Palladacycles of sulfated and selenated Schiff bases of ferrocene-carboxaldehyde as catalysts for O-arylation and Suzuki-Miyaura coupling

• Published in: Dalton transactions : an international journal of inorganic chemistry Vol. 46; no. 8; pp. 2485 - 2496
• Main Authors: Sharma, Alpesh K., Joshi, Hemant, Bhaskar, Renu, Kumar, Satyendra, Singh, Ajai K.
• Format: Journal Article
• Language: English
• Published: CAMBRIDGE Royal Soc Chemistry 2017
• Subjects: Chemistry; Chemistry, Inorganic & Nuclear; Physical Sciences; Science & Technology; SULFUR-CONTAINING PALLADACYCLES; C-O; HIGHLY-ACTIVE CATALYSTS; PALLADIUM COMPLEXES; PHENYLBORONIC ACID; ARYL HALIDES; SINGLE-SOURCE PRECURSORS; N-HETEROCYCLIC CARBENES; ALKYL CHAIN-LENGTH; REDUCTIVE ELIMINATION
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c7dt00083a

Schiff base ligands (L1: sulfated and L2: selenated) having a ferrocene core synthesized by reacting ferrocene-carboxaldehyde with 2-(phenylthio/seleno) ethylamine on treatment with Na2PdCl4 in the presence of NaOAc give cyclopalladated complexes [Pd(L1/L2-H)Cl] (1/2). Complex 1 of a sulfated Schiff base L1, on reacting with one equivalent of triphenylphosphine gives complex [Pd(L1-H)PPh3Cl] (3), formed due to cleavage of a Pd-S bond. With 2 such a reaction does not occur, as a Pd-Se bond being stronger than that of its sulfur analogue does not get cleaved. L1, L2 and their complexes 1-3 were authenticated with HR-MS, H-1, C-13{H-1} and Se-77{H-1} NMR spectroscopy. The single crystal structures of 1-3 were determined with X-ray diffraction. Palladium in all three complexes has nearly a square planar geometry. The Pd-S, Pd-Se and Pd-P bond distances are 2.4249(12), 2.5058(14) and 2.2445(17) <(A)over dot> respectively. The catalytic activity of complexes 1-3 was explored for O-arylation of phenol and Suzuki-Miyaura coupling (SMC) of phenylboronic acid with aryl bromides and chlorides. The optimum reaction time for SMC of ArBr is 3 h whereas for ArCl it is 6 h. The TON values of O-arylation catalyzed with complexes 1-3 are up to similar to 170 (TOF, 28 h(-1)) and SMC similar to 9300 (TOF, 3100 h(-1)) for the reaction time of the order of 3 and 6 h respectively. The catalytic process is somewhat more efficient with 2 (Pd bonded with a selenoether group), than 3, followed by 1.