Crystalline Na–Si(NN) derivatives [Si(NN)= Si{(NCH2tBu)2C6H4-1,2}]: the silylenoid [Si(NN)OMe]^–, the dianion [(NN)Si–Si(NN)]^2–, and the radical anion c-[Si(NN)]^3–

Reactions of the silylene Si[(NCH2Bu^t)2C6H4-1,2], [Si(NN)], with NaOMe, excess Na or 1/3 Na yield the X-raycharacterised crystalline compounds [Na{(mu)-Si(NN)OMe}(THF)(OEt2)]2(2b), [Na(THF)2Si(NN)]2(3) and [Na(THF)4] [{Si(NN)}3-c](4).