Sulfur Donor Atom Effects on Copper(I)/O2 Chemistry with Thioanisole Containing Tetradentate N3S Ligand Leading to μ-1,2-Peroxo-Dicopper(II) Species

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• 作者：Yunho Lee ; Dong-Heon Lee ; Ga Young Park ; Heather R. Lucas ; Amy A. Narducci Sarjeant ; Matthew T. Kieber-Emmons ; Michael A. Vance ; Ashley E. Milligan ; Edward I. Solomon ; Kenneth D. Karlin
• 刊名：Inorganic Chemistry
• 出版年：2010
• 出版时间：October 4, 2010
• 年：2010
• 卷：49
• 期：19
• 页码：8873-8885
• 全文大小：1230K
• 年卷期：v.49,no.19(October 4, 2010)
• ISSN：1520-510X

文摘

To better understand the effect of thioether coordination in copper-O₂ chemistry, the tetradentate N₃S 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 CH₃CN 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(CH₃OH)]²⁺ (1c) and [(L^ESE)Cu^II(CH₃OH)]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(O₂²⁻)]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(O₂²⁻)]²⁺ (2b^P). Resonance Raman data for [{(L^ASM)Cu^II}₂(O₂²⁻)]²⁺ (1b^P) support the formation of μ-1,2-peroxo species ν(O−O) = 828 cm⁻¹(Δ(¹⁸O₂) = 48), ν_sym(Cu−O) = 547 cm⁻¹ (Δ(¹⁸O₂) = 23), and ν_asym(Cu−O) = 497 cm⁻¹ (Δ(¹⁸O₂) = 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(μ-oxo) species [{(L^EOE)Cu^III}₂(O²⁻)₂]²⁺ (3b^O; 380 nm, ε 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.