Investigations on the synthesis of silicon-arsenic double bonds and the preparation of MxEy nanoparticles from single-source-precursors (M = Ga, Ge, Sn; E = P, As)

In summary, the present work provides a variety of potential single source precursors for the synthesis of group 14 element pnictogenide nanoparticles (MxEy with M = Ge, Sn; E = P, As), which are stabilized by a β-diketiminato ligand that can easily be removed by acidic or basic reagents under mild conditions. Furthermore, five novel compounds exhibiting a rare silicon arsenic double bond with a coordinating benzamidinato ligand could be synthesized and characterized and also studies on the preparation and the reactivity of hitherto unknown benzamidinato zinc complexes were successfully performed. Five novel arsasilene complexes Following the reaction of [PhC(NtBu)2]SiCl and LiP(SiMe3)2 reported by Driess et al. in 2011, it could be shown that a simple one-pot synthesis using [PhC(NtBu)2]SiCl and the arsenic compound LiAs(SiMe3)2 leads to the formation of [PhC(NtBu)2]Si(SiMe3)=As(SiMe3) (3-1) (Figure 6-1 - 1 top left). Studies on the reactivity of the reaction mixture of the starting materials towards water and oxygen revealed the formation of a hydrolysis product [PhC(NtBu)2]Si(H)=As(SiMe3) (3-2) and an oxidation product [PhC(NtBu)2]Si(OSiMe3)=As(SiMe3) (3-5) (Figure 6-1 - 1 top middle and right). Additionally, the species {[PhC(NtBu)2]Si}2=AsSiMe3 (3-3) and {[PhC(NtBu)2]Si=AsSiMe3}2 (3-4) could be obtained in reactions which were performed to reproduce 3-1 (Figure 6-1 - 1 bottom). Yet, all attempts to synthesize 3-3 and 3-4 selectively failed. Figure 6-1 - 1: The solid state structures of the compounds 3-1, 3-2, 3-3, 3-4 and 3-5. 3-1 was prepared from the reaction of [PhC(NtBu)2]SiCl with LiAs(SiMe3)2, it was fully characterized by NMR spectroscopy, EI mass spectrometry and X-ray structure analysis whereby it was necessary for the latter to permanently cool the reaction mixtures to –80°C to grow suitable crystals. 3-2 could be obtained by adding a defined amount of water to the thf solutions (H2O:[PhC(NtBu)2]SiCl:LiAs(SiMe3)2 = 1:5:5), which may not be exceeded to avoid decomposition. It was also fully characterized by the typical spectroscopic methods but in addition by 29Si NMR spectroscopy to unequivocally detect the Si–H coupling. In a similar way to 3-2, a stoichiometric quantity of (SiMe3)2O2 mixed with [PhC(NtBu)2]SiCl and LiAs(SiMe3)2 leads to the formation of compound 3-5 (Scheme 6-1 - 1). In the case of 3-3 and 3-4, just a few crystals appeared as side products of the synthesis of 3-1. It was also possible to detect the molecular peak of 3-4 by solid state EI mass spectrometry. Scheme 6-1 - 1: Overview of the preparation of the arsasilenes 3-1 to 3-5. Also, some studies concerning the reactivity of 3-1 were performed, especially investigations in order to transform 3-1 into 3-2 and 3-5, but these attempts were not conclusive as 3-2 and 3-5 can only be obtained from the reaction of the monochlorosilylene with LiAs(SiMe3)2 and water or (SiMe3)2O2, respectivley. Additionally, VT NMR investigations were done to elucidate the mechanistic details of the formation of 3-1 and possibly to gain hints on the formation of the arsenic analogue of Driess’ [PhC(NtBu)2]SiP(SiMe3)2, which was not successful. But instead, crystals of the literature known compound {[PhC(NtBu)2]SiAs}2 3-F with a yet unknown unit cell were isolated from the thf-d8 mixture. Nanoparticles from [CH(C(Me)N(2,6-iPr2C6H3))2]ME(SiMe3)2 (M = Ge, Sn; E = P, As) As it has already been described in the chapters 1.3.7 and 4.2, numerous possibilities exist to utilize nanoparticles and especially the still scarcely explored nanoscale material containing elements of group 14 and 15 might show interesting properties. In general, nanoparticles can be synthesized by various methods, starting either from bulk material (top down approaches like milling) or from atoms and molecules (bottom up method). The bottom up approach of hot injections starts with the solution of the precursors in a high boiling, sometimes coordinating solvent, followed by a fast heating step, that leads to the decomposition of the starting material and the formation of the nanoscopic material. If a separate starting material for each component of the resulting nanoparticles is used, the method is called multi source precursor approach. In contrast to this is the single source precursor method, in which all components of the nanoparticles are combined in one molecule. As this approach shows important advantages like mild reaction conditions and the avoidance of volatile and/or pyrophoric substances, the single source precursor approach was the method of choice to prepare MxEy nanoparticles (M = Ge, Sn; E = P, As). As the most promising complexes to decompose in order to achieve the desired nanoscopic matter, the two literature known compounds [CH(C(Me)N(2,6-iPr2C6H3))2]MP(SiMe3)2 (M = Ge (4-D), Sn(4-E)) and the novel [CH(C(Me)N(2,6-iPr2C6H3))2]SnAs(SiMe3)2 (4-4) were studied. Previously, the heavier homologues of 4-D and 4-E [CH(C(Me)N(2,6-iPr2C6H3))2]MAs(SiMe3)2 (M = Ge (4-3), Sn(4-4)) were successfully synthesized and fully characterized (Figure 6-1 - 2). 4-3 and 4-4 are prepared by the reaction of [CH(C(Me)N(2,6-iPr2C6H3))2]MCl (M = Ge, Sn) with LiAs(SiMe3)2, whereby 4-4 is achieved in good yields, while 4-3 can only be isolated in minor quantities amounts because of which 4-3 is discarded as single source precursor. Figure 6-1 - 2: Left: Solid state structure of 4-3. Right: Solid state structure of 4-4. Therefore, only the tin analogon 4-4 was used in the hot injection nanoparticles tests with PA as starting material, leading to the formation of agglomerated spherical particles, which could not be separated. Nevertheless, the particles show an average size of 10 to 14 nm and a composition of mostly Sn4As3, proving the applicability of 4-4 for the synthesis of tin arsenide nanoscale material (Figure 6-1 - 3). Figure 6-1 - 3: Left: TEM images of the nanoparticles formed during the decomposition of 4-4 with 1 eq. PA. Right: XRD diffractogram of the nanoparticles revealing a composition of Sn4As3. Beside 4-4, also the phosphorus compounds 4-D and 4-E were studied for their potential use in the synthesis of nanoparticles, which showed that the Ge compound 4-D is not a suitable precursor. Despite decomposing to the desired germanium phosphide Ge4P3 which could be proven by EDX, investigations using TEM analysis clearly displayed the absence of regular shaped and similar sized nanoparticles leading to the discard of 4-D (Figure 6-1 - 4). Figure 6-1 - 4: Left: TEM images of the decomposition of 4-D with 1 eq. PA (1 h). Right: EDX spectrum of the precipitate obtained from the decomposition of 4-D consisting of Ge4P3. On the other hand, its heavier homologue 4-E provided in the reactions with HDA very satisfactory results as the complex not only decomposes to Sn4P3 as required, but also forms agglomerated spherical nanoparticles with an average size of about 10 to 22 nm (Figure 6-1 - 5). Figure 6-1 - 5: Left: Nanoparticles from the reaction of 4-E with 0.5 eq. HDA (1 h). Right: XRD diffractogram of the reaction products of 4-E with a composition of Sn4P3. In summary, the analyses performed in the course of the experiments show that both tin compounds [CH(C(Me)N(2,6-iPr2C6H3))2]SnE(SiMe3)2 (E = P (4-E), As (4-4)) are suitable and promising single source precursors for the synthesis of nanoparticles. Additionally to the synthesis of 4-3 and 4-4 which were especially prepared for their use as single source precursors, also basic reactivity studies were done using [CH(C(Me)N(2,6-iPr2C6H3))2]MCl (M = Ge, Sn) and the lithiated compound LiCH2SiMe3 as starting material. Those approaches led to the formation of [CH(C(Me)N(2,6-iPr2C6H3))2]MCH2SiMe3 (M = Ge (4-1), Sn (4-2)), that were fully characterized by NMR spectroscopy, mass spectrometry, elemental analysis and X-ray structure analysis (Figure 6-1 - 6). Figure 6-1 - 6: Left: Crystal structure of 4-1. Right: Solid state structure of 4-2. 6.1.3. Single source precursors containing phosphorus, zinc and gallium Zinc phosphide precursors As nanoscale Zn2P3 is thought to be a promising material for future photovoltaic application easy and non-toxic synthetic methods like the single source precursor approach are very attractive raising the interest in the preparation novel zinc phosphorus compounds useful for the decomposition to nanoparticles. Here, the focus is on the synthesis of a new family of zinc complexes stabilized by a variable benzamidinato ligand which might be convertible into P containing precursors. Thus, the isolation of three different Zn compounds [PhC(NtBu)2]2Zn (5-1-1), {[PhC(NtBu)2]Zn2Br3}n (5-1-2) and [PhC(NtBu)2]H • ZnBr2 (5-1-3) was successful, of which the reaction of the latter with LiP(SiMe3)2 results in {Zn[P(SiMe3)2]2}2 (5-1-C). While 5-1-1 can be obtained by mixing one eq. tBuN=C=NtBu, one eq. PhLi and one eq. ZnBr2, the polymeric 5-1-2 is the unexpected product of the reaction of one eq. tBuN=C=NtBu with one eq. PhLi and two eq. ZnBr2 (Figure 6-1 - 7 top). Because both of the more obvious approaches didn’t lead to a monomeric zinc bromine complex, [PhC(NtBu)2]Li, the product of the reaction of tBuN=C=NtBu and PhLi, was isolated and then reacted in a 1:1 stoichiometry with ZnBr2. However, due to traces of water that could not be avoided, the reaction resulted in compound 5-1-3 (Figure 6-1 - 7 bottom left) which was then mixed with LiP(SiMe3)2 in order to obtain a precursor for zinc phosphide nanoparticles. The achieved product is the literature known species 5-1-C, that was already thermally decomposed by the authors of the corresponding publication who did not get the desired Zn2P3. As the crystal structure of 5-1-C was previously determined at room temperature, it was now possible to detect a phase transition at 137 K while performing the X-ray analysis at low temperatures (Figure 6-1 - 7 bottom right). Figure 6-1 - 7: Crystal structure of 5-1-1, 5-1-2, 5-1-3 and 5-1-C. Preliminary investigations for the usage of [CH(C(Me)N(2,6-iPr2C6H3))2]Ga(PH2)2 in nanoparticle synthesis Also, studies concerning the preparation of GaP nanoparticles were realized using the gallium compound [CH(C(Me)N(2,6-iPr2C6H3))2]Ga(PH2)2 (5-2-B) which was initially synthesized and characterized by Susanne Bauer. The experiments were performed similar to those described in chapter 4.4 with HDA and PA as decomposing and stabilizing agents. Unfortunately, it was not possible to obtain any nanocorpuscles (Figure 6-1 - 8), yet, the EDX analyses of the precipitate revealed the desired composition of GaP with a slight excess of Ga. Figure 6-1 - 8: TEM image of the precipitate of reaction of 5-2-B with 1 eq. HDA

Synthesis and Reactivity of Low Valent Main Group Element Complexes

The β-diketiminate aluminum(I) complex NacNacAl (III-1) was shown to activate a range of substrates containing robust single and double bonds. Compound III-1 oxidatively adds a variety of H–X bonds (X = H, B, Al, C, Si, N, P, O) to give a series of four-coordinate aluminum hydride derivatives including the first example of an aluminum boryl hydride. In the case of Al–H addition, the reaction was shown to be in equilibrium and reversible. Furthermore, cleavage of aryl and alkyl C–F bonds, the latter a rare reaction with only a handful of examples in the literature, was observed with III-1. Robust C–O and C–S bonds were also activated by III-1 along with RS–SR and R2P–PR2 bonds. All novel aluminum complexes were characterized by spectroscopic methods and X-ray diffraction analysis for the majority of them. Activation of the C=S or P=S bonds in a thiourea or phosphine sulfide, respectively, was accomplished by III-1 to give the first examples of Lewis base-stabilized monomeric terminal aluminum sulfides. The nature of the Al=S bond was examined computationally as well as experimentally. Related reaction with a urea derivative gave an unexpected aluminum hydride while reaction of III-1 with phosphine oxides gave a putative aluminum oxide as a result of P=O bond cleavage. However, the aluminum oxo promptly deprotonates a neighbouring molecule to furnish an aluminum hydroxide as the isolated product. Reduction of the cationic germanium(II) complex IV-1 affords the formally zero valent germanium complex IV-4 stabilized by the bis(imino)pyridine platform. Compound IV-4 was fully characterized by spectroscopic methods and X-ray diffraction analysis. The molecule has a singlet ground state and DFT studies revealed partial delocalization of one of the germanium lone pairs into the ligand framework. Complex IV-4 was unreactive towards H–X bond activation, the lack of reactivity ascribed to the large singlet-triplet energy gap calculated. The same bis(imino)pyridine ligand was also used to prepare reduced zinc complexes. Monoreduction of the zinc dichloride precursor gave the formally Zn(I) compound IV-6. Further reduction of IV-6 in the presence of DMAP gave the formally zero valent zinc complex IV-9. Both compounds were fully characterized by spectroscopic methods, DFT calculations, and X-ray diffraction analysis which revealed that both zinc atoms are four-coordinate and adopt unusual square planar and see-saw geometry, respectively

Synthesis and Reactivity of Low Valent Silicon and Phosphorus Compounds

The research described in this thesis is focused on studying the use of phosphinoamidinato ligand NP (NP = [ArNC(Ph)NPiPr2]– (Ar = 2,6-iPr2C6H3)) to stabilize low-valent main group element compounds. Reduction of silane (NP)SiCl3 by magnesium allows for the high-yield preparation of base-stabilized disilylene [(NP)Si-]2. Although it is stable at room temperature, upon heating it rearranges via intermolecular N-P activation into an N,Si-heterocyclic silylene supported by a phosphine donor. The reactivity of [(NP)Si-]2 in the single bond activation of pinacolborane, phenylsilane and diphenylphosphine was tested. Additionally, the phosphidosilylene (NP)SiPPh2 that is formed in the last reaction was found to perform P-P coupling when reacted with diphenylphosphine. Experimental pursuits were taken to elucidate the mechanism of formation of disilylene [(NP)Si-]2, and some insights into its fluxionality in solution were obtained. Disilylene [(NP)Si-]2 was reacted with Si(II) and Ge(II) chlorides to yield the products of tetrylene insertion into the Si-Si bond, the low-valent compounds [(NP)Si-Si(Cl)2-Si(NP)], [(NP)Si(Cl)2Si-Si(NP)] and [(NP)Si(Cl)2Ge-Si(NP)]. Compound [(NP)Si-Si(Cl)2-Si(NP)] is the kinetic product of the direct insertion of SiCl2 fragment into Si-Si bond of [(NP)Si-]2. The thermodynamic product of the insertion of silicon dichloride is disilylene [(NP)Si(Cl)2Si-Si(NP)] that is the consequence of migration of chlorides to terminal Si center. The reaction of [(NP)Si-]2 with GeCl2 produced only one compound [(NP)Si(Cl)2Ge-Si(NP)] that is a rear example of germylene-silylene. Interaction of [(NP)Si-]2 with SiCl4 and SiHCl3 produced a new example of acyclic disilyl silylene. Reduction of (NP)PCl2 with potassium graphite allowed isolation of the base-stabilized phosphinidene (NP)P. Its reactivity was studied. The use of substrates with E-H bonds like pinacolborane, phenylsilane and diphenylphosphine yielded compounds (NP)Bpin (pin = (OC(CH3)2)2) and NPH, (NP)SiH2Ph and NPH, NPH-P-PPh2, respectively, which are the result of N-P and E-H bond metathesis. Upon reaction with tetrachlorobenzoquinone both phosphorus atoms of phosphinidene (NP)P underwent oxidation. (NP)P reacted with benzaldehyde and phenylisocyanate as a phospha-Wittig reagent. Additionally, (NP)P was transformed into phosphinidene oxide (NP)P=O, iminophosphine (NP)P=Np-Tol and phosphinidene sulfide (NP)P=S. Transient (NP)P=O and (NP)P=Np-Tol were captured by para-tolyl isocyanate to form compound (NP)P(N,N-(Np-Tol)2CO). All the compounds were fully characterized by NMR and for most of them single crystal X-ray structure was obtained

Filling Single-Walled Carbon Nanotubes with Highly Reactive Chemicals

Since the discovery of single-walled carbon nanotubes (SWCNTs) in 1993, there has been a deep fascination with the 1D (one dimensional) nanometre sized cavity that they possess. Having the ability to confine all manner of materials in such a small space had never been possible before, and the surge of new allotropes and chemicals that have either been grown or encapsulated in this nano-test tube has been staggering. Salts and elements have formed the bulk of the confined materials, but chemistry has also been achieved within the cavity, and the reduction of metal oxides has proven straightforward. Consistency in filling SWCNTs in high yields has been difficult to achieve and finding a routine technique that can ascertain a filling yield have been stumbling blocks for the research area. No standard definition of the filling yield has even been agreed upon. These issues have held the field back from becoming a more popular and viable method for enhancing the properties of SWCNTs. To combat some of these issues, this thesis uses consistent and simple practices to determine the filling yield and aims to make consistently high purity materials which can be used for novel purposes. Elemental phosphorus, arsenic and antimony have all been confined within a range of SWCNTs and have been fully characterised to determine their properties. Tetrahedral phosphorus and arsenic molecules have been stabilised by this method in quantities higher than achieved using other techniques. These can be produced either from melt reactions or vapour phase fillings which confirms that these elements fill the voids of the SWCNT in the form of tetrahedral molecules. The confined phosphorus and arsenic tetrahedra have been shown form two new allotropes namely the zigzag ladders and single zigzag chains. These are expected to form either from thermal excitation or when exposed to an electron beam during high resolution transmission electron microscopy (HRTEM). The structure produced is dependent on the diameter of nanotube and has shown consistent results with what is predicted by DFT calculations. There seems to be some dynamic behaviour at play between the conversion of the allotropes due to the small activation energy calculated for transitioning between the structures. SWCNTs have also been filled with aluminium iodide, a strong Lewis acid, in order to induce charge transfer effects. A reliable method of producing high purity samples was developed and Raman spectroscopy has shown that these materials show chargetransfer in the correct direction. Unfortunately, despite the enhanced properties of the SWCNTs, the samples were found to be no more effectively functionalised than their empty counterparts

Reactivity of Tetrahedral E4 Molecules (E4 = P4, As4, AsP3) and En Ligand Complexes

The dissertation with the title “Reactivity of Tetrahedral E4 Molecules (E4 = P4, As4, AsP3) and En Ligand Complexes" deals on the one hand with the reactivity of white phosphorus, yellow arsenic and the interpnictogen compound AsP3 towards low valent transition metal and main group metal compounds stabilized by β-diiminato (nacnac) ligands and cyclic alkyl amino carbenes (CAACs). On the other hand, it is about the reactivity of M(I) (M = Cu, Ga) nacnac compounds towards En (E = P, As) ligand complexes. In the first part, a Cu(I) nacnac compound was reacted with complexes containing aromatic cyclo-En ligands yielding molecular heterometallic complexes. In the next chapters, the reactivity of E4 towards transition metal (Ni, Cu) and main group metal (Al, Ga) complexes stabilized by β-diiminato ligands was investigated. Thereby, a broad variety of different En-structural motifs formed. Moreover, the reactivity of gallium complexes towards unsaturated transition metal units or polypnictogen ligand complexes were investigated, the resulting complexes unite different ligand systems and also different metal types (main group and transition metals). The last chapter is about the reactivity of yellow arsenic towards CAACs. Therefore, different CAACs were reacted with yellow arsenic yielding compounds with Asn units in dependence of the substituents. Moreover, the different reaction outcome and structural difference of the reactions with white phosphorus, yellow arsenic and the interpnictogen compound AsP3 was investigated

Stibasilene SbSi and Its Lighter Homologues: A Comparative Study

The multiply bonded derivatives of the heavier main group elements are among the most challenging targets for synthetic pursuits. Those of them featuring a double bond between the silicon and group 15 element are represented mostly by the silaimines <i>N</i>Si< and phosphasilenes PSi< with a very few examples of arsasilenes AsSi<. In this contribution, we report on the synthesis and structural elucidation of the first stable stibasilene and novel phosphasilene and arsasilene derivatives, featuring an identical substitution pattern. A systematic comparison within the series phosphasilene–arsasilene–stibasilene is made on the basis of their experimental and computational studies

Stibasilene SbSi and Its Lighter Homologues: A Comparative Study

The multiply bonded derivatives of the heavier main group elements are among the most challenging targets for synthetic pursuits. Those of them featuring a double bond between the silicon and group 15 element are represented mostly by the silaimines <i>N</i>Si< and phosphasilenes PSi< with a very few examples of arsasilenes AsSi<. In this contribution, we report on the synthesis and structural elucidation of the first stable stibasilene and novel phosphasilene and arsasilene derivatives, featuring an identical substitution pattern. A systematic comparison within the series phosphasilene–arsasilene–stibasilene is made on the basis of their experimental and computational studies