Dimetallaheteroborane clusters containing group 16 elements: A combined experimental and theoretical study

Recently we described the synthesis and structural characterization of various dimetallaherteroborane clusters, namely nido-[(Cp∗Mo2B4EClxH6−x], 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 [(Cp∗Mo)2B4H6EFe(CO)3] (4: E = S, 6: E = Te) reported earlier, reaction of 2 with [ Fe2(CO)9] yielded mixed-metallaselenaborane [(Cp∗Mo)2B4H6SeFe(CO)3], 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

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

Cluster expansion reactions of cobaltaboranes were carried out using mono metal-carbonyls, metal halides and dichalcogenide ligands. Thermolysis of an in situ generated intermediate, obtained from the reaction of [Cp*CoCl]₂ (Cp* = C₅Me₅) and [LiBH₄·thf], with three equivalents of [Mo(CO)₃(CH₃CN)₃] followed by the reaction with methyl iodide yielded isocloso-[(Cp*Co)₃B₆H₇Co(CO)₂] (1) and closo-[(Cp*Co)₂B₂H₅Mo₂(CO)₆I] (2). Cluster 1 is ascribed to the isocloso structure based on a 10-vertex bicapped square antiprism geometry. In a similar manner, the reaction of [Cp*CoCl]₂ with [LiBH₄·thf] and the dichalcogenide ligand RS–SR (R = 1-OH-2,6-(tBu)₂-C₆H₂) yielded nido cluster [(Cp*Co)₂B₂H₂S₂] (3). In parallel with the formation of the compounds 1–3, these reactions also yielded known cobaltaboranes [(Cp*Co)₂B₄H₆] (4) and [(Cp*Co)₃B₄H₄] in good yields. After the isolation of compound 4 in good yield, we verified its reactivity with PtBr₂, which yielded closo-[(Cp*Co)₂B₄H₂Br₄] (5). To the best of our knowledge this is the second perhalogenated metallaborane cluster which has been recognized. All the new compounds were characterized by elemental analysis, IR, ¹H, ¹¹B and ¹³C NMR spectroscopy, and the geometric structures were unequivocally established by the X-ray diffraction analysis of compounds 1, 2, 3 and 5. Geometries obtained from the electronic structure calculations employing density functional theory (DFT) are in close agreement with the solid state X-ray structures. In addition, we analyzed the variation in the stability of the model compounds 1′ (1′: Cp analogue of 1, Cp = C₅H₅), [(CpCo)₄B₆H₆] (1a) and [(CpRh)₄B₆H₆] (1b)

First-row transition-metal-diborane and -borylene complexes

A combined experimental and quantum chemical study of Group 7 borane, trimetallic triply bridged borylene and boride complexes has been undertaken. Treatment of [{Cp*CoCl}₂] (Cp*=1,2,3,4,5-pentamethylcyclopentadienyl) with LiBH₄⋅thf at −78 °C, followed by room-temperature reaction with three equivalents of [Mn₂ (CO)₁₀] yielded a manganese hexahydridodiborate compound [{(OC)₄Mn}(η⁶-B₂H₆){Mn(CO)₃}₂ (μ-H)] (1) and a triply bridged borylene complex [(μ₃-BH)(Cp*Co)₂ (μ-CO)(μ-H)₂MnH(CO)₃] (2). In a similar fashion, [Re₂ (CO)₁₀] generated [(μ₃-BH)(Cp*Co)₂(μ-CO)(μ-H)₂ReH(CO₎₃] (3) and [(μ₃-BH)(Cp*Co)₂ (μ-CO)₂ (μ-H)Co(CO)₃] (4) in modest yields. In contrast, [Ru₃ (CO)₁₂] under similar reaction conditions yielded a heterometallic semi-interstitial boride cluster [(Cp*Co)(μ-H)₃Ru₃(CO)₉B] (5). The solid-state X-ray structure of compound 1 shows a significantly shorter boron–boron bond length. The detailed spectroscopic data of 1 and the unusual structural and bonding features have been described. All the complexes have been characterized by using ¹H, ¹¹B, ¹³C NMR spectroscopy, mass spectrometry, and X-ray diffraction analysis. The DFT computations were used to shed light on the bonding and electronic structures of these new compounds. The study reveals a dominant B[BOND]H[BOND]Mn, a weak B[BOND]B[BOND]Mn interaction, and an enhanced B[BOND]B bonding in 1

Hypoelectronic metallaboranes: Synthesis, structural characterization and electronic structures of metal-rich cobaltaboranes

Reaction of [Cp∗CoCl]2 (Cp∗ = η5-C5Me5) with [LiBH4·THF] in toluene at −70 °C, followed by thermolysis with 2-mercaptobenzothiazole (C7H5NS2) in boiling toluene led to the isolation of a range of cobaltaborane clusters, [(Cp∗Co)2B7H6OMe], 1; [(Cp∗Co)3B8H7R], 2a, b (2a: R = H; 2b: R = Me); [(Cp∗Co) 3B8H8S], 3 and [(Cp∗Co)2B4H4RR′], 4a–d (4a: R, R′ = H; 4b: R = Me, R′ = H; 4c: R = H, R′ = Me and 4d: R, R′ = Me). In parallel to the formation of compounds 1–4, the reaction also yielded known [(Cp∗Co)3B4H4] in good yield. Compound 1 may be considered as 9-vertex hypoelectronic cluster with C1 symmetry, where cobalt atoms occupy the degree 5 vertices. All the dicobaltaboranes 4a–d contains two μ3-H protons and found to be very reactive. As a result, one of them (4a) when reacted with Fe2(CO)9 and sulfur powder yielded, almost immediately, [(Cp∗Co)2B4H5SFe3(CO)9], 5 and [(Cp∗Co)2B3H3(μ-CO)Fe(CO)3], 6. All the new compounds have been characterized in solution by mass, 1H, 11B, 13C NMR spectroscopy and elemental analysis. The structural types were unequivocally established by X-ray crystallographic analysis of compounds 1–6. Density functional theory (DFT) calculations on the model compounds 1′ and 2′ (1′, and 2′ are the Cp analog of 1, and 2a respectively, Cp = C5H5) yield geometries in agreement with the structure determinations. The existence of large HOMO–LUMO gap of these molecules rationalizes the isocloso description for 2a. Bonding patterns in the structure have been analyzed on the grounds of DFT calculations

Synthesis, characterization and electronic structures of Rh and Co analogs of Decaborane-14

We report the synthesis, isolation and structural characterization of several crystalline, moderately air stable nido-metallaboranes which represent novel metal rich open cage systems. The reaction of [Cp*CoCl]2, (Cp* = η5-C5Me5), with [LiBH4·thf] in toluene at −78 °C, followed by thermolysis with [BH3·thf] in boiling toluene yielded clusters, [(Cp*Co)3B6H8O] (1) and [(Cp*Co)2B8H11Me] (2). Under the similar reaction condition, [Cp*RhCl2]2 yielded [(Cp*Rh)3B7H11] (3) and [(Cp*Rh)2B8H12] (4). All the new compounds, 1–4 have been characterized by elemental analysis, IR, 1H, 11B, 13C NMR spectroscopy, and the geometric structures were unequivocally established by X-ray diffraction analysis of compound 1–4. Quantum chemical calculation by using density functional theory method is implemented on model compounds 1′–4′ (1′–4′ are the Cp analogs of 1–4 respectively, Cp = C5H5) and yields geometries in agreement with the X-ray detaermined geometries. Large HOMO–LUMO gaps are in tally with the higher stabilities of 1′ and 3′

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