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In an attempt to isolate boron-containing tri-niobium polychalcogenide species, we have carried out prolonged thermolysis reactions of [Cp*NbCl4] (Cp* = ɳ5-C5Me5) with four equivalents of Li[BH2E3] (E = Se or S). In the case of the heavier chalcogen (Se), the reaction led to the isolation of the tri-niobium cubane-like cluster [(NbCp*)3(μ3-Se)3(BH)(μ-Se)3] (1) and the homocubane-like cluster [(NbCp*)3(μ3-Se)3(μ-Se)3(BH)(μ-Se)] (2). Interestingly, the tri-niobium framework of 1 stabilizes a selenaborate {Se3BH}− ligand. A selenium atom is further introduced between boron and one of the selenium atoms of 1 to yield cluster 2. On the other hand, the reaction with the sulfur-containing borate adduct [LiBH2S3] afforded the trimetallic clusters [(NbCp*)3(μ-S)4{μ-S2(BH)}] (3) and [(NbCp*)3(μ-S)4{μ-S2(S)}] (4). Both clusters 3 and 4 have an Nb3S6 core, which further stabilizes {BH} and mono-sulfur units, respectively, through bi-chalcogen coordination. All of these species were characterized by 11B{1H}, 1H, and 13C{1H} NMR spectroscopy, mass spectrometry, infrared (IR) spectroscopy, and single-crystal X-ray crystallography. Moreover, theoretical investigations revealed that the triangular Nb3 framework is aromatic in nature and plays a vital role in the stabilization of the borate, borane, and chalcogen units. [ABSTRACT FROM AUTHOR]

Treatment of Li[BH3ER] (E=Se or Te, R=Ph; E=S, R=CH2Ph) with [Cp*CoCl]2 led to the formation of hydridoborate complexes, [{CoCp*Ph}{Cp*Co}{μ‐EPh}{μ‐κ2‐E,H‐EBH3}], 1a and 1 b (1 a: E=Se; 1 b: E=Te) and a bis‐hydridoborate species [Cp*Co{μ‐κ2‐Se,H‐SeBH3}]2, 2. All the complexes, 1 a, 1 b and 2 are stabilized by β‐agostic type interaction in which 1 b represents a novel bimetallic borate complex with a rare B−Te bond. QTAIM analysis furnished direct proof for the existence of a shared and dative B‐chalcogen and Co‐chalcogen interactions, respectively. In parallel to the formation of the hydridoborate complexes, the reactions also yielded tetracyclic species, [Cp*Co{κ3‐E,H,H‐E(BH2)2‐C5Me5H3}], 3 a and 3 b (3 a: E=Se and 3 b: E=S), wherein the bridgehead boron atoms are surrounded by one chalcogen, one cobalt and two carbon atoms of a cyclopentane ring. Molecules 3 a and 3 b are best described as the structural mimic of tetracyclo[4.3.0.02,4.03,5]nonane having identical structure and similar valence electron counts. [ABSTRACT FROM AUTHOR]

Treatment of a dirhodium analogue of pentaborane(9), [(Cp*Rh)2B3H7] (nido‐1; Cp* = η5‐C5Me5), with [Fe2(CO)9] at room temperature led to the formation of [(Cp*Rh)2Fe(CO)3(µ‐CO)B3H2Cl] (2) and the metal‐rich metallaborane [(Cp*Rh)2Fe(CO)3Fe(CO)2(µ‐CO)2B2H2] (3). When the same reaction was carried out at moderate temperature, two metal‐rich metallaboranes, [(Cp*Rh)3Fe(CO)2(µ3‐CO)2B2HX] 4 (X = H) and 5 (X = Cl), and a heterometallic µ9‐boride cluster, [(Cp*Rh)3(RhCO)3Fe(CO)3(µ‐CO)3B3H2] (6), were obtained. Compounds 4 and 5 can be viewed as cubane clusters with 62 cluster valence electrons (cves) and five metal–metal bonds. In another reaction, the treatment of nido‐1 with [Mn2(CO)10] yielded the heterometallic µ9‐boride cluster [(Cp*Rh)3Rh(CO)2{Mn(CO)3}2B4H3] (7). The cluster cores of both 6 and 7 are comprised of tricapped trigonal prisms containing a µ9‐B atom bonded to seven/six metals and two/three boron atoms, respectively. All the new compounds have been characterized by mass spectrometry, IR, 1H, 11B{1H}, and 13C{1H} NMR spectroscopy, and X‐ray crystallographic analysis. [ABSTRACT FROM AUTHOR]

In a quest for efficient precursors for the synthesis of boratrane complexes of late transition metals, we have developed a useful synthetic method using [L′M(μ-Cl)Clx]2 as precursors (L′=η6-p-cymene, M=Ru, x=1; L′=COD, M=Rh, x=0 and L′=Cp*, M=Ir or Rh, x=1; COD=1,5-cyclooctadiene, Cp*=η5-C5Me5). For example, treatment of Na[(H3B)bbza] or Na[(H2B)mp2] (bbza=bis(benzothiazol-2-yl)amine; mp=2-mercaptopyridyl) with [L′M(μ-Cl)Clx]2 yielded [(η6-p-cymene)RuBH{(NCSC6H4)(NR)}2] (2; R=NCSC6H4), [{N(NCSC6H4)2}RhBH{(NCSC6H4)(NR)}2] (3; R=NCS-C6H4), [(η6-p-cymene)RuBH(L)2] (5; L=C5H4NS), and [Cp*MBH(L)2] (6 and 7; L=C5H4NS, M=Ir or Rh). In order to delineate the significance of the ligands, we studied the reactivity of [(COD)Rh(μ-Cl)]2 with Na[(H3B)bbza], which led to the formation of the isomeric agostic complexes [(η4-COD)Rh(μ-H)BHRh(C14H8N3S2)3], 4 a and 4 b, in parallel to the formation of 16-electron square-pyramidal rhodaboratrane complex 3. Compounds 4 a and 4 b show two different geometries, in which the Rh−B bonds are shorter than in the reported Rh agostic complexes. The new compounds have been characterized in solution by various spectroscopic analyses, and their structural arrangements have been unequivocally established by crystallographic analyses. DFT calculations provide useful insights regarding the stability of these metallaboratrane complexes as well as their M→B bonding interactions. [ABSTRACT FROM AUTHOR]

Treatment of [Cp*IrCl2]2 (Cp* = pentamethylcyclopentadienyl) with Li[BH3(SePh)] at room temperature led to the isolation of a dimetala analogue of hexaborane(10), nido-[(Cp*Ir)(µ-SePh)2Ir{(Cp*Ir)SePh}B4H8] ( 1). Solid-state X-ray structure analysis of 1 showed an extended sandwich molecule with two iridium atoms between Cp* and a [B4Ir] ring. Further, in an effort to synthesize the Rh analogue of 1 under similar reaction conditions, we isolated arachno-[{(Cp*Rh)(µ-SePh)3}Rh(µ-SePh)B3H6] ( 2), a rhodium analogue of tetraboarane(10) in which the {RhB3} unit shows geometric equivalence with a metal π-allyl {MC3} species. Ir complex 1, having an Ir-Ir bond, can be considered similar to the dizinc sandwich complex [Cp*Zn-ZnCp*] in terms of the valence electron count at the metal centers. [ABSTRACT FROM AUTHOR]

Trinuclear complexes of group 6, 8, and 9 transition metals with a (μ3-BH) ligand [(μ3-BH)(Cp*Rh)2(μ-CO)M′(CO)5], 3 and 4 ( 3: M′=Mo; 4: M′=W) and 5- 8, [(Cp*Ru)3(μ3-CO)2(μ3-BH)(μ3-E)(μ-H){M′(CO)3}] ( 5: M′=Cr, E=CO; 6: M′=Mo, E=CO; 7: M′=Mo, E=BH; 8: M′=W, E=CO), have been synthesized from the reaction between nido-[(Cp*M)2B3H7] ( nido- 1: M=Rh; nido- 2: M=RuH, Cp*=η5-C5Me5) and [M′(CO)5 ⋅thf] (M′=Mo and W). Compounds 3 and 4 are isoelectronic and isostructural with [(μ3-BH)(Cp*Co)2(μ-CO)M′(CO)5], (M′=Cr, Mo and W) and [(μ3-BH)(Cp*Co)2(μ-CO)(μ-H)2M′′H(CO)3], (M′′=Mn and Re). All compounds are composed of a bridging borylene ligand (B−H) that is effectively stabilized by a trinuclear framework. In contrast, the reaction of nido- 1 with [Cr(CO)5 ⋅thf] gave [(Cp*Rh)2Cr(CO)3(μ-CO)(μ3-BH)(B2H4)] ( 9). The geometry of 9 can be viewed as a condensed polyhedron composed of [Rh2Cr(μ3-BH)] and [Rh2CrB2], a tetrahedral and a square pyramidal geometry, respectively. The bonding of 9 can be considered by using the polyhedral fusion formalism of Mingos. All compounds have been characterized by using different spectroscopic studies and the molecular structures were determined by using single-crystal X-ray diffraction analysis. [ABSTRACT FROM AUTHOR]

A combined experimental and quantum-chemical study of a series of homometallic metallaheteroboranes [(Cp*M)2-E6B2H2] (M = Rh or RuH; E = S or Se; Cp* = η5-C5Me5), which are analogues of 1,3-bishomocubane, is reported. The thermolysis of nido-[(Cp*Rh)2B3H7] (1) in the presence of S or Se powder in toluene yielded bishomocubane clusters [(Cp*Rh)2-(μ-E)2(μ3-E)4B2H2], (3: E = S; 4: E = Se). In a similar fashion, the treatment of nido-[(Cp*RuH)2B3H7] (2) with S or Se powder in p-xylene yielded [(Cp*Ru)2(μ-E)2(μ3-E)4B2H2] (5: E = S; 6: E = Se) and [(Cp*Ru)2(μ3-Se)(μ4-Se)B3H5] (7). One of the noteworthy features of 3-6 is the presence of an electronprecise trichalcogenoborato ligand. All of the compounds have been characterized by mass spectrometry; IR spectroscopy; and 1H, 11B, and 13C NMR spectroscopy. The structures of 3, 4, 6, and 7 were established unequivocally by Xray crystallographic analysis. Quantum-chemical calculations by DFT methods for 3, 4, and 6 showed reasonable agreement with the experimentally observed structural parameters. The large HOMO-LUMO gaps are consistent with the high stabilities of these complexes. [ABSTRACT FROM AUTHOR]

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 5 a, b [Cp*RuBH3L] ( 5 a: L=C7H4NS2; 5 b: L=C7H4NOS)) and agostic complexes 7 a, b [Cp*RuBH2(L)2], ( 7 a: L=C7H4NS2; 7 b: 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. [ABSTRACT FROM AUTHOR]

Thermolysis of an in situ generated intermediate [(Cp*Ta)2(BH3)2Cl2], 1 generated from the reaction of [Cp*TaCl4], (Cp* = η5-C5Me5) and [LiBH4·thf], in presence of [Ru3(CO)12] yielded pileo-[Cp*TaCl(μ-Cl)-B2H4Ru3(CO)8], 2 having two electrons fewer than seven pairs required for the observed square pyramidal geometry. Cluster 2 is the first example of an unsaturated cluster comprising early and late transition metals in a square pyramid core. This reaction also yielded [(Cp*Ta)2(B2H6)(B2H4Cl2)], 3 as a by-product. In addition, the reaction of [Cp*MoCl4] (Cp* = η5-C5Me5) with [LiBH4.thf] in presence of excess [MeI] at mild condition led to the isolation of periodinated dimolybdatetraborane [(Cp*Mo)2B4H3I5], 4 that hints a possible existence of [(Cp*Mo)2B4H8]. After the isolation of periodinated 4, we extended this chemistry towards the late transition metallaborane [(Cp*Rh)3B4H4], 5 using [PtBr2] as brominating source. Although all the attempts to isolate perbrominated rhodaborane failed, we have isolated partially brominated rhodaborane clusters [(Cp*Rh)3(BH)-(BBr)3], 6 and [(Cp*Rh)3(BH)3(BBr)], 7. All the compounds were characterized by IR and 1H, 11B and 13C NMR spectroscopy in solution, and the solid-state structures of 2, 4 and 6 were established by crystallographic analysis. [ABSTRACT FROM AUTHOR]

The photolysis of [M2(CO)10] (M=Re or Mn) with BH3⋅thf at room temperature yields arachno -1 and 2, [(CO)8M2B2H6] ( 1: M =Re, 2: M =Mn). Both the compounds show a butterfly structure with seven skeletal electron pairs and 42 valence electrons. This result presents a new method for general access to low-boron-content metal-boron compounds without the cyclopentadienyl ligand at the metal centers. This new synthetic route is superior to the existing procedures because it avoids the use of [LiBH4] and metal polychlorides, for which the synthesis is very tedious. Compound 1 catalyzes the cyclotrimerization of a series of internal and terminal alkynes to yield mixtures of 1,3,5- and 1,2,4-substituted benzenes. The reactivity of 1 with alkynes demonstrates for the first time that the introduction of the [B2H6] moiety into the [Re2(CO)10] framework significantly enhances the catalytic activity. Note that [Re2(CO)10] catalyzes the same set of alkynes under harsh conditions over a prolonged period of time. Quantum-chemical calculations using DFT methods are applied to afford further insight into the electronic structure, stability, and bonding of 1 and 2. All the compounds are characterized by IR and 1H, 11B, and 13C NMR spectroscopy, and the geometry of 1 is established unambiguously through crystallographic analysis. [ABSTRACT FROM AUTHOR]

The synthesis, structural characterization, and reactivity of new bridged borylene complexes are reported. The reaction of [{Cp*CoCl}2] with LiBH4 ⋅THF at −70 °C, followed by treatment with [M(CO)3(MeCN)3] (M=W, Mo, and Cr) under mild conditions, yielded heteronuclear triply bridged borylene complexes, [(μ3-BH)(Cp*Co)2(μ-CO)M(CO)5] ( 1- 3; 1: M=W, 2: M=Mo, 3: M=Cr). During the syntheses of complexes 1- 3, capped-octahedral cluster [(Cp*Co)2(μ-H)(BH)4{Co(CO)2}] ( 4) was also isolated in good yield. Complexes 1- 3 are isoelectronic and isostructural to [(μ3-BH)(Cp*RuCO)2(μ-CO){Fe(CO)3}] ( 5) and [(μ3-BH)(Cp*RuCO)2(μ-H)(μ-CO){Mn(CO)3}] ( 6), with a trigonal-pyramidal geometry in which the μ3-BH ligand occupies the apical vertex. To test the reactivity of these borylene complexes towards bis-phosphine ligands, the room-temperature photolysis of complexes 1- 3, 5, 6, and [{(μ3-BH)(Cp*Ru)Fe(CO)3}2(μ-CO)] ( 7) was carried out. Most of these complexes led to decomposition, although photolysis of complex 7 with [Ph2P(CH2) nPPh2] ( n=1-3) yielded complexes 9- 11, [3,4-(Ph2P(CH2) nPPh2)- closo-1,2,3,4-Ru2Fe2(BH)2] ( 9: n=1, 10: n=2, 11: n=3). Quantum-chemical calculations by using DFT methods were carried out on compounds 1- 3 and 9- 11 and showed reasonable agreement with the experimentally obtained structural parameters, that is, large HOMO-LUMO gaps, in accordance with the high stabilities of these complexes, and NMR chemical shifts that accurately reflected the experimentally observed resonances. All of the new compounds were characterized in solution by using mass spectrometry, IR spectroscopy, and 1H, 13C, and 11B NMR spectroscopy and their structural types were unequivocally established by crystallographic analysis of complexes 1, 2, 4, 9, and 10. [ABSTRACT FROM AUTHOR]

A neutral metallaborane comprising a Rh4B12 polyhedron with icosioctahedron geometry with 16 vertices and 28 triangular faces was prepared (see structure; Rh: red, B: green). The cage has the shape of a 12‐membered truncated tetrahedron with four capped hexagonal faces. [ABSTRACT FROM AUTHOR]

Room temperature photolysis of a triply-bridged borylene complex, [(μ3-BH)(Cp*RuCO)2(μ-CO)Fe(CO)3] ( 1 a; Cp*=C5Me5), in the presence of a series of alkynes, 1,2-diphenylethyne, 1-phenyl-1-propyne, and 2-butyne led to the isolation of unprecedented vinyl-borylene complexes ( Z)-[(Cp*RuCO)2(μ-CO)B(CR)(CHR′)] ( 2: R, R′=Ph; 3: R=Me, R′=Ph; 4: R, R′=Me). This reaction permits a hydroboration of alkyne through an anti -Markovnikov addition. In stark contrast, in the presence of phenylacetylene, a metallacarborane, closo-[1,2-(Cp*Ru)2(μ-CO)2{Fe2(CO)5}-4-Ph-4,5-C2BH2] ( 5 a), is formed. A plausible mechanism has been proposed for the formation of vinyl-borylene complexes, which is supported by density functional theory (DFT) methods. Furthermore, the calculated 11B NMR chemical shifts accurately reflect the experimentally measured shifts. All the new compounds have been characterized in solution by mass spectrometry and IR, 1H, 11B, and 13C NMR spectroscopies and the structural types were unequivocally established by crystallographic analysis of 2, 5 a, and 5 b. [ABSTRACT FROM AUTHOR]

The reaction of nido-[1,2-(Cp*RuH)2B3H7] ( 1 a, Cp*=η5-C5Me5) with [Mo(CO)3(CH3CN)3] under mild conditions yields the new metallaborane arachno-[(Cp*RuCO)2B2H6] ( 2). Compound 2 catalyzes the cyclotrimerization of a variety of internal- and terminal alkynes to yield mixtures of 1,3,5- and 1,2,4-substituted benzenes. The reactivities of nido- 1 a and arachno- 2 with alkynes demonstrates that a change in geometry from nido to arachno drives a change in the reaction from alkyne-insertion to catalytic cyclotrimerization, respectively. Density functional calculations have been used to evaluate the reaction pathways of the cyclotrimerization of alkynes catalyzed by compound 2. The reaction involves the formation of a ruthenacyclic intermediate and the subsequent alkyne-insertion step is initiated by a [2+2] cycloaddition between this intermediate and an alkyne. The experimental and quantum-chemical results also show that the stability of the metallacyclic intermediate is strongly dependent on the nature of the substituents that are present on the alkyne. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Thermolysis of [Ru 3 (CO) 12 ] with an in-situ generated intermediate, obtained from the reaction of [Cp*MoCl 4 ] and [LiBH 4 .THF], led to the formation of [{Cp*Mo(CO) 2 }(μ 4 -B){Ru(CO) 3 } 3 (μ-H) 2 ], 2 and [{Cp*Mo(CO) 2 } 2 (μ 4 -B){Ru(CO) 3 } 2 (μ-H)], 3 (Cp* = η 5 -C 5 Me 5 ). In a similar fashion, when [Ru 3 (CO) 12 ] was thermalized with [(Cp*Rh) 2 B 2 H 6 ], obtained from a fast metathesis reaction of [Cp*RhCl 2 ] 2 , 4 and [LiBH 4 .THF], yielded a novel heterometallic boride cluster [(Cp*Rh)(μ 6 -B){Ru(CO) 3 } 4 {RuH(CO) 2 }], 5 . Both compounds 2 and 3 can be described as 50-cluster valence electron (cve) hetero-metallic boride clusters, in which the boron atom is in semi-interstitial position of a M 4 -butterfly geometry. Compound 5 contains 86 cluster valence-electrons, in which the boron atom is inside of an octahedral hole composed of one rhodium and five ruthenium atoms. Computational studies on the ground of density functional theory has been undertaken to analyze the bonding of 2 , 3 and 5 . The structural optimization yields geometries in agreement with the structure determinations and computed 11 B chemical shifts accurately reflect the observed shifts. The molecular orbital analysis of them shows that all the valence orbitals of boron have been participated in bonding and therefore provides the “encapsulation” picture of the boron atom. All the compounds have been characterized by IR and 1 H, 11 B, and 13 C NMR spectroscopy, and the geometries of the structures were unequivocally established by crystallographic analyses of compounds 2 , 3 and 5 . [ABSTRACT FROM AUTHOR]

Building on our earlier results, the condensation of rhodium polychlorides with borane reagents (LiBH 4 ·thf, BH 3 ·thf, BHCl 2 ·SMe 2 etc.), we continue to explore the chemistry of the same system with metal carbonyl compounds. As a result, the reaction of [(Cp*Rh) 2 B 2 H 6 ], generated from fast metathesis of [Cp*RhCl 2 ] 2 and LiBH 4 , with heavier group 8 metal carbonyl compounds, yielded [(Cp*Rh) 2 B 4 H 4 Rh{Cp*RhB 3 H 8 }], 1 , [(Cp*Rh)B 3 H 7 {Ru(CO) 2 }(Cp*RhCO) 2 ], 2 [(Cp*Rh) 2 B 3 H 3 {Ru(CO) 3 } 2 ], 3 and [(Cp*Rh) 2 {Os 4 (CO) 12 }(B)H], 4 . Further, these reaction also generated two mixed-metal tetrahedral hydrido clusters [(Cp*Rh){Os(CO) 3 } 3 (μ-H) 4 ], 5 and [(Cp*Rh) 2 {Os(CO) 3 } 2 (μ-CO) (μ-H) 2 ], 6 as minor products. Compound 1 is an octahedra and a square pyramid fused cluster, whereas for 2 a square pyramid and a triangle are fused through a vertex. Both 1 and 2 follow Mingos's formalism for fused clusters. Cluster 4 is an interstitial boride composed of one boron, two rhodium and four osmium atoms. Based on its compositions, compound 4 is a rare example of heteronuclear borides. All the compounds have been characterized by IR, 1 H, 11 B, 13 C NMR spectroscopy in solution and the solid state structures were established by crystallographic analysis of 1 – 5 . [ABSTRACT FROM AUTHOR]

[Display omitted] • Metallaheteroborane clusters with group 16 elements are reviewed elaborately. • Syntheses, structures and bonding of metallaheteroborane clusters are discussed. • Various reactions of these clusters reported by others and us are summarized. Metallaheteroborane clusters containing group-16 elements as cluster constituents were initially of interest solely for the synthesis of high-nuclearity clusters. However, owing to recent developments in their chemistry towards hydrogenation and isomerization of olefins, nido to closo dehydrogenation of clusters, the development of new and improved routes for the synthesis of novel metallaheteroborane clusters have become of interest. In recent years, the chemistry of metallaheteroboranes, with chalcogen(s) as the heteroatom(s), has noted significant growth both in terms of synthetic methodology as well as the advent of unique frameworks ranging from polyhedral cages and macropolyhedral clusters to triple-decker sandwich complexes and hydrocarbon-mimics like cubanes and homocubanes. This review provides a brief account of the syntheses of diverse structural motifs adopted by the metallachalcogenaborane clusters; their electron counts along with latest advances in their chemistry. [ABSTRACT FROM AUTHOR]

• Synthesis and structural characterization of tri-niobium cluster with a trithiaborate ligand. • Synthesis and structural characterization of three nido -ruthenium clusters. • Theoretical investigations have been performed to understand the electronic structure and bonding scenario in these clusters. In an effort to synthesize niobaheteroboranes and ruthenaheteroboranes, two different synthetic methods are developed. The reactions of [Cp*NbCl 4 ] (1) with chalcogenaborate ligands [LiBH 2 E 3 ] (E = S , Se) were carried out under reflux conditions. The reaction with sulfur yielded a triniobium polysulfide cluster [(Cp*Nb) 3 (μ 3 -S) 3 {B(OCH 3)}(μ -S) 3 ] (2) in which a trithiaborate ligand [S 3 B(OCH 3)]− is coordinated to Nb 3 framework in a cubane-type geometry. While the reaction with selenium generated a diniobium polyselenide cluster [(Cp*NbCl) 2 (μ -Se 2 -κ 1Se: κ 2Se') 2 (μ -O)] (3) in which two diselenide ligands {[Se 2 ]2−} are coordinated with both the metal centres in an unsymmetrical κ 1: κ 2 fashion. On the other hand, efforts were directed towards expliciting the coordinative sulfur centres of a preformed arachno ‑ruthenaborane [(Cp*Ru) 2 (B 3 H 8)(CS 2 H)] (arachno ‑ 4) , by carrying out the pyrolysis of arachno ‑ 4 with excess [BH 3 ⋅THF]. The reaction led to the formation of sulfido stabilized pileo cluster nido ‑ruthenathiaborane [2,3-(Cp*Ru) 2 (μ -H)(B 3 H 6)S] (5) , nido ‑ruthenaborane [2,3-(Cp*Ru) 2 (μ -H)(B 4 H 5 Me)] (6) and thiomethyl bridged nido ‑ruthenaborane [2,3-(Cp*Ru) 2 (μ -SMe)(B 3 H 6)] (7). One of the key features of complex 5 is the presence of an unusual pentacoordinated sulfido ligand(μ 5 -S). All the complexes have been characterized by multinuclear NMR, mass spectrometry and their structural architectures have been unambiguously established by single-crystal X-ray diffraction studies. In addition, theoretical investigations provided valuable insights into the electronic structures and bonding of these clusters. [ABSTRACT FROM AUTHOR]

Abstract: Chalcogen-stabilized dimolybdaboranes 3–5 (3: [(Cp∗Mo)2B4H5Se(Ph)], 4: [(Cp∗Mo)2B4H3Se2(SeCH2Ph)] and 5: [(Cp∗Mo)2B3H6(BSR)(μ-η1-SR)] (R=2,6-( t Bu)2-C6H2OH)) have been isolated from the mild pyrolysis of dichalcogenide ligands, RE-E‘R (R=Ph: E=S, E‘=Se; R=CH2Ph, [2,6-( t Bu)2-C6H2OH]: E=E‘=Se, S) and [(Cp∗Mo)2B4H8], 2, an intermediate generated from the reaction of [Cp∗MoCl4] (1) (Cp∗ =η5-C5Me5), with [LiBH4.thf]. The geometry of [(Cp∗Mo)2B4H5Se(Ph)] is similar to that of [(Cp∗Mo)2B5H9], in which one BH3 unit on the open face is replaced by a triple bridged selenium atom. All the compounds have been characterized in solution by 1H, 11B, 13C NMR and IR spectroscopy and elemental analysis. The structural types were unequivocally established by X-ray crystallographic analysis of compounds 3–5. [Copyright &y& Elsevier]

Abstract: Reaction of [(η5-C5Me5)MCl4], 1–2 (1: M=Mo and 2: W) with six fold excess of [LiBH4·thf] followed by thermolysis with excess chalcogen powders (S, Se and Te) yielded dichalcomolybda- and tungstaboranes, [(η5-C5Me5M)2B4H4E2], 5–8 (5: M=Mo, E=S; 6: M=Mo, E=Se; 7: M=Mo, E=Te; 8: M=W, E=Se) in modest yields. The geometry of 5–8 resembles a hexagonal bipyramid with a missing connectivity of two chalcogen vertices and a very short cross cage metal–metal bonding. All these new dichalcometallaboranes have been characterized by mass, 1H, 11B, 13C NMR spectroscopy, and the structural types were unequivocally established by crystallographic analysis of compound 6. [Copyright &y& Elsevier]

Metal-rich metallaboranes featuring bridging borylene and boride units of various transition metals. [Display omitted] • Metal-rich metallaborane clusters featuring triply/tetra bridging borylene and boride units are reviewed here. • Different structural motifs, bonding and chemistry of these clusters are presented. • Electron counts and spectroscopic and structural comparison have been discussed. Metal-rich metallaborane clusters, having triply and tetra bridging borylenes, and multicentred boride units are demanding renewed interest because of their diverse reactivity and unique structural features. Recent years have witnessed significant progress in the field of metal-rich metallaborane clusters. In spite of high instability of free borylene species, modern synthetic strategies utilizing transition metals have enabled to the isolation of borylene species, particularly as triply bridging borylene species. On the other hand, naked boron 'boride' has been encapsulated inside different types of transition metal and metallaborane clusters. The unique bonding ability of the boron of borylene and boride with multiple transition metals afforded a series of metal-rich metallaboranes. In this review, we have discussed the history of the synthesis of metal-rich clusters containing triply bridging borylene and boride moieties and their structure, bonding, and electron count. The reactivity of these metal-rich metallaboranes toward various substrates has also been discussed. [ABSTRACT FROM AUTHOR]

A new structural analogue of nido -homobimetallahexaborane(10), nido -[3,6-{(OC) 3 Mn} 2 (B 4 H 8 ·THF)], 1 is synthesized (see picture). • Bimtellahexaborane(10) analogue, nido -[3,6-{(OC) 3 Mn} 2 (B 4 H 8 ·thf)], 1 is synthesised. • 1 is a novel homometallic M 2 B 4 cluster known without a M−M bond. • Theoretical calculation indicated the higher relative thermodynamic stability for 1. • Reaction of nido -[1,2-(Cp*Ru) 2 (µ -H)B 4 H 9 ] with borane led to cluster build-up. Cluster nido -[3,6-{(OC) 3 Mn} 2 (B 4 H 8 ·THF)], 1 , (THF = tetrahydrofuran), has been synthesized from the irradiation of [Mn 2 (CO) 10 ] with [BH 3 ·THF] at 255 nm along with [{(OC) 4 Mn}(η 6-B 2 H 6){Mn(CO) 3 } 2 (µ -H)], 2. Cluster 1 represents the new structural analogue of nido -homobimetallahexaborane(10) where the metal centers are arranged symmetrically in the non-adjacent basal positions of a pentagonal pyramid core. Theoretical calculation suggests that nido- 1 is thermodynamically more stable as compared to the other hypothetical possible isomer nido -[4,5-{(OC) 3 Mn} 2 (B 4 H 8 ·THF)], II. Further, the reactivity of another homobimetallahexborane(10), nido -[1,2-(Cp*Ru) 2 (µ -H)B 4 H 9 ], 3 has been explored with borane that led to cluster build-up reaction to yield bimetallaoctaborane(12) analogues, nido -[(Cp*Ru) 2 B 6 H 10 (OH) 2 ], 4 and nido -[(Cp*Ru) 2 B 6 H 11 (OH)], 5. All the clusters have been characterized by multinuclear NMR and IR spectroscopies as well as by mass spectrometric analysis. The structural types of 1 and 4 were unequivocally established by crystallographic analysis. [ABSTRACT FROM AUTHOR]

To build upon our earlier results of heterometallic metallaboranes employing metal carbonyls, we performed the reaction of nido -[(Cp*Rh) 2 B 3 H 7 ] ( 1 ) ( nido - 1 ) with [M(CO) 5 ·THF] (M = Mo or W) that yielded the trimetallic metallaborane clusters [(Cp*Rh) 2 M(CO) 3 (μ-CO)(μ 3 -BH)(B 2 H 4 )] ( 3 : M = Mo; 4 : M = W) having a capped borylene fragment and trimetallic triply bridging borylene complexes [(Cp*Rh) 2 (μ 3 -BH)(μ-CO)M(CO) 5 ] ( 5 : M = Mo; 6 : M = W). The chemistry of trimetallic triply bridging borylene complexes ( 5 and 6 ) were explored with Lewis bases such as tert- butyl isocyanide and bisphosphine ligands. Photolysis of 5 and 6 with tert -butyl isocyanide yielded [(Cp*Rh) 2 (μ 3 -BH)(μ-CO)M(CO) 4 (CN- t Bu)] ( 7 : M = Mo; 8 : M = W) and with phosphines, PPh 2 (CH 2 ) n PPh 2 (n = 1, 2) they resulted in the formation of [(Cp*Rh) 2 (μ 3 -BH)(μ-CO)M(CO) 4 ((PPh 2 ) 2 (CH 2 ) n )] ( 9 : n = 1, M = Mo; 10 : n = 1, M = W; 11 : n = 2, M = Mo; 12 : n = 2, M = W). All the new compounds have been characterized in solution by mass spectrometry and NMR spectroscopic techniques. The structural aspects were unambiguously established by X-ray crystallographic analysis of 3 – 4 and 7 – 10 . [ABSTRACT FROM AUTHOR]

We report the synthesis and structural characterization of moderately air stable metal rich metallaboranes of iridium. Treatment of [Cp*IrCl 2 ] 2 with BH 3 ·thf at high temperature led to the isolation of a trimetallic [ nido -5-(Cp*Ir) 3 B 7 H 11 ], 1 . Compound 1 is isoelectronic and isostructural with decaborane-14 where three BH units in [B 10 H 14 ] 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) 3 B 4 H 4 ], 2 . The geometry of 2 can be viewed as a condensed polyhedron composed of Ir 3 B 3 octahedron capped by a BH unit. 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. 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. [ABSTRACT FROM AUTHOR]

Chloro-rhodaboratrane [(Cp*Rh)(L 2 )BCl] 4 has been synthesized from rhodium N,S-heterocyclic carbene complex [(Cp*Rh)(L 2 )(1-benzothiazol-2-ylidene)], 1 , (L = C 7 H 4 NS 2 ) and borane reagent BHCl 2 .SMe 2 . The Rh B bond in 4 is buttressed between two benzothiazolyl units in [3.3.0] fashion. The presence of B Cl bond allowed us to explore the chemistry of boratrane 4 at the boron centre. The reaction of ethynylmagnesium bromide with 4 yielded η 1 -vinyl complex [Cp*RhBr(C 2 H 2 )L] 5 , containing a five membered metallaheterocycle. In an objective to abstract the chloride, alike borylene synthesis from haloboryl, we performed the reaction of 4 with NaBAr F 4 that resulted the thiolato bridged bimetallic compound [Cp*Rh(μ-L) 3 RhCp*][BAr F 4 ] 6 (Ar F : C 6 H 3 (CF 3 ) 2 -3,5). [ABSTRACT FROM AUTHOR]

Thermolysis of an in situ generated intermediate [(Cp*Ta)2(BH3)2Cl2], 1 generated from the reaction of [Cp*TaCl4], (Cp* = η5-C5Me5) and [LiBH4·thf], in presence of [Ru3(CO)12] yielded pileo-[Cp*TaCl(μ-Cl)-B2H4Ru3(CO)8], 2 having two electrons fewer than seven pairs required for the observed square pyramidal geometry. Cluster 2 is the first example of an unsaturated cluster comprising early and late transition metals in a square pyramid core. This reaction also yielded [(Cp*Ta)2(B2H6)(B2H4Cl2)], 3 as a by-product. In addition, the reaction of [Cp*MoCl4] (Cp* = η5-C5Me5) with [LiBH4.thf] in presence of excess [MeI] at mild condition led to the isolation of periodinated dimolybdatetraborane [(Cp*Mo)2B4H3I5], 4 that hints a possible existence of [(Cp*Mo)2B4H8]. After the isolation of periodinated 4, we extended this chemistry towards the late transition metallaborane [(Cp*Rh)3B4H4], 5 using [PtBr2] as brominating source. Although all the attempts to isolate perbrominated rhodaborane failed, we have isolated partially brominated rhodaborane clusters [(Cp*Rh)3(BH)-(BBr)3], 6 and [(Cp*Rh)3(BH)3(BBr)], 7. All the compounds were characterized by IR and 1H, 11B and 13C NMR spectroscopy in solution, and the solid-state structures of 2, 4 and 6 were established by crystallographic analysis. [ABSTRACT FROM AUTHOR]

Abstract: Reaction of [Cp∗MoCl4] (Cp∗ = η5-C5Me5) with excess of [LiBH4·thf] followed by pyrolysis with NaI yielded B–I inserted [(Cp∗Mo)2B5H9−n I n ], 1–3 (1: n = 1; 2: n = 2; 3: n = 3). In parallel to the formation of 1–3, the reaction also produced known [(Cp∗Mo)2B5H9] and [(Cp∗Mo)2(μ-I)4] in good yields. Under the similar reaction conditions, dimolybdathiaborane [(Cp∗Mo)2B4H4S2] yielded iodine substituted dimolybdathiaboranes, [(Cp∗Mo)2B4S2H4−n I n ], 4 and 5 (4: n = 2; 5: n = 3) in good yields. All the new compounds have been characterized in solution by IR, 1H and 11B NMR as simple substituted derivatives of [(Cp∗Mo)2B5H9] and [(Cp∗Mo)2B4H4S2]. The solid state structures were established unambiguously by crystallographic analysis of compounds 1–5. [Copyright &y& Elsevier]

Room temperature photolysis of a triply-bridged borylene complex, [(μ3-BH)(Cp*RuCO)2(μ-CO)Fe(CO)3] ( 1 a; Cp*=C5Me5), in the presence of a series of alkynes, 1,2-diphenylethyne, 1-phenyl-1-propyne, and 2-butyne led to the isolation of unprecedented vinyl-borylene complexes ( Z)-[(Cp*RuCO)2(μ-CO)B(CR)(CHR′)] ( 2: R, R′=Ph; 3: R=Me, R′=Ph; 4: R, R′=Me). This reaction permits a hydroboration of alkyne through an anti -Markovnikov addition. In stark contrast, in the presence of phenylacetylene, a metallacarborane, closo-[1,2-(Cp*Ru)2(μ-CO)2{Fe2(CO)5}-4-Ph-4,5-C2BH2] ( 5 a), is formed. A plausible mechanism has been proposed for the formation of vinyl-borylene complexes, which is supported by density functional theory (DFT) methods. Furthermore, the calculated 11B NMR chemical shifts accurately reflect the experimentally measured shifts. All the new compounds have been characterized in solution by mass spectrometry and IR, 1H, 11B, and 13C NMR spectroscopies and the structural types were unequivocally established by crystallographic analysis of 2, 5 a, and 5 b. [ABSTRACT FROM AUTHOR]

Thermolysis of an in situ generated intermediate, produced from the reaction of [Cp*MoCl4] (Cp* = η5-C5Me5) and [LiBH4.THF], with excess Te powder yielded isomeric [(Cp*Mo)2B4TeH5Cl] (2 and 3), [(Cp*Mo)2B4(μ3-OEt)TeH3Cl] (4), and [(Cp*Mo)4B4H4(μ4-BH)3] (5). Cluster 4 is a notable example of a dimolybdaoxatelluraborane cluster where both oxygen and tellurium are contiguously bound to molybdenum and boron. Cluster 5 represents an unprecedented metal-rich metallaborane cluster with a cubane core. The dimolybdaheteroborane 2 was found to be very reactive toward metal carbonyl compounds, and as a result, mild pyrolysis of 2 with [Fe2(CO)9] yielded distorted cubane cluster [(Cp*Mo)2(BH)4(μ3-Te){Fe(CO)3}] (6) and with [Co2(CO)8] produced the bicapped pentagonal bipyramid [(Cp*MoCo)2B3H2(μ3-Te)(μ-CO){Co3(CO)6}] (7) and pentacapped trigonal prism [(Cp*MoCo)2B3H2(μ3-Te)(μ-CO)4{Co6(CO)8}] (8). The geometry of 8 is an example of a heterometallic boride cluster in which five Co and one Mo atom define a trigonal prismatic framework. The resultant trigonal prism core is in turn capped by two boron, one Te, and one Co atom. In the pentacapped trigonal prism unit of 8, one of the boron atoms is completely encapsulated and bonded to one molybdenum, one boron, and five cobalt atoms. All the new compounds have been characterized in solution by IR, 1H, 11B, and 13C NMR spectroscopy, and the structural types were unambiguously established by crystallographic analysis of 2 and 4-8. [ABSTRACT FROM AUTHOR]

Abstract: The reaction of an intermediate, generated from [Cp#MoCl4] [Cp# = Cp or Cp∗; Cp = (η 5-C5H5), Cp∗ = (η 5-C5Me5)] and LiBH4.thf, with different chalcogen ligands yielded trimolybdaborane clusters 1–3, [(Cp#Mo)3(μ-H)B8H6X2], (1: Cp# = Cp, X = H; 2: Cp# = Cp∗, X = H; 3: Cp# = Cp∗, X = Cl). Compounds 1–3 constitute an example of an unsaturated (n-4) sep cluster having very close structural similarities. These clusters represent 11-vertex boron-rich metallaboranes containing 66 cluster valence electrons (cve). All the compounds were fully characterized by various spectroscopic techniques, elemental analysis and the solid state structures were unequivocally established by X-ray diffraction analysis of 1–3. [Copyright &y& Elsevier]

The reaction of [Cp*TaCl4], 1 (Cp* = η5-C5Me5), with [LiBH4·THF] at -78 °C, followed by thermolysis in the presence of excess [BH3·THF], results in the formation of the oxatantalaborane cluster [(Cp*Ta)2B4H10O], 2 in moderate yield. Compound 2 is a notable example of an oxatantalaborane cluster where oxygen is contiguously bound to both the metal and boron. Upon availability of 2, a room temperature reaction was performed with [Fe2(CO)9], which led to the isolation of [(Cp*Ta)2B2H4O{H2Fe2(CO)6BH}], 3. Compound 3 is an unusual heterometallic boride cluster in which the [Ta2Fe2] atoms define a butterfly framework with one boron atom lying in a semi-interstitial position. Likewise, the diselenamolybdaborane, [(Cp*Mo)2B4H4Se2], 4 was treated with an excess of [Fe2(CO)9] to afford the heterometallic boride cluster [(Cp*MoSe)2Fe6(CO)13B2(BH)2], 5. The cluster core of 5 consists of a cubane [Mo2Se2Fe2B2] and a tricapped trigonal prism [Fe6B3] fused together with four atoms held in common between the two subclusters. In the tricapped trigonal prism subunit, one of the boron atoms is completely encapsulated and bonded to six iron and two boron atoms. Compounds 2, 3, and 5 have been characterized by mass spectrometry, IR, 1H, 11B, 13C NMR spectroscopy, and the geometric structures were unequivocally established by crystallographic analysis. The density functional theory calculations yielded geometries that are in close agreement with the observed structures. Furthermore, the calculated 11B NMR chemical shifts also support the structural characterization of the compounds. Natural bond order analysis and Wiberg bond indices are used to gain insight into the bonding patterns of the observed geometries of 2, 3, and 5. [ABSTRACT FROM AUTHOR]

Abstract: Reaction of [CpFe(CO)2I], 1 (Cp=η5-C5H5) and di(organyl)dichalcogenides, E2R2 (E=S, Se; R=Ph, CH2Ph, 2,6-( t Bu)2-C6H2OH) with [LiBH4·thf] at −70°C in toluene, followed by stirring at room temperature for 18h yielded heteroferraboranes, [CpFe(CO)B2H4(μ-L)], 2–4 (2: L=SePh; 3: SeCH2Ph and 4: S(2,6-( t Bu)2-C6H2OH). Compounds 2–4 are highly unstable and concurrent lose of boron atoms yielded organochalcogenolato-bridged complexes, [CpFe(CO)(μ-L)]2, 5–7, respectively (5: L=SePh; 6: SeCH2Ph and 7: S(2,6-( t Bu)2-C6H2OH). In contrast, the reaction of 1 with di(2-furyl)ditelluride, (C4H3O)2Te2, yielded organotellurato-bridged complex, [CpFe(CO)(μ-TeC4H3O)]2, 8 and all of our attempts to isolate the boron precursor [CpFe(CO)B2H4(μ-TeC4H3O)] in pure form failed. The accuracy of these predictions in each case is established by IR, 1H, 11B, 13C, 77Se, 125Te NMR and mass spectrometry and complex 8 is further structurally confirmed by X-ray crystallography. [Copyright &y& Elsevier]

Abstract: Reaction of (η5-C5Me5)MoCl4 with 6-fold excess of LiBH4·thf followed by pyrolysis with BHCl2·SMe2 in toluene at 90°C yielded known (η5-C5Me5Mo)2B5H9 (1) and B-Cl inserted (η5-C5Me5Mo)2B5H8Cl (2), (η5-C5Me5Mo)2B5H7Cl2 (3–5, three isomers) and (η5-C5Me5Mo)2B5H5Cl4 (6). In addition, reaction of (η5-C5Me5Mo)2B5H9 with 5-fold excess of n-BuLi followed by excess of MeI in THF yielded B-Me inserted metallaboranes (η5-C5Me5Mo)2B5H7(CH3)2 (7, 8 two isomers) and (η5-C5Me5Mo)2B5H6(CH3)3 (9, 10 two isomers). Isolated yields of 2–6 are poor but 7–10 are modest to good. Compounds 2–10 can be viewed as bicapped closo trigonal bipyramidal geometry. All the new compounds have been characterized in solution by IR, 1H, 11B, 13C NMR and mass spectroscopy as simple substitution derivatives of (η5-C5Me5Mo)2B5H9 and the structural types were unequivocally established by crystallographic analysis of compounds 2, 3, 5 and 6. [Copyright &y& Elsevier]

Examples of transition metal boryl complexes featuring different types of boryl ligand. [Display omitted] • A detailed overview on the recent advances in the field of transition metal boryl complexes has been provided. • Structure and bonding of transition metal boryl complexes and their reactivity have been discussed. • Various organic/organometallic reactions of these species reported by others and us have been summarized. Transition metal (TM) complexes of boron comprising two-center two-electron (2c–2e) bond/s are systematically developed over the decades. Among them, TM boryl complexes (i.e. L n M–BR 2) featuring tri-coordinated boron have been studied extensively because of their unique bonding pattern and diverse reactivity towards organic substrates. These TM boryl complexes were found to be the key intermediates in many catalytic cycles, for example, diboration, hydroboration and C–H borylation reactions. As a result, this field has drawn immense attention in the recent years to develop new molecules. Synthesis and structural characterization of various TM boryl complexes implicitly directed to the isolation of TM complexes containing hitherto unknown structural motif, which could not be isolated in pure main group chemistry. The present review gives a summary of the contemporary progresses for the synthesis and reactivity of various TM boryl complexes reported by others and us. This review offers a detailed discussion on the structure and bonding of the TM boryl complexes. In addition, some of the potential applications of these species in various organic transformations are discussed. [ABSTRACT FROM AUTHOR]

The preparation, characterization, and electronic structure of the first heterometallic μ9-boride cluster [(Cp*Rh)2{Co6(CO)I2}(μ-H)(BH)B)] has been reported. The interstitial boron atom in the title cluster is within the bonding contact of eight metal and one boron atom in a unique tricapped trigonal prism geometry. [ABSTRACT FROM AUTHOR]

Thermolysis of nido- [(Cp*Mo)2B4TeClH5], with an excess of Co2(CO)8 at room temperature, afforded a triple-decker sandwich complex [(Cp*Mo)2{μ-η6:η6-B3H3TeCo2(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. [ABSTRACT FROM AUTHOR]

Diborane(6), diborane(4) and diborene(2) complexes of various transition metals. • Diboranes are valuable compounds for numerous synthetic reactions. • The diborene(2) complexes having boron-boron double bond are sparsely explored unlike alkene complexes. • Diborane(4/6) and diborene(2) complexes stabilized in the coordination sphere of transition metals are reviewed here. • Various synthetic routes for the synthesis of diborane and diborene complexes are discussed. • Photophysical properties of diborene species have been also discussed here. Diborane(4) and diborane(6) molecules are demanding renewed interest due to their varied reactivity towards diverse substrates. The chemistry of molecules comprising electron-precise B-B bonds has witnessed swift developments in the recent years. In spite of the continuous interest and extensive efforts in the synthesis of diborane compounds, the formation of boron-boron bonds is still difficult and uncontrolled. On the other hand, the diborene molecules (R-B B-R′; R, R′ = H, phosphine, amine, NHC etc), are also of significant interest owing to their ability to regulate the property of biradicals by changing the substituents of the parent diborene(2), HB BH. In addition, transition metal diborene species exhibit fascinating photo-physical properties. In this review, we have delivered a background of B-B bond formation and a synopsis of the latest developments in the synthesis of boron-boron single and multiple bonds. The reactivity of diborane/diborene complexes towards various transition metals has also been discussed in detail. [ABSTRACT FROM AUTHOR]

Thermolysis of nido-[(Cp*Mo)2B4TeClH5] with an excess of Co2(CO)8 at room temperature results in two boride clusters [(Cp*Mo-CO)2B3H2(μ3-Te) (μ-CO){Co3(CO)6}] and [(Cp*Mo-CO)2B3H2(μ3-Te) (μ-CO)4{Co6(CO)8}] as major products and a triple-decker sandwich complex [(Cp*Mo)2{.mu±eta.6:η6-B3 H3TeCo2(CO)5}] as a by-product. [ABSTRACT FROM AUTHOR]