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Catalytic Synthesis of Bi‐ and Teraryls in Aqueous Medium with Palladium(II) Complexes of 2‐(Pyridine‐2‐ylmethylsulfanyl)benzoic Acid
Author(s) -
Prakash Om,
Joshi Hemant,
Sharma Kamal Nayan,
Sharma Alpesh Kumar,
Singh Ajai K.
Publication year - 2015
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201403003
Subject(s) - chemistry , phenylboronic acid , catalysis , pyridine , palladium , benzoic acid , ligand (biochemistry) , coupling reaction , medicinal chemistry , yield (engineering) , aqueous solution , suzuki reaction , homogeneous catalysis , solubility , inorganic chemistry , nuclear chemistry , organic chemistry , biochemistry , materials science , receptor , metallurgy
Abstract Suzuki–Miyaura coupling reactions of phenylboronic and 1,4‐phenylenediboronic acid with ArBr to form bi‐ and teraryls have been efficiently catalyzed by the air‐ and moisture‐insensitive complexes [PdCl 2 L1 ] [ 1 , L1 = 2‐(pyridine‐2‐ylmethyl)sulfanylbenzoic acid; 0.05–0.5 mol‐%] and [Pd( L2 ‐H) 2 ] ( 2 , L2 ‐H = 2‐pyridin‐2‐yl‐benzo[b]thiophen‐3‐ol; 0.01–0.5 mol‐%). The complexes were formed by the reaction of [Pd(CH 3 CN) 2 Cl 2 ] with L1 , and the catalysis proceeds in water for 1 . The loading of 0.1–0.5 mol‐% of Pd is very promising for the coupling reactions to form teraryls. The COOH group imparts solubility to 1 in water. Ligand L2 is formed by the unprecedented cyclization of L1 in the course of the complexation reaction. The yield of 2 increases with the reaction time (5 h: 70 %; 24 h: 85 %). The two complexes and L1 have been characterized by NMR spectroscopy ( 1 H and 13 C{ 1 H}). The single‐crystal structures of 1 and 2 have been solved, and the Pd–S, Pd–N, and Pd–O bond lengths are 2.269(2), 1.999(6)–2.057(2), and 1.9787(17) Å, respectively. Nanoparticles (NPs) with a narrow size distribution (ca. 3.0–5.5 nm for 80–85 % of the particles) formed at the start of these reactions and appear to be important for the catalytic coupling. Poisoning experiments and a two‐phase test have shown that the catalysis is largely homogeneous and involves [Pd 0 –Pd II ] processes. The bond lengths and angles calculated by DFT are consistent with the experimental ones.