Electrospray ionization mass spectrometric study of 1,3,4‐oxadiazole–copper complexes

Abstract

The complexes of 2,5-disubstituted-1,3,4-oxadiazoles, namely 2,5-diphenyl-1,3,4-oxadiazole (1), 2,5-bis(2-pyridyl)-1,3,4-oxadiazole (2) and 2,5-bis(4-pyridyl)-1,3,4-oxadiazole (3), with copper cation were studied by electrospray ionization mass spectrometry (ESI-MS). The ability of the compounds studied to form complexes with copper (under the ESI conditions) can be ordered as 2 > 1 > 3. The compounds studied tend to form both 1 : 1 and 2 : 1 chelate complexes with both copper(II) and copper(I). The complexes with copper(I) are formed in the ESI process. The influence of solvent polarity, solution flow-rate, counter ions (Cl − , NO 3 − , CH 3 COO − , SO 4 2− , acetylacetonates) on the type of the ions observed was studied.

Oxadiazoles

“…A study regarding the electron-spray ionization mass spectra of 2,5-diaryl and 2-arylamino-5-aryl-1,3,4-oxadiazoles together with their complexes with copper cations has been reported [507]. In this latter case, loss of NH 3 and HNCO was observed.…”

Electrospray ionization mass spectrometric study of 1,3,4‐thiadiazole–copper complexes: comparison with 1,3,4‐oxadiazole derivatives

“…The concentration of 1-6 and CuCl 2 was 3.0 ð 10 5 M (always in a 1 : 1 ratio). The sample solutions were infused into the ESI source using a Harvard pump; the flow-rate was 40 µl min 1 . The ESI source potentials were capillary 3 kV, lens 0.5 kV, extractor 4 V and cone voltage 30 V. The source temperature was 120°C and the desolvation temperature was 300°C.…”

Aerobic Oxidation of Benzylic Alcohols in Water by 2,2,6,6‐Tetramethylpiperidine‐1‐oxyl (TEMPO)/Copper(II) 2‐N‐Arylpyrrolecarbaldimino Complexes

“…Such peak patterns are common during the electrospray ionization. [20] After addition of benzyl alcohol and TEMPO to the mixture of K 2 CO 3 and 1 no peaks related to the substrate or TEMPO coordination could be identified. It is worthy of note that the identified complex cations in the MS appear formally as Cu(I) species and their formation is presumably related to the redox processes that can occur in the gas phase.…”

“…It is worthy of note that the identified complex cations in the MS appear formally as Cu(I) species and their formation is presumably related to the redox processes that can occur in the gas phase. [20] To summarize, in alkaline media one ligand from the initial complex has cleaved and this opens two new coordination sites at the Cu center.…”