[(Trimethylsilyl) methyl] sodium [NaCH(2)SiMe(3)] (1) was prepared by a metathesis reaction of [(trimethylsilyl) methyl] lithium [LiCH(2)SiMe(3)] with sodium tert-butoxide in n-hexane. Polydentate donors such as N,N,N',N'-tetramethylethylenediamine (TMEDA) and N,N,N', N '', N ''-pentamethyldiethylenetriamine (PMDETA) form n-hexane-soluble complexes of 1 and the potassium congener [KCH(2)SiMe(3)] (2). The crystal structures of the polymers [(TMEDA) NaCH(2)SiMe(3)] (1a) and [(PMDETA) KCH(2)SiMe(3)] (2a) were determined as infinite helical chains exhibiting 3(1) or 3(2) screw-axis symmetry. Compound 2b was obtained as the donor-deficient heterocubane pseudotetramer [(TMEDA)(3)(KCH(2)SiMe(3))(4)], with intermolecular interactions of the TMEDA-uncoordinated potassium atom with a peripheral methyl group of a neighbouring tetramer to form infinite chains. The relatively easy accessibility and stability should make these (trimethylsilyl) methyl compounds of sodium and potassium valuable starting points for further exploration of the chemistry of these common-utility heavier alkali metals.