Tris(boratabenzene) Lanthanum Complexes: Synthesis, Structure, and Reactivity

A series of tris­(boratabenzene) lanthanum complexes were synthesized and structurally characterized. Salt elimination of anhydrous LaCl₃ with Li­[C₅H₅BR] (R = H, NEt₂) provided tris­(boratabenzene) lanthanum complexes [C₅H₅BH]₃­LaLiCl (<b>1</b>) and [C₅H₅BNEt₂]₃­LaLiCl­(THF) (<b>2</b>) in high yields. Hydroboration of 1-hexene or 3-hexyne with <b>1</b> gave the alkyl- or alkenyl-functionalized boratabenzene lanthanum complexes, [C₅H₅B­(CH₂)₅CH₃]₃­LaLiCl­(THF) (<b>3</b>) and [C₅H₅BC­(C₂H₅)CH­(C₂H₅)]₃­LaLiCl­(THF) (<b>4</b>), in good yields. Hydroboration of <i>N</i>,<i>N</i>′-diisopropylcarbodiimide with <b>1</b> gave the monohydroboration product [C₅H₅BN­(^<i>i</i>Pr)­CHN­(^<i>i</i>Pr)]­[C₅H₅BH]₂La (<b>5</b>) due to the steric bulk of the [C₅H₅BN­(^<i>i</i>Pr)­CHN­(^<i>i</i>Pr)]⁻ ligand. Complex <b>5</b> can undergo further hydroboration with 3-hexyne or dehydrogenative coupling with phenyl acetylene to afford [C₅H₅BN­(^<i>i</i>Pr)­CHN­(^<i>i</i>Pr)]­[C₅H₅BC­(C₂H₅)CH­(C₂H₅)]₂La (<b>6</b>) or [C₅H₅BN­(^<i>i</i>Pr)­CHN­(^<i>i</i>Pr)]­[C₅H₅BCCPh)]₂La (<b>7</b>)

Yttrium Anilido Hydride: Synthesis, Structure, and Reactivity

The synthesis, structure, and reactivity of the yttrium anilido hydride [LY(NH(DIPP))(μ-H)]₂ (<b>3</b>; L = [MeC(N(DIPP))CHC(Me)(NCH₂CH₂NMe₂)]⁻, DIPP = 2,6-^<i>i</i>Pr₂C₆H₃)) are reported. The protonolysis reaction of the yttrium dialkyl [LY(CH₂SiMe₃)₂] (<b>1</b>) with 1 equiv of 2,6-diisopropylaniline gave the yttrium anilido alkyl [LY(NH(DIPP))(CH₂SiMe₃)] (<b>2</b>), and a subsequent σ-bond metathesis reaction of <b>2</b> with 1 equiv of PhSiH₃ offered the yttrium anilido hydride <b>3</b>. The structure of <b>3</b> was characterized by X-ray crystallography, which showed that the complex is a μ-H dimer. <b>3</b> shows high reactivity toward a variety of unsaturated substrates, including imine, azobenzene, carbodiimide, isocyanide, ketone, and Mo(CO)₆, giving some structurally intriguing products

Cobalt-Catalyzed Cyclization/Hydrosilylation Reaction of 1,6-Diynes Enabled by an Oxidative Cyclization–Hydrosilylation Mechanism

Transition-metal-catalyzed cyclization/hydrosilylation of 1,6-diynes is a useful method for the preparation of five-membered ring-fused silyl dienes that are useful reagents in organic synthesis. Only a handful of noble metal catalysts facilitating this transformation are known, and nonprecious metal catalysts effecting the reaction have remained elusive. Herein, we report that low-coordinate Co(0)-N-heterocyclic carbene complexes can catalyze the cyclization/hydrosilylation of 1,6-diynes with tertiary and secondary hydrosilanes, furnishing five-membered ring-fused (Z)-1-silyldienes in good yields and excellent stereoselectivity. Mechanistic study disclosed that the catalytic cycle likely has oxidative cyclization of 1,6-diynes with Co(0) species as the key step. This mechanism accounts for the high stereoselectivity and absence of uncyclized hydrosilylation byproducts in the cobalt-catalyzed cyclization/hydrosilylation reaction, which is different from the hydrosilylation-cyclization mechanism of the noble metal-catalyzed reactions

C–P or C–H Bond Cleavage of Phosphine Oxides Mediated by an Yttrium Hydride

Reactions of the yttrium anilido hydride [LY­(NH­(DIPP))­(μ-H)]₂ (<b>1</b>; L = [MeC­(N­(DIPP))­CHC­(Me)­(NCH₂CH₂NMe₂)]⁻, DIPP = 2,6-ⁱPr₂C₆H₃)) with three phosphine oxides and two phosphine sulfides are reported. The reaction of <b>1</b> with Ph₃PO gives C–P bond cleavage and an yttrium anilido phosphinoyl complex, while those with R₂MePO (R = Me, Ph) result in C–H bond cleavage and two yttrium anilido alkyl complexes. <b>1</b> also reacted with R₃PS (R = Me, Ph), which demonstrated P–S bond cleavage via hydride-based reduction and gave an yttrium anilido sulfide

Cobalt-Catalyzed Cyclization/Hydrosilylation Reaction of 1,6-Diynes Enabled by an Oxidative Cyclization–Hydrosilylation Mechanism

Transition-metal-catalyzed cyclization/hydrosilylation of 1,6-diynes is a useful method for the preparation of five-membered ring-fused silyl dienes that are useful reagents in organic synthesis. Only a handful of noble metal catalysts facilitating this transformation are known, and nonprecious metal catalysts effecting the reaction have remained elusive. Herein, we report that low-coordinate Co(0)-N-heterocyclic carbene complexes can catalyze the cyclization/hydrosilylation of 1,6-diynes with tertiary and secondary hydrosilanes, furnishing five-membered ring-fused (Z)-1-silyldienes in good yields and excellent stereoselectivity. Mechanistic study disclosed that the catalytic cycle likely has oxidative cyclization of 1,6-diynes with Co(0) species as the key step. This mechanism accounts for the high stereoselectivity and absence of uncyclized hydrosilylation byproducts in the cobalt-catalyzed cyclization/hydrosilylation reaction, which is different from the hydrosilylation-cyclization mechanism of the noble metal-catalyzed reactions

Synthesis and Structure of Silicon-Bridged Boratabenzene Fluorenyl Rare-Earth Metal Complexes

A silicon-bridged boratabenzene fluorenyl ligand [Me₂Si­(C₁₃H₈)­(C₅H₄BNEt₂)]^2– (<b>L</b>^2–) was designed and synthesized. By employment of this ligand, two divalent rare-earth metal complexes [Me₂Si­(C₁₃H₈)­(C₅H₄BNEt₂)]­Ln­(THF)₂ (Ln = Sm (<b>1</b>), Yb (<b>2</b>)) were obtained from salt metathesis of K₂[Me₂Si­(C₁₃H₈)­(C₅H₄BNEt₂)] (<b>K</b>_<b>2</b><b>L</b>) with LnI₂­(THF)₂ in THF. Complex <b>2</b> undergoes redox reaction with cyclooctatetraene to give a trivalent Yb complex [(C₈H₈)­Yb]₂­[μ-{Me₂Si­(C₁₃H₈)­(C₅H₄BNEt₂)}₂] (<b>3</b>), accompanied with oxidative coupling of two fluorenyl groups. A series of chloro-bridged trimeric trivalent rare-earth metal complexes [Li­(THF)₄]₂­[{[Me₂Si­(C₁₃H₈)­(C₅H₄BNEt₂)]­Ln­(μ-Cl)­Li­(THF)₃}₃­(μ-Cl)₃­(μ₃-Cl)₂] (Ln = Nd (<b>4</b>), Sm (<b>5</b>), and Gd (<b>6</b>)) were synthesized by reactions of Li₂[Me₂Si­(C₁₃H₈)­(C₅H₄BNEt₂)] (<b>Li</b>_<b>2</b><b>L</b>) with LnCl₃ in THF. Treatment of K₂[Me₂Si­(C₁₃H₈)­(C₅H₄BNEt₂)] (<b>K</b>_<b>2</b><b>L</b>) with LnI₃(THF)_<i>n</i> gave the monomeric complexes [Me₂Si­(C₁₃H₈)­(C₅H₄BNEt₂)]­LnI­(THF) (Ln = La (<b>7</b>), Nd (<b>8</b>), Sm (<b>9</b>), and Gd (<b>10</b>)). These iodides were subsequently reacted with K­[CH₂C₆H₄-<i>o</i>-NMe₂] to afford THF coordinated benzyl complexes [Me₂Si­(C₁₃H₈)­(C₅H₄BNEt₂)]­Ln­(CH₂C₆H₄-<i>o</i>-NMe₂)­(THF) (Ln = La (<b>11</b>), Nd (<b>12</b>), and Gd (<b>13a</b>)) and non-THF coordinated complex [Me₂Si­(C₁₃H₈)­(C₅H₄BNEt₂)]­Gd­(CH₂C₆H₄-<i>o</i>-NMe₂) (<b>13b</b>)

Reversible Addition of the Si–H Bond of Phenylsilane to the ScN Bond of a Scandium Terminal Imido Complex

The facile and reversible addition of the Si–H bond of phenylsilane to the ScN bond of the scandium terminal imido complex [LScNDIPP­(DMAP)] (<b>1</b>; L  [MeC­(N­(DIPP))­CHC­(Me)­(NCH₂CH₂NMe)]⁻, DIPP = 2,6-^<i>i</i>Pr₂C₆H₃) is reported. The reaction gives the scandium anilido hydride [LSc­(H)­(N­(DIPP)­(SiH₂Ph))] (<b>2</b>), and a labeling experiment shows a rapid σ-bond metathesis between Sc–H of the formed scandium anilido hydride and Si–H of phenylsilane during the reaction. <b>2</b> was trapped by an insertion reaction with diphenylcarbodiimide, giving the stable scandium anilido amidinate [LSc­(N­(DIPP)­(SiH₂Ph))­(κ²(<i>N</i>,<i>N</i>′)-PhNCHNPh)] (<b>3</b>). Furthermore, the scandium terminal imido complex can efficiently catalyze the hydrosilylation of <i>N</i>-benzylidenepropan-1-amine. The reaction was completed within 2 h at 50 °C with 5 mol % of catalyst loading and highly selectively produced the monoaminosilane

Synthesis and Structure of Silicon-Bridged Boratabenzene Fluorenyl Rare-Earth Metal Complexes

A silicon-bridged boratabenzene fluorenyl ligand [Me₂Si­(C₁₃H₈)­(C₅H₄BNEt₂)]^2– (<b>L</b>^2–) was designed and synthesized. By employment of this ligand, two divalent rare-earth metal complexes [Me₂Si­(C₁₃H₈)­(C₅H₄BNEt₂)]­Ln­(THF)₂ (Ln = Sm (<b>1</b>), Yb (<b>2</b>)) were obtained from salt metathesis of K₂[Me₂Si­(C₁₃H₈)­(C₅H₄BNEt₂)] (<b>K</b>_<b>2</b><b>L</b>) with LnI₂­(THF)₂ in THF. Complex <b>2</b> undergoes redox reaction with cyclooctatetraene to give a trivalent Yb complex [(C₈H₈)­Yb]₂­[μ-{Me₂Si­(C₁₃H₈)­(C₅H₄BNEt₂)}₂] (<b>3</b>), accompanied with oxidative coupling of two fluorenyl groups. A series of chloro-bridged trimeric trivalent rare-earth metal complexes [Li­(THF)₄]₂­[{[Me₂Si­(C₁₃H₈)­(C₅H₄BNEt₂)]­Ln­(μ-Cl)­Li­(THF)₃}₃­(μ-Cl)₃­(μ₃-Cl)₂] (Ln = Nd (<b>4</b>), Sm (<b>5</b>), and Gd (<b>6</b>)) were synthesized by reactions of Li₂[Me₂Si­(C₁₃H₈)­(C₅H₄BNEt₂)] (<b>Li</b>_<b>2</b><b>L</b>) with LnCl₃ in THF. Treatment of K₂[Me₂Si­(C₁₃H₈)­(C₅H₄BNEt₂)] (<b>K</b>_<b>2</b><b>L</b>) with LnI₃(THF)_<i>n</i> gave the monomeric complexes [Me₂Si­(C₁₃H₈)­(C₅H₄BNEt₂)]­LnI­(THF) (Ln = La (<b>7</b>), Nd (<b>8</b>), Sm (<b>9</b>), and Gd (<b>10</b>)). These iodides were subsequently reacted with K­[CH₂C₆H₄-<i>o</i>-NMe₂] to afford THF coordinated benzyl complexes [Me₂Si­(C₁₃H₈)­(C₅H₄BNEt₂)]­Ln­(CH₂C₆H₄-<i>o</i>-NMe₂)­(THF) (Ln = La (<b>11</b>), Nd (<b>12</b>), and Gd (<b>13a</b>)) and non-THF coordinated complex [Me₂Si­(C₁₃H₈)­(C₅H₄BNEt₂)]­Gd­(CH₂C₆H₄-<i>o</i>-NMe₂) (<b>13b</b>)

A Scandium Complex Bearing Both Methylidene and Phosphinidene Ligands: Synthesis, Structure, and Reactivity

The scandium complex bearing both methylidene and phosphinidene ligands, [(LSc)₂­(μ₂-CH₂)­(μ₂-PDIPP)] (L = [MeC­(NDIPP)­CHC­(NDIPP)­Me]⁻, DIPP = 2,6-(^<i>i</i>Pr)₂C₆H₃) (<b>2</b>), has been synthesized, and its reactivity has been investigated. Reaction of scandium methyl phosphide [LSc­(Me)­{P­(H)­DIPP}] with 1 equiv of scandium dimethyl complex [LScMe₂] in toluene at 60 °C provided complex <b>2</b> in good yield, and the structure of complex <b>2</b> was determined by single-crystal X-ray diffraction. Complex <b>2</b> easily undergoes nucleophilic addition reactions with CO₂, CS₂, benzonitrile, and <i>tert</i>-butyl isocyanide. In the above reactions, the unsaturated substrates insert into the Sc–C­(methylidene) bond to give some interesting dianionic ligands while the Sc–P­(phosphinidene) bond remains untouched. The bonding situation of complex <b>2</b> was analyzed using DFT methods, indicating a more covalent bond between the scandium ion and the phosphinidene ligand than between the scandium ion and the methyl­idene ligand

Zwitterionic Cobalt(I)–NHC Complexes with Tetraphenylborate Ligation: Synthesis, Characterization, and Reactivity

Zwitterionic metal complexes of Rh and Ru featuring a tetraphenylborate ancillary ligand have been explored widely in organometallic chemistry. Analogous 3d metal complexes, however, are rarely known. From the oxidation reaction of cobalt(0)-N-heterocyclic carbene complexes [(NHC)­Co­(η2:η2-(CH2CHSiMe2)2O)] (NHC = N-heterocyclic carbene) with [Cp2Fe]­[BPh4], we synthesized the zwitterionic cobalt­(I)–NHC complexes [(IMes)­Co­((η6-C6H5)­BPh3)] (IMes = 1,3-bis­(2,4,6-trimethylphenyl)-imidazole-2-ylidene, 1) and [(IPr)­Co­((η6-C6H5)­BPh3)] (IPr = 1,3-bis­(2,6-diisopropylphenyl)-imidazole-2-ylidene, 2) in good yields. Characterization data and computational studies revealed the S = 1 ground spin state for 1 and 2. These zwitterionic cobalt­(I) complexes can act as cobalt­(I) synthons to prepare cobalt­(I)–NHC complexes bearing other ancillary ligands. Their reactions to CO and CNBut form the zwitterionic cobalt­(I) complexes [(IMes)­Co­((η6-C6H5)­BPh3)­(CO)] (3), [(IPr)­Co­((η6-C6H5)­BPh3)­(CO)] (4), and [(IMes)­Co­((η6-C6H5)­BPh3)­(CNBut)] (5) and the ionic cobalt­(I) complex [(IMes)­Co­(CNBut)4]­[BPh4] (6). In the reactions of 2 with pyridine, IPr, and IMes, the ionic cobalt­(I)–NHC complexes [(IPr)­Co­(py)3]­[BPh4] (7), [(IPr)2Co]­[BPh4] (8) and [(IPr)­Co­(IMes)]­[BPh4] (9) were formed. The structures of these complexes were established by single-crystal X-ray diffraction studies