Metal-metal bonds are found in wide varieties of dinuclear and polynuclear species with or without bridging ligands. This chapter reviews the synthesis, structure, and reactivity of distinct group 5 metal-metal bonded dinuclear and coordinatively unsaturated organodimetallic complexes. In spite of a large amount of work in the area of divanadium compounds-preparation, nonorganometallic metal-metal bonded divanadium complexes are limited due to the absence of suitable metal-metal bonded divanadium precursors. The area of niobium hydride chemistry continues to be an extremely important area. It has been observed that hydrides, supported by bulky aryloxo ligands, catalyze homogenous hydrogenation of arenes. The field of hydride complexes of Ta is a prosperous area in organometallic chemistry. Recent progress has shown that electrophilic mono-and binuclear tantalum hydride complexes are capable of reducing CO and N2, whereas the alkyl/aryl complexes are important in organic and organometallic chemistry. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA.

Sundargopal Ghosh

Department Of Chemistry

Chemical bonds

Hydrides

Ligands

Metals

Niobium compounds

Organometallics

Synthesis (chemical)

Vanadium Compounds

CO-ORDINATIVELY UNSATURATED

Hydride complexes

METAL-METAL BONDS

MONO AND BINUCLEAR

NIOBIUM COMPLEXES

Organometallic chemistry

TANTALUM COMPLEXES

VANADIUM COMPLEXES

Tantalum compounds

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Molecular Metal-Metal Bonds: Compounds, Synthesis, Properties

Treatment of group 5 metal polychlorides such as [CpnMCl 4-x] (M = Nb: n = 1, x = 0; M = V: n, x = 2), (Cp = η5-C5H5) with [LiBH4·THF] followed by thermolysis in presence of diphenyl dichalcogenide ligands, E 2Ph2 (E = Se or Te) yielded dimetallaheteroborane clusters [(CpNb)2BH(Se)4], 1 and [(CpV)2B 3H9(μ3-Te)], 2 in modest yields. Compound 1 can be considered as an edge fused cluster in which a trigonal bipyramidal unit [Nb2Se2B] has been fused with a tetrahedral core [Nb 2Se2] by means of a common [Nb2] edge. Compound 2 can be described as a dimetallaheteroborane built from two edge-fused V 2B2 tetrahedra, in which one of the BH3 units is replaced by an isoelectronic Te ligand. All the compounds have been characterized by mass spectrometry, 1H, 11B, 13C, 51V and 77Se NMR spectroscopy. In addition the geometry of compound 1 has been established by crystallographic analysis. © 2012 Elsevier B.V. All rights reserved.

Journal of Organometallic Chemistry

Synthesis and structural characterization of group 5 dimetallaheteroboranes

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)nPPh 2)-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. Love can build a bridge: The thermolysis of [M(CO)3(MeCN)3] (M=W, Mo, Cr) with an in situ generated cobaltaborane that was obtained from [{Cp*CoCl}2] and [LiBH4×THF] yielded heterometallic bridged borylenes [(μ3-BH)(Cp*Co) 2(μ-CO)M(CO)5] (see figure). © 2013 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.

Chemistry - A European Journal

New heteronuclear bridged borylene complexes that were derived from [{Cp*CoCl}2] and mono-metal-carbonyl fragments

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. Unique metal-borylene complexes: Photolysis of a triply bridged borylene complex [(μ3-BH) (Cp*RuCO)2(μ-CO)Fe(CO)3] (Cp*= η5-C5Me5) with various internal alkynes led to hydroboration yielding new vinyl-borylene complexes (see figure). A plausible mechanism has been proposed for the formation of vinyl-borylene complexes, which is supported by density functional theory (DFT) methods. Copyright © 2013 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.

Syntheses and characterization of new vinyl-borylene complexes by the hydroboration of alkynes with [(μ3-BH)(Cp*RuCO) 2(μ-CO)Fe(CO)3]

The recently discovered ditantalaboranes Cp 2Ta 2B nH n+6 (n = 4, 5) are isoelectronic with the previously discovered dimetallaboranes Cp 2M 2B nH n+4 of the group 6 metals Cr, Mo, and W where Cp = η 5-cyclopentadienyl or substituted cyclopentadienyl. Their oblatonido polyhedral structures can be derived from the oblate (flattened) deltahedra of the oblatocloso dirhenaboranes Cp 2Re 2B n+1H n+1 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 Cp 2Ta 2B nH n+6 (n = 4, 5) and Cp 2M 2B nH n+4 (M=Cr, Mo, W). However, the synthesis of Cp 2Ta 2B nH n+6 (n = 4, 5) from CpTaCl 4 + LiBH 4/BH 3 also gives a less-reduced product Cp 2Ta 2Cl 2B 5H 11 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 Cp 2Ta 2B 4H 10 have the favorable degree or 5. © 2012 Springer-Verlag.

Theoretical Chemistry Accounts

Chemical bonding in oblatonido ditantalaboranes and related compounds

The reaction of [CpnMCl4-x] (M=V: n=2, x=2; M=Nb: n=1, x=0; Cp=Î·5-C5H5) with LiBH4·THF followed by thermolysis in the presence of dichalcogenide ligands E2R2 (E=S, Te; R=2,6-(tBu) 2-C6H2OH, Ph) and 2-mercaptobenzothiazole (C7H5NS2) yielded dimetallaheteroboranes [{CpV(μ-TePh)}2(μ3-Te)BH·thf] (1), [(CpV)2(BH3S)2] (2), [(CpNb)2B 4H10S] (3), [(CpNb)2B4H 11S(tBu)2C6H2OH] (4), and [(CpNb)2B4H11TePh] (5). In cluster 1, the V2BTe atoms define a tetrahedral framework in which the boron atom is linked to a THF molecule. Compound 2 can be described as a dimetallathiaborane that is built from two edge-fused V2BS tetrahedron clusters. Cluster 3 can be considered as an edge-fused cluster in which a trigonal-bipyramidal unit (Nb2B2S) has been fused with a tetrahedral core (Nb2B2) by means of a common Nb2 edge. In addition, thermolysis of an in-situ-generated intermediate that was produced from the reaction of [Cp2VCl2] and LiBH 4·THF with excess BH3·THF yielded oxavanadaborane [(CpV)2B3H8(μ3- OEt)] (6) and divanadaborane cluster [(CpV)2B5H 11] (7). Cluster 7 exhibits a nido geometry with C2v symmetry and it is isostructural with [(Cp*M)2B 5H9+n] (M=Cr, Mo, and W, n=0; M=Ta, n=2; Cp*=Î·5-C5Me5). All of these new compounds have been characterized by 1H NMR, 11B NMR, and 13C NMR spectroscopy and elemental analysis and the structural types were established unequivocally by crystallographic analysis of compounds 1-4, 6, and 7. Group 5 alive: Divanadatellura- and divanadathiaboranes were obtained from the treatment of Group 5 metal polychlorides with dichalcogenides and monoboranes. The treatment of [Cp2VCl2] with monoboranes yielded an oxavanadaborane and a divanadaborane (see structures). Copyright © 2012 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.

Synthesis and structural characterization of new divanada- and diniobaboranes containing chalcogen atoms

Group 5 Metal-Metal Bonds

Journal	Data powered by TypesetMolecular Metal-Metal Bonds: Compounds, Synthesis, Properties
Publisher	Data powered by TypesetWiley Blackwell
Open Access	No