Synthetic routes to the metallole species C(4)Me(4)E(H)R (9, E = Si, R = Si(SiMe(3))(3); 10, E = Si, R = Mes (mesityl); 11, E = Ge, R = Si(SiMe(3))(3); 12, E = Ge, R = Mes), C(4)R(4)E(SiMe(3))(2) (13, E = Si, R = Me; 14, E = Ge, R = Me; 19, E = Si, R = Et; 20, E = Ge, R = Et), and C(4)Me(4)E(R)E(R)Me(4)C(4) (15, E = Si, R = SiMe(3); 16, E = Si, R = Me; 17, E = Ge, R = SiMe(3); 18, E = Ge, R = Me) are described. In the presence of 18-crown-6, dihalides 1 and 2 are reduced by potassium in tetrahydrofuran to give crystalline samples of the silole dianion [K(18-crown-6)(+)](2)[C(4)MeSi(2-)] (21) and the germole dianion [K-4(18-crown-6)(3)][C(4)Me(4)Ge](2) (22). Compound 21 adopts an inverse-sandwich geometry, while 22 is a dimer with a bridging [K(18-crown-6)K](2+) group and eta(5)-binding modes for all of the potassium atoms. The metallole dianions in these structures appear to possess delocalized pi-systems, as evidenced by nearly equivalent C-C bond lengths in the five-membered rings. Silolyl and germolyl anions have been obtained by various methods involving nucleophilic cleavage of bonds to germanium and silicon. Deprotonation of 11 and 12 in the presence of a crown ether gave the anions [K(18-crown-6)][C(4)Me(4)GeR] (23, R = Si(SiMe(3))(3); 24, R = Mes) and [Li(12-crown-4)(2)][C(4)Me(4)GeR] (25, R = Si(SiMe(3))(3); 26, R = Mes). NMR parameters for these species, and X-ray structures for 25 and 26, indicate that the anionic rings possess pyramidal germanium centers and bond localization in the diene portion of the ring. Spectroscopic and X-ray crystallographic data for [Na(15-crown-5)]-[C(4)Me(4)GeMe] (28), prepared by reductive cleavage of the Ge-Ge bond in 18, reveal a similar structure for the germolyl ring. The latter compound possesses a Na ... Ge interaction in the solid state. Silolyl and germolyl anions M[C(4)Me(4)E(SiMe(3))] (30, E = Si, M = Li; 31, E = Si, M = K; 32, E = Si, M = Li(12-crown-4)(2); 33, E = Si, M = K(18-crown-6); 34, E = Ge, M = K; 35, E = Ge, M = K(18-crown-6)) have been prepared by nucleophilic cleavage of the E-SiMe(3) bond in C(4)Me(4)E(SiMe(3))(2) with MCH(2)Ph (M = Li, K). By similar methods, the monoanionic species [K(18-crown-6)][C(4)Me(4)E(SiMe(3))C(4)Me(4)E] (36, E = Si; 37, E = Ge) were obtained. A crystal structure determination for 33 revealed a highly pyramidalized Si center (the angle between the C4Si plane and the Si-Si bond is 99.6 degrees) and pronounced double bond localization in the ring. Interaction between the [K(18-crown-6)](+) cation and the anion is rather weak, as indicated by the K ... Si distance (3.604(2) Angstrom) and the atomic position for K. By variable-temperature H-1 NMR spectroscopy, inversion barriers for the compounds [Li(12-crown-4)(2)][C(4)Et(4)ESiMe(3)] (38, E = Si; 40, E = Ge) and K[C(4)Et(4)SiMe(3)] (39, E = Si; 41, E = Ge) were estimated. Barriers for the germolyl anions 40 and 41 (10.5(1) and 9.4(1) kcal mol(-1), respectively) are distinctly higher than those for the corresponding silolyl anions 38 and 39, as might be expected from periodic trends.