Sulfur Donor Atom Effects on Copper(I)/O(2) Chemistry with Thioanisole Containing Tetradentate N(3)S Ligand Leading to mu-1,2-Peroxo-Dicopper(II) Species

Abstract

To better understand the effect of thioether coordination in copper-O-2 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-l] (1a). and (L-EOE)Cu-l ](+) (3a), were studied as were the related compound [(L-ESE)Cu-l](+) (2a, L-ESE = (2-ethylthio-N,N-bis((pyridin-2-yl)methy)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(l)-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 (la is similar to 200 mV more positive than 2a). The structures of [(L-ASM)Cu-ll(CH3OH)](2+) (1c) and [(L-ESE)Cu-ll(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 [{(LAsm)Cum}2(022)](2+) (1 bv) 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 [{(LEsE)Cu"}2(022)}2+ (2. 12,. o) Resonance Raman data for [{(LASM)cull}2(022-2+ P)1 (lb)) support the formation of At1,2-peroxo species 11(0-0). 828 cm-10(1802) = 48), v.vm(Cu 0) = 547 cm-1 (418-2, u) = 23), and vasyn,(Cu 0) = 497 cm-1 (418-2, u) = 22) and suggest the LAsm ligand is a poorer electron donor to copper than is LEsE. In contrast, the oxygenation of KLE E)Cuir (3a), possessing an ether donor as an analogue of the thioether in LEsE, led to the formation of a bis(p-oxo) species [{(LEoE)cuiii}2(02)2}2+ (3bo; 380 mil, e,,, 10,000 rvi-1 cm-1). This result provides further support for the sulfur influence in lbP and 2bP, in particular coordination of the sulfur to the Cu. Thermal decomposition Df 11b is accompanied by ligand sulfoxidation. The structure of [{(LE0E)Cu5(C1)}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 1bP, 2bP, and 3b is presented.