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Copper(I)/O2 chemistry with imidazole containing tripodal tetradentate ligands leading to mu-1,2-peroxo-dicopper(II) species.

ABSTRACT: Cuprous and cupric complexes with the new imidazolyl containing tripodal tetradentate ligands {L(MIm), (1H-imidazol-4-yl)-N,N-bis((pyridin-2-yl)methyl)methanamine, and L(EIm), 2-(1H-imidazol-4-yl)-N,N-bis((pyridin-2-yl)methyl)ethanamine}, have been investigated to probe differences in their chemistry, especially in copper(I)-dioxygen chemistry, compared to that already known for the pyridyl analogue TMPA, tris(2-pyridyl)methyl)amine. Infrared (IR) stretching frequencies obtained from carbon monoxide adducts of [(L(MIm))Cu(I)](+) (1a) and [(L(EIm))Cu(I)](+) (2a) show that the imidazolyl donor is stronger than its pyridyl analogue. Electrochemical data suggest differences in the binding constant of Cu(II) to L(EIm) compared to TMPA and L(MIm), reflecting geometric changes. Oxygenation of [(L(MIm))Cu(I)](+) (1a) in 2-methyltetrahydrofuran (MeTHF) solvent at -128 degrees C leads to an intensely purple colored species with a UV-vis spectrum characteristic of an end-on bound peroxodicopper(II) complex [{(L(MIm))Cu(II)}(2)(mu-1,2-O(2)(2-))](2+) (1b(P)) {lambda(max) = 528 nm}, very similar to the previously well characterized complex [{(TMPA)Cu(II)}(2)(mu-1,2-O(2)(2-))](2+) {lambda(max) = 520 nm (epsilon = 12 000 M(-1) cm(-1)), in MeTHF; resonance Raman (rR) spectroscopy: nu(O-O) = 832 (Delta((18)O(2)) = -44) cm(-1)}. In the low-temperature oxygenation of 2a, benchtop (-128 degrees C) and stopped-flow (-90 degrees C) experiments reveal the formation of an initial superoxo-Cu(II) species [(L(EIm))Cu(II)(O(2)(*-))](+) (2b(S)), lambda(max) = 431 nm in THF) . This converts to the low-temperature stable peroxo complex [{(L(EIm))Cu(II)}(2)(mu-1,2-O(2)(2-))](2+) (2b(P)) {rR spectroscopy: nu(O-O) = 822 (Delta((18)O(2)) = -46) cm(-1)}. Complex 2b(P) possess distinctly reduced Cu-O and O-O stretching frequencies and a red-shifted UV-vis feature {to lambda(max) = 535 nm (epsilon = 11 000 M(-1) cm(-1))} compared to the TMPA analogue due to a distortion from trigonal bipyramidal (TBP) to a square pyramidal ligand field. This distortion is supported by the structural characterization of related ligand-copper(II) complexes: A stable tetramer cluster complex [(mu(2)-L(EIm-))(4)(Cu(II))(4)](4+), obtained from thermal decomposition of 2b(P) (with formation of H(2)O(2)), also exhibits a distorted square pyramidal Cu(II) ion geometry as does the copper(II) complex [(L(EIm))Cu(II)(CH(3)CN)](2+) (2c), characterized by X-ray crystallography and solution electron paramagnetic resonance (EPR) spectroscopy.

SUBMITTER: Lee Y

PROVIDER: S-EPMC2787896 | biostudies-literature | 2009 Dec

REPOSITORIES: biostudies-literature

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Copper(I)/O2 chemistry with imidazole containing tripodal tetradentate ligands leading to mu-1,2-peroxo-dicopper(II) species.

Lee Yunho Y Park Ga Young GY Lucas Heather R HR Vajda Peter L PL Kamaraj Kaliappan K Vance Michael A MA Milligan Ashley E AE Woertink Julia S JS Siegler Maxime A MA Narducci Sarjeant Amy A AA Zakharov Lev N LN Rheingold Arnold L AL Solomon Edward I EI Karlin Kenneth D KD

Inorganic chemistry 20091201 23

Cuprous and cupric complexes with the new imidazolyl containing tripodal tetradentate ligands {L(MIm), (1H-imidazol-4-yl)-N,N-bis((pyridin-2-yl)methyl)methanamine, and L(EIm), 2-(1H-imidazol-4-yl)-N,N-bis((pyridin-2-yl)methyl)ethanamine}, have been investigated to probe differences in their chemistry, especially in copper(I)-dioxygen chemistry, compared to that already known for the pyridyl analogue TMPA, tris(2-pyridyl)methyl)amine. Infrared (IR) stretching frequencies obtained from carbon mono ...[more]

PMID: 19886646

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Project description:To better understand the effect of thioether coordination in copper-O(2) chemistry, the tetradentate N(3)S ligand L(ASM) (2-(methylthio)-N,N-bis((pyridin-2-yl)methyl)benzenamine) and related alkylether ligand L(EOE) (2-ethoxy-N,N-bis((pyridin-2-yl)methyl)ethanamine) have been studied. The corresponding copper(I) complexes, [(L(ASM))Cu(I)](+) (1a) and [(L(EOE))Cu(I)](+) (3a), were studied as were the related compound [(L(ESE))Cu(I)](+) (2a, L(ESE) = (2-ethylthio-N,N-bis((pyridin-2-yl)methyl)ethanamine). The X-ray structure of 1a and its solution conductivity reveal a monomeric molecular structure possessing thioether coordination which persists in solution. In contrast, the C-O stretching frequencies of the derivative Cu(I)-CO complexes reveal that for these complexes, the modulated ligand arms, whether arylthioether, alkylthioether, or ether, are not coordinated to the cuprous ion. Electrochemical data for 1a and 2a in CH(3)CN and N,N-dimethylformamide (DMF) show the thioanisole moiety to be a poor electron donor compared to alkylthioether (1a is ?200 mV more positive than 2a). The structures of [(L(ASM))Cu(II)(CH(3)OH)](2+) (1c) and [(L(ESE))Cu(II)(CH(3)OH)](2+) (2c) have also been obtained and indicate nearly identical copper coordination environments. Oxygenation of 1a at reduced temperature gives a characteristic deep blue intermediate [{(L(ASM))Cu(II)}(2)(O(2)(2-))](2+) (1b(P)) with absorption features at 442 (1,500 M(-1) cm(-1)), 530 (8,600 M(-1) cm(-1)), and 605 nm (10,400 M(-1) cm(-1)); these values compare well to the ligand-to-metal charge-transfer (LMCT) transitions previously reported for [{(L(ESE))Cu(II)}(2)(O(2)(2-))](2+) (2b(P)). Resonance Raman data for [{(L(ASM))Cu(II)}(2)(O(2)(2-))](2+) (1b(P)) support the formation of ?-1,2-peroxo species ?(O-O) = 828 cm(-1)(?((18)O(2)) = 48), ?(sym)(Cu-O) = 547 cm(-1) (?((18)O(2)) = 23), and ?(asym)(Cu-O) = 497 cm(-1) (?((18)O(2)) = 22) and suggest the L(ASM) ligand is a poorer electron donor to copper than is L(ESE). In contrast, the oxygenation of [(L(EOE))Cu(I)](+) (3a), possessing an ether donor as an analogue of the thioether in L(ESE), led to the formation of a bis(?-oxo) species [{(L(EOE))Cu(III)}(2)(O(2-))(2)](2+) (3b(O); 380 nm, ? ? 10,000 M(-1) cm(-1)). This result provides further support for the sulfur influence in 1b(P) and 2b(P), in particular coordination of the sulfur to the Cu. Thermal decomposition of 1b(P) is accompanied by ligand sulfoxidation. The structure of [{(L(EOE))Cu(II)(Cl)}(2)](+) (3c) generated from the reductive dehalogenation of organic chlorides suggests that the ether moiety is weakly bound to the cupric ion. A detailed discussion of the spectroscopic and structural characteristics of 1b(P), 2b(P), and 3b(O) is presented.

Project description:Current interest in copper/dioxygen reactivity includes the influence of thioether sulfur ligation, as it concerns the formation, structures, and properties of derived copper-dioxygen complexes. Here, we report on the chemistry of {L-Cu(I)}2-(O2) species L = (DMM)ESE, (DMM)ESP, and (DMM)ESDP, which are N3S(thioether)-based ligands varied in the nature of a substituent on the S atom, along with a related N3O(ether) (EOE) ligand. Cu(I) and Cu(II) complexes have been synthesized and crystallographically characterized. Copper(I) complexes are dimeric in the solid state, [{L-Cu(I)}2](B(C6F5)4)2, however are shown by diffusion-ordered NMR spectroscopy to be mononuclear in solution. Copper(II) complexes with a general formulation [L-Cu(II)(X)](n+) {X = ClO4(-), n = 1, or X = H2O, n = 2} exhibit distorted square pyramidal coordination geometries and progressively weaker axial thioether ligation across the series. Oxygenation (-130 °C) of {((DMM)ESE)Cu(I)}(+) results in the formation of a trans-μ-1,2-peroxodicopper(II) species [{((DMM)ESE)Cu(II)}2(μ-1,2-O2(2-))](2+) (1(P)). Weakening the Cu-S bond via a change to the thioether donor found in (DMM)ESP leads to the initial formation of [{((DMM)ESP)Cu(II)}2(μ-1,2-O2(2-))](2+) (2(P)) that subsequently isomerizes to a bis-μ-oxodicopper(III) complex, [{((DMM)ESP)Cu(III)}2(μ-O(2-))2](2+) (2(O)), with 2(P) and 2(O) in equilibrium (K(eq) = [2(O)]/[2(P)] = 2.6 at -130 °C). Formulations for these Cu/O2 adducts were confirmed by resonance Raman (rR) spectroscopy. This solution mixture is sensitive to the addition of methylsulfonate, which shifts the equilibrium toward the bis-μ-oxo isomer. Further weakening of the Cu-S bond in (DMM)ESDP or substitution with an ether donor in (DMM)EOE leads to only a bis-μ-oxo species (3(O) and 4(O), respectively). Reactivity studies indicate that the bis-μ-oxodicopper(III) species (2(O), 3(O)) and not the trans-peroxo isomers (1(P) and 2(P)) are responsible for the observed ligand sulfoxidation. Our findings concerning the existence of the 2(P)/2(O) equilibrium contrast with previously established ligand-Cu(I)/O2 reactivity and possible implications are discussed.

Dataset Information

Copper(I)/O2 chemistry with imidazole containing tripodal tetradentate ligands leading to mu-1,2-peroxo-dicopper(II) species.

Publications

Copper(I)/O2 chemistry with imidazole containing tripodal tetradentate ligands leading to mu-1,2-peroxo-dicopper(II) species.

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