Inorg Chem 2020 Sep 20;59(17):12586-12594. Epub 2020 Aug 20.
Departamento de Química Inorgánica, Facultad de Ciencias, Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), CSIC-Universidad de Zaragoza, Pedro Cerbuna 12, 50009 Zaragoza, Spain.
The model -DFT for the butterfly complex [{Pt(CC*)(μ-pz)}] (; HCC* = 1-(4-(ethoxycarbonyl)phenyl)-3-methyl-1-imidazol-2-ylidene) shows two minima in the potential energy surface of the ground state in acetone solution: the butterfly-wing-spreading molecules , ( ≈ 3.20 Å) and the wing-folding molecules ( ≤ 3.00 Å). Both minima are very close in energy (Δ° = 1.7 kcal/mol) and are connected through a transition state, which lies only 1.9 kcal/mol above and 0.2 kcal/mol above . These very low barriers support a fast interconversion process, resembling a , and the presence of both conformers in acetone solution. However, the ratio is so low that it is undetectable in the excitation and emission spectra of in 2-MeTHF of diluted solutions (10 M) at 77 K, while it is seen in more concentrated solutions (10 M). In acetone solution, undergoes a [2c, 2e] oxidation by CHX (X = Cl, Br) in the sunlight to render the Pt(III,III) compounds [{Pt(CC*)(μ-pz)X)}] (X = Cl (), Br ()). In concentrated solutions, can react with CHCl under blue light to give and with CHBr in the dark, the latter rendering the compound [BrPt(CC*)(μ-pz)Pt(CC*)CHBr] () or mixtures of and if the reaction is performed under an argon atmosphere or in the air, respectively. Mechanistic studies showed that in concentrated solutions the oxidation processes follow a radical mechanism being the MMLCT-based species , those which trigger the reaction of with CHBr and CHCl. In the ground state (S), it promotes the thermal oxidation of by CHBr and in the first singlet excited state (S) the blue-light-driven photooxidation of by CHCl. Complexes, , , and were selectively obtained and fully characterized, showing Pt-Pt distances (ca. 2.6 Å) shorter than that of the starting complex, . They are, together with the analogous [{Pt(CC*)(μ-pz)I)}] and [IPt(CC*)(μ-pz)Pt(CC*)CHI], the only dinuclear metal-metal-bonded Pt(μ-pz)Pt compounds reported to date.