Three-Component [2+2+1] Cross-cyclotrimerization of Carboryne, Unactivated Alkene, and Trimethylsilylalkyne Co-mediated by Zr and Ni

Quan, Yangjian; Zhang, Jiji; Xie, Zuowei

doi:10.1021/ja410233e

Cited by 32 publications

(26 citation statements)

References 53 publications

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“…36 The results show that the ligand has a major influence on product formation with triphenylphosphine offering the excellent selectivity for dihydrobenzocarboranes and trimethylphosphine giving the best selectivity for dihydrofulvenocarboranes. The E/Z selectivity (configuration of alkenes) is dominated by the relative size of R/TMS.…”

Section: Reaction With Alkenesmentioning

confidence: 96%

Recent advances in transition metal-mediated functionalization of o-carboranes

Qiu

2015

Tetrahedron Letters

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a b s t r a c tIcosahedral carboranes constitute a class of structurally unique molecules with exceptionally thermal and chemical stabilities, which limits the derivatization of these clusters. In view of the spectacular role of transition metals in synthetic chemistry, novel o-carborane functionalization methods for both cage carbon and boron vertices have been developed by using transition metal-promoted reactions. These methods offer a series of exceptionally efficient synthetic routes to a wide range of functionalized carboranes from readily available starting materials. An overview of recent advances in this field is presented in this digest.

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Section: Reaction With Alkenesmentioning

confidence: 96%

Recent advances in transition metal-mediated functionalization of o-carboranes

Qiu

2015

Tetrahedron Letters

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“…According to previous reports [17], alkene insertion into the Ni-C bond is preferred over alkyne insertion when the Ni-carboranyl compound undergoes cycloaddition with alkene and alkyne. Also, in the presence of NiCl 2 (PMe 3 ) 2 , o-carboranylzirconacycle R1 would interact with alkene R2 and the catalyst to form a nickelacyclopentane intermediate M1 by transmetallation [16,20,26], then M1 complexes with alkyne to form a new compound INT1 (Scheme 2). However, affected by variable orientation of n Bu group in intermediate M1 and subsequent B-H activation sites of o-carborane, the reaction shown in Scheme 1 led to a diastereoselective mixture of P1a and P1b (dr ≈ 1:1) [25].…”

Section: Formation Mechanism Of Dihydrofulvenocarborane Intermediate mentioning

confidence: 99%

“…However, owing to simultaneous existence of multiple B-H bonds with varying chemical environment, the regioselective activation of B-H bond in o-carborane remains a challenging topic Pioneered by previous reports [20,26], authors speculated that the reaction of ocarboranylzirconacycle (R1), n-hexene (R2) and 2-bromophenyltrimethylsilylacetylene (R3), as shown in Scheme 1, might go through the nickelacyclopentane intermediate M1, dihydrofulvenocarborane intermediates M2 and M3, the nickelacycloheptene intermediates M4 (or M4') sequentially, and form the C,C,B-substituted o-carborane-fused tricyclic derivative P1a/b in the end. However, due to the limitation of experimental means in detecting unstable and reactive intermediates, the aforementioned mechanism is still under proposal.…”

Section: Introductionmentioning

confidence: 99%

Computational Investigation of Nickel-Mediated B–H Activation and Regioselective Cage B–C(sp2) Coupling of o-Carborane

Liu

Cheng

et al. 2019

Catalysts

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Density functional theory (DFT) methods including LC-ωPBE, CAM-B3LYP, B3LYP, and B3LYP-D3, combined with double Zeta all-electron DZVP basis set, have been employed to conduct computational investigations on nickel-mediated reaction of o-carboranylzirconacycle, n-hexene, and 2-bromophenyltrimethylsilylacetylene in toluene solution. A multistep mechanism leading to the C,C,B-substituted carborane-fused tricyclics, including (1) sequential insertion of alkene and alkyne into Ni-C bonds; (2) double 1,2-migration of the TMS group; (3) B-H activation assisted by Cs 2 CO 3 additive; and (4) reduction cage B-C (sp 2 ) coupling, was proposed. Among these steps, the B-H activation of o-carborane was located as rate-determining step (RDS). With assistance of Cs 2 CO 3 additive (replaced by K 2 CO 3 in simulation), the RDS free-energy barrier at PCM-LC-ωPBE/DZVP level was calculated to be 23.1-23.9 kcal·mol −1 , transferring to a half-life of 3.9-15.1 h at 298 K. The predicted half-life coincides well with 80% experimental yields of C,C,B-substituted carborane-fused tricyclics after 12 h. Kinetic data obtained by employing LC-ωPBE method also reproduced the experimental diastereoselective ratio well. Various B-H activation pathways with and without Cs 2 CO 3 additive were taken into consideration, which illustrates Cs 2 CO 3 as an essential guarantee for smooth occurrence of this reaction at room temperature.Catalysts 2019, 9, 548 2 of 16 and has always been a focus in the field [10][11][12][13]. In recent decades, people have made significant achievements in nickel-catalyzed selective activation of B-H bonds in o-carborane, generally by introducing a directing group in substrates. For example, in 2010, Qiu and Xie had realized the palladium/nickel co-mediated [2+2+2] cyclization of 1-lithium-2-methyl-3-iodo-o-carborane with twice equivalent of alkynes, and prepared 1-C-3-B-substituted o-carborane derivative successfully [24]. This reaction has not only excellent yield but also good regioselectivity. In 2014, Xie's group had achieved three-component cyclization of o-carborane with olefin and halogenated phenyl alkyne through zirconium/nickel co-mediated coupling, and prepared a series of novel C,C,B-substituted carborane-fused tricyclics successfully (Scheme 1) [25]. This work represents the first example of cage B-C(sp 2 ) coupling by direct B-H activation of o-carborane, which is of great significance for the regioselective B-H activation and functionalization of o-carborane derivatives. What particularly worth mentioning is, the reaction can process at room temperature and corresponding C,C,B-substituted carborane-fused tricyclics (P1) can be obtained with a yield up to 80% by adding Cs 2 CO 3 additive (Entry 2 in Scheme 1). Catalysts 2019, 9, x FOR PEER REVIEW 2 of 16 achievements in nickel-catalyzed selective activation of B-H bonds in o-carborane, generally by introducing a directing group in substrates. For example, in 2010, Qiu and Xie had realized the palladium/nickel co-mediated [2+2+2] cyclization of 1-lithium-2-...

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“…Carboranes are biocompatible, resistant to enzymatic modification, and can be linked to or incorporated within a variety of different targeting vectors. Their unique reactivity allows for ease of derivatization of either of the CH vertices and regioselective modification of select boron atoms within the cage, in high yield [18][19][20][21][22][23][24]. Carboranes have been incorporated into small molecules as hydrophobic pharmacophores [5,[24][25][26][27][28][29][30][31][32][33][34], novel biomaterials including liposomes [14,35], and dendrimers [36,37].…”

Section: Introductionmentioning

confidence: 99%