Bisimino-functionalized dibenzo[a, c]acridines as highly conjugated pincer frameworks for palladium(ii): synthesis, characterization and catalytic performance in Heck coupling. Issue 12 (29th September 2016)

• Record Type: Journal Article
• Authors: Mahmood, Qaiser; Yue, Erlin; Zhang, Wenjuan; Solan, Gregory A.; Liang, Tongling; Sun, Wen-Hua
• Is Part Of: Organic chemistry frontiers. Volume 3:Issue 12(2017:Dec.)
• Page Start: 1668
• Page End: 1679
• Publication Date: 2016-09-29
• Subjects: Chemistry, Organic -- Periodicals; 547.005
• DOI: 10.1039/c6qo00469e
• Languages: English
• ISSNs: 2052-4110

Abstract

Abstract : The NNC-Pd pincer complexes, systematically derived from phenanthrene-9, 10-dione, are able to efficiently mediate the coupling of haloarenes with vinyl-containing substrates (up to TON = 174 000) with a broad substrate scope. Abstract : A new pair of highly conjugated ligands, 10-[1-(arylimino)ethyl]-14-[(arylimino)methyl]dibenzo[ a, c ]acridine (aryl = 2, 6-Me2 PhL1, 2, 6-Et2 PhL2 ) incorporating both aldimine and ketimine units, have been prepared by a straightforward sequence of organic transformations from phenanthrene-9, 10-dione. Cyclopalladation occurs readily at ambient temperature on treatingL1 orL2 with PdCl2 (NCCH3 )2 in aprotic solvents to afford exclusively (Nketimine NC)Pd(ii ) chloride pincer complexesPd1 orPd2, respectively. By contrast in methanol, Pd1 orPd2 are isolated as the minor product with aldehyde-containingPd3 orPd4 as the major one, the result of hydrolysis of the pendant aldimine units inPd1 andPd2, respectively. All the ligands and palladium complexes have been characterized by FT-IR, 1 H and 13 C NMR spectroscopy, mass spectrometry and elemental analysis; the molecular structures forL1, Pd1, Pd2, Pd3 andPd4 are also reported. Using low catalyst loadings (0.0005–0.002 mol%) and elevated temperatures (140–200 °C), Pd1–Pd4 are able to efficiently mediate the coupling of haloarenes with vinyl-containing substrates with turnover numbers as high as 174 000; the effects of steric/electronic variation within the substrate and NNC-pincer complex on catalyst performance are examined.