Synthesis and Structural Characterisation of cis‐ and trans‐[(hppH)₂PtCl₂], [(hppH)₃­PtCl]⁺Cl^– and Some New Salts of the [hppH₂]⁺ Cation (hppH = 1,3,4,6,7,8‐Hexahydro‐2H‐pyrimido[1,2‐a]pyrimidine): The Importance of Hydrogen Bonding

Abstract

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)

Double proton transfer in crystals of 1,3,4,6,7,8‐hexahydro‐2H‐pyrimido[1,2‐a] pyrimidine (hppH):13C and15N CPMAS NMR study of (hppH)2

“…Figure 6 shows the CPMAS spectrum of a sample of commercial hppH that was crystallized and handled under inert atmosphere at all times (therefore corresponding to 1 2 ). These precautions were taken to prevent the formation of hydrolysis products which readily occurs due to the highly basic nature of the compound 47–49. The most distinctive features of this spectrum are the splitting of the signals at 42–43 and 48–49 ppm and the broadening of the signal for C1 at 151.7 ppm.…”

Mono‐ and Diprotonation of the Superbasic Bisguanidine 1,2‐Bis(N,N,N′,N′‐tetramethylguanidino)benzene (btmgb) and PtII and PtIV Complexes of Chelating Bisguanidines and Guanidinates

“…) (DP = degree of pyramidalization; dp,ip = directly and indirectly protonated [23] They compare with a Pt À N bond length of 200.1(6) pm in (2,2'-bipyridine)dichloroplatinum.…”

An Isolated CO2 Adduct of a Nitrogen Base: Crystal and Electronic Structures

“…The 1 H and 13 C NMR spectra were recorded on a Bruker DPX 200 instrument at 23 8C when not otherwise specified; the IR spectra were recorded in Nujol mulls between KBr cell windows on a Bruker Vertex 70 spectrometer. TBD-CO 2 : A flask containing TBD (60.5 mg, 0.43 mmol) in THF (0.5 mL) was frozen in liquid nitrogen, degassed under vacuum, and filled with CO 2 (1 atm).…”