Air- and Water-Tolerant (PNP)Ir Precatalyst for the Dehydrogenative Borylation of Terminal Alkynes

Foley, Bryan J.; Ozerov, Oleg V.

doi:10.1021/acs.organomet.0c00250

Cited by 10 publications

(7 citation statements)

References 29 publications

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“…42,48,56 Alternatively, [(COD)M(OAc)] 2 (M = Ir, Rh) was also used in the metalation of the pincer ligands to yield the products (L)Ir(H)(OAc). 30,48 The κ 2 -acetate ligand provides protection to the sixth coordination site of the Ir center (Scheme 3, method C). Another approach (Scheme 3, method D) was described by Waterman and co-workers, who reported that the reaction of the ligand precursor L1-H with [(COE) 2 IrCl] 2 under an atmosphere of H 2 gave a high yield of (L1)Ir(H)(Cl).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…The pyridine ligand can then be abstracted with boron trifluoride diethyl etherate (BF 3 ·OEt 2 ) to give the desired five-coordinate complex ( L )Ir(H)(Cl). This approach has been reported to access clean (POCOP)Ir and (POCOP)Rh complexes. ,, Alternatively, [(COD)M(OAc)] 2 (M = Ir, Rh) was also used in the metalation of the pincer ligands to yield the products ( L )Ir(H)(OAc). , The κ 2 -acetate ligand provides protection to the sixth coordination site of the Ir center (Scheme , method C). Another approach (Scheme , method D) was described by Waterman and co-workers, who reported that the reaction of the ligand precursor L1-H with [(COE) 2 IrCl] 2 under an atmosphere of H 2 gave a high yield of ( L1 )Ir(H)(Cl) …”

Section: Resultsmentioning

confidence: 99%

“…The synthesis of derivatives of organoboronic acids via homogeneous catalysis of C–H bond borylation (Scheme A) is an attractive method of preparation of versatile synthetic building blocks. − The most impressive foundational successes in this chemistry have been associated with catalysis of aromatic C–H borylation by Ir complexes supported by neutral bidentate ligands. − Catalytic borylation of aromatic and other sp 2 and sp 3 C–H bonds has also been realized with a variety of transition-metal and main-group complexes. − Our group has reported on the catalysis of dehydrogenative borylation of the sp C–H bonds in terminal alkynes (DHBTA) using Ir complexes supported by diarylamido-centered SiNN , or PNP − pincer − ligands. Catalysis of DHBTA with other metals has also been reported, − but the activity and the chemoselectivity of the Ir catalysts are superior.…”

Section: Introductionmentioning

confidence: 99%

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Examination of a Series of Ir and Rh PXL Pincer Complexes as (Pre)catalysts for Aromatic C–H Borylation

et al. 2021

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This work follows a previously published study of high-turnover aromatic C–H borylation by Ir complexes supported by POCOP-type ligands incorporating −PiPr2 side donors (L1–L3) using HBpin in the presence of olefins. A variety of pincer-supported Ir and Rh complexes have been tested as precatalysts in the analogous aromatic C–H borylation. The ligands in this study included a number of aryl/bis(phosphine) pincers of the PCP type, as well as PCS, PNP, PNSb, PSiP, and PBP ligands. The syntheses primarily targeted precursors of the (PXL)M(H)(Cl) type (M = Rh, Ir); exceptions included complexes (L15)Ir(H)(OAc), (L17)Ir(COE), (L18)Ir(H)4, and (L16)Rh(H2). The catalytic competence was tested using C6D6 as the substrate (and solvent) with HBpin and 1-hexene as reagents. C–H borylation and hydroboration of 1-hexene were the two competing catalytic reactions. None of the Rh complexes tested displayed any C–H borylation activity. Among the Ir complexes, only those possessing a central aryl site in the pincer showed significant C–H borylation activity with C6D6. The most promising precatalysts (L3)Ir(H)(Cl), (L4)Ir(H)(Cl), (L7)Ir(H)(Cl), (L11)Ir(H)(Cl), (L13)Ir(H)(Cl), and (L15)Ir(H)(OAc) were tested in the C–H borylation of C6H5F and C6H5CF3. All of these catalysts showed a roughly statistical preference for the borylation of only meta and para sites in C6H5CF3. For C6H5F borylation of all three sites (ortho, meta, para) was observed. Catalysts supported by the ligands L3 and L11 showed the highest rate of reaction and higher selectivity for C–H borylation vs hydroboration. Borylation of m-ClC6H4Me catalyzed by (L3)Ir(H)(Cl) and (L11)Ir(H)(Cl) resulted in only the borylation of only one aromatic C–H site (meta to both substituents), <10% of borylation of the benzylic site, and no borylation of the C–Cl moiety.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Examination of a Series of Ir and Rh PXL Pincer Complexes as (Pre)catalysts for Aromatic C–H Borylation

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“…However, due to the common intermediates and the small differences of the barriers, the system could jump among the three cycles, making the mechanism very complicated (Scheme ). Very recently, Ozerov developed an air‐ and water‐stable (PNP)Ir precatalyst, allowing the reaction to take place under an air atmosphere, simplifying the manipulation …”

Section: Formation Of Spc−heteroatom Bondsmentioning

confidence: 99%

Cross‐Dehydrogenative Alkynylation: A Powerful Tool for the Synthesis of Internal Alkynes

et al. 2020

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“…Although the catalysts from other literature reports mentioned above − are based on cheaper metals (Fe, Cu, Zn), the (PNP)Ir catalysts are much more active and can be used at much lower catalyst loading while displaying equal or superior scope and chemoselectivity. We have also been able to demonstrate that (PNP)Ir-catalyzed DHBTA exhibits reasonable tolerance of the presence of air and water and that >10 5 turnovers were possible …”

Section: Introductionmentioning

confidence: 76%

Combined Experimental and Computational Studies of the Mechanism of Dehydrogenative Borylation of Terminal Alkynes Catalyzed by PNP Complexes of Iridium

et al. 2020

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Iridium complexes supported by four different diarylamido/bis(phosphine) PNP ligands have been studied as catalysts for the dehydrogenative borylation of terminal alkynes (DHBTA). Experimental mechanistic investigations on a representative ligand system established that the reaction rate is zeroth order in the concentration of the borylating agent HBpin, first order in [alkyne] and in [Ir], and inverse first order in [H 2 ]. These findings are understood as arising from the formation of the saturated, 18-electron resting state (PNP)IrH 3 Bpin (5a), which is required to dissociate H 2 in order to enter the C−H oxidative addition reaction with the alkyne. However, the overall highest transition state corresponds to the B−H rotation following C−H oxidative addition. This realization follows from the density functional theory (DFT) calculations and is consistent with the modest experimentally determined kinetic isotope effect of 1.5(1) for C−H/C−D. DFT-calculated ΔG 298 ⧧ = 17.6 kcal/mol and ΔH ⧧ = 13.9 kcal/mol match the experimentally determined values (ΔG 298 ⧧ = 20(2) kcal/mol and ΔH ⧧ = 16(2) kcal/mol) reasonably well. DFT calculations were used to demonstrate that the boryl migration from the amido N to Ir is too high in energy to play a part in the DHBTA mechanism in the (PNP)Ir system. This is in surprising contrast to the seemingly closely related (SiNN)Ir system studied previously. DFT calculations further provide insights into the greater kinetic barrier for activating a C−H bond of a terminal alkyne trans to a boryl ligand versus trans to a hydride, explaining why diboryl Ir compounds are not catalytically competent in this system.

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Air- and Water-Tolerant (PNP)Ir Precatalyst for the Dehydrogenative Borylation of Terminal Alkynes

Cited by 10 publications

References 29 publications

Examination of a Series of Ir and Rh PXL Pincer Complexes as (Pre)catalysts for Aromatic C–H Borylation

Examination of a Series of Ir and Rh PXL Pincer Complexes as (Pre)catalysts for Aromatic C–H Borylation

Cross‐Dehydrogenative Alkynylation: A Powerful Tool for the Synthesis of Internal Alkynes

Combined Experimental and Computational Studies of the Mechanism of Dehydrogenative Borylation of Terminal Alkynes Catalyzed by PNP Complexes of Iridium

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