Polymer-Supported-Cobalt-Catalyzed Regioselective Cyclotrimerization of Aryl Alkynes

Abstract

A convoluted poly­(4-vinylpyridine) cobalt­(II) (P4VP-CoCl2) system was developed as a stable and reusable heterogeneous catalyst. The local structure near the Co atom was determined on the basis of experimental data and theoretical calculations. This immobilized cobalt catalyst showed high selectivity and catalytic activity in the [2 + 2 + 2] cyclotrimerization of terminal aryl alkynes. With 0.033 mol % P4VP-CoCl2, the regioselective formation of 1,3,5-triarylbenzene was realized without 1,2,4-triarylbenzene formation. Further, a multigram-scale (11 g) reaction proceeded efficiently. In addition, the polymer-supported catalyst was successfully recovered and used three times. X-ray photoelectron spectroscopy analysis of the recovered catalyst suggested that cobalt was in the +2 oxidation state. The 1,3,5-triarylbenzene derivatives were applied to the synthesis of a molecular beam electron resist and a polycyclic aromatic hydrocarbon.

An overview of the synthetic strategies ofC3-symmetric polymeric materials containing benzene and triazine cores and their biomedical applications

“…Moreover, the polymer-supported catalyst was successfully recovered and used three times ( Table 1 , entry 1-c). 25 …”

Continuous‐Flow Suzuki‐Miyaura Coupling in Water and Organic Solvents Promoted by Blends of Stabilized Convoluted Polymeric Palladium Catalysts and Polymeric Auxiliary Materials

“…Self-assembled convoluted polymeric palladium catalysts were prepared from (NH 4 ) 2 PdCl 4 and polymeric ligands via our molecular convolution method (Table S3). [10,12] An aqueous solution of (NH 4 ) 2 PdCl 4 was dropwise added to a suspension of poly(4VP-co-4tBS) in propan-2-ol, and the resulting mixture was stirred at 60 °C for 20 h. The yellowish precipitate of poly(4VP-co-4tBS)-Pd was filtered and washed. The molar ratio of Pd atoms to pyridine units was adjusted to 1 : 3, as reported in our previous work.…”

Regioselectively switchable alkyne cyclotrimerization catalyzed by a Ni(ii)/bidentate P-ligand/Zn system with ZnI2 as an additive

“…Our exploration was initiated by performing a benchmark reaction of 4-tolylacetylene (1a) in the presence of 10 mol% Ni (PPh 3 ) 2 Cl 2 and 20 mol% zinc powder in acetonitrile at room temperature, which afforded a mixture of 1,2,4-tris(4-tolyl) benzene (2a) and 1,3,5-tris(4-tolyl)benzene (3a) in an overall yield of 56% with a 69 : 31 ratio of 2a to 3a (Table 1, entry 1). Initial variations in Ni(II) pre-catalysts (see the ESI, Table S1, † entries 1-8), solvents (see the ESI, Table S1, † entries 9-12) or reductants (see the ESI, Table S1, † entries [13][14][15][16][17] were very unsuccessful, leading to a lower or even no conversion and poor selectivity. To our pleasure, when an additional ligand, 1,4-bis(diphenylphosphino)butane (dppb), was utilized, an excellent outcome was achieved: a 94% overall yield and a 97 : 3 ratio of the 1,2,4-isomer to the 1,3,5-isomer (see the ESI, Table S1, † entry 18).…”

“…To the best of our knowledge, such a 1,3,5-regioisomer synthesis from alkynes, with the advantages of simple catalytic systems, mild conditions, cheap reagents and excellent outcomes, has not yet been disclosed. [11][12][13][14][15][16] Substrate scope. I.…”

“…In contrast, very limited catalytic systems were found to selectively prepare the 1,3,5-substitution pattern of poly-substituted benzenes, which feature geometric symmetry and electronic uniformity and could have intriguing applications in materials science and biochemistry. 10 The synthesis of 1,3,5-substituted benzenes usually involves expensive reagents, elaborately designed ligands or structurally complicated complexes, as shown in the cases of mononuclear titanium, 11 iron 12 and indium 13 complexes, dinuclear chromium 14 and niobium 15 catalysts and polymer-supported cobalt 16 catalysts (Scheme 1A(b)). A very recent publication 17 reported the Ni( ii )–B(OH) 2 co-catalyzed cycloaddition reaction of terminal alkynes for the highly regioselective synthesis of 1,3,5-substitution products at a relatively high temperature (Scheme 1A(c)).…”