Chlorinated Hypoelectronic Dimetallaborane Clusters: Synthesis, Characterization, and Electronic Structures of (η5-C5Me5W)2B5HnClm (n = 7, m = 2 and n = 8, m = 1)

Heterometallic Triply-Bridging Bis-Borylene Complexes

Triply-bridging bis-{hydrido(borylene)} and bis-borylene species of groups 6, 8 and 9 transition metals are reported. Mild thermolysis of [Fe₂ (CO)₉ ] with an in situ produced intermediate, generated from the low-temperature reaction of [Cp*WCl₄ ] (Cp*=η⁵ -C₅ Me₅ ) and [LiBH₄ ⋅THF] afforded triply-bridging bis-{hydrido(borylene)}, [(μ₃ -BH)₂ H₂ {Cp*W(CO)₂ }₂ {Fe(CO)₂ }] (1) and bis-borylene, [(μ₃ -BH)₂ {Cp*W(CO)₂ }₂ {Fe(CO)₃ }] (2). The chemical bonding analyses of 1 show that the B-H interactions in bis-{hydrido (borylene)} species is stronger as compared to the M-H ones. Frontier molecular orbital analysis shows a significantly larger energy gap between the HOMO-LUMO for 2 as compared to 1. In an attempt to synthesize the ruthenium analogue of 1, a similar reaction has been performed with [Ru₃ (CO)₁₂ ]. Although we failed to get the bis-{hydrido(borylene)} species, the reaction afforded triply-bridging bis-borylene species [(μ₃ -BH)₂ {WCp*(CO)₂ }₂ {Ru(CO)₃ }] (2'), an analogue of 2. In search for the isolation of bridging bis-borylene species of Rh, we have treated [Co₂ (CO)₈ ] with nido-[(RhCp*)₂ (B₃ H₇ )], which afforded triply-bridging bis-borylene species [(μ₃ -BH)₂ (RhCp*)₂ Co₂ (CO)₄ (μ-CO)] (3). All the compounds have been characterized by means of single-crystal X-ray diffraction study; ¹ H, ¹¹ B, ¹³ C NMR spectroscopy; IR spectroscopy and mass spectrometry.

A combined experimental and theoretical study of bimetallic bis- and tris-homocubane analogues

Various bimetallic bis- and tris-homocubane analogues of group 9 transition metals have been isolated and structurally characterized employing Li[BH₂E₃] (E = S or Se).

Synthesis, Structures and Chemistry of the Metallaboranes of Group 4–9 with M2B5 Core Having a Cross Cluster M–M Bond

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.

Use of Single-Metal Fragments for Cluster Building: Synthesis, Structure, and Bonding of Heterometallaboranes

The synergic property of the CO ligand, in general, can stabilize metal complexes at lower oxidation states. Utilizing this feature of the CO ligand, we have recently isolated and structurally characterized a highly fluxional molybdenum complex [{Cp*Mo(CO)₂}₂{μ-η²:η²-B₂H₄}] (2; Cp* = η⁵-C₅Me₅) comprising the diborane(4) ligand. Compound 2 represents a rare class of bimetallic diborane(4) complex corresponding to a singly bridged C _s structure. In an attempt to isolate the tungsten analogue of 2, [{Cp*W(CO)₂}₂{μ-η²:η²-B₂H₄}], we have isolated a rare vertex-fused cluster, [(Cp*W)₃WB₉H₁₈] (5). Having a structural likeness with the dimolybdenum alkyne complex [{CpMo(CO)₂}₂C₂H₂], we have further explored the chemistry of 2 with CO gas that yielded a homoleptic trimolybdenum complex, [(Cp*Mo)₃(μ-H)₂(μ₃-H)(μ-CO)₂B₄H₄] (4). In an attempt to replace the 16-electron {Cp*MoH(CO)₂} moiety in 4 with isolobal fragment {W(CO)₅}, we treated the intermediate, obtained from the reaction of Cp*MoCl₄ and LiBH₄, with the monometal carbonyl fragment {W(CO)₅·THF}. The reaction indeed yielded two bimetallic clusters, [(Cp*Mo)₂B₄H₈W(CO)₄] (7) and [(Cp*Mo)₂B₄H₆W(CO)₅] (8), that seem to have been generated by the replacement of one {BH} or {BH₃} vertex from [(Cp*Mo)₂B₅H₉], respectively. All of the compounds have been characterized by various spectroscopic analyses and single-crystal X-ray diffraction studies. Electron-counting rules and molecular orbital analyses provided further insight into the electronic structure of all of these molecules.

Synthesis of Trithia-Borinane Complexes Stabilized in Diruthenium Core: [(Cp*Ru)2(η1-S)(η1-CS){(CH2)2S3BR}] (R = H or SMe)

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.

Hypoelectronic 8-11-Vertex Irida- and Rhodaboranes

A series of novel isocloso-diiridaboranes [(Cp*Ir)2B6H6], 1, 2; [1,7-(Cp*Ir)2B8H8], 4; [1,4-(Cp*Ir)2B8H8], 5; [(Cp*Ir)2B9H9], 8; isonido-[(Cp*Ir)2B7H7], 3; and 10-vertex cluster [5,7-(Cp*Ir)2B8H12], 6 (Cp* = η(5)-C5Me5) have been isolated and structurally characterized from the pyrolysis of [Cp*IrCl2]2 and BH3·thf. On the other hand, the corresponding rhodium system afforded 10- and 11-vertices clusters [5-(Cp*Rh)B9H13)], 7, and [(Cp*Rh)2B9H9], 9, respectively. Clusters 1 and 2 are topological isomers. The geometry of 1 is dodecahedral, similar to that of its parent borane [B8H8](2-), in which two of the [BH] vertices are replaced by two [Cp*Ir] fragments. The geometry of 2 can be derived from a nine-vertex tricapped trigonal prism by removing one of the capped vertices. Compounds 4 and 5 are 10-vertex isocloso clusters based on a 10-vertex bicapped square antiprism structure. The only difference between them is the presence of a metal-metal bond in 5. The solid-state structures of 8 and 9 attain an 11-vertex geometry in which a unique six-membered B6H6 moiety is bonded to the metal center. In addition, quantum-chemical calculations have been used to provide further insight into the electronic structure and stability of the clusters. 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.

Hypo-electronic triple-decker sandwich complexes: synthesis and structural characterization of [(Cp*Mo)2{μ–η6:η6-B4H4E-Ru(CO)3}] (E = S, Se, Te or Ru(CO)3 and Cp* = η5-C5Me5)

Electron-poor triple-decker complexes, [(Cp*Mo)₂{μ–η⁶:η⁶-B₄H₄ERu(CO)₃}] (E = S, Se, Te, Ru(CO)₃) with hexagonal bridging ring composed of boron, ruthenium and chalcogen atoms.

Reactivity of cyclopentadienyl transition metal(ii) complexes with borate ligands: structural characterization of the toluene-activated molybdenum complex [Cp*Mo(CO)2(η3-CH2C6H5)]

Unprecedented formation of a toluene activated complex, [Cp*Mo(CO)₂(CH₂C₆H₅)], in an η³-fashion was elucidated by the reaction of [Cp*Mo(CO)₃Cl] with [NaBt₂].

Homometallic Cubane Clusters: Participation of Three-Coordinated Hydrogen in 60-Valence Electron Cubane Core

This work describes the synthesis, structural characterizations, and electronic structures of a series of novel homometallic cubane clusters [(Cp*Ru)2{Ru(CO)2}2BH(μ3-E)(μ-H)B(μ-H)3M], (2, M = Cp*Ru, E = CO; 3, M = Ru(Cp*Ru)2(μ-CO)3(μ-H)BH), E = BH), [(Cp*Ru)3(μ3-CO)(BH)3(μ3-H)3], 4, and [(Cp*Ru)2(μ3-CO){Ru(CO)3}2(BH)2(μ-H)B], 5 (Cp* = η(5)-C5Me5). These cubane clusters have been isolated from a thermally driven reaction of diruthenium analogue of pentaborane(9) [(Cp*RuH)2B3H7], 1, and [Ru3(CO)12]. Structural and spectroscopic studies revealed the existence of triply bridged hydrogen (μ3-H) atoms that participate as a vertex in the cubane core formation for compounds 2, 3, and 4. In addition, the crystal structure of these clusters clearly confirms the presence of an electron precise borane ligand (borylene fragment) which is triply bridged to the trimetallic units. Bonding of these novel complexes has been studied computationally by DFT methods, and the studies demonstrate that the cubane clusters 2 and 3 possess 60 cluster valence electrons (cves) with six metal-metal bonds. All the new compounds have been characterized in solution by mass spectrometry; IR; and (1)H, (11)B, and (13)C NMR studies, and the structural types were unequivocally established by crystallographic analysis of compounds 2-5.

Synthesis, characterization and crystal structure analysis of cobaltaborane and cobaltaheteroborane clusters

A novel class of cobaltaborane and cobaltaheteroborane clusters, isocloso-[(Cp*Co)₃B₆H₇Co(CO)₂], closo-[(Cp*Co)₂B₂H₅Mo₂(CO)₆I], nido-[(Cp*Co)₂B₂H₂S₂], and closo-[(Cp*Co)₂B₄H₂Br₄] were investigated (see picture).