Untersuchungen zu disilanbasierten Makrocyclen als Liganden für p- und d-Block Metallionen sowie zu siloxanbasierten Käfigverbindungen

Im Rahmen dieser Arbeit wurden makrocyclische Si-O-haltige Verbindungen untersucht. Dabei lag der Schwerpunkt des ersten Teiles der Arbeit auf der Untersuchung des Koordinationsverhaltens von hybriden Kronenethern gegenüber p-, d- und f-Block Metallionen. Koordinationsverbindungen von siliziumba...

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Bibliographic Details
Main Author: Köster, Marcel
Contributors: Hänisch, Carsten von (Prof. Dr.) (Thesis advisor)
Format: Doctoral Thesis
Published: Philipps-Universität Marburg 2020
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In this work, macrocyclic Si-O-containing compounds were investigated. The focus of the first part of this work was the investigation of the coordination behavior of hybrid crown ethers towards p-, d-, and f-block metal ions. Complexes of silicon based crown ethers with transition metal compounds In particular, Mn2+ was used as a d-block metal ion because of its suitable ionic radius, depending on the coordination number, for different sizes of crown ether. It was found that MnCl2 and MnI2 did not form complexes with the silacrown ethers. Only when using an excess of iodine to form the triiodide anion a coordination with hybrid crown ethers was observed. While these complexes with disila [15]crown-5[94] (1) led to the expected product [(I3)2Mn(1,2 disila[15]crown-5)] (2), other disila- and tetrasilacrown ethers lead to the cleavage of the Si2Me4-units. Along with this bond cleavage one additional oxygen atoms incorporated, as in [(I3)2Mn(1-sila[17]crown-6)] (4) and [(I3)2Mn(1,3,5-trisila[15]crown-6)] (10), or more, as in [(I3)2Mn(1,3,8,10-tetrasila[14]crown-6)] (7) and [(I3)2(μ IMn)2(1,3,11,13 tetrasila[20]crown-8)] (8). With compound 10, which contains a coordinative bond of a siloxane oxygen atom to the metal ion, we have obtained, to my knowledge, the first structural evidence for such a bond to a manganese atom. The incorporation of additional oxygen atoms was attributed to small traces of water. However, it has been shown with reactions of the free ligands with dry iodine that the latter plays as an oxidizing agent a significant role in the formation of monosilyl units. In addition to the complexes of hybrid crown ethers with manganese ions, another d-block ion was coordinated with Co2+. Thus, in an in situ reaction with CoCl2, Me3SiOTf and disila[15]crown-5 (1), the compound [(OTf)2Co(1,2 disila[15]crown-5)] (11) was obtained. In the complexes obtained with sila crown ethers and d-block metal ions, the OSi/C atoms with an adjacent disilane unit (2 and 11) showed, in contrast to the OSi/C atoms (4, 7, 8, and 10) with an adjacent monosilane unit, a similar coordination to the metal ion as the OC/C atoms in the respective complexes. This is due to the influence of the Si2Me4 unit on the angle around the OSi/C atoms, as well as the reduction of the positive polarization of the silicon atoms and the reduction of the ring strain within the cycle compared to SiMe2 units. Complexes of silicon based crown ethers with p-block compounds The investigations of p-block metal salts with hybrid crown ethers were performed with group 13, group 14 and group 15 ions. An initial successful coordination was observed in the reaction of disila[15]crown-5 (1) with an excess of InCl. This reaction led to the formation of the compound [Cl3InIn(1,2-disila[15]crown-5)Cl] (13), in which In(I)Cl coordinates as a Lewis base to the Lewis acid In(III)Cl3. In an attempt to coordinate other Lewis acids such as GaCl3 to the In(I)ion, the insertion of the indium metal center into the C-Cl bond of a solvent molecule DCM and the formation of a [GaCl4]- anion was observed. Thus the compound [H2CClIn(1,2-disila[15]crown-5)Cl][GaCl4] (14) was obtained. In order to obtain a substituent-free metal center coordinated only by the silicon-containing ligand, the solvent α,α,α-trifluorotoluene was used and [In(1,2 disila[15]crown-5)][GaCl4] (15) as well as [Tl(1,2-disila[18]crown-6)][GaCl4] (16) were isolated. Since 15 and 16 have a very different structure, quantum chemical calculations were performed. The deviations in the arrangement are among other things due to the position of the non-bonding electron pairs at the metal ions. Thus, the electron density at the In(I) ion is oriented away from the ligand in the HOMO-1 of 15, while the electron density around the Tl(I) ion of 16 in the HOMO-7 shows a more spherical form, which points to a higher s-character. Reactions of the disila[15]crown-5 (1) with low-valent group 14 compounds were not successful until the E14-triflates (E14 = Ge, Sn, Pb) were synthesized in situ, with which crystals of the complexes [TfOE14(1,2-disila[15]crown-5)][OTf] (19: E14 = Ge, 20: E14 = Sn, 21: E14 = Pb) were obtained. Using a disilacrown ether that is too large for the metal ion results in the formation of mismatch structures, as in [(TfO)2Sn(1,2-disila[18]crown-6)] (22). In addition, [Pb(1-sila[14]crown-5)2][I10] (23) gave a first sandwich complex with hybrid crown ethers, as the ligand is too small for the metal ion and an excess of the hybrid crown ether was used. In compound 23 the use of iodine, as in the manganese-containing complexes, led to the cleavage of the disilane unit. Coordination compounds of group 15 (E15 = Sb, Bi) were obtained in an analogous manner as 19-21 by an in situ reaction of the respective low-valent halides with Me3SiOTf and ligand. However, complete substitution of the chloride anions did not occur and only two triflate groups were introduced: [ClSb(1,2-disila [15]crown-5)][OTf]2 (25) and [ClBi(1,2-disila[15]crown-5)OTf][OTf] (26). The structural comparison of the coordination compounds of disilacrown ethers and the various p-block metal ions with the organic derivatives shows that the complexes of group 13 (13-16) behave very similar to these. This is also true for compound 19. But with the complexes of the higher homologues of germanium (20-22), and with group 15 metal salts (25, 26), different arrangements compared to the organic analogues are observed. This is a result of the difference in size of the hybrid crown ethers in comparison with the pure organic crown ethers. In almost all coordination compounds with disilacrown ethers and p-block metal ions, the metal-oxygen bond lengths with oxygen atoms adjacent to a silicon atom are shorter or equal to the metal-oxygen bond lengths with purely carbon-substituted oxygen atoms. This observation suggests that the OSi/C-atoms do not coordinate worse than the OC/C-atoms through the incorporation of Si2Me4-units. The reactions of the tetrasilacrown ethers with p-block metal salts resulted mostly in the decomposition of the ligand and, as a consequence, the formation of glycol-containing complexes. As a by-product the formation of the cyclic siloxane (SiMe4O)2 was usually observed. However, the reaction of GaCl3 with the tetrasilacrown ether 1,2,7,8 tetrasila[12]crown-4[94] (5) led to the coordination compound [IGa(1,2,7,8 tetrasila[12]crown 4)][GaI4][Ga2I7] (12), in which all oxygen atoms bind equally to the metal ion. In addition, with [SnCl(1,2,4,5 tetrasila benzo[15]crown-5)]2[Sn(OTf)4] (24), a complex was isolated which exhibits a coordinative bond of a siloxane oxygen atom to a p-block metal ion. Compound 24 is, to my knowledge, the first structural evidence of such a bonding, wherein the siloxane oxygen atom binds the weakest to the metal ion compared to the remaining oxygen atoms of the complex. Quantum chemical calculations of compounds 20, 22 and 24 show that the shape and position of the electron density on the tin atoms are nearly identical. Attempts to coordinate silicon based crown ethers with f-block compounds For the implementation of f-block elements to the hybrid crown ethers only uranium-containing starting materials were used in collaboration with the research group Kraus. However, a direct reaction was not expedient, which is why ethylene glycol and HO-SiMe2-O-SiMe2-OH[140] were used as model compounds. In a reaction of ethylene glycol and UBr5 in the presence of the auxiliary base NEt3, [HNEt3]2[UBr6] (27) was obtained. In further reactions of ethylene glycol or HO-SiMe2-O-SiMe2-OH with UCl6, [HNEt3]Cl was detected by crystal structure analysis. This formation is an indication for the successful preparation of U(O-C2H4-O)3 or U(O SiMe2 O SiMe2-O)3, which, however, could not be isolated. In order to receive a coordination compound of the silicon-containing crown ethers with UBr5 or UCl6, further investigations for the optimal reaction conditions are necessary. Influence of the anions on the synthesized complexes Coordination and crystallization were only observed for all the shown complexes containing hybrid crown ethers and p-, d-, and f-block metal ions if complex anions, such as in these cases [I3]-, [OTf]-, or [GaCl4]-, are used. This may be because the complex anions are more suited to delocalize the negative charge, thus reducing the interaction between the anion and the cation. The latter is apparently necessary for a successful coordination of silicon-containing crown ethers with metal ions. Synthesis of a novel silicon based crown ether In addition to complexes with hybrid crown ethers, a novel silicon-containing crown ether should be synthesized within this work. The reaction to such a ligand with three Si2Me4-units starting from HO-Si2Me4-OH[144] did not lead to the desired outcome, since the synthesis to the novel hexasilaether H-(Si2Me4O)2-Si2Me4-H led to a product mixture. However, the reaction of HO SiMe2 O SiMe2-OH with the tetrasilaether O(Si2Me4Cl)2[97] in the presence of the auxiliary base NEt3 revealed a hybrid crown ether with two disilane and two monosilane units: 1,2,4,6,8,9-hexasila[10]crown-4 (28). Attempts to coordinate this ligand with various metal salts have not yielded results to date, possibly related to the small size of the ligand and the associated higher electrostatic repulsion between the positively polarized silicon atoms of the crown ether and a potential cation. Novel bicyclic Trisiloxanes The second part of this work focused on the preparation of novel bicyclic siloxanes starting from ClSi{O(SiMe2)2}3SiCl[91] and TfOSi{O(SiMe2)2}3SiOTf[91]. On the way to these inorganic cryptands, the branched tetrasilanes BrSi (SiMe2Ph)3 (29) and ISi(SiMe2Ph)3 (30) were isolated. Compared to ClSi(SiMe2Ph)3,[92] there are no large structural differences, so that the influence of the halogen atom on the quaternary silicon atom on the structure is small. The substitution on the bridgehead atom of Cl Si{O(SiMe2)2}3SiCl or TfOSi{O(SiMe2)2}3SiOTf by salt metathesis led to no reaction or decomposition of the cryptands. Also, the use of different bases such as NH3, KOH or BenzylK showed the same results. However, using SIMesPK as base, the novel bicyclic siloxane SIMesPSi(Me)2Si{μ-(O(SiMe2)2)2μ-(O)}SiSi(Me)2PSIMes (31) was obtained. Its bicyclic structure consists of two Si4O2-six-membered rings and thus differs from the starting material ClSi{O(SiMe2)2}3SiCl. With this result it can be seen that, before there is a substitution on the silicon bridgehead atom of ClSi{O(SiMe2)2}3SiCl, cleavage of an Si-O-Si bond takes place. One explanation for this observation may be that a reaction by a SN2 mechanism is hindered because of an impossible backside attack. However, reactions with ClSi{O(SiMe2)2}3SiCl, which should proceed by a SN1 mechanism, led to no reaction or decomposition. These results indicate that the compound ClSi{O(SiMe2)2}3SiCl contains one of the most stable known Si-Cl bonds.