CpCo(<scp>i</scp>) precatalysts for [2 + 2 + 2] cycloaddition reactions: synthesis and reactivity

Fischer, Fabian; Pientka, Tobias; Jiao, Haijun; Spannenberg, Anke; Hapke, Marko

doi:10.1039/d0cy00876a

Cited by 6 publications

(9 citation statements)

References 47 publications

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“…Clearly, the substitution did not change the reactivity profile significantly. Interestingly, the yield obtained in this transformation for catalyst 2 is in the range of the most reactive CpCo(olefin)(phosphite) precatalysts for the reaction at 75 • C [19]. Investigation of other ligands containing partially thus being less electron-rich like in complexes 4, 6 an 8% to 27% (Table 1, entries [4][5][6].…”

Section: Screening On Catalytic Activity Of the Cpco(iii) Precatalystsmentioning

confidence: 91%

“…Utilization of 10 mol% (estimated for assumed complete conversion of 2) for the catalytic cyclization of 16 furnished the expected product 16cycl, albeit with slightly lower yield than before, not providing any significant advantage. A comparable investigation of 1,6-heptadiyne and benzonitrile as standard system for pyridine formation by co-cyclo-trimerization gave mediocre 30% yield of pyridine 19, which is significantly lower compared to CpCo(olefin)(phosphite) precatalysts under identical conditions [19]. Replication of the experiment by treating partially fluorinated complex 4 with MeMgBr and direct subsequent reaction of the reaction product with triyne 16 gave cyclization product 16cycl with 31% yield (44% 16 recovered).…”

Section: Screening On Catalytic Activity Of the Cpco(iii) Precatalystsmentioning

confidence: 93%

“…These complexes are air-stable compounds, soluble in polar organic solvents. It is interesting to note that the 31 P NMR shifts in complexes 2 (117.4 ppm) and 3 (118.0 ppm) are shifted around 50 ppm to higher field compared to the CpCo(CO)(phosphite) complexes and shifted still roughly 30 ppm to higher field in the case of CpCo(olefin)(phosphite) complexes [19]. Both classes of neutral ligands with low-lying * orbitals inherit ligand back-bonding capabilities for electron density from the cobalt center, thus allowing larger electron-density donation from the phosphites to the metal center compared to the iodide atoms in 2 and 3.…”

Section: Synthesis Of Cpco(iii) Complexesmentioning

confidence: 96%

“…Subsequent direct use of the generated species 9-Me as catalyst gave surprising results compared to Scheme 5. In the case of pyridine (19) synthesis, the yields are slightly lower, independent from the reaction temperature and no difference appeared for 9-Me at both temperatures (compare Schemes 5 and 6, below). The picture is different for the cyclization of 16, where the yield was basically doubled at 100 • C reaction temperature and are still significantly higher at 75 • C compared to 2-Me (Scheme 6, top).…”

Section: Screening On Catalytic Activity Of the Cpco(iii) Precatalystsmentioning

confidence: 97%

“…31 P NMR (122 MHz, CDCl3): δ = 126.7 ppm. 19 F NMR (282 MHz, CDCl3): δ = −71.9 ppm. Synthesis of CpCoI 2 [P(OC 6 F 5 ) 3 ] (6): According to GP1, the phosphite P(OC 6 F 5 ) 3 (1.43 g, 2.46 mmol, 1 eq.)…”

Section: Synthesis Of Complexesmentioning

confidence: 99%

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CpCo(III) Precatalysts for [2+2+2] Cycloadditions

2021

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Catalysts applied in cobalt-catalyzed cyclotrimerizations reactions in general rely on the use of Co(I) precatalysts or the in situ generation of Co(I) catalysts from Co(II) sources by reduction in the presence of steering ligands, often by addition of less noble metals. In this paper, we report the synthesis and properties of novel stable CpCo(III) complexes as precatalysts and their exemplary evaluation for application in catalytic [2+2+2] cycloadditions. The role of phosphite neutral ligands, as well as iodide and cyanide as anionic ligands, on the reactivity of the complexes was evaluated. A modified one-pot approach to the synthesis of Cp ring-functionalized Cp’Co(III) complexes was developed. The investigations demonstrated that CpCo(III) complexes can be directly applied as catalysts in catalytic cyclotrimerizations of triynes without reducing agents as additives.

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Section: Screening On Catalytic Activity Of the Cpco(iii) Precatalystsmentioning

confidence: 91%

Section: Screening On Catalytic Activity Of the Cpco(iii) Precatalystsmentioning

confidence: 93%

Section: Synthesis Of Cpco(iii) Complexesmentioning

confidence: 96%

Section: Screening On Catalytic Activity Of the Cpco(iii) Precatalystsmentioning

confidence: 97%

Section: Synthesis Of Complexesmentioning

confidence: 99%

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CpCo(III) Precatalysts for [2+2+2] Cycloadditions

2021

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Cobalt‐Catalyzed [2 + 2 + 2] Cycloaddition Reactions

Glasel,

Hapke

2023

Patai's Chemistry of Functional Groups

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Cobalt‐catalyzed [2 + 2 + 2] cycloaddition reactions are an important tool for the assembly of carbo‐ and hetero‐cyclic ring systems from simple precursor molecules such as alkynes, alkenes, nitriles, and other heterocumulenes such as isocyanates. Cyclopentadienyl (Cp)‐cobalt complexes are still one of the most important classes of catalysts, but in situ generated cobalt catalyst systems are becoming increasingly important for the assembly of achiral as well as chiral target molecules from a large variety of substrates. Substrates comprise simple terminal as well as internal alkynes, diynes, and higher oligoynes and also allow target‐oriented syntheses of unusually large as well as highly substituted molecules as well as natural product synthesis with a cyclotrimerization as the key step of the synthetic sequence. The utilization of olefins as cyclization partners allows the synthesis of products with lesser degree of unsaturation such as cyclohexadienes, cyclohexenes, and dihydropyridines, just to name a view examples. Chiral catalyst systems allow the enantioselective synthesis of biaryls and products with central chirality, and chiral starting materials allow the synthesis of diastereomeric helicenes in an efficient manner. Novel catalysts and reaction engineering allow reaction conditions such as conventional thermal or microwave heating, photochemically assisted cyclizations, and the use of plug‐flow reactors.

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Photoredox‐Enabled Manganese‐Catalyzed [2+2+2] Cycloaddition of Alkynes

Zhou,

He,

Wang

et al. 2024

Adv Synth Catal

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Manganese (Mn) is the third most abundant transition metal on Earth and is known for its exceptional biocompatibility. The development of novel catalytic mode for Mn is of great significance to advancing organic synthesis. In this study, the first manganese (Mn)‐catalyzed [2+2+2] cycloaddition of alkynes is achieved with the aid of visible‐light photoredox catalysis. Photoredox catalysis is proposed to promote the transformation by in situ reduction of high‐valent Mn(II) complex to Mn(0) species, thereby initiating the reaction. Additionally, a photooxidation‐induced reductive ellimination step is also suggested. This system is further distinguished by its notable tolerance towards both terminal and internal alkynes as counterparts of diynes.

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CpCo(i) precatalysts for [2 + 2 + 2] cycloaddition reactions: synthesis and reactivity

Abstract: The efficient synthesis and structural characterisation of a series of novel CpCo(I)-olefin-phosphite/phosphoramidite complexes and their evaluation in catalytic cyclotrimerisation reactions is reported. The synthetic protocol for precatalyst synthesis is widely...

Cited by 6 publications

References 47 publications

CpCo(III) Precatalysts for [2+2+2] Cycloadditions

CpCo(III) Precatalysts for [2+2+2] Cycloadditions

Cobalt‐Catalyzed [2 + 2 + 2] Cycloaddition Reactions

Photoredox‐Enabled Manganese‐Catalyzed [2+2+2] Cycloaddition of Alkynes

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