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Herein we report on CO 2 fixation by insertion into the Zn-N bonds of the two molecular compounds EtZnN(iPr) 2 and EtZnN(iBu) 2 . The tetrameric carbamate complexes [EtZn-(O 2 CNR 2 )] 4 (R = iPr and iBu) were found to be the products of these reactions. The structures of the complexes were established by single-crystal X-ray diffraction. Thermal decomposition of the carbamate complexes was studied by apply-

)] (E = Si, R = Ph; E = Sn, R = Ph, Bu) are rather similar. While they contain six-coordinate cobalt with the formal oxidation state of cobalt being +III the coordination geometry is not octahedral: the heteroelement E deviates from the position which it would have in octahedral coordination by around 40°while the other five ligands, three phosphorus and two hydrogen, have the expected interligand angles of around 90°and 180°, respectively. The deviation of the heteroelement E is such that it approaches the

Reaction between the diborane (4) B2Cl2(NMe2)2 and Li(hpp) (hpp-=1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinate) leads to [(Me2N)B(mu-hpp)] 2. This species can be protonated by HCl.OEt2 to give [(Me2HN)B(mu-hpp)]2Cl2 featuring two B(II) cations with direct B-B bonding. The unsymmetrical monocation [(Me2N)B2(mu-hpp)2(NHMe2)]+ is also obtained. [(Me2HN)B(mu-hpp)]2Cl2 eliminates NHMe2 in a slow reaction leading to [ClB2(mu-hpp)2(NHMe2)]Cl and ultimately, presumably, to [ClB(mu-hpp)]2. We report the crystal structures of the two monocations [ClB2(mu-hpp)2(NHMe2)]Cl and [(Me2N)B2(mu-hpp)2(NHMe2)]Cl. The experimental results are accompanied by some quantum chemical density-functional theory calculations.

The reaction between the guanidine derivative hppH (hppH = 1,3,4,6,7,8‐hexahydro‐2H‐pyrimido[1,2‐a]pyrimidine) and K2PtCl4 in H2O affords the salt [hppH2]2[PtCl4], which reacts further with Li(hpp) in thf to give cis‐[(hppH)2PtCl2]. The corresponding trans isomer is obtained from the reaction between [(dmso)2PtCl2] and hppH. hppH easily replaces another chlorido ligand to give [(hppH)3PtCl]+Cl–. [hppH2]Cl is formed as a hygroscopic side‐product in the synthesis of [(hppH)2PtCl2] and takes up 1 equiv. of H2O to give [hppH2]Cl·H2O. We report the crystal structures of cis‐ and trans‐[(hppH)2PtCl2], [(hppH)3PtCl]+Cl– and some salts of the [hppH2]+ cation, namely [hppH2]2[PtCl4] and the Pt‐free salts [hppH2][BPh4], [hppH2]Cl and [hppH2]Cl·H2O, which have an increasing degree of directed intermolecular hydrogen contacts. The crystal structure of [hppH2]Cl·H2O features helical chains of Cl–·H2O connected via [hppH2]+ cations. The effects of hydrogen bonding on the structures of these compounds in the solid state are discussed. Finally, quantum chemical calculations provide further insight into the structures and properties of some of these compounds. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)