Metal halides, reactions yielding electronically excited

For systems that are powerful excited-state reductants, photoreduction of alkyl halides is observed (6.16). This reaction was initially interpreted to be an outer-sphere electron transfer to form the radical anion, which rapidly decomposes to yield R- and X . Subsequent thermal reactions yield the observed products, an SrnI mechanism (Figure 3a). While such a mechanism, SrnI, appears plausible for a metal complex with E°(M2 /3M2 ) < -1.5 V (SSCE), it seems unlikely for complexes with E°(M2 /3M2 ) > -1.0 V (SSCE). Reduction potentials for alkyl halides of interest are generally more negative than -1.5 V (SSCE) (1/7). Alkyl halide photoreduction is observed for binudear d complexes whose excited-state reduction potentials are more positive than -1.0 V (SSCE) in CH3CN. 

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