A COMPARATIVE-STUDY OF THERMAL-INDUCED AND RADIATION-INDUCED SINGLE-ELECTRON TRANSFER IN REACTIONS OF 1,4-DIAZA-1,3-BUTADIENES WITH DIALKYLZINC COMPOUNDS

The reaction of R2Zn with t-BuDAB (t-BuN=CH-CH=N-t-Bu) results in the quantitative formation of the red 1:1 coordination charge transfer complexes R2Zn-t-BuDAB (R = Me (1a), CH2SiMe3 (5a)). Upon heating (T > 35-degrees-C), both complexes undergo an inner-sphere single electron transfer (SET) leading to the radical pair [(Rzn-t-BuDAB).(R.)], that collapses, depending on R., to several alkylation products, i.e. the N-alkylated product MeZn(t-BuN-CH=CH-N(Me)-t-Bu) (1b) and the exocyclic enamines Rzn(t-BuN=CH-C(=CHR')N-t-Bu) (R = Me (1f), CH2SiMe3 (5f/5g); R' = H, SiMe3). Alternatively, the alkyl radical R. escapes from the organozinc radical (Rzn-t-BuDAB)., that subsequently dimerizes to the dinuclear species (Rzn-t-BuDAB)2 (R = Me (1e), CH2SiMe3 (5e)). The charge transfer complex Me2-Zn-t-BuDAB was irradiated in order to induce a SET reaction within the complex. The irradiation reaction resulted in the formation of the symmetric dinuclear species 1e (30%) and the unsymmetric dinuclear species [MeZn{t-Bu(H)NCH(Me)CH(N-t-Bu)-} {-CH(N-t-Bu)Cme=N-t-Bu)ZnMe] (1h) (70%). Product 1h was independently prepared from MeZn(t-BuN-CH-(Me)-CH=N-t-Bu) (1c). The latter complex is in a tautomeric equilibrium with its enamine MeZn(t-BuN-CH(Me)=CH-N(H)-t-Bu), that reacts via a condensation reaction with a parent molecule 1c to give 1h.