Metal−Metal Multiply-Bonded Complexes of Technetium. 4.1 Photodissociation of the Tc≡Tc Triple Bond in [Tc2(CH3CN)10][BF4]4

Abstract

Efficient (i.e., essentially quantitative) photolysis of multiple bonds, including metal-metal multiple bonds, neither is to be generally expected nor has been observed, with the sole exception of photocleavage of the quadruple bond in [Re{sub 2}Cl{sub 8}]{sup 2-}, which occurs in acetonitrile and affords ReCl{sub 3}(CH{sub 3}CN){sub 3} as the final product. We report here a striking example of such a process, wherein the [(CH{sub 3}CN){sub 5}Tc=Tc(CH{sub 3}CN){sub 5}]{sup 4+} ion is photolyzed in CH{sub 3}CN to give two [Tc(CH{sub 3}CN){sub 6}]{sup 2+} ions in nearly quantitative isolated yield. A plausible idea (admittedly not yet supported experimentally) is that photoexcitation produces a mixed-valent, charge-separated Tc(I)-Tc(III) complex that undergoes metal-metal bond cleavage to produce mononuclear Tc(I) and Tc(III) nitrile complexes. These mononuclear species could then undergo a comproportionation reaction to yield 2 consistent with the observed electrochemical potentials of the Tc(I)/Tc(II) and Tc(II)/Tc(III) redox couples. 17 refs., 2 figs.