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Polyhedral boron cluster chemistry has been dominated over the last six decades by icosahedral borate dianions, carboranes, metallacarboranes and metallaboranes owing to their high stabilities and rich chemistry. After the first isolation of the closo-borate dianion [B10H10]2− in 1959, many other closo-[BnHn]2− anions (n = 5–9, 11 and 12) were synthesized by Hawthorne, Lipscomb, Muetterties and others. However, the first crystallographic characterization of icosahedral K2[B12H12] by Lipscomb in 1960 stimulated the chemistry and bonding investigations of these closo-[BnHn]2− (n = 6–12) anions. Interestingly, although the closo-[B7H7]2− was synthesized and partially characterized, the X-ray structure of the heptaborane dianion was not established until very recently. Bernhardt and co-worker have fully characterized closo-[B7H7]2− very recently and subsequently, we have isolated a transition metal guarded closo-heptaborane. After exploring the lower borane series, chemists have started envisaging supraicosahedral boranes. Although theoretical calculations by Lipscomb, Jemmis and Schleyer suggested that closo-borate dianions beyond icosahedron [BnHn]2− (n ˃ 12) are stable, the parent closo-borate dianions [BnHn]2− (n ˃12) have not been isolated yet. Following the first isolation of a supraicosahedral metallacarborane in 1971, carboranes, metallacarboranes and metallaboranes have been synthesized with supraicosahedral geometries. The bonding and characteristic electron counts of these supraicosahedral clusters are quite different from those of the lower nuclearity clusters. This chapter describes the synthesis, structural features and electron counts of 13–16-vertex borane, carborane, metallacarborane and metallaborane polyhedral molecules. [ABSTRACT FROM AUTHOR]

Syntheses and structural elucidations of a series of chalcogen stabilized binuclear complexes of group 5 and 6 transition metals have been described. Room temperature reaction of [Cp*CrCl]2 (Cp* = η5-C5Me5) with Li[BH3(SePh)] afforded a Se inserted binuclear chromium complex, [(Cp*Cr)2(µ-Se2SePh)2], 1. In an attempt to make the analogous complexes with heavier group 6 metals, reactions of [Cp*MCl4] (M = Mo and W) with Li[BH3(SePh)] were carried out that yielded Se inserted binuclear complexes [(Cp*M)2(µ-Se)2(µ-SePh)2], 2 and 3 (2: M = Mo and 3: M = W) along with known [(Cp*M)2B5H9], 4a–b (4a: M = Mo and 4b: M = W). Similarly, the reactions of [Cp*NbCl4] with Li[BH3(EPh)] (E = S or Se) followed by thermolysis led to the formation of binuclear chalcogen complexes [(Cp*Nb)2(µ-E2)2], 5 and 6 (5: E = S and 6: E = Se) and known [(Cp*Nb)2(B2H6)2], 7. All these complexes have been characterized by 1H and 13C NMR spectroscopy and mass spectrometry. The structural integrity of complexes 1, 3, 5 and 6 was established by the X-ray diffraction studies. The DFT studies further exemplify the bonding interactions present in these complexes, especially the multiple bond character between the metals in 1–3. The syntheses and structural characterizations of three chalcogen-bridged bimetallic complexes of group 5 and 6 metals, such as [(Cp*Nb)2(µ-E2)2] (E = S and Se) (right), [(Cp*Cr)2(µ-Se2SePh)2] (centre) and [(Cp*M)2(µ-Se)2(µ-SePh)2], (M = Mo and W) (left) are reported. [ABSTRACT FROM AUTHOR]

Reactivity of [Cp*Mo(CO) Me], 1 with various chalcogenide ligands such as Li[BH E] and Li[BH EFc] (E = S, Se or Te; Fc = (C H-Fe-C H)) has been described. Room temperature reaction of 1 with Li[BH E] (E = S and Se) yielded metal chalcogenide complexes [Cp*Mo(CO) ( η-S CCH)], 2 and [Cp*Mo(CO) ( η-SeC H)], 3. In compound 2, {Cp*Mo(CO) } fragment adopts a four-legged piano-stool geometry with a η-dithioacetate moiety. In contrast, treatment of 1 with Li[BH (EFc)] (E = S, Se or Te; Fc = C H-Fe-C H) yielded borate complexes [Cp*Mo(CO) (μ-H)(μ-EFc)BH ], 4-6 in moderate yields. Compounds 4-6 are too unstable and gradual conversion to [{Cp*Mo(CO) } (μ-H)(μ-EFc] ( 7: E = S; 8: Se) and [{Cp*Mo(CO) } (μ-TeFc) ], 9 happened by subsequent release of BH . All the compounds have been characterized by mass spectrometry, IR, multinuclear NMR spectroscopy and structures were unequivocally established by crystallographic analysis for compounds 2, 3 and 7. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Recently we described the synthesis and structural characterization of various dimetallaherteroborane clusters, namely nido-[(CpMo)BEClH], 1- 3; ( 1: E = S, x = 0; 2: E = Se, x = 0; 3: E = Te, x = 1). A combined theoretical and experimental study was also performed, which demonstrated that the clusters 1- 3 with their open face are excellent precursors for cluster growth reaction. In this investigation process on the reactivity of dimetallaheteroboranes with metal carbonyls, in addition to [(CpMo)BHEFe(CO)] ( 4: E = S, 6: E = Te) reported earlier, reaction of 2 with [ Fe(CO)] yielded mixed-metallaselenaborane [(CpMo)BHSeFe(CO)], 5 in good yield. The quantum chemical calculation using DFT method has been carried out to probe the bonding, NMR chemical shifts and electronic properties of dimolybdaheteroborane clusters 4- 6. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The recent achievements and progress in the field of high-nuclearity supraicosahedral metallaborane chemistry are reviewed and compared to those made in borane, carborane and metallacarborane chemistry. In contrast to metallacarboranes, characterized large supraicosahedral metallaboranes only adopt isocloso deltahedral structural arrangements with n vertices and a non-Wadean n skeletal-electron-pair count. This anomaly can be rationalized by the preference of metal atoms for 6-connect vertices present in the cluster cages. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) calculations were used to probe the reaction of the diruthenaborane nido-[1,2-(Cp*RuH)BH] (Cp* = η-CMe), ( 1) with MeC ≡ CMe to form the major product nido-[1,2-(Cp*Ru)( μ-H)( μ-BH)-4,5-Me-4,5-CBH] ( 2) along with minor product nido-(Cp*Ru)-4,5-Me-4,5-CBH ( 3). The structural features of the other related diruthenacarboranes, nido-(Cp*Ru)-4,5-Me-4,5-CBH ( 4) and closo-1,2-(Cp*RuH)-4,5-Me-4,5-CBH ( 5), were also studied. Since metallaheteroboranes with p-block group-14 elements are rare, we extend our DFT studies to explore the reaction of 1 with heavier group-14 alkyne analogs, RE ≡ ER (E = Si, Ge, and Sn; R = alkyl or aryl groups). The geometrical and electronic structures of the products nido-[1,2-(Cp*Ru)( μ-H)( μ-BH)-4,5-Me-4,5-EBH] (E = Si ( 6), Ge ( 7), Sn ( 8)) are described and compared with the ruthenacarborane analog, nido-[1,2-(Cp*Ru)( μ-H)( μ-BH)-4,5-Me-4,5-CBH] species, 2. The computed energetics and the geometries support the feasibility of the reaction and the stability of the products. NBO analysis was performed to delve further into the nature of the bonding in this kind of clusters. [ABSTRACT FROM AUTHOR]

Two Cu-specific colorimetric sensors, based on ferrocene-carbohydrate bioconjugates, 2, CHONFe and 3, CHONFe were designed and synthesized in good yields. Both the compounds, 2 and 3, behave as very selective and sensitive chromogenic and electrochemical chemosensor for Cu ion in aqueous environment (CHCN/HO (2:8, v/ v). The analytical detection limit (ADL) for receptor 2 was 7.5 × 10 M. The considerable changes in their absorption spectra of 2 and 3 are accompanied by the appearance of a new low energy (LE) peak at 630 nm ( 2: ε = 1600 M cm and 3: 822 M cm). This is further accompanied by a strong colour change from yellow to dark green that allows the prospective for 'naked eye' detection of Cu ion. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The recently discovered ditantalaboranes CpTaBH ( n = 4, 5) are isoelectronic with the previously discovered dimetallaboranes CpMBH of the group 6 metals Cr, Mo, and W where Cp = η-cyclopentadienyl or substituted cyclopentadienyl. Their oblatonido polyhedral structures can be derived from the oblate (flattened) deltahedra of the oblatocloso dirhenaboranes CpReBH by removal of an equatorial BH vertex with adjustment of the skeletal electron count by changing the metal atoms and adding hydrogen atoms. In these oblatocloso dirhenaborane deltahedra, the approximately antipodal rhenium atoms are close enough together to form a formal Re=Re double bond with lengths in the range 2.69-2.82 Å. Similarly, short M=M distances are maintained in the related oblatonido derivatives CpTaBH ( n = 4, 5) and CpMBH (M=Cr, Mo, W). However, the synthesis of CpTaBH ( n = 4, 5) from CpTaCl + LiBH/BH also gives a less-reduced product CpTaClBH with a longer Ta-Ta distance of ~3.2 Å. This may be regarded as a formal single bond bridged by one of the hydrogen atoms. Vertices of degree 5 (excluding terminal atoms/groups but not edge-bridging hydrogens) are sites of highest stability/lowest chemical reactivity not only in metal-free boranes but also in the dimetallaboranes discussed in this paper. For example, all four boron vertices in CpTaBH have the favorable degree or 5. Graphical Abstract: The recently discovered ditantalaboranes CpTaBH ( n = 4, 5) are isoelectronic with the previously discovered dimetallaboranes CpMBH (M=Cr, Mo, W). They have oblatonido structures derived by removal of one BH vertex from the flattened oblatocloso polyhedra of the dirhenaboranes CpReBH. All of these structures have internal M=M formal double bonds inside the deltahedron. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Chemistry and reactivity of dimolybdathiaborane, [(CpMo)BSH], 1, obtained from the reaction of 2-mercaptobenzothiazole, [CpMoCl] and [LiBH.thf], has been explored with dinuclear metal carbonyl [Fe(CO)]. As a result, reaction of 1 with [Fe(CO)] yielded heterometallathiaborane, [(CpMo)BHSFe(CO)], 2 in good yield. Both the new compounds have been characterized in solution by H, B and C NMR spectroscopy and the structural types were unequivocally established by X-ray crystallographic analysis of compound 2. Cluster 2 has a bicapped octahedral geometry with the {Fe(CO)} fragment occupying one of the high-connectivity cluster vertexes rather than a capping position. Interestingly, cluster 1 undergoes geometric changes (bicapped trigonal bipyramid → bicapped octahedron) on the addition of two-electron {Fe(CO)} fragment to 1. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Treatment of [Cp*MoCl], 1 (Cp* = η-CMe), with [LiBH.thf] in toluene at −40 °C, followed by thermolysis with [(thf)Li{CH(PPh-BH)}] results in the formation of a new class of phosphido bridged molybdaborane [(Cp*Mo)BH( μ-PPh)], 2 which has been characterized crystallographically. In addition, the above reaction also produces known [(Cp*Mo)BH], 3 and an unusual molybdaborane [(Cp*Mo)BH(OPr)], 4 (Pr = -CH(CH)). All the new compounds have been characterized in solution by H, B, C, P NMR spectroscopy and the structural types were unambiguously established by X-ray crystallographic analysis of compounds 2 and 4. Graphical Abstract: Treatment of [CpMoCl] (Cp = η-CMe), with [LiBH.thf] in toluene at −40 °C, followed by thermolysis with [(thf)Li{CH(PPh-BH)}] results in the formation of a new class of phosphido bridged molybdaborane [(CpMo)BH( μ-PPh)] which has been characterized crystallographically.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Scheme 1 was published incorrectly in the original version. The correct Scheme 1 is provided below. [ABSTRACT FROM AUTHOR]

Abstract : Treatment of nido-[1,2-(Cp*Ru)2(μ-H)2B3H7], 1 with five equivalents of Te powder led to the isolation of diruthenium pentalene analogue [(Cp*Ru){(Cp*Ru)2B6H14}(RuCp*)], 2 and a metal indenyl complex [(Cp*Ru)2B2H6C6H3(CH3)], 3. The [(Cp*Ru)2B6H14] fragment in 2 may be considered as a true metal-boron analogue of η5-η5-pentalene ligand (C8H6) and [(Cp*Ru)B2H6C6H3(CH3)] fragment in 3 is an analogue of η5-indenyl ligand. The solid-state X-ray structures were unambiguously determined by crystallographic analysis of compounds 2 and 3. Further, the density functional theory (DFT) calculations were performed to investigate the bonding and the electronic properties of 2a (Cp analogue of 2). The frontier molecular orbital analysis of both 2a and 2b (Cp analogue of [(Cp*Ru)B8H14(RuCp*)]) reveals a lower HOMO-LUMO gap indicating less thermodynamic stability.Graphical Abstract: SYNOPSIS Treatment of nido-[1,2-(Cp∗Ru)2(μ-H)2B3H7] with Te powder led to the isolation of diruthenium pentalene analogue [(Cp*Ru){(Cp*Ru)2B6H14}(RuCp*)] and a metal indenyl complex [(Cp*Ru)2B2H6C6H3(CH3)]. [ABSTRACT FROM AUTHOR]