Untersuchungen zur Reaktivität disilanbasierter Silylpnictogene gegenüber starken Basen

In the work presented herein, the functionalization of the symmetric and asymmetric disilanes (SiR2Cl)2/ HSi2iPr4Cl (R = Me, iPr) with group 15 elements is shown. Within this compounds several electronical and structural trends were revealed: 1. In the 29Si NMR spectra the chemical shifts of the signals of methyl substituted disilanes is shifted towards highfield compared to their isopropyl analogues due to a stronger electronic withdrawing and sterical effect of the iPr-groups. 2. The signals of the silicon atoms bonded to a pnictide atom exhibit a stronger downfield shift with an increasing electronegativity of the pnictide atom. 3. The tendency of simple disilanes (HSi2R4EH2) to form secondary amines/ phosphanes of the type HE(Si2R4H)2 (E = N, P; R = Me, iPr) decreases with an increasing sterical demand at the silyl units, which leads to the NH/PH bridged tetrasilanes HN(Si2Me4H)2 (19) and HP(Si2Me4)2 (20). Moreover, it was possible to determine the solid state structure of the antimony-based cage compound Sb(Si2Me4)3Sb (5), which was first mentioned by HASSLER.[11,12] Instead of using insoluble pnictide sources like Na3E (E = P, As, Sb, Bi), the use of lithium-bis(trimethylsilyl)pnictides (Li(dme)E(SiMe3)2) (E = P, As, Sb) offered homogeneous reactions, which result in an overall better yield. With the introduction of more disilane units in new ligand systems, through the reaction of N(EtOH)3 with HSi2R4Cl (R = Me, iPr), it was possible to obtain two new disilane based lariathethers 11 and 12. Subsequent reaction with BaI2 and trace amounts of iodine lead to the formation of iodide- and triiodide bridged complexes. Pnictide funtionalization of O(Si2Me4Cl)2 and further reactions The reaction of O(Si2Me4Cl)2 with different pnictide based bases generates cyclic compounds of the composition O(Si2Me4)2EH (E = N (14), P (15)) along with the open chain product O(Si2Me4PH2)2, which was synthesized through the reaction of V with Li(tmeda)PH2. All open chain products (16-18) tend to condensate upon heating, by adding a base or, in case of compound 17, upon partial vacuum. The resulting cyclic silylpnictides were characterized by NMR spectroscopy. The condensation tendency of compound 16 to form 15 is the main reason why no cryptand of the composition P(Si2Me4OSi2Me4)3P was obtained. The reaction of 1,3-dichlorotetramethylsiloxane with Na3E (E = P, As, Sb, Bi) in dimethoxyethane leads to cage compounds including SiMe2OSiMe2-units. In contrast to this the analogue reaction of V results in the formation of O(Si2Me4)2PH (15) besides decomposition products. The formation of 15 is caused by ether cleavage by the phosphide leading to the formation of Na2PH. The reactions of 15 with strong bases led to deprotonation of the latter and the formation of dimers in the solid state, wherein the metal ions are coordinated by solvent molecules. With the LEWIS-acids AlEt3, GaEt3 and InEt3 the formation of novel silylphosphinotriel compounds of the composition [Et2MP(Si2Me4)2O]2 (M = Al (25), Ga (26), In (27)) was observed. Metalation of HN(Si2Me4H)2 (19), HP(Si2iPr4H)2 (21) and O(Si2Me4)2NH (14) with the benzyl bases of the alkali metals The last two chapters of this work deal with the reaction behaviour of 14, 19 and 21 against strong bases. The lithiation of 19 with nBuLi yielded a novel silyl amide, wherein one lithium cation shows anagostic Siδ+-Hδ-•••Liδ+-interaction leading to stabilization of the compound in the solid state. For the heavier alkali metals polymeric structures of the composition [K(tol)N(Si2Me4H)2]∞ and [Rb(tol)N(Si2Me4H)2]∞ were obtained. Therein, the central N2A2-cycles (A = K, Rb) are linked by toluene molecules through metal-π-interactions. Like in 30 the cations in [K(tol)N(Si2Me4H)2]∞, [Rb(tol)N(Si2Me4H)2]∞, [NaN(Si2Me4H)2]2 and [CsN(Si2Me4H)2]2 are stabilized by anagostic Siδ+-Hδ-•••Aδ+-interactions (A = Na, K, Rb, Cs). These interactions lead to a reduction of the wavenumber of the Si-H valence vibration, which helps to distinguish the strengths of these interactions in the metal amides. The NMR spectroscopic data of 30-34 show no anagostic interaction in solution. Instead the metalation leads to a reduced 1JSi-H coupling constant and a highfield shift for the silicon bonded hydrogen atom in the 1H NMR spectra. The metalation of HP(Si2iPr4H)2 (21) with benzyl potassium in toluene yielded the phosphanide [KP(Si2iPr4H)2]∞ (35). In contrast to the compounds 30-34, the main structural motiv contains a helix like polymeric chain of K-P-K-P atoms, which is caused by a high sterical demand of the iPr-groups. The potassium cations are stabilized by anagostic Siδ+-Hδ-•••Kδ+- and agostic K-Me-interactions. Through metalation the 1JSiH coupling constant is reduced to the same values as in the silylamides 30-34. The main difference between the phosphanide 35 and the silylamides 30-34 lies in the chemical shift of the α-Si-atoms, which is shifted toward highfield for the amides and toward downfield for compound 35. The investigation of the alkali metal salts of the silylamine O(Si2Me4)2NH (14) represents the highlight of this work. Herein, the first structurally characterized fully disila substituted aza-crown ether 36a was obtained by the reaction of O(Si2Me4)2NH with benzyl sodium. The formation is based on the cleavage of O(Si2Me4)NNa, which was proven by a protonation reaction of the sodium salt with NEt3HBr and analysed by NMR spectroscopy. While the reaction of 14 with BzNa leads to the cleavage of the OSi4N-cyle in 14, the reaction with the heavier homlogues BzA (K, Rb, Cs) gives unique 2D-networks, which consist of dimers of the type [O(Si2Me4)2NA]2. Moreover, these dimers show a coordination of the siloxane oxygen atoms to neighbouring potassium atoms, resulting in polymeric plains, which show a MOF like structure motive. In the potassium compound [K(tol)0.5N(Si2Me4)2O]∞ 37 toluene molecules are located between the layers without an interaction with the potassium atoms. Although siloxane oxygen atoms prefer rather hard LEWIS-acids like Li+ or Mg2+, this work showed that even very soft LEWIS-acids like Rb+ and Cs+ can be coordinated by a siloxane fragment, if a suitable ligand is chosen.