Abstract
A series of tridentate pincer ligands, each possessing two sulfur and one nitrogen donor (SNS), based on bis-imidazolyl or bis-triazolyl salts were metallated with CuCl2 to give new tridentate SNS pincer copper(I) complexes [(SNS)Cu]+. These orange complexes exhibit a three-coordinate pseudo-trigonal-planar geometry in copper. During the formation of these copper(I) complexes, disproportionation is observed as the copper(II) salt precursor is converted into the Cu(I) [(SNS)Cu]+ cation and the [CuCl4]2– counteranion. The [(SNS)Cu]+ complexes were characterized with single crystal X-ray diffraction, electrospray mass spectrometry, EPR spectroscopy, attenuated total reflectance infrared spectroscopy, UV–Vis spectroscopy, cyclic voltammetry, and elemental analysis. The EPR spectra are consistent with anisotropic Cu(II) signals with four hyperfine splittings in the lower-field region (g||) and g values consistent with the presence of the tetrachlorocuprate. Various electronic transitions are apparent in the UV–Vis spectra of the complexes and originate in the copper-containing cations and anions. Density functional calculations support the nature of the SNS binding, allowing assignment of a number of features present in the UV–Vis and IR spectra and cyclic voltammograms of these complexes.
Highlights
We have reported a series of tridentate pincer ligand precursors possessing sulfur- and one nitrogen-donor functionalities (SNS) donor atoms [1,2]
The driving force for the metallation is the formation of the the copper complex, which is sparingly soluble in CH2Cl2
Crystals of 5 and 6 suitable for Xray diffraction were grown by allowing diethyl ether vapor to slowly diffuse into an methanol solution containing the copper complex
Summary
We have reported a series of tridentate pincer ligand precursors possessing SNS donor atoms [1,2]. We were able to fine-tune further the electronic environment within the framework of these systems by using imidazolyl- (2a-c) and triazolyl- (3a-c) based precursors in the preparation of the pincer ligands. Use of these variously tuned tridentate ligand sets has allowed us to compare the effect of ligand flexibility on the reactivity of their zinc-bound complexes toward the catalytic reduction of electron-poor aldehydes [1,2]. We present here the syntheses, X-ray crystallographic, spectroscopic and electrochemical characterizations, and computational analysis of our new threecoordinate copper(I) complexes containing a tridentate ligand with two sulfur and one 7 nitrogen donor atoms
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