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Copper‐Mediated Oxygenolysis of Flavonols via Endoperoxide and Dioxetan Intermediates; Synthesis and Oxygenation of [Cu II (Phen) 2 (Fla)]ClO 4 and [Cu II (L)(Fla) 2 ] [FlaH = Flavonol; L = 1,10‐Phenanthroline (Phen), 2,2′‐Bipyridine (Bpy), N , N , N ′, N ′‐Tetramethylethylenediamine (TMEDA)] Complexes
Author(s) -
BaloghHergovich Éva,
Kaizer József,
Pap József,
Speier Gábor,
Huttner Gottfried,
Zsolnai László
Publication year - 2002
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 - 10.1002/1099-0682(200209)2002:9<2287::aid-ejic2287>3.0.co;2-3
Subject(s) - chemistry , triclinic crystal system , copper , phenanthroline , trigonal bipyramidal molecular geometry , medicinal chemistry , ligand (biochemistry) , crystallography , stereochemistry , crystal structure , organic chemistry , biochemistry , receptor
[Cu(phen) 2 (fla)]ClO 4 was prepared by treating [Cu(CH 3 CN) 4 ]ClO 4 with flavonol (flaH) in the presence of 1,10‐phenanthroline (phen) as a co‐ligand. Its oxygenation in DMF (or CH 3 CN) solution at elevated temperature gave the ( O ‐benzoylsalicylato)copper(II) complex [Cu(phen) 2 ( O ‐bs)]ClO 4 (bs = benzoylsalicylato) and carbon monoxide via an endoperoxide intermediate. Crystallographic characterisation of [Cu(phen) 2 ( O ‐bs)]ClO 4 as the CH 2 Cl 2 solvate [triclinic, space group P $\bar 1$ , a = 10.499(3) Å, b = 12.556(4) Å, c = 17.094(5) Å, α = 72.69(2), β = 89.35(2), γ = 69.19(2)°, V = 1999.7(10) Å 3 , Z = 2, R 1 = 0.0962] shows that the molecule has a distorted trigonal‐bipyramidal structure (τ = 0.96). The oxygenolysis was monitored by spectrophotometry, and the pseudo‐first‐order rate constant k′ phen was found to be (2.47 ± 0.11) × 10 −4 s −1 at 120 °C. Complexes of [Cu(L)(4′R‐fla) 2 ] (L = phen, bpy, TMEDA; R = H, OCH 3 , CH 3 , Cl) were also prepared by treating the complexes Cu(4′R‐fla) 2 with nitrogen‐containing co‐ligands. Their oxygenation resulted in the corresponding complexes Cu(L)(2HOpg) 2 (2HOpg =2‐hydroxyphenylglyoxylate) derived by spontaneous hydrolysis of Cu(L)(bpg) 2 (bpg = 2‐benzoatophenylglyoxylate). The (phenylglyoxylato)copper complexes were probably formed via 1,2‐dioxetan intermediates, since the oxygenation of Cu(phen)(fla) 2 showed chemiluminescence with bands at 506, 546, and 578 nm in the emission spectrum due to the decomposition of a 1,2‐dioxetan species. Labelling experiments with an 18 O 2 / 16 O 2 mixture (1:3) showed the incorporation of both 18 O atoms of 18 O 2 into the flavonolate ligand. The kinetics of the oxygenolysis of Cu(L)(fla) 2 gave rate constants according to the rate law −d[Cu(L)(4′R‐fla) 2 ]/dt = k [Cu(L)(4′R‐fla) 2 ][O 2 ]: k / M −1 s −1 = (9.50 ± 0.60) × 10 −2 (L = phen), (2.40 ± 0.10) × 10 −2 (L = bpy), (2.00 ± 0.10) × 10 −2 (L = TMEDA) M −1 s −1 at 353.16 K. The oxygenolysis of the complexes Cu(phen)(4′R‐fla) 2 fits a Hammett linear free energy relationship and an increase of the electron density on the copper ion makes the oxygenation reaction faster. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)