by mass spectrometry. Single-crystal X-ray diffraction analyses confirmed the structures of the compounds. Additionally, density functional theory (DFT) calculations were performed in order to study and interpret the nature of bonding and electronic structures of these complexes. Full article

A large number of metallaborane clusters and their derivatives with various structural arrangements are known. Among them, M₂B₅ clusters and derivatives constitute a significant class. Transition metals present in these species span from group 4 to group 7. Their structure can vary from oblatonido, oblatoarachno, to arachno type open structures. Many of these clusters appear to be hypoelectronic and are often considered as ‘rule breakers’ with respect to the classical Wade–Mingos electron counting rules. This is due to their unique highly oblate (flattened) deltahedral structures featuring a cross-cluster M−M interaction. Many theoretical calculations were performed to elucidate their electronic structure and chemical bonding properties. In this review, the synthesis, structure, and electronic aspects of the transition metal M₂B₅ clusters known in the literature are discussed. The chosen examples illustrate how, in synergy with experiments, computational results can provide additional valuable information to better understand the electronic properties and electronic requirements which govern their architecture and thermodynamic stability. Full article

Boron compounds now have many applications in a number of fields, including Medicinal Chemistry. Although the uses of boron compounds in pharmacological science have been recognized several decades ago, surprisingly few are found in pharmaceutical drugs. The boron-containing compounds epitomize a new class for medicinal chemists to use in their drug designs. Carboranes are a class of organometallic compounds containing carbon (C), boron (B), and hydrogen (H) and are the most widely studied boron compounds in medicinal chemistry. Additionally, other boron-based compounds are of great interest, such as dodecaborate anions, metallacarboranes and metallaboranes. The boron neutron capture therapy (BNCT) has been utilized for cancer treatment from last decade, where chemotherapy and radiation have their own shortcomings. However, the improvement in the already existing (BPA and/or BSH) localized delivery agents or new tumor-targeted compounds are required before realizing the full clinical potential of BNCT. The work outlined in this short review addresses the advancements in boron containing compounds. Here, we have focused on the possible clinical implications of the new and improved boron-based biologically active compounds for BNCT that are reported to have in vivo and/or in vitro efficacy. Full article

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. Full article

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. Full article