Syntheses, Structures, and O2-Reactivities of Copper(I) Complexes with Bis(2-pyridylmethyl)amine and Bis(2-quinolylmethyl)amine Tridentate Ligands

The structure and O2-reactivity of the copper(I) complexes supported by bis[(6-phenyl-2-pyridyl)methyl]amine tridentate ligands (L5R) and bis(2-quinolylmethyl)amine tridentate ligands (L6R) have been investigated in detail in order to get insights into the steric effects of the tridentate ligands on copper(I)/O2 chemistry. In the cases of benzyl amine and phenethyl amine derivatives [R = –CH2Ph (Bz) and –CH2CH2Ph (Phe)], the reaction between the ligands and [CuI(CH3CN)4]+ gave the corresponding copper(I)–acetonitrile complexes having a distorted tetrahedral geometry. On the other hand, the 2,2-diphenylethyl amine derivative L6R [R = –CH2CHPh2 (PhePh)] afforded a copper(I) complex without an ancillary ligand (CH3CN) and having intramolecular d–π interaction between the copper(I) ion and the phenyl group of the alkyl substituent PhePh. The acetonitrile complexes were then converted to the corresponding CO-complexes by reacting with CO gas. The X-ray structures of all CO-complexes have been determined, and the complexes have a similar distorted tetrahedral geometry. In addition, the 6-phenyl group of L5R imparts a large steric effect on the metal-binding. The CO-complexes were converted to the copper(I) complexes without having any ancillary ligands in order to examine their O2-reactivity. Significantly large differences in O2-reactivity were found among the copper(I) complexes. On the basis of O2-reactivity together with the X-ray structures and the oxidation potentials of the copper(I) complexes, the steric effects of the hetero-aromatic donor groups (6-substituted pyridine and quinoline) as well as the alkyl substituents (R) are discussed in detail.