Dipak Kumar Roy

Boron Beyond the Icosahedral Barrier: A 16‐Vertex Metallaborane

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.

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

The reaction of [Cp(n)MCl(4-x)] (M=V: n=2, x=2; M=Nb: n=1, x=0; Cp=η(5)-C(5) H(5)) with LiBH(4)⋅THF followed by thermolysis in the presence of dichalcogenide ligands E(2)R(2) (E=S, Te; R=2,6-(tBu)(2)-C(6)H(2)OH, Ph) and 2-mercaptobenzothiazole (C(7)H(5)NS(2)) yielded dimetallaheteroboranes [{CpV(μ-TePh)}(2)(μ(3) -Te)BH⋅thf] (1), [(CpV)(2)(BH(3)S)(2)] (2), [(CpNb)(2)B(4)H(10)S] (3), [(CpNb)(2)B(4)H(11)S(tBu)(2)C(6)H(2)OH] (4), and [(CpNb)(2)B(4)H(11)TePh] (5). In cluster 1, the V(2)BTe 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 V(2)BS tetrahedron clusters. Cluster 3 can be considered as an edge-fused cluster in which a trigonal-bipyramidal unit (Nb(2)B(2)S) has been fused with a tetrahedral core (Nb(2)B(2)) by means of a common Nb(2) edge. In addition, thermolysis of an in-situ-generated intermediate that was produced from the reaction of [Cp(2)VCl(2)] and LiBH(4)⋅THF with excess BH(3)⋅THF yielded oxavanadaborane [(CpV)(2)B(3)H(8)(μ(3)-OEt)] (6) and divanadaborane cluster [(CpV)(2)B(5)H(11)] (7). Cluster 7 exhibits a nido geometry with C(2v) symmetry and it is isostructural with [(Cp*M)(2)B(5)H(9+n)] (M=Cr, Mo, and W, n=0; M=Ta, n=2; Cp*=η(5)-C(5)Me(5)). All of these new compounds have been characterized by (1)H NMR, (11)B NMR, and (13)C NMR spectroscopy and elemental analysis and the structural types were established unequivocally by crystallographic analysis of compounds 1-4, 6, and 7.

Synthesis and Structure of Dirhodium Analogue of Octaborane-12 and Decaborane-14

We present the results of our investigation of a thermally driven cluster expansion of rhodaborane systems with BH(3)·THF. Four novel rhodaborane clusters, for example, nido-[(Cp*Rh)(2)B(6)H(10)], 1; nido-[(Cp*Rh)B(9)H(13)], 2; nido-[(Cp*Rh)(2)B(8)H(12)], 3; and nido-[(Cp*Rh)(3)B(8)H(9)(OH)(3)], 4 (Cp* = η(5)-C(5)Me(5)), have been isolated from the thermolysis of [Cp*RhCl(2)](2) and borane reagents in modest yields. Rhodaborane 1 has a nido geometry and is isostructural with [B(8)H(12)]. The low temperature (11)B and (1)H NMR data demonstrate that compound 1 exists in two isomeric forms. The framework geometry of 2 and 3 is similar to that of [B(10)H(14)] with one BH group in 2 (3-position), and two BH groups in 3 (3, 4-positions) are replaced by an isolobal {Cp*Rh} fragment. The 11 vertex cluster 4 has a nido structure based on the 12 vertex icosahedron, having three rhodium and eight boron atoms. In addition, the reaction of rhodaborane 1 with [Fe(2)(CO)(9)] yielded a condensed cluster [(Cp*Rh)(2){Fe(CO)(3)}(2)B(6)H(10)], 5. The geometry of 5 consists of [Fe(2)B(2)] tetrahedron and an open structure of [(Cp*Rh)(2)B(6)], fused through two boron atoms. The accuracy of these results in each case is established experimentally by spectroscopic characterization in solution and structure determinations in the solid state.

Reactivity of Diruthenium and Dirhodium Analogues of Pentaborane(9): Agostic versus Boratrane Complexes

A series of novel Cp*-based (Cp*=η(5)-C5Me5) 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).

Supraicosahedral polyhedra in metallaboranes: synthesis and structural characterization of 12-, 15-, and 16-vertex rhodaboranes.

Syntheses and structural characterization of supraicosahedral rhodaborane clusters are reported. Reaction of [(Cp*RhCl2)2], (Cp* = η(5)-C5Me5) with [LiBH4·thf] followed by thermolysis with excess of [BH3·thf] afforded 16-vertex closo-[(Cp*Rh)3B12H12Rh{Cp*RhB4H9}], 1, 15-vertex [(Cp*Rh)2B13H13], 2, 12-vertex [(Cp*Rh)2B10Hn(OH)m], (3a: n = 12, m = 0; 3b: n = 9, m = 1; 3c: n = 8, m = 2) and 10-vertex [(Cp*Rh)3B7H7], 4, and [(Cp*Rh)4B6H6], 5. Cluster 1 is the unprecedented 16-vertex cluster, consists of a sixteen-vertex {Rh4B12} with an exo-polyhedral {RhB4} moiety. Cluster 2 is the first example of a carbon free 15-vertex supraicosahedral metallaborane, exhibits icosihexahedron geometry (26 triangular faces) with three degree-six vertices. Clusters 3a-c have 12-vertex isocloso geometry, different from that of icosahedral one. Clusters 4 and 5 are attributed to the 10-vertex isocloso geometry based on 10-vertex bicapped square antiprism structure. In addition, quantum-chemical calculations with DFT methods at the BP86 level of theory have been used to provide further insight into the electronic structure and stability of the optimized structures which are in satisfactory agreement with the structure determinations. 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 compounds 1-5.

New Routes to a Series of σ-Borane/Borate Complexes of Molybdenum and Ruthenium

A series of agostic σ-borane/borate complexes have been synthesized and structurally characterized from simple borane adducts. A room-temperature reaction of [Cp*Mo(CO)3 Me], 1 with Li[BH3 (EPh)] (Cp*=pentamethylcyclopentadienyl, E=S, Se, Te) yielded hydroborate complexes [Cp*Mo(CO)2 (μ-H)BH2 EPh] in good yields. With 2-mercapto-benzothiazole, an N,S-carbene-anchored σ-borate complex [Cp*Mo(CO)2 BH3 (1-benzothiazol-2-ylidene)] (5) was isolated. Further, a transmetalation of the B-agostic ruthenium complex [Cp*Ru(μ-H)BHL2 ] (6, L=C7 H4 NS2 ) with [Mn2 (CO)10 ] affords a new B-agostic complex, [Mn(CO)3 (μ-H)BHL2 ] (7) with the same structural motif in which the central metal is replaced by an isolobal and isoelectronic [Mn(CO)3 ] unit. Natural-bond-orbital analyses of 5-7 indicate significant delocalization of the electron density from the filled σBH orbital to the vacant metal orbital.

Chemistry of Diruthenium and Dirhodium Analogues of Pentaborane(9): Synthesis and Characterization of Metal N,S‐Heterocyclic Carbene and B‐Agostic Complexes

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* = η(5)-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.

New Heteronuclear Bridged Borylene Complexes That Were Derived from [{Cp*CoCl}2] and Mono-MetalCarbonyl Fragments†

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)(n)PPh2] (n=1-3) yielded complexes 9-11, [3,4-(Ph2P(CH2)(n)PPh2)-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 (1)H, (13)C, and (11)B NMR spectroscopy and their structural types were unequivocally established by crystallographic analysis of complexes 1, 2, 4, 9, and 10.

Chemistry of N,S‐Heterocyclic Carbene and Metallaboratrane Complexes: A New η3‐BCC‐Borataallyl Complex

A high-yielding synthetic route for the preparation of group 9 metallaboratrane complexes [Cp*MBH(L)2], 1 and 2 (1, M=Rh, 2, M=Ir; L=C7H4NS2) has been developed using [{Cp*MCl2}2] as precursor. This method also permitted the synthesis of an Rh-N,S-heterocyclic carbene complex, [(Cp*Rh)(L2)(1-benzothiazol-2-ylidene)] (3; L=C7H4NS2) in good yield. The reaction of compound 3 with neutral borane reagents led to the isolation of a novel borataallyl complex [Cp*Rh(L)2B{CH2C(CO2Me)}] (4; L=C7H4NS2). Compound 4 features a rare η(3)-interaction between rhodium and the B-C-C unit of a vinylborane moiety. Furthermore, with the objective of generating metallaboratranes of other early and late transition metals through a transmetallation approach, reactions of rhoda- and irida-boratrane complexes with metal carbonyl compounds were carried out. Although the objective of isolating such complexes was not achieved, several interesting mixed-metal complexes [{Cp*Rh}{Re(CO)3}(C7H4NS2)3] (5), [Cp*Rh{Fe2(CO)6}(μ-CO)S] (6), and [Cp*RhBH(L)2W(CO)5] (7; L=C7H4NS2) have been isolated. All of the new compounds have been characterized in solution by mass spectrometry, IR spectroscopy, and (1)H, (11)B, and (13)C NMR spectroscopies, and the structural types of 4-7 have been unequivocally established by crystallographic analysis.

A Novel Heterometallic μ9-Boride Cluster: Synthesis and Structural Characterization of [(η5-C5Me5Rh)2{Co6(CO)12}(μ-H)(BH)B]

The preparation, characterization, and electronic structure of the first heterometallic μ9-boride cluster [(Cp*Rh)2{Co6(CO)12}(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.