Neuartige tert-Butylhydrazin-basierte Ligandtemplate für molekulare Metallkomplexe – Potentielle Präkursoren für die MOCVD

This Thesis deals with the development of new hydrazine-based chelating ligands. The wellknown CVD nitrogen sources 1,1-di-methyl hydrazine and tert-butyl hydrazine served as hydrazine components for the reaction with carboxylic acid-, carbonic acid- and oxalic acidsynthons to generate formazanes and oxal-di-amidrazones. The potential of the obtained ligands was primarily evaluated for the group 13 elements boron, aluminium, gallium and indium. Furthermore coordination compounds of the elements Ti, Zr, Cu, Zn and Sn were investigated exemplarily. Especially 1,5-di-tert-butyl-3-methylformazane (Hdbmf), which was previously developed in the own diploma thesis previously, is suitable as a ligand of potential MOCVD precursors, because of its high volatility and its interesting structural properties. Therefore the primary aim of this Thesis was the optimization of the Hdbmf synthesis (Scheme 4.1). The hydrazidine hydrochlorid 2 was obtained in 17% yield and structurally characterized (Figure 4.1). This step represents the bottleneck of the synthesis. The formazane was gained from this intermediate by oxidation under air in quantitative yield. However, the following isolation seems to lead to disproportionation. Therefore the appropriate potassium salt was gained in a storable state in 40% yield (Figure 4.1). By the use of a THF-solution of Hdbmf or of [K(dbmf)] it was possible to synthesize the following coordination compounds: [Ca(dbmf)2], [F2B(dbmf)], [Me2Al(dbmf)], [Cl2Al(dbmf)], [Me2Ga(dbmf)], [Cl2Ga(dbmf)], [H2Ga(dbmf)], [Me2In(dbmf)], [Cl2In(dbmf)], [ClSn(dbmf)], [Sn(dbmf)]2, [Cl2Ti(dbmf)], [Cu(dbmf)], [Zn(dbmf)2] and [La(dbmf)3]. Thereof [F2B(dbmf)], [Me2Al(dbmf)], [Me2Ga(dbmf)], [Cl2Ga(dbmf)], [Me2In(dbmf)], [Cl2In(dbmf)], [ClSn(dbmf)] and [Zn(dbmf)2] were obtained in high purity. In addition, the molecular structures of [Cl2In(dbmf)] 5, [ClSn(dbmf)] 6 und [Zn(dbmf)2] 7 were analyzed by x-ray diffraction (Figure 4.2). Because of irreversible subsequent reactions, the electrochemical investigations (CV) of [F2B(dbmf)], [Cl2Ga(dbmf)], [Cl2In(dbmf)] and [Zn(dbmf)2] provided non-interpretable results. Since Hdbmf could not be prepared in high yields and the ligand, in particular in its protonated state, does not show any sufficient thermal stability under argon atmosphere, new nitrogen-rich ligand systems 8 - 12 based on tert-butyl hydrazine were developed (Figure 4.3). Similar to Hdbmf the two formazanes 8, 9 and the triazole derivative 10 were detected only in low yield and purity. However the amidrazone derivative 11 and the N-tert-butyl-functionalized oxal-di-amidrazone 12 were prepared in moderate or good yields of 31% and 80%. For 8, 10 and 12 a XRD molecular structure was obtained (Figure 4.4). In case of 1-tert-butyl-4-(trimethylsilyl)acetamidrazone (H2btaa) 11- it was possible to get the coordination compounds [Me2Ga(Hbtaa)] 13 and [Sn(btaa)] in high purity. For the gallium complex a molecular structure was obtained via XRD analysis (Figure 4.5). By reacting N,N`-Di-tert-butyl-oxal-di-amidrazone 12 with organometallic compounds of group 13, the following di- and tetranuclear complexes were synthesized and structurally characterized (Figure 4.6). Literature-known compounds (Figure 4.7) were introduced to synthesize new complexes as well. By reacting the well described tert-butylacetylhydrazide 18 with TMA, an aluminum hydrazide complex 21, with a five-coordinate aluminum cation, was obtained (Figure 1.8). Complexation reactions of triphenylformazane (Htpf) 19 and elements of group 13 were already discussed in preliminary work of our and other groups. For this reason, the coordination chemistry in this work is focused on the preparation of complexes with group 4 metals by salt metathesis reaction. For this purpose, the alkaline metal formazanido salts had to be synthesized first (scheme 4.2). The sodium- and the potassium salt of triphenylformazane were obtained in yields of 73% and 71%, respectively. The subsequent salt metathesis generated the complexes [Cl2Ga(tpf)] and [Cu(tpf)(Htpf)] as well as the tetrazoliumzirconate [tpt][ZrCl5(THF)]. For [tpt][ZrCl5(THF)] and [Cu(tpf)(Htpf)] molecular structures were obtained (Figure 4.9). The literature-known N,N`-Tetra-methyl-oxal-di-amidrazone was reproduced in this group and for the first time used as a complex ligand. The following di- and tetranuclear polycyclic compounds were synthesized by the reaction with the corresponding organometallic precursors: [(H2Al)4(moda)], [(Me2Al)3(Hmoda)], [(Me2Al)4(moda)], [(Me2Ga)(H3moda)], [(Me2Ga)2(H2moda)], [(Me2Ga)4(moda)], [(Me2In)2(moda)], [(Me2In)4(moda)], [(MeZn)2(H2moda)]. Thereby particularly the synthesis of the tetranuclear group 13 complexes proceeded almost in quantitative yield. Molecular structures were obtained for the group 13 complexes in Figure 4.10. So far N,N`-alkylformazanes have not been mentioned in the literature. Due to the research on Hdbmf new insight into the mechanism and the difficulties in synthesizing N,N`-alkyl-substituted formazanes was gained. Hdbmf fulfills the physical and structural requirements of a CVD-precursor, however the low yield and purity as well as the low stability of the ligand aggravate the handling. With the preparation of its potassium salt, it was possible to convert Hdbmf in a storable state ([K(dbmf)]) under inert atmosphere. Salt metathesis reactions of this precursor with group 4 metal halides did not yield reasonable results. In contrast, by the reactions of group 13, tin as well as zinc halides with [K(dbmf)], numerous new complexes were synthesized, which can be applied in photo- and electrochemical areas. Due to low yields, the application fields of these formazanido compounds seemed to be limited. Therefore with the oxal-di-amidrazones 12 and 20 another class of nitrogen-rich ligand templates was exploited. This class turned out to be an ideal ligand system for the absorption of up to four organometallic units. The volatility of Hdbmf cannot be reached by the oxal-di-amidrazones, but the ligands are stable under air and accessible in good yields (H4boda: 80%; H4moda: 67%). Moreover, the percentage nitrogen amounts of these compounds (H4boda: 37% H4moda: 49%) are higher than in case of Hdbmf (28%). In this way, very nitrogen-rich group 13/15 complexes were synthesized, which constitute potential precursors for the preparation of 13/15 semiconductor materials by spin coating and annealing processes.