(Thio)Carbonyl Pseudohalogenide – Synthese, Spektroskopie und Reaktivität

In this dissertation the synthesis and characterization (first part), as well as the reactivity (second part) of carbonyl dipseudohalides (CDPsH) were the focal point of research. The crystal structures of carbonyl diisothiocyanate (CO(NCS)2) and oxalyl diisothiocyanate ((CONCS)2) were elucidated alongside their Hirshfeld surfaces, as well as their spectroscopic signatures. These findings extend the knowledge about synthetic procedure, conformation and molecule packing in the solid state of small molecules. Furthermore, a conformer study of carbonyl diisothiocyanate was performed by chirped-pulse Fourier transform microwave spectroscopy in cooperation with the working group SCHNELL (DESY in Hamburg) and led to the observation of a syn-syn to syn-anti ratio of 10:1. The syn-syn conformer exists as two nuclear spin isomers ortho and para like a boson. In addition, the photochemical induced decomposition of oxalyl diisothiocyanate in solid argon matrices was investigated with IR spectroscopy in collaboration with working group WAGNER (Eberhard Karls University Tubingen). Upon irradiation with UV light carbon monoxide is released and forms carbonyl diisothiocyanate in its less favored syn-anti conformer. Annealing the matrix after irradiation at higher temperature (30 K) leads to a conformer switch to the more stable syn-syn conformer. Many attempts to synthesize other carbonyl dipseudohalides (CDPsH) e.g. carbonyl diselenocyanate or thiocarbonyl diisocyanate did not end in isolable products. Carbonyl diselenocyanate (CO(SeCN)2) could possibly be observed in solution by 13C-NMR spectroscopy with chemical shifts of 185.3 ppm and 98.1 ppm, but the collected solid product decomposes above −30 °C or during dissolution. Therefore, the alkyl substituted tert-butylcarbonyl isoselenocyanate (CO(NCSe)tBu) was synthesized to confirm the existence of carbonyl selenocyanates. The isolation of this compound as crude solid was not possible due to decomposition during solvent removal, but it is manageable in solution and detectable by 13C-NMR spectroscopy with signals at 171.4 ppm and 144.0 ppm. The synthesis of thiocarbonyl group containing pseudohalides was first attempted for thiocarbonyl diisocyanate (CS(NCO)2). It was not possible to synthesize this compound through the employed synthetic routes, but in the meantime HENNES GÜNTHER (working group TAMBORNINO) could observe it in solution and isolate a defined reaction product with ethanol. The next compound is thiocarbonyl diisothiocyanate (CS(NCS)2) from which the synthesis yielded in the isolation of the known, albeit hitherto poorly characterized, thiocarbonyl dithiocyanate (CS(SCN)2). Despite the former being the thermodynamically more stable reaction product, it was not possible to find a synthetic pathway resulting in the isolation of the pure compound. DFT calculations confirmed that the kinetic reaction product thiocarbonyl dithiocyanate (CS(SCN)2) is formed via a lower transition state. Its crystal structure was determined along with the monosubstituted chlorothiocarbonyl thiocyanate (CS(SCN)Cl), which concludes to the sixth known structure of CDPsH. Lastly, an effort to synthesize thiocarbonyl diselenocyanate (CS(SeCN)2) was made and resulted in the possible detection by 13C-NMR spectroscopy with signals at 185.8 ppm and 103.2 ppm. The shifts match the observation made for the synthesis attempt of carbonyl diselenocyanate (CO(SeCN)2) and underline the above stated conclusions. At the end of part one, oxalylchloride isothiocyanate (Cl(CO)2NCS) and chlorocarbonyl isothiocyanate (CO(NCS)Cl) were synthesized. During the synthesize of oxalylchloride isothiocyanate an equilibrium with 2-chlorothiazol-4,5-dione in solution was observed. Further investigations with SC-XRD analysis and vibrational spectroscopy led to the conclusion that only the latter one exists in the solid state. Both compounds decompose in solution at room temperature to chlorocarbonyl isothiocyanate, which was extensively studied by SVEN RINGELBAND (working group TAMBORNINO). The second part of this dissertation deals with the reactivity of CDPsH. Carbonyl diisocyanate (CO(NCO)2) and -diisothiocyanate (CO(NCS)2) react with hydrogen halides to form carbonyl bis(carbamoylhalides) and halogenido substituted 1,3,5-thiadiazine-4- ones, respectively. Carbonyl diisocyanate adds two equivalents nucleophile, while carbonyl diisothiocyanate only adds one and undergoes intramolecular ring-closure. The different reaction pathways are thermodynamically driven by the preference of oxygen to form an ex-ring double bond versus the sulfur to form in-ring single bonds with carbon atoms. Both compound classes show extended hydrogen bonding networks in the solid state, which were examined in detail by the reaction products between carbonyl diiso(thio)cyanate and nucleophiles e.g. alcohols, thiols and amines. N,N’-Carbonyl bis(carbamates), -bis(S-thiocarbamates) and N,N’-biscarbamoyl ureas are formed during the reaction with carbonyl diisocyanate, respectively. All molecules form an intramolecular hydrogen bond and intermolecular hydrogen bonds to form either dimers or chains. The reaction of nucleophiles with carbonyl diisothiocyanate yields substituted 1,3,5-thidiazine-4-ones, all of which form dimers via intermolecular hydrogen bonds. This is in contrast to the chain forming halogenido substituted 1,3,5-thiadiazine-4-ones. Further packing of the molecules of all compound classes depends on the size of the substituted group, e.g. methyl versus phenyl. For small alkyl groups polar interactions predominate, while non-polar interactions dominate as the size of the alkyl or aryl groups increases. These reactions of carbonyl diisocyanate and carbonyl diisothiocyanate with nucleophiles led to the crystallisation of some side products like derivatives of isocyanuric acid and biuret, which could possibly hint at reactive species being present in solution during the reaction. Nucleophilic additions of organolithium compounds to carbonyl diisocyanate were tested with methyl lithium, n-butyl lithium and lithium methoxide, but defined reaction products were not collected. It is assumed that the formed anions are too unstable to isolate, therefore an acidious workup to protonate them is suggested. Surprisingly exciting was the result of the reaction of carbonyl diisocyanate with iron bis(diisopropylphenyltrimethylsilyamide), in which a reaction with the ligands and crystallization of a new type of metal complex was observed. This new complex, featuring a substituted biuret ligand and tetrahedral coordination of iron, is the first one to be reported. While crystals of reactions with cobalt or nickel, as well as carbonyl diisothiocyanate were not obtained, the equivalent metal complex from nickel and carbonyl diisothiocyanate was observed in mass spectrometry. This proofs that the reaction or crystallization conditions need to be adjusted in order to obtain more of these complexes. Future prospects of this dissertation are to investigate in collaboration the rotational spectrum of carbonyl diisocyanate, the IR spectrum of oxalyl chloride isothiocyanate or rather 2-chlorothiazol-4,5-dione in solid argon-matrix and its behavior upon irradiation with UV light. Further, the isolation of a pure sample and solid-state characterization of carbonyl diselenocyanate and thiocarbonyl diselenocyanate should be possible by filtration over a cooled frit or the use of other solvents e.g. dioxane. A complete new approach would be the synthesis from (thio)urea, carbon diselenide and mercury chloride. In addition, it is worth taking a look at the missing NMR spectroscopic and molecular structure data of carbonyl dicyanide (CO(CN)2) mentioned in the introduction. In this work asymmetrical carbonyl dipseudohalides were not considered, but to study their synthesis, characterization and reactivity should enhance the knowledge of conformations and crystal packing of small molecules even further. Aside from the synthesis of new carbonyl pseudohalides an investigation of the starting materials phosgene, thiophosgene and oxalyl chloride is also of interest. For instance, neutron diffraction experiments of phosgene and thiophosgene at ISIS in Oxford are planned.