Spectroscopy and kinetics of intermediates in photochemistry of xanthate Ni(S2COEt)2 complex in CCl4

The laser flash photolysis made it possible to determine the mechanism of photochemical reactions of the xanthate Ni(S2COEt)(2) = Ni(xan)(2) complex in CCl4. Upon the excitation of Ni(xan)(2) complex, several fast processes occur. In the first of them, an electron is transferred from -S2COEt = (center dot)xan ligand to Ni(II) ion with the formation of (S2COEt)-S-center dot = (center dot)xan radical in coordination sphere of now Ni(I) ion. Then electron is transferred from Ni(I) to CCl4 molecule located in the second coordination sphere (CCl4 is a good electron acceptor). The nascent CCl4 center dot- anion-radical rapidly dissociates into Cl- ion and CCl3 center dot radical. In the solvent with low dielectric constant, a negatively charged Cl- ion is incorporated into the coordination sphere of positively charged [Ni+2 ((-)xan)((center dot)xan)](+) complex with the formation of neutral primary transient [Cl-Ni2+(S--(2) COEt) (center dot S2 COEt)] = [Cl- Ni2+ ((-)xan) ((center dot)xan)](+) radical complex during a laser pulse (5 ns). This particle disappears in a fast reaction with the initial Ni(xan)(2) complex with the formation of [ClNi(xan)((center dot)xan)Ni(xan)(2)] dimer (rate constant 2 x 10(9) M-1 s(-1)). The dimers disappear in second-order reaction (recombination) in millisecond time range with the formation of (xan)(2) disulfide and ClNi(xan) complex. The ClNi(xan) complexes in a slow disproportionation reaction are transformed into NiCl2 and initial Ni(xan)(2) complex. Thus, the final products of Ni(xan)(2) photolysis are the (xan)(2) disulfide and NiCl2 complex insoluble in CCl4.

Automated summary

The mechanism of photochemical reactions of the xanthate Ni(S2COEt)(2) = Ni(xan)(2) complex in CCl4 was determined using laser flash photolysis.