Carbon Insertion into <i>arachno-</i>6,9‑C₂B₈H₁₄ via Acyl Chlorides. Skeletal Alkylcarbonation (SAC) Reactions: A New Route for Tricarbollides

Reactions between <i>arachno</i>-6,9-C₂B₈H₁₄ (<b>1</b>) and selected acyl chlorides, RCOCl, in the presence of PS (PS = “proton sponge”, 1,8-dimethylamino naphthalene) in CH₂Cl₂ for 24 h at reflux, followed by in situ acidification with concentrated H₂SO₄ at 0 °C, generate a series of neutral alkyl and aryl tricarbollides 8-R-<i>nido</i>-7,8,9-C₃B₈H₁₁ (<b>2</b>) (where R = CH₃, <b>2a</b>; C₂H₅, <b>2b</b>; <i>n</i>-C₄H₉, <b>2c</b>; C₆H₅, <b>2d</b>; 4-Cl-C₆H₄, <b>2e</b>; 4-Br-C₆H₄, <b>2f</b>; 4-I-C₆H₄, <b>2g</b>; 1-C₁₀H₇, <b>2h</b>; and 2-C₁₀H₇, <b>2i</b>). The best yields were achieved for aryl derivatives (80–95%) while the yields of the corresponding alkyl substituted compounds are lower (60–70%). These skeletal alkylcarbonation (SAC) reactions are consistent with an aldol-type condensation between the RCO group and open-face hydrogen atoms on the dicarbaborane <b>1</b>, which is associated with the insertion of the carbonyl carbon atom into the structure of <i>arachno</i>-6,9-C₂B₈H₁₄ (<b>1</b>) under elimination of three extra hydrogen atoms as H₂O and HCl. The reactions thus result in an effective R–tricarbaborane cross-coupling. Individual compounds of structure <b>2</b> have been purified by chromatography on a silica gel support, using hexane as the mobile phase (<i>R</i>_F = ∼0.3). Deprotonation agents, such as NEt₃, NaOH, NaH, etc., convert tricarbaboranes <b>2</b> into the corresponding conjugated anions [8-R-<i>nido</i>-7,8,9-C₃B₈H₁₀]⁻ (<b>2</b>^–) which were isolated as salts with suitable countercations (for example, Et₃NH⁺, Tl⁺, NEt₄⁺, etc.). The compounds have been characterized by multinuclear (¹¹B, ¹H, and ¹³C) NMR spectroscopy, mass spectrometry, and elemental analyses. The structures of anions [8-R-<i>nido</i>-7,8,9-C₃B₈H₁₀]¯ (where R = C₆H₅, 4-I-C₆H₄ and 1-C₁₀H₇; <b>2a^–</b>, <b>2g^–</b>, and <b>2h</b>^–) and that of the neutral 8-(1-C₁₀H₇)-<i>nido</i>-7,8,9-C₃B₈H₁₁ (<b>2h</b>) have been established by X-ray diffraction analyses

Effect of the Substitution on the Protonation of Allyl Cyclopentadienyl Molybdenum(II) Compounds

Synthesis, characterization, and reactivity of new allyl cyclopentadienyl molybdenum­(II) compounds [(η³-C₃H₄R¹)­(η⁵-C₅H₃(R²)₂)­Mo­(CO)₂] (R¹ = H, COOMe; R² = COOMe, CONH^<i>t</i>Bu) are reported. Although these compounds are structural analogues of [(η³-C₃H₅)­(η⁵-Cp)­Mo­(CO)₂], their reactivity is very different. While protonation of [(η³-C₃H₅)­(η⁵-Cp)­Mo­(CO)₂] gives a cationic cyclopentadienyl complex, the presented compounds give cationic allyl complexes [(η³-C₃H₄R)­Mo­(CO)₂(NCMe)₃]­[BF₄] (R = H, COOMe) or stable cationic allyl cyclopentadienyl complexes. The theoretical calculations have shown that this behavior is a result of high affinity of the functional groups in the cyclopentadienyl ligand toward protonation

Effect of the Substitution on the Protonation of Allyl Cyclopentadienyl Molybdenum(II) Compounds

Synthesis, characterization, and reactivity of new allyl cyclopentadienyl molybdenum­(II) compounds [(η³-C₃H₄R¹)­(η⁵-C₅H₃(R²)₂)­Mo­(CO)₂] (R¹ = H, COOMe; R² = COOMe, CONH^<i>t</i>Bu) are reported. Although these compounds are structural analogues of [(η³-C₃H₅)­(η⁵-Cp)­Mo­(CO)₂], their reactivity is very different. While protonation of [(η³-C₃H₅)­(η⁵-Cp)­Mo­(CO)₂] gives a cationic cyclopentadienyl complex, the presented compounds give cationic allyl complexes [(η³-C₃H₄R)­Mo­(CO)₂(NCMe)₃]­[BF₄] (R = H, COOMe) or stable cationic allyl cyclopentadienyl complexes. The theoretical calculations have shown that this behavior is a result of high affinity of the functional groups in the cyclopentadienyl ligand toward protonation

Carbon Insertion into <i>arachno-</i>6,9‑C₂B₈H₁₄ via Acyl Chlorides. Skeletal Alkylcarbonation (SAC) Reactions: A New Route for Tricarbollides

Reactions between <i>arachno</i>-6,9-C₂B₈H₁₄ (<b>1</b>) and selected acyl chlorides, RCOCl, in the presence of PS (PS = “proton sponge”, 1,8-dimethylamino naphthalene) in CH₂Cl₂ for 24 h at reflux, followed by in situ acidification with concentrated H₂SO₄ at 0 °C, generate a series of neutral alkyl and aryl tricarbollides 8-R-<i>nido</i>-7,8,9-C₃B₈H₁₁ (<b>2</b>) (where R = CH₃, <b>2a</b>; C₂H₅, <b>2b</b>; <i>n</i>-C₄H₉, <b>2c</b>; C₆H₅, <b>2d</b>; 4-Cl-C₆H₄, <b>2e</b>; 4-Br-C₆H₄, <b>2f</b>; 4-I-C₆H₄, <b>2g</b>; 1-C₁₀H₇, <b>2h</b>; and 2-C₁₀H₇, <b>2i</b>). The best yields were achieved for aryl derivatives (80–95%) while the yields of the corresponding alkyl substituted compounds are lower (60–70%). These skeletal alkylcarbonation (SAC) reactions are consistent with an aldol-type condensation between the RCO group and open-face hydrogen atoms on the dicarbaborane <b>1</b>, which is associated with the insertion of the carbonyl carbon atom into the structure of <i>arachno</i>-6,9-C₂B₈H₁₄ (<b>1</b>) under elimination of three extra hydrogen atoms as H₂O and HCl. The reactions thus result in an effective R–tricarbaborane cross-coupling. Individual compounds of structure <b>2</b> have been purified by chromatography on a silica gel support, using hexane as the mobile phase (<i>R</i>_F = ∼0.3). Deprotonation agents, such as NEt₃, NaOH, NaH, etc., convert tricarbaboranes <b>2</b> into the corresponding conjugated anions [8-R-<i>nido</i>-7,8,9-C₃B₈H₁₀]⁻ (<b>2</b>^–) which were isolated as salts with suitable countercations (for example, Et₃NH⁺, Tl⁺, NEt₄⁺, etc.). The compounds have been characterized by multinuclear (¹¹B, ¹H, and ¹³C) NMR spectroscopy, mass spectrometry, and elemental analyses. The structures of anions [8-R-<i>nido</i>-7,8,9-C₃B₈H₁₀]¯ (where R = C₆H₅, 4-I-C₆H₄ and 1-C₁₀H₇; <b>2a^–</b>, <b>2g^–</b>, and <b>2h</b>^–) and that of the neutral 8-(1-C₁₀H₇)-<i>nido</i>-7,8,9-C₃B₈H₁₁ (<b>2h</b>) have been established by X-ray diffraction analyses

Addition of Lappert's Stannylenes to Carbodiimides, Providing a New Class of Tin(II) Guanidinates

Reactions of bis­[bis­(trimethylsilyl)­amino]tin and the dimer of [bis­(trimethylsilyl)­amino]tin chloride with various carbodiimides give pure corresponding tin­(II) guanidinates in essentially quantitative yields. Heteroleptic bis­(trimethylsilyl)­amido ({R-NC­[N­(SiMe₃)₂]­N-R}­SnN­(SiMe₃)₂)- and chloro-substituted ({R-NC­[N­(SiMe₃)₂]­N-R}­SnCl) tin­(II) guanidinates were obtained from reactions of <i>N</i>,<i>N</i>′-diisopropyl-, <i>N</i>,<i>N</i>′-dicyclohexyl-, <i>N</i>,<i>N</i>′-bis­(4-methylphenyl)-, and <i>N</i>-[3-(dimethylamino)­propyl]-<i>N</i>′-ethylcarbodiimides, respectively. Homoleptic tin­(II) guanidinates {R-NC­[N­(SiMe₃)₂]­N-R}₂Sn were obtained from the <i>N</i>,<i>N</i>′-bis­(4-methylphenyl)- and <i>N</i>-[3-(dimethylamino)­propyl]-<i>N</i>′-ethyl-substituted carbodiimides. Similar reactions of <i>N,N</i>′-bis­(2,6-diisopropylphenyl)- and <i>N,N</i>′-bis­(trimethylsilyl)­carbodiimide, respectively, having the bulkiest substituents of the series, failed to take place under various conditions. The complexes prepared were characterized as monomers in solution by ¹H, ¹³C, and ¹¹⁹Sn NMR spectroscopy in C₆D₆ and THF-<i>d</i>₈. The solid-state NMR spectra were recorded for structure comparison. X-ray diffraction studies of one homoleptic monomer, two heteroleptic chloro complexes with the structures of two different types of dimers, and the oxidation product of the heteroleptic bis­(trimethylsilyl)­amido-substituted guanidinatea centrosymmetric (guanidinato)­tin­(IV) oxidewere performed on appropriate crystals. Attempts to prepare homoleptic types of isopropyl- and cyclohexyl-substituted tin­(II) guanidinate complexes were unsuccessful. The structures were also evaluated by DFT methods

Toward the Synthesis of Indenyl Molybdenum Compound [(η³‑Ind)(η⁵‑Cp)Mo(CO)₂]: Modified Compounds and Structure of a Previously Unrecognized Intermediate

The mechanism of synthesis of [(η³-Ind′)­(η⁵-Cp)­Mo­(CO)₂] was studied on methyl-substituted derivatives (Ind′ = 2-MeC₉H₆; 4,7-Me₂C₉H₅). It was observed that the initial step involving reaction with HCl gives dimeric chloride species [{(η⁵-Ind′)­Mo­(CO)₂(μ-Cl)}₂]. This outcome differs from the structure suggested in the literature. Furthermore, it was demonstrated by various examples that compounds of the formula [{(η⁵-Ind′)­Mo­(CO)₂(μ-Cl)}₂] are convenient starting materials giving [(η³-Ind′)­(η⁵-Cp′)­Mo­(CO)₂] through the reaction with appropriate cyclopentadienides. The variability of this method was demonstrated on several examples including weakly donating Cp ligands bearing strong electron-withdrawing functional groups [C₅H₄COOMe, (1,2-MeOCO)₂C₅H₃, and 1,2-(^<i>t</i>BuNHCO)₂C₅H₃] as well as Cp ligands bearing a pendant amine arm (C₅H₄CH₂CH₂NMe₂). Similar η³-indenyl complexes are formed when using other univalent six-electron ligands such as carbaborane (9-Me₂S-7,8-<i>nido</i>-C₂B₉H₁₀) or scorpionate (Tp, Tp*). The attempts to synthesize [(η³-Ind)­(η⁵-Cp)­Mo­(CO)₂] from [(η³-C₃H₅)­(η⁵-Cp)­Mo­(CO)₂] have failed because the initial reaction with HCl does not give the expected [{(η⁵-Cp)­Mo­(CO)₂­(μ-Cl)}₂] but trivial [(η⁵-Cp)­Mo­(CO)₃Cl]

Three Isomers of Aryl-Substituted Twelve-Vertex Ferratricarbollides

A series of the first types of monoaryl-substituted 12-vertex ferratricarbollide complexes of general constitution [1-(CpFe)-<i>closo</i>-ArC₃B₈H₁₀] (where Ar = C₆H₅, 1′-C₁₀H₇, 2′-C₁₀H₇) with three different aryl substituents and arrangements of cluster carbon vertexes were isolated from high-temperature reactions between 8-Ar-<i>nido</i>-7,8,9-C₃B₈H₁₁ compounds and [CpFe­(CO)₂]₂. The Fe complexation is accompanied by extensive rearrangement of the cluster carbon atoms over the 12-vertex cage

Amino Group Functionalized N‑Heterocyclic 1,2,4-Triazole-Derived Carbenes: Structural Diversity of Rhodium(I) Complexes

The synthesis of the amino group functionalized NHC precursor 1-<i>tert</i>-butyl-4-(2-((dimethylamino)­methyl)-phenyl)-3-phenyl-4<i>H</i>-1,2,4-triazol-1-ium perchlorate has been developed. The generation and bonding properties of the NHC ligand have been evaluated in reactions toward three Rh­(I) complexes[Rh­(COD)­Cl]₂, [Rh­(cyclooctene)₂Cl]₂, and [Rh­(ethylene)₂Cl]₂, respectively. For the first complex, [(NHC)­RhCl­(COD)], the coordination of the dangling amino group was not observed because of the fully occupied coordination neighborhood of the Rh atom. On the other hand, in the case of [(NHC)­RhCl­(ethylene)], [(NHC)­RhCl­(cyclooctene)], [(NHC)­Rh­(COD)]⁺[BF₄]⁻, and [(NHC)­RhCl­(CO)] a strong intramolecular coordination of the amino nitrogen atom was revealed, thus forming the unusual seven-membered diazametallacycle. All of the products of these reactions were characterized in solution by NMR spectroscopy as well as in the solid state by X-ray diffraction analysis

Toward the Synthesis of Indenyl Molybdenum Compound [(η³‑Ind)(η⁵‑Cp)Mo(CO)₂]: Modified Compounds and Structure of a Previously Unrecognized Intermediate

The mechanism of synthesis of [(η³-Ind′)­(η⁵-Cp)­Mo­(CO)₂] was studied on methyl-substituted derivatives (Ind′ = 2-MeC₉H₆; 4,7-Me₂C₉H₅). It was observed that the initial step involving reaction with HCl gives dimeric chloride species [{(η⁵-Ind′)­Mo­(CO)₂(μ-Cl)}₂]. This outcome differs from the structure suggested in the literature. Furthermore, it was demonstrated by various examples that compounds of the formula [{(η⁵-Ind′)­Mo­(CO)₂(μ-Cl)}₂] are convenient starting materials giving [(η³-Ind′)­(η⁵-Cp′)­Mo­(CO)₂] through the reaction with appropriate cyclopentadienides. The variability of this method was demonstrated on several examples including weakly donating Cp ligands bearing strong electron-withdrawing functional groups [C₅H₄COOMe, (1,2-MeOCO)₂C₅H₃, and 1,2-(^<i>t</i>BuNHCO)₂C₅H₃] as well as Cp ligands bearing a pendant amine arm (C₅H₄CH₂CH₂NMe₂). Similar η³-indenyl complexes are formed when using other univalent six-electron ligands such as carbaborane (9-Me₂S-7,8-<i>nido</i>-C₂B₉H₁₀) or scorpionate (Tp, Tp*). The attempts to synthesize [(η³-Ind)­(η⁵-Cp)­Mo­(CO)₂] from [(η³-C₃H₅)­(η⁵-Cp)­Mo­(CO)₂] have failed because the initial reaction with HCl does not give the expected [{(η⁵-Cp)­Mo­(CO)₂­(μ-Cl)}₂] but trivial [(η⁵-Cp)­Mo­(CO)₃Cl]

Palladium(II) Complexes of 1,2,4-Triazole-Based <i>N</i>‑Heterocyclic Carbenes: Synthesis, Structure, and Catalytic Activity

Six palladium­(II) complexes bearing three different triazole-based N-heterocyclic carbene (NHC) ligands, [1-<i>tert</i>-butyl-4-{2-[(<i>N</i>,<i>N</i>-dimethylamino)­methyl]­phenyl}-3-phenyl-1<i>H</i>-1,2,4-triazol-4-ium-5-ide, 1-<i>tert</i>-butyl-4-(2-methoxyphenyl)-3-phenyl-1<i>H</i>-1,2,4-triazol-4-ium-5-ide, and 1-<i>tert</i>-butyl-4-(4-methylphenyl)-3-phenyl-1<i>H</i>-1,2,4-triazol-4-ium-5-ide], were synthesized and fully characterized. NMR spectroscopy and X-ray diffraction analysis revealed that the amino-group-substituted NHC ligand is coordinated in bidentate fashion, forming a monocarbene chelate complex with an additional intramolecular Pd ← N bond with the nitrogen donor atom. The 4-methylphenyl- and 2-methoxyphenyl-substituted NHC ligands coordinate as C-monodentate donors, forming simple biscarbene Pd­(II) complexes. The evaluation of the catalytic performance in the Suzuki–Miyaura cross-coupling reaction revealed very promising performance of the intramolecularly coordinated monocarbene complexes under relatively mild conditions even in direct comparison with the commercially available PEPPSI catalyst. In contrast, the biscarbene complexes proved inactive in this catalytic process. According to theoretical calculations (EDA and NOCV analysis), functionalization of the 1,2,4-triazole-based NHC with the 2-[(<i>N</i>,<i>N</i>-dimethylamino)­methyl]­phenyl group has a significant effect on the stability of the NHC–metal bond