Alkali metal reduction of alkali metal cations.

Counter to synthetic convention and expectation provided by the relevant standard reduction potentials, the chloroberyllate, [{SiN Dipp }BeClLi] 2 [{SiN Dipp } = {CH 2 SiMe 2 N(Dipp)} 2 ; Dipp = 2,6-i-Pr 2 C 6 H 3 )], reacts with the group 1 elements (M = Na, K, Rb, Cs) to provide the respective heavier alkali metal analogues, [{SiN Dipp }BeClM] 2 , through selective reduction of the Li + cation. Whereas only [{SiN Dipp }BeClRb] 2 is amenable to reduction by potassium to its nearest lighter congener, these species may also be sequentially interconverted by treatment of [{SiN Dipp }BeClM] 2 by the successively heavier group 1 metal. A theoretical analysis combining density functional theory (DFT) with elemental thermochemistry is used to rationalise these observations, where consideration of the relevant enthalpies of atomisation of each alkali metal in its bulk metallic form proved crucial in accounting for experimental observations.