Unusual chelated o-carborane transition metal complex

Sayler, Alice A.; Beall, Herbert; Sieckhaus, John F.

doi:10.1021/ja00798a074

Cited by 57 publications

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“…The carboryne reactions are usually complicated and do not proceed in a controlled manner. On the other hand, nickel–carboryne complex [(η 2 ‐C 2 B 10 H 10 )Ni(PPh 3 ) 2 ]3 can undergo regioselective [2+2+2] cycloaddition reactions with 2 equivalents of alkyne to afford benzocarboranes,4 can react with 1 equivalent of alkenes to generate alkenylcarborane coupling products,5 and can undergo a three‐component [2+2+2] cyclotrimerization reaction with 1 equivalent of activated alkene and 1 equivalent of alkyne to give dihydrobenzocarboranes 6. However, these reactions require a stoichiometric amount of nickel reagent.…”

Section: Optimization Of Reaction Conditions[a]mentioning

confidence: 99%

Nickel‐Catalyzed Regioselective [2+2+2] Cycloaddition of Carboryne with Alkynes

2010

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Carboryne (1,2-dehydro-ortho-carborane), a three-dimensional relative of benzyne, was first reported in 1990 as a highly reactive intermediate. [1] Subsequent studies of its reactivity showed that it can react with alkenes, dienes, and alkynes in [2+2] and [2+4] cycloaddition, and ene-reaction patterns, [2] similar to that of benzyne. The carboryne reactions are usually complicated and do not proceed in a controlled manner. On the other hand, nickel-carboryne complex [(h 2 -C 2 B 10 H 10 )Ni(PPh 3 ) 2 ][3] can undergo regioselective [2+2+2] cycloaddition reactions with 2 equivalents of alkyne to afford benzocarboranes, [4] can react with 1 equivalent of alkenes to generate alkenylcarborane coupling products, [5] and can undergo a three-component [2+2+2] cyclotrimerization reaction with 1 equivalent of activated alkene and 1 equivalent of alkyne to give dihydrobenzocarboranes.[6] However, these reactions require a stoichiometric amount of nickel reagent. In view of the analogy between metal-benzyne and metalcarboryne complexes [7, 8] and the metal-catalyzed reactions of benzyne with alkenes and alkynes, [9] we wondered if a catalytic version of these nickel-mediated carboryne reactions could be developed.We learnt from the previous stoichiometric reactions that high temperatures were necessary for the insertion of alkynes into the NiÀC cage bonds in nickel-carborynes, and that the final metal complex was a Ni 0 species. [4][5][6] Also, 1-bromo-2-lithiocarborane is a known precursor of carboryne. [2a-e] Therefore, it is rational to assume that 1-bromo-2-lithiocarborane can undergo oxidative addition with Ni 0 to give the desired nickel-carboryne complex after elimination of LiBr. Unfortunately, such an oxidative addition reaction does not proceed at temperatures less than 0 8C and 1-bromo-2-lithiocarborane is not stable at temperatures greater than 0 8C. [1, 2a] Therefore, a new precursor to carboryne is required. After many attempts, we discovered that 1-iodo-2-lithiocarborane is a good precursor for this catalytic cycle. Herein, we report the nickel-catalyzed [2+2+2] cycloaddition of carboryne with 2 equivalents of an alkyne to afford benzocarborane compounds.1-Iodo-2-lithiocarborane was conveniently prepared in situ from the reaction of dilithiocarborane with 1 equivalent of iodine in toluene at room temperature; importantly, 1-iodo-2-lithiocarborane was much more thermally stable than 1-bromo-2-lithiocarborane. Heating a solution of 1-iodo-2-lithiocarborane in benzene overnight afforded the [4+2] cycloaddition product 1,2-(2,5-cyclohexadiene-1,4-diyl)-ortho-carborane in 25 % yield, much higher than the 8 % yield that is afforded from the 1-bromo-2-lithiocarborane precursor.[10] This result suggests that 1-iodo-2-lithiocarborane is a more efficient precursor than the bromo one. We then examined the catalytic activity of various metal complexes in the reaction of 1-iodo-2-lithiocarborane with an excess amount of 3-hexyne in toluene at 110 8C for 2 hours and the results are summarized in Table 1. The Ni 0 ...

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Section: Optimization Of Reaction Conditions[a]mentioning

confidence: 99%

Nickel‐Catalyzed Regioselective [2+2+2] Cycloaddition of Carboryne with Alkynes

2010

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“…The carboryne reactions are usually complicated and do not proceed in a controlled manner. On the other hand, nickel-carboryne complex [(h 2 -C 2 B 10 H 10 )Ni(PPh 3 ) 2 ] [3] can undergo regioselective [2+2+2] cycloaddition reactions with 2 equivalents of alkyne to afford benzocarboranes, [4] can react with 1 equivalent of alkenes to generate alkenylcarborane coupling products, [5] and can undergo a three-component [2+2+2] cyclotrimerization reaction with 1 equivalent of activated alkene and 1 equivalent of alkyne to give dihydrobenzocarboranes. [6] However, these reactions require a stoichiometric amount of nickel reagent.…”

mentioning

confidence: 99%

Nickel‐Catalyzed Regioselective [2+2+2] Cycloaddition of Carboryne with Alkynes

2010

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“…Structural data show that the C cage -C cage bond distance in (η 2 -C 2 B 10 H 10 )Ni(PPh 3 ) 2 (40) [72] is shorter than the corresponding value observed in Zr-carboryne complex [64] , suggestive of the effects of electronic configuration of the metal center on the bonding interactions between the metal atom and carboryne unit. As a result, 40 does not react with any polar unsaturated molecules, but it reacts well with alkynes and alkenes.…”

Section: Reactivity Of Ni-c Cage Bond In Nickel-carborynementioning

confidence: 78%

Unique chemical properties of metal-carbon bonds in metal-carboranyl and metal-carboryne complexes

Qiu

Xie

2009

Sci. China Ser. B-Chem.

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The metal-carbon bonds in metal-carboranyl and metal-carboryne complexes behave very differently from those in classical organometallic complexes. The unique electronic and steric properties of icosahedral carboranyl moiety make the M-C bond in metal-carboranyl complexes inert toward unsaturated molecules, and on the other hand, the sterically demanding carborane cage can induce unexpected C-C coupling reactions. The M-C bonds in metal-carboryne complexes are, however, active toward various kinds of unsaturated molecules and the reactivity patterns are dependent upon the electronic configurations of the metal ions. This account provides an overview of our recent work in this area.boron cluster, carborane, carboryne, insertion, metal-carbon bond

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Unusual chelated o-carborane transition metal complex

Cited by 57 publications

References 0 publications

Nickel‐Catalyzed Regioselective [2+2+2] Cycloaddition of Carboryne with Alkynes

Nickel‐Catalyzed Regioselective [2+2+2] Cycloaddition of Carboryne with Alkynes

Nickel‐Catalyzed Regioselective [2+2+2] Cycloaddition of Carboryne with Alkynes

Unique chemical properties of metal-carbon bonds in metal-carboranyl and metal-carboryne complexes

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