The structure of a triclinic form of the organolithium derivative LiR, R = C(SiMe3)2(SiMe2{hpp}) (1) (hppH = 1,3,4,6,7,8,-hexahydro-2H-pyrimido[1,2-a]pyrimidine) comprises dimers [1]2 held together by Li···H3C interactions like those in the polymeric structure [1]∞ of the previously described orthorhombic form. Compound 1 reacts with the chlorides MCl2 (M = Hg or Sn) to give compounds HgRCl (2) or SnRCl (3), which have been characterised by NMR spectroscopy and X-ray crystallography. The structural parameters and conformations of the metallacycles MRLn are compared with those in related compounds containing bulky organosilicon ligands with pendant nitrogen donors. Compound 3 reacts with Li[P{H}Ar*] (Ar* = 2,4,6-tBu3C6H2) to give the crowded phosphanide SnR(P{H}Ar*) (4).

Single-crystal X-ray diffraction of MC(SiMe3)(2)(SiMe(2)hpp) (M = Li, K; hppH = 1,3,4,6,7,8,-hexahydro-2H-pyrimido[1,2-a]pyrimidine) showed nonsolvated organometallic compounds in which the iminonitrogen of the guanidine forms strong intramolecular bonds to generate six-membered metallacycles.

The title compounds have been made by treatment of SnCl2 or PbCl2 in tetrahydrofuran with the appropriate reagent LiR, where R = (PhMe2Si)3C, (Me3Si)3C, or (MeOMe2Si)(Me3Si)2C, and their crystal structures determined. In all four compounds, as in the previously reported [Pb{C(SiMe2Ph)3}Cl]2, the metal atoms are linked by bridging Cl atoms, unsymmetrically except in the case of the trimeric [Pb{C(SiMe3)3}Cl]3 (in which the six-membered ring has a distorted boat form). = Sn or Pb, which are isomorphous, there are (relatively weak) intramolecular MeO···M interactions in addition. The compounds [Pb{C(SiMe2Ph)3}Cl]2 and [Pb{C(SiMe3)3}Cl]3 are the only known σ-bonded mono(organo)lead(II) compounds to have been structurally characterized, and [Sn{C(SiMe2Ph)3}Cl]2 is only the second solvent-free mono(alkyl)tin(II) compound. All of the compounds are yellow and air-sensitive in the solid and in solution, and the lead compounds are readily decomposed in solution by exposure to daylight.

The title compounds have been made by treatment of SnCl2 or PbCl2 in tetrahydrofuran with the appropriate reagent LiR, where R = (PhMe2Si)(3)C, (Me3Si)(3)C, or (MeOMe2Si)(Me3Si)(2)C, and their crystal structures determined. In all four compounds, as in the previously reported [Pb{C(SiMe2Ph}(3))Cl](2), the metal atoms are linked by bridging Cl atoms, unsymmetrically except in the case of the trimeric [Pb{C(SiMe3)(3)}Cl](3) (in which the six-membered ring has a distorted boat form). In [M{C(SiMe3)(2)(SiMe2OMe)}Cl](2), M = Sn or Pb, which are isomorphous, there are (relatively weak) intramolecular MeO...M interactions in addition. The compounds [Pb{C(SiMe2Ph)(3)}Cl](2) and [Pb{C(SiMe3)(3)}Cl](3) are the only known sigma-bonded mono(organo)lead(II) compounds to have been structurally characterized, and [Sn{C(SiMe2Ph)(3)}Cl](2) is only the second solvent-free mono(alkyl)tin(II) compound. All of the compounds are yellow and air-sensitive in the solid and in solution, and the lead compounds are readily decomposed in solution by exposure to daylight.