Photochemical reactivity of two gold(I) dinuclear complexes, cis/trans-(AupNBT)2dppee: Isomerization for the cis-(AupNBT)2dppee isomer, radical substitution for trans-(AupNBT)2dppee

Two complexes, cis (1) and trans (2) (AupNBT)2dppee (pNBT = p-nitrobenzenethiol; dppee = bis(diphenylphosphino)ethylene) have been synthesized and characterized. X-ray diffraction studies reveal that cis-(AupNBT)2dppee has an intramolecular gold–gold distance of 3.0036(3) Å while the trans-(AupNBT)2dppee crystal is a dimer with an intermolecular gold–gold distance of 3.1201(4) Å. We have used UV–Vis spectroscopy, 1H NMR, and 31P {1H} NMR to investigate the photochemical reactivity of both complexes. In a range of organic solvents with λ > 230 nm cis-(AupNBT)2dppee readily isomerizes to the trans isomer. Under these same conditions, the trans isomer does not isomerize to cis-(AupNBT)2dppee, but undergoes a photochemical substitution reaction. In chlorinated solvents (CH2Cl2, CH3Cl) trans-(AupNBT)2dppee reacts to form trans-(AuCl)2dppee (3) which crystallizes into an extended chain of molecules linked via intermolecular gold–gold distances of 3.0203(2) Å. TDDFT calculations support the observed experimental results. We propose that at high energies the reaction is initiated by chlorine radicals from direct photolysis of the solvent. At longer wavelengths the excited state of the metal complex is the photoactive species, abstracting a chlorine radical from the solvent.

Cis and trans isomers of (AupNBT)2dppee were synthesized and characterized. Cis-(AupNBT)2dppee isomerizes to the trans isomer. The trans-(AupNBT)2dppee, when photolyzed at high and low (λ > 420 nm) energies in chlorinated solvents, produces the trans-(AuCl)2dppee. Two mechanisms are proposed to explain the formation of trans-(AuCl)2dppee at both wavelength ranges. TDDFT calculations support the experimental results.Figure optionsDownload as PowerPoint slideHighlights
► Synthesis and characterization of two gold(I) dinuclear complexes.
► Cis-(AupNBT)2dppee isomerizes to trans when exposed to light.
► Light initiates ligand substitution for trans-(AupNBT)2dppee in CH2Cl2.
► TDDFT analysis of frontier orbitals of both complexes.