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Cyclometalated Iridium(III) Complexes with Ligand Effects on the Catalytic C–H Bond Activation of Toluene
Author(s) -
Chen TsunRen,
Liu PeiChun,
Lee HsiuPen,
Wu FangSiou,
Chen Kelvin H. C.
Publication year - 2017
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.201601548
Subject(s) - chemistry , toluene , iridium , catalysis , denticity , ligand (biochemistry) , xanes , medicinal chemistry , organic chemistry , spectroscopy , crystal structure , receptor , biochemistry , physics , quantum mechanics
New cyclometalated iridium(III) complexes have been designed, prepared and applied as catalytic systems for the C–H bond activation (CHA) of toluene through a clean, highly efficient, and environmentally friendly process. The complexes have the general formula [(C ^ N) 2 Ir(N ^ O)]. The C ^ N ligands are the monoanionic bidentate cyclometalating ligands 2‐phenylpyridinato (ppy), 2‐phenylbenzoxazolato (pbo), and 2‐(3.5‐difluorophenyl)benzoxazolato (dfpbo). The (N ^ O) ligand is also a monoanionic bidentate cyclometalating ligand, namely picolinato (pic). The complexes [(ppy) 2 Ir(pic)] ( 1 ), [(pbo) 2 Ir(pic)] ( 2 ), and [(dfpbo) 2 Ir(pic)] ( 3 ) were structurally characterized by 1 H and 13 C NMR spectroscopy, FAB‐MS, and X‐ray crystallography. The activation energies for the catalytic CHA oxidation of toluene when using complexes 1 – 3 as catalysts are quite low, between 14.4 and 25.5 kcal mol –1 . The catalytic turnover frequencies (TOFs) are fairly high (up to 4.0 × 10 3 mol toluene mol catalyst –1 h –1 ) with excellent reliability and the turnover number (TON) can reach 2.40 × 10 4 mol toluene mol catalyst –1 after 6 h of reaction time. A combination of catalytic tests, DFT calculations, X‐ray absorption near‐edge structure (XANES) analysis, and kinetic modeling was used to derive detailed insights into the characteristics of the catalysts and their effect on the reactions featured in the CHA oxidation of toluene.