Sterically hindered selenoether ligands: palladium(ii) complexes as catalytic activators for Suzuki–Miyaura coupling

Abstract

52-Hydroxy/(benzyloxy)-3,5-ditertbutyl benzaldehyde reacts with PhSeCH 2 CH 2 NH 2 resulting in sterically hindered selenoether ligand (Schiff base) [2−HO−3,5−(C(CH 3 ) 3 ) 2 −C 6 H 2 −C=N−(CH 2 ) 2 SePh] (L1)/ [2−PhCH 2 O−3,5−(C(CH 3 ) 3 ) 2 −C 6 H 2 −CH 2 −NH−(CH 2 ) 2 SePh] (L2). The reactions of L1 and L2 with Na 2 PdCl 4 in methanol and acetone-water mixture at room temperature have resulted in complexes, [PdCl (L1-H)] (1) and [PdCl 2 (L2)] (2)], respectively. Both the complexes and their ligands have been 10 characterized with 1 H, 13 C{ 1 H} and 77 Se{ 1 H} NMR spectroscopy. The molecular structures of complexes 1 and 2 have been determined with single crystal X-ray diffraction. The Pd−Se bond lengths in 1 and 2 are 2.370(1) and 2.366(1) Å, respectively. The geometry around palladium in both the complexes is nearly square planar. Complexes 1 and 2 (0.1 mol % Pd) have been found efficient as catalyst for Suzuki-Miyaura C−C coupling reactions in the presence of K 2 CO 3 in ethanol. The catalysis in water with 15 complex 1 in the presence of K 2 CO 3 was found feasible but with low conversion (up to 40%). The efficiency of 1 in carrying out the coupling is marginally better than that of 2. 65 range of substrates and many functional groups are tolerated due to mild reaction conditions. This is very helpful in the total synthesis of complex molecules including drugs. (ii) Phenylboronic acid, starting material is readily available, stable and sustainable. 15 (iii) The product biaryl is a very important core 70 component of various biologically and pharmaceutically important compounds (viz. anti-hypertensive, anti-cancer, antibiotic, anti-inflammatory, and antifungal) and in nonlinear optical materials. 16 75

Palladium(II) Chloride Complexes of N,N′-Disubstituted Imidazole-2-thiones: Syntheses, Structures, and Catalytic Performances in Suzuki–Miyaura and Sonogashira Coupling Reactions

“…Complex 3d exhibited the highest catalytic activity of the five binuclear complexes, indicating that introducing two bulky C 6 Me 3 H 2 groups on the 2 and 5 positions of imidazole-2-thione did improve the catalytic performance. As discussed above, the longest Pd−μ-S bond and the enlarged S–Pd–S angle in 3d may favor the reductive elimination and thus increase the stability of coordinatively unsaturated active catalytic species. , Such a structure-to-activity relationship is in good agreement with previous observations , and is confirmed by our theoretical calculations described below. Complexes 3d , 4a , and 5a were thus chosen as a model system to optimize reaction conditions.…”

Design, Synthesis, and Characterization of a Novel Magnetically Recoverable Copper Nanocatalyst Containing Organoselenium Ligand and Its Application in the A3 Coupling Reaction

“…In the past few decades, organic compounds containing selenium have attracted remarkable concern because of numerous uses in the synthesis of organic and natural products, , pharmacological properties, , biochemistry, catalytic activity, , and synthesis of conducting and semiconducting materials . Also, a series of unique features of these compounds such as the potency of strong electron donating of selenium, stability against moisture and air, and solubility in diverse solvents have led to the preparation of diverse metal complexes of organoselenium ligands. − The promising catalytic activity of these complexes has been displayed in different organic chemical transformations including carbon–carbon coupling reactions, direct boronation of allyl alcohols, oxidation of alcohols, transfer hydrogenation of ketones, and coupling of allyl alcohols and aldehydes …”

“…The catalytic role of these metal complexes, which are especially thermally stable and resistant to aerial oxidation, makes them not only rivals but special alternatives to their respective sulfur and phosphorus analogues . All of the aforementioned selenium-containing complexes are homogeneous catalysts, and there exist only a few reports in the literature on which solid supports are used for the immobilization of metal complexes of selenium-containing ligands as heterogeneous catalytic systems. − Although common catalysts with homogeneous nature possess many advantages, such as excellent activity, efficient selectivity, high product yields, and high turnover number, various problems including tedious and time-consuming separation processes and remaining impurities inclusive the ligand or metal in the structure of final products, the lack of catalyst reusability, and the loss of valuable metals cause some limitations to the wide use of these catalysts in industrial applications. − On the other hand, despite having outstanding characteristics such as reusability and much less leaching, the activity and selectivity of heterogeneous catalysts are decreased compared with those of homogeneous ones .…”

A Selenium-Containing Diarylamido Pincer Ligand: Synthesis and Coordination Chemistry with Group 10 Metals

“…These values are consistent with reported values of bidentate ligands (2.3575(3) Å for [PdCl 2 { o -NH 2 (SePh)­C 6 H 4 }]; 2.3806(7) Å for [PdCl 2 {1-PhSe-2-(4–Br-C 3 H 3 N 2 )­C 2 H 4 }]) and tridentate ligands (2.370(1) Å for [PdCl­{2-O-3,5-(C­(CH 3 ) 3 ) 2 -C 6 H 2 –CN-(CH 2 ) 2 SePh}]; 2.3910(13) Å for Na­[PdCl­{2,6-(CH 2 (SePh)) 2 -C 5 H 3 N}]­[PdCl 4 ]) . The Pd–N bond length of 3-Pd is 1.999(4) Å, which is very similar to the value of 2.035(3) Å for [PdCl 2 {1-PhSe-2-(4-Br-C 3 H 3 N 2 )­C 2 H 4 }], and within experimental error of the distance of 1.996(4) Å for [PdCl­{2-O-3,5-(C­(CH 3 ) 3 ) 2 -C 6 H 2 -CN-(CH 2 ) 2 SePh}] …”