Cobalt-Catalyzed C–H Borylation

Obligacion, Jennifer V.; Semproni, Scott P.; Chirik, Paul J.

doi:10.1021/ja500712z

Cited by 288 publications

(207 citation statements)

References 37 publications

Supporting

Mentioning

198

Contrasting

Unclassified

Order By: Relevance

“…The 31 P NMR spectrum displays a broad peak at 121.0 ppm. The IR absorption spectrum of solid 2b displays a clear N−H stretch at 3322 cm 4 ] 2 in THF/CH 3 CN, followed by cooling to 238 K and addition of an equivalent of KC 8 . The dark purple product, 2c, was filtered, washed with diethyl ether, and isolated in 72% yield.…”

Section: ■ Introductionmentioning

confidence: 99%

Reactivity of a Series of Isostructural Cobalt Pincer Complexes with CO₂, CO, and H⁺

et al. 2014

View full text Add to dashboard Cite

The preparation and characterization of a series of isostructural cobalt complexes [Co(t-Bu)2PEPyEP(t-Bu)2(CH3CN)2][BF4]2 (Py = pyridine, E = CH2, NH, O, and X = BF4 (1a–c)) and the corresponding one-electron reduced analogues [Co(t-Bu)2PEPyEP(t-Bu)2(CH3CN)2][BF4]2 (2a–c) are reported. The reactivity of the reduced cobalt complexes with CO2, CO, and H+ to generate intermediates in a CO2 to CO and H2O reduction cycle are described. The reduction of 1a–c and subsequent reactivity with CO2 was investigated by cyclic voltammetry, and for 1a also by infrared spectroelectrochemistry. The corresponding CO complexes of (2a–c) were prepared, and the Co–CO bond strengths were characterized by IR spectroscopy. Quantum mechanical methods (B3LYP-d3 with solvation) were used to characterize the competitive reactivity of the reduced cobalt centers with H+ versus CO2. By investigating a series of isostructural complexes, correlations in reactivity with ligand electron withdrawing effects are made.

show abstract

Section: ■ Introductionmentioning

confidence: 99%

Reactivity of a Series of Isostructural Cobalt Pincer Complexes with CO₂, CO, and H⁺

et al. 2014

View full text Add to dashboard Cite

show abstract

“…50−54 Furthermore, the ( iPr PNP)cobalt platform promotes two-electron oxidative addition 53 and has been applied to catalytic C–H borylation. 50,52 …”

mentioning

confidence: 99%

“…Synthesis of the target ( iPr PNP)CoOR complexes was accomplished by protonolysis of the cobalt(I) alkyl complex ( iPr PNP)CoCH 2 SiMe 3 52 with a stoichiometric quantity of the appropriate alcohol (ROH, Scheme 3). In this manner, a series of paramagnetic cobalt(I) aryloxides ( iPr PNP)CoOR and alkoxides were prepared.…”

mentioning

confidence: 99%

Insight into Transmetalation Enables Cobalt-Catalyzed Suzuki–Miyaura Cross Coupling

2016

Self Cite

View full text Add to dashboard Cite

Among the fundamental transformations that comprise a catalytic cycle for cross coupling, transmetalation from the nucleophile to the metal catalyst is perhaps the least understood. Optimizing this elementary step has enabled the first example of a cobalt-catalyzed Suzuki–Miyaura cross coupling between aryl triflate electrophiles and heteroaryl boron nucleophiles. Key to this discovery was the preparation and characterization of a new class of tetrahedral, high-spin bis(phosphino)pyridine cobalt(I) alkoxide and aryloxide complexes, (iPrPNP)CoOR, and optimizing their reactivity with 2-benzofuranylBPin (Pin = pinacolate). Cobalt compounds with small alkoxide substituents such as R = methyl and ethyl underwent swift transmetalation at 23 °C but also proved kinetically unstable toward β–H elimination. Secondary alkoxides such as R = iPr or CH(Ph)Me balanced stability and reactivity. Isolation and structural characterization of the product following transmetalation, (iPrPNP)Co(2-benzofuranyl), established a planar, diamagnetic cobalt(I) complex, demonstrating the high- and low-spin states of cobalt(I) rapidly interconvert during this reaction. The insights from the studies in this elementary step guided selection of appropriate reaction conditions to enable the first examples of cobalt-catalyzed C–C bond formation between neutral boron nucleophiles and aryl triflate electrophiles, and a model for the successful transmetalation reactivity is proposed.

show abstract

“…Under the standard conditions, C 6 H 5 Bpin (2b) and C 6 D 5 Bpin (2b¤) were obtained in 82% combined yield in a ratio of 1.99:1. We also independently monitored the reaction progress 10 of the CH borylation of toluene (1a) and toluene-d 8 (Figure 3b). These experiments indicate that CH cleavage is probably involved in the rate-determining step of …”

Section: Boron Sourcementioning

confidence: 99%

“…Although these precious metals exhibit high efficiency, the utilization of inexpensive catalysts in CH borylation is attractive for good reasons. Recently, several non-noble metal catalysts such as cyclopentadienyl iron N-heterocyclic carbene, 5 Fe 2 O 3 nanoparticles, 6 heterobimetallic copper complexes, 7 and pincerligated cobalt complexes 8 have been reported to catalyze CH borylation reactions. On the other hand, nickel has not been utilized as a catalyst for CH borylation although various nickelcatalyzed CH functionalizations have been reported in recent years.…”

mentioning

confidence: 99%

Aromatic C–H Borylation by Nickel Catalysis

2015

View full text Add to dashboard Cite

The first nickel-catalyzed aromatic CH borylation is described. In the presence of catalytic amounts of [Ni(cod) 2 ], tricyclopentylphosphine, and CsF, benzene and indole derivatives can be borylated with B 2 pin 2 . The N-heterocyclic carbene IPr was also found to be an effective ligand. Kinetic isotope effect experiments showed that CH cleavage is likely involved in the rate-determining step.In recent years, CH functionalization has been extensively investigated and widely used as it allows the streamlined synthesis of functional molecules such as pharmaceuticals, natural products, and organic materials.1 For example, increasing efforts have been devoted to the development of CH borylation for aromatic compounds, due to the significant opportunity of using organoboron compounds in synthesis ( Figure 1 9 We herein report our discovery of enabling ligands and additives to achieve the first nickel-catalyzed CH borylation (Figure 1). We began our study by examining various nickel salts, ligands, and additives in the reaction of toluene (1a) and bis(pinacolato)diboron (B 2 pin 2 ). After extensive screening, we determined that the reaction of 1a (56 equiv, 3 mL) with B 2 pin 2 (0.5 mmol, 1.0 equiv) in the presence of [Ni(cod) 2 ] (10 mol %; cod: 1,5-cyclooctadiene), tricyclopentylphosphine (PCyp 3 , 20 mol %), and CsF (25 mol %) at 140°C for 24 h afforded the corresponding borylated product 2a in 88% GC yield (based on B 2 pin 2 ) as a mixture of regioisomers (o/m/p = 8:61:31) (Figure 2).The list in Figure 2 contains some examples of variations from the standard conditions. In the absence of [Ni(cod) 2 ] or using nickel(II) salts, essentially no CH borylation reaction occurred. The use of HBpin resulted in a much lower yield of 2a (29%). The product 2a was obtained in lower yield without PCyp 3 . Triisopropylphosphine (P i Pr 3 ) and tributylphosphine (P n Bu 3 ) showed less efficiency than PCyp 3 , and triphenylphosphine (PPh 3 ) was completely ineffective for CH borylation. Bidentate ligands such as 1,2-bis(dicyclohexylphosphino)ethane (dcype) and 4,4¤-di-tert-butyl-2,2¤-dipyridyl (dtbpy), 3 the standard ligands for iridium-catalyzed CH borylation, were also not effective. However, we found that the N-heterocyclic carbene ligand 1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene (IPr) showed efficiency similar to PCyp 3 under these conditions and a dramatic additive effect of CsF was notable. No products were obtained in the absence of CsF or presence of other alkali fluorides. Lowering the temperature led to decreased yield.With the optimized conditions in hand, the substrate scope of the [Ni(cod) 2 ]/PCyp 3 -catalyzed CH borylation was investigated (Table 1 Figure 2. Discovery of nickel-catalyzed CH borylation and effect of parameters.

show abstract

Cobalt-Catalyzed C–H Borylation

Cited by 288 publications

References 37 publications

Reactivity of a Series of Isostructural Cobalt Pincer Complexes with CO₂, CO, and H⁺

Reactivity of a Series of Isostructural Cobalt Pincer Complexes with CO₂, CO, and H⁺

Insight into Transmetalation Enables Cobalt-Catalyzed Suzuki–Miyaura Cross Coupling

Aromatic C–H Borylation by Nickel Catalysis

Contact Info

Product

Resources

About

Cobalt-Catalyzed C–H Borylation

Cited by 288 publications

References 37 publications

Reactivity of a Series of Isostructural Cobalt Pincer Complexes with CO2, CO, and H+

Reactivity of a Series of Isostructural Cobalt Pincer Complexes with CO2, CO, and H+

Insight into Transmetalation Enables Cobalt-Catalyzed Suzuki–Miyaura Cross Coupling

Aromatic C–H Borylation by Nickel Catalysis

Contact Info

Product

Resources

About

Reactivity of a Series of Isostructural Cobalt Pincer Complexes with CO₂, CO, and H⁺

Reactivity of a Series of Isostructural Cobalt Pincer Complexes with CO₂, CO, and H⁺