Table of Contents:
This work comprises the synthesis and characterization of organic functionalized tetreltrichlorides Cl3TRf (T = Ge, Sn; Rf = functional organic group). In following steps these new compounds were converted to tetrelchalgonide cluster and used for derivatisation reactions. Based on the obtained experimental results, further studies related to stability and reactivity had been undertaken, using experimental and quantum chemical methods.
An optimization of established hydrogermylation and hydrostannylation reactions afforded the first crystallographic description of a Cl3GeR1 (R1 = derivatized in 3-position of 4-methyl pentanone) and produced new trichlorogermylatet carbonic acid derivates (1 : R3 = derivatized in 3-position of methyl propanoate, 2 : R4 = derivatized in 3-position of ethyl propanoate, 3 : R5 = derivatized in 3-position of pentanedioic acid and 4 : R6 = derivatized in 3-position of propanenitrile). Using transmetallation (5, 6) und GeCl2-insertion reactions (7 - 9) new starting materials without the previous restriction to α,β-unsaturated carbonyl compounds were obtained.
The results of cluster syntheses demonstrated the structural variance within the investigated class of compounds. Dependent on the elemental combination several defect heterocubane (10 = R5Sn3Se4), adamantane (12 = R6Ge4S6, 13 = R6Ge4Se6) and noradamantane structures (11 = R5Ge4Te5, 14 = R6Ge4Te5) were observable but yet, cluster syntheses using bis-trichlorogermylatet precursors (5) were not successfully. Also the usage of organic functionalities which are sensitive towards side reactions with chalcogenides resulted in not sufficiently isolatable and characterizable products. Reasons for this may be the formation of polymeric compounds as well as numerous non crystallizable thio and selenium esters.
Further investigations concerning inorganic and organic derivatization methods demonstrated the advantage of using precursors instead of cluster compounds for this approach. Besides sensitivity towards light, heat and extreme pH conditions of the cluster compounds also a deactivating influence of the inorganic core to the organic ligand hinders subsequent reactions.
Based on carbonic acid containing precursors (R2 - R4) several derivatization reactions towards acid chlorides 15 and amides 16 (para-methoxy aniline), 17 (N-methyl aniline) were performed and in case of compound 18 the first conversion of a Ge/Se complexes with functional organic ligands has been successful. In this connection the synthesis of a semicarbazone derivate and caused a transformation of the double-decker type cage towards an adamantane type structure without causing further fragmentations of the inorganic cluster.
Wide knowledge concerning the stability of the keto functionalized germaniumselenide cluster [R1Ge4Se6] under different reaction conditions provides several anionic fragments such as the [(R1Ge2)Se4]2−-fragment 19 by using specific calibrated alkaline solutions. In addition the light sensitivity leads to an Ge−Ge-Bond formation and the preparation of the mixed-valence compound [Na(thf)2[(R1GeIV)2(R1GeIII)(GeIIISe)Se5]] (20).
Based on experimental results DFT calculations performed by means of the program system Turbomole® allowed the energetic determination of different structure motifs and enabled the predictions of yet not synthesized compounds. Calculations concerning the shared electron number (SEN) of the terminal nitrile ligands conduced the understanding of deactivating interaction between inorganic core and organic ligand which hinder subsequent reactions as well as the shortening of bond lengths inside the nitrile function of germaniumchalcogenide clusters compared to those inside the precursors.
Further studies may use now accessible neutral or anionic organic functionalized germaniumchalcogenide clusters for reactions with transition metals especially in different reaction conditions like polychalcogenid flux or ionic liquids due to the fact that so far even use of coordinated cations and reduced reaction speed were not sufficient. Furthermore knowledge about light induced fragmentation of Ge−C bond, as used for the preparation of compound 20, may be useful to generate newly pure inorganic cluster compounds by eliminating the organic ligands after successfully realized cluster synthesis. In particular for solid state synthesis and generation of super tetrahedral molecules with zeolith type structure and special electronic properties, these compounds would be interesting. Furthermore organic functionalized germaniumchalcogenide cluster may find applications as precursors for the generation of molecular capsules or metal organic frameworks