Reaction of 13-Vertex Carborane μ‑1,2-(CH₂)₃‑1,2‑C₂B₁₁H₁₁ with Nucleophiles: Scope and Mechanism

13-Vertex carborane, μ-1,2-(CH₂)₃-1,2-C₂B₁₁H₁₁ (<b>1</b>), reacted with a series of nucleophiles (Nu) to give the cage carbon extrusion products [μ-1,2-(CH₂)₃­CH­(Nu)-1-CB₁₁H₁₀]⁻, [μ-1,2-(CH₂)₂­CH­(Nu)­CH₂-1-CB₁₁H₁₀]⁻, and/or [μ-1,2-(CH₂)₂­CHCH-1-CB₁₁H₁₀]⁻, depending on the nature of Nu and the reaction conditions. The key intermediates for the formation of CB₁₁^– anions were isolated and structurally characterized as [μ–η:η:η-7,8,10-(CH₂)₃­CHB­(Nu)-7-CB₁₀H₁₀]⁻ (Nu = OMe, NEt₂). The reaction mechanism is thus proposed, which involves the attack of Nu at the most electron-deficient cage boron, followed by H-migration to one of the cage carbons, leading to the formation of the intermediate. Nu-migration gives the products

Reactivity of Traditional Metal–Carbon (Alkyl) versus Nontraditional Metal–Carbon (Cage) Bonds in Organo-Rare-Earth Metal Complexes [η⁵:σ-(C₉H₆)(C₂B₁₀H₁₀)]­Ln(CH₂C₆H₄‑<i>o</i>‑NMe₂)(THF)₂

Equimolar reaction of 1-indenyl-1,2-carborane with Ln­(CH₂C₆H₄-<i>o</i>-NMe₂)₃ in THF gave highly constrained-geometry complexes [η⁵:σ-(C₉H₆)­C₂B₁₀H₁₀]­Ln­(CH₂C₆H₄-<i>o</i>-NMe₂)­(THF)₂ (Ln = Y (<b>1a</b>), Gd (<b>1b</b>), Dy (<b>1c</b>)). They reacted with RNCNR or 2,6-Me₂C₆H₃NCS to generate the Ln–C_alkyl insertion products [η⁵:σ-(C₉H₆)­C₂B₁₀H₁₀]­Ln­[η²<i>-</i>(RN)₂C­(CH₂C₆H₄-<i>o</i>-NMe₂)]­(THF) (R = TMS, Ln = Y (<b>2a</b>), Gd (<b>2b</b>); R = ^<i>t</i>Bu, Ln = Y (<b>3a</b>)) or [η⁵:σ-(C₉H₆)­C₂B₁₀H₁₀]­Dy­[η²<i>-</i>(2,6-Me₂C₆H₃)­NC­(CH₂C₆H₄-<i>o</i>-NMe₂)­S]­(THF)₂ (<b>4c</b>). Treatment of <b>2a</b> with 1 equiv of R′NCNR′ to give the Y–C_cage insertion complexes [η⁵:σ-(C₉H₆)­{N­(R′)­C­(NR′)}­C₂B₁₀H₁₀]­Y­[η²<i>-</i>{(TMS)­N}₂­C­(CH₂C₆H₄-<i>o</i>-NMe₂)] (R′ = Cy (<b>5a</b>), ^<i>i</i>Pr (<b>6a</b>)). Similarly, unsaturated compounds Ph₂CCO and Py₂CO (Py = 2-pyridyl) also inserted into the Y–C_cage bond in <b>2a</b> to yield [η⁵:σ-(C₉H₆)­{OC­(CPh₂)}­C₂B₁₀H₁₀]­Y­[η²<i>-</i>{(TMS)­N}₂C­(CH₂C₆H₄-<i>o</i>-NMe₂)] (<b>7a</b>) and [η⁵:σ-(C₉H₆)­{OC­(Py)₂}­C₂B₁₀H₁₀]­Y­[η²<i>-</i>{(TMS)­N)}₂­C­(CH₂C₆H₄-<i>o</i>-NMe₂)]­(THF) (<b>8a</b>), respectively. In sharp contrast to the earlier reports that the nontraditional metal–C_cage σ bonds in metal–carboranyl complexes are generally inert toward electrophiles, the insertion of unsaturated molecules into the Y–C_cage σ bond in <b>2a</b> represents the first example of this type of reactions. These results shed some light on how to activate the nontraditional metal–carbon (cage) bonds in metal–carboranyl complexes. All new complexes were characterized by spectroscopic techniques and elemental analyses. Some were further confirmed by single-crystal X-ray analyses

Palladium-Catalyzed Regioselective Intramolecular Coupling of <i>o</i>‑Carborane with Aromatics via Direct Cage B–H Activation

Palladium-catalyzed intramolecular coupling of <i>o</i>-carborane with aromatics via direct cage B–H bond activation has been achieved, leading to the synthesis of a series of <i>o</i>-carborane-functionalized aromatics in high yields with excellent regioselectivity. In addition, the site selectivity can also be tuned by the substituents on cage carbon atom

Tantallacarborane Mediated Consecutive C–C and C–N Coupling Reactions of Alkyl Isonitriles: A Facile Route to N‑Heterocycles

Reactions of tantallacarborane methyl complexes ([η¹:η⁵-(Me₂NCH₂CH₂)­C₂B₉H₁₀]­TaMe₃ (<b>1</b>) and [η¹:η⁵-(MeOCH₂CH₂)­C₂B₉H₁₀]­TaMe₃ (<b>8</b>)) with alkyl isonitriles have been studied. Complex <b>1</b> reacted with 1 equiv of RNC (R = TMSCH₂, Cy, and ^<i>i</i>Pr) to afford double migratory insertion products [η¹:η⁵-(Me₂NCH₂CH₂)­C₂B₉H₁₀]­Ta­[η²-<i>C</i>,<i>N</i>-C­(Me₂)­NCH₂TMS]­Me (<b>2</b>) and [σ:η¹:η⁵-{MeN­(CH₂)­CH₂CH₂}­C₂B₉H₁₀]­Ta­[N­(^<i>i</i>Pr)­R]­Me (R = Cy (<b>3</b>), ^<i>i</i>Pr (<b>4</b>)). However, treatment of <b>1</b> or <b>8</b> with 4 equiv of alkyl isonitriles gave two fused six-membered <i>N</i>-heterocycles <b>5</b>–<b>7</b> and <b>9</b> via consecutive C–C/C-N bond-forming reactions. All new complexes were characterized by ¹H, ¹³C, and ¹¹B NMR spectra as well as elemental analyses. Their structures were further confirmed by single-crystal X-ray analyses. The results show that aryl and alkyl isonitriles exhibit significantly different reactivity patterns. This work also offers a very efficient method for the synthesis of N-heterocycles

Reaction of 13-Vertex Carborane μ‑1,2-(CH₂)₄‑1,2‑C₂B₁₁H₁₁ with Nucleophiles: Linkage Effect on Product Formation

The length of C,C′-linkage has a great influence on the reactivity of 13-vertex carboranes. Reaction of 1,2-(CH₂)₄-1,2-C₂B₁₁H₁₁ (<b>1a</b>) with Et₂NH gave a 1:1 adduct <i>nido</i>-7-NEt₂H-μ-1,3-(CH₂)₄-1,3-C₂B₁₁H₁₁ (<b>2</b>). Compound <b>1a</b> reacted with Me₂NLi or Et₂NLi to afford <i>nido</i>-[9-Nu-μ-7,8,10-(CH₂)₄CCH-B₁₁H₁₀]⁻ (Nu = NMe₂, [<b>3</b>]⁻; Nu = NEt₂, [<b>4</b>]⁻). Complex [<b>4</b>]⁻ was also obtained by deprotonation of <b>2</b>. Treatment of <b>1a</b> with MeOH/base generated <i>nido</i>-[3-OMe-μ-1,2-(CH₂)₄-1,2-C₂B₁₁H₁₁]⁻ ([<b>5</b>]⁻) at room temperature, which was converted to <i>nido</i>-[μ-7,8-(CH₂)₄CHB­(OMe)₂-7-CB₁₀H₁₁]⁻ ([<b>6</b>]⁻) upon heating in the presence of Et₃N. Complex [<b>6</b>]⁻ was oxidized by H₂O₂ to the corresponding alcohol [μ-7,8-(CH₂)₄CHOH-7-CB₁₀H₁₁]⁻ ([<b>7</b>]⁻) or hydrolyzed to the boronic acid [μ-7,8-(CH₂)₄CHB­(OH)₂-7-CB₁₀H₁₁]⁻ ([<b>8</b>]⁻). Reaction of <b>1a</b> with (4-MeC₆H₄)­SNa produced a CB₁₁^– anion <i>closo</i>-[μ-1,2-(CH₂)₄CHS­(4-MeC₆H₄)-1-CB₁₁H₁₀]⁻ ([<b>9</b>]⁻). The above complexes were fully characterized by ¹H, ¹³C, and ¹¹B NMR spectroscopic data and elemental analyses. Molecular structures of <b>1</b>–[<b>7</b>]⁻ and [<b>9</b>]⁻ were further confirmed by single-crystal X-ray analyses

Iridium Catalyzed Regioselective Cage Boron Alkenylation of <i>o-</i>Carboranes via Direct Cage B–H Activation

Iridium catalyzed alkyne hydroboration with <i>o-</i>carborane cage B–H has been achieved, leading to the formation of a series of 4-B-alkenylated-<i>o</i>-carborane derivatives in high yields with excellent regioselectivity via direct B–H bond activation. In this reaction the carboxy group is used as a traceless directing group, which is removed during a one-pot process. After the confirmation of a key intermediate, a possible mechanism is proposed, involving a tandem sequence of Ir-mediated B–H activation, alkyne insertion, protonation, and decarboxylation

Reaction of 13-Vertex Carborane μ‑1,2-(CH₂)₄‑1,2‑C₂B₁₁H₁₁ with Nucleophiles: Linkage Effect on Product Formation

The length of C,C′-linkage has a great influence on the reactivity of 13-vertex carboranes. Reaction of 1,2-(CH₂)₄-1,2-C₂B₁₁H₁₁ (<b>1a</b>) with Et₂NH gave a 1:1 adduct <i>nido</i>-7-NEt₂H-μ-1,3-(CH₂)₄-1,3-C₂B₁₁H₁₁ (<b>2</b>). Compound <b>1a</b> reacted with Me₂NLi or Et₂NLi to afford <i>nido</i>-[9-Nu-μ-7,8,10-(CH₂)₄CCH-B₁₁H₁₀]⁻ (Nu = NMe₂, [<b>3</b>]⁻; Nu = NEt₂, [<b>4</b>]⁻). Complex [<b>4</b>]⁻ was also obtained by deprotonation of <b>2</b>. Treatment of <b>1a</b> with MeOH/base generated <i>nido</i>-[3-OMe-μ-1,2-(CH₂)₄-1,2-C₂B₁₁H₁₁]⁻ ([<b>5</b>]⁻) at room temperature, which was converted to <i>nido</i>-[μ-7,8-(CH₂)₄CHB­(OMe)₂-7-CB₁₀H₁₁]⁻ ([<b>6</b>]⁻) upon heating in the presence of Et₃N. Complex [<b>6</b>]⁻ was oxidized by H₂O₂ to the corresponding alcohol [μ-7,8-(CH₂)₄CHOH-7-CB₁₀H₁₁]⁻ ([<b>7</b>]⁻) or hydrolyzed to the boronic acid [μ-7,8-(CH₂)₄CHB­(OH)₂-7-CB₁₀H₁₁]⁻ ([<b>8</b>]⁻). Reaction of <b>1a</b> with (4-MeC₆H₄)­SNa produced a CB₁₁^– anion <i>closo</i>-[μ-1,2-(CH₂)₄CHS­(4-MeC₆H₄)-1-CB₁₁H₁₀]⁻ ([<b>9</b>]⁻). The above complexes were fully characterized by ¹H, ¹³C, and ¹¹B NMR spectroscopic data and elemental analyses. Molecular structures of <b>1</b>–[<b>7</b>]⁻ and [<b>9</b>]⁻ were further confirmed by single-crystal X-ray analyses

Iridium-Catalyzed Selective B(4)–H Amination of <i>o</i>‑Carboranes with Anthranils

We report here a catalytic selective cage B4–H amination of o-carboranes employing an Ir(III) complex as a catalyst and anthranils as aminating agents, leading to a large class of B4-aminated o-carboranes with very high yields and a broad substrate scope under mild conditions without any oxidants. In these reactions, the carboxyl group serves as a traceless directing unit to determine the site selectivity and degree of substitution

Reaction of Carboryne with Alkylbenzenes

Carboryne (1,2-dehydro-<i>o</i>-carborane), in situ generated from the precursor 1-iodo-2-lithiocarborane, reacted with alkylbenzenes to give two regioisomers of the [4 + 2] cycloadducts as the major products in moderate to good yields, in which the steric factors play an important role in the regioselectivity. Minor products derived from benzylic C–H insertion reaction, annulation reaction, tandem [4 + 2] cycloaddition/homo Diels–Alder reaction, and tandem ene reaction/[2 + 2] cycloaddition were also isolated and characterized in the reaction of carboryne with toluene. The presence of AgF in the above reaction produced no notable changes in the product distributions and yields

Reaction of [η¹:η⁵‑(R₂NCH₂CH₂)C₂B₉H₁₀]TaMe₃ with Isonitriles: Effects of Nitrogen Substituents on Product Formation

Tantallacarborane trimethyl complexes show diverse reactivity patterns toward isonitriles. Reaction of [η¹:η⁵-(Me₂NCH₂CH₂)­C₂B₉H₁₀]­TaMe₃ (<b>1</b>) with 1-adamantyl isonitrile (AdNC) led to the clean formation of an imido complex, [σ:η⁵-(MeNCH₂CH₂)­C₂B₉H₁₀]­Ta­(NAd)­(THF) (<b>2</b>) with elimination of methane and 2-methylpropene, whereas treatment of [η¹:η⁵-{(CH₂)₅NCH₂CH₂}­C₂B₉H₁₀]­TaMe₃ (<b>3</b>) with AdNC under the same reaction conditions gave the cage B–H activated product {σ:η¹:η⁵-[(CH₂)₅NCHCH₂]­(CHMe₂)­C₂B₉H₉}­Ta­(NAd)­(THF) (<b>4</b>). An equimolar reaction of <b>1</b> with R¹NC (R¹ = Cy, Ad), followed by 1 equiv of R²NC (R² = Xyl, Cy), afforded the imido amido complexes [η¹:η⁵-(Me₂NCH₂CH₂)­C₂B₉H₁₀]­Ta­(NR¹)­[N­(CMeCMe₂)­R²] (R¹ = Ad, R² = Cy (<b>5</b>); R¹ = Cy, R² = Xyl (<b>6</b>)). If 2 equiv of 2,6-dimethylphenyl isonitrile (XylNC) was used in the above reaction, the cage B–H alkylation products [η¹:η⁵-(Me₂NCH₂CH₂)­C₂B₉H₉]­Ta­(NR¹)­[N­(Xyl)­{CHC­(Me₂)­C­(Me)NXyl}] (R¹ = Cy (<b>7</b>), Ad (<b>8</b>)) were isolated. On the other hand, η²-iminoacyl imido complexes [η¹:η⁵-(Me₂NCH₂CH₂)­(CHMe₂)­C₂B₉H₉]­Ta­(NXyl)­(η²-<i>C</i>,<i>N</i>-MeCNR) (R = ^<i>i</i>Pr (<b>9</b>), Cy (<b>10</b>)) were obtained from an equimolar reaction of <b>1</b> with XylNC, followed by 1 equiv of alkyl isonitriles. A double methyl migratory insertion tantallaaziridine species is proposed as a crucial intermediate for all aforementioned reactions, and follow-up steps are dependent upon N-substituents and the type and stoichiometry of isonitriles. All new complexes were characterized by spectroscopic methods and single-crystal X-ray analyses