Alkynes electron transfer bridge

When more than one metal is present in an organometallic complex rather different electrochemical behaviour is possible. For example, metal-metal bonds can function as electron sinks so that extended redox series, linked by sequential one-electron transfer steps, may become available. In addition, the paramagnetic members of such series may show unusual properties associated with mix valency. Here we describe not only the reactions of binuclear species which undergo two or more sequential electron-transfer reactions but also a study of the bonding in alkyne-bridged binuclear species. 

NaCioHg or photolysis of [ (nacnac )FeH 2] under an N2 atmosphere yield [ (nacnac )Fe 2(li-T T -N2)] (251, Vnn= 1778 cm ). Despite this moderate activation of the N2 unit, no direct N2 functionalization was observed instead N2 loss occurs with associated electron transfer back to the Fe atom, and coordination of an additional ligand (commonly a t-acceptor) or reaction with an oxidant.Furthermore, binding of olefins, alkynes, and phosphines is thermodynamically more favorable than that of N2. ° Compound 251 may therefore be considered as an interesting Fe(l) synthon for the [(nacnac )Fe] fragment. Further reduction of the 251 with K or Na additionally weakens the N—N bond to form the (N2) bridged species K2[ (nacnac )... 

For the series of complexes (12) (n = 1,2) containing alkyne spacers, Harriman and Ziessel have estimated an attenuation factor of the order of 0.17 A" [106, 127). This relatively small value indicates that through alkyne bridges the electronic conduction for energy transfer is more efficient with respect to the polyphenylene counterparts. 

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