INTERMOLECULAR COMPLEXES OF GERMANIUM(II

This thesis examines the synthesis, structural characterization, and reactivity of neutral and charged intermolecular donor complexes of germanium(II). Base stabilized complexes of dimesitylgermylene (Mes2Ge) (mes = mesityl = 2,4,6- trimethylphenyl) with either an anionic diisopropylphenyl-substituted N-heterocyclic gallium® (NHGa\u27) ligand or a diisopropyl substituted N-heterocyclic carbene (NHC) ligand were synthesized by the addition of two equivalents of either NHGa\u27 or NHC to tetramesityldigermene (Mes2Ge=GeMes2). The complexes [NHGa-GeMes2] and NHC- GeMes2 are the first two examples of a transient germylene (Mes2Ge) being stabilized by intermolecular donors. A series of NHC complexes of GefG (R = F, Cl, Br, I, CI/O3SCF3,0\u27Bu, NCS, Mes) were synthesized. The !H NMR spectra of the NHC-GeR2 complexes show broad signals at room temperature which was rationalized by either conformational interchanges or intermolecular exchanges. The NHC-GeR2 complexes were also examinedcomputationally. Theenergyofcomplexationwasfoundtodecreaseif7T donor atoms are located adjacent to the germanium centre. The reactivity of selected NHC-GeR2 (R = Cl, OlBu, or Mes) complexes towards 2,3-dimethylbutadiene, S^-di-Wtyl-orthoquinone, methyl iodide, pivalic acid and benzophenone was examined. In comparison with uncomplexed GeR2 species, the NHC-GeR2 complexes are less reactive. The prospect of using the NHC-GeR2 complexes as a synthon for GeR2 appears to be reaction specific. Finally, a series of cationic germanium(II) complexes were synthesized and characterized, including examples of germanium(II) centred dications. A germanium 111 centred dication supported by three NHC ligands [NHC3Ge][I]2 was characterized and examined computationally. The structure of (cryptand[2.2.2]Ge) , as the inflate salt, was reported and is the first example of a non-metal cation situated within a cryptand. A number cationic germanium crown ether complexes were are also synthesized including [[12]crown-4)2*Ge]2+, [[15]crown-5*GeOTf]+ and [benzo[15]crown-5•GeC1]+ and [benzo[15]crown-5•GeOTf. The geometries of the crown ether-germanium complexes were found to be highly dependent on the size of the crown ether and the substituent located on the germanium

In-Depth Analysis of the Effect of Fragmentation on the Crystallization-Driven Self-Assembly Growth Kinetics of 1D Micelles Studied by Seed Trapping

Studying the growth of 1D structures formed by the self-assembly of crystalline-coil block copolymers in solution at elevated temperatures is a challenging task. Like most 1D fibril structures, they fragment and dissolve when the solution is heated, creating a mixture of surviving crystallites and free polymer chains. However, unlike protein fibrils, no new nuclei are formed upon cooling and only the surviving crystallites regrow. Here, we report how trapping these crystallites at elevated temperatures allowed us to study their growth kinetics at different annealing times and for different amounts of unimer added. We developed a model describing the growth kinetics of these crystallites that accounts for fragmentation accompanying the 1D growth process. We show that the growth kinetics follow a stretched exponential law that may be due to polymer fractionation. In addition, by evaluating the micelle growth rate as a function of the concentration of unimer present in solution, we could conclude that the micelle growth occurred in the mononucleation regime

Non-Centrosymmetric Cylindrical Block Copolymer Micelles by Unidirectional Growth

Unidirectional Growth Block copolymers, in which two dissimilar polymers are covalently joined together, can be designed to form micelles in solution and can be used as self-assembling injectable gels for tissue engineering or wound healing. One challenge is to find ways to create asymmetrical structures, because normally, block addition would occur at both ends of the polymer chain. Rupar et al. (p. 559 ; see the Perspective by Pochan ) devised a route to link together three diblock copolymers with a capping approach. Protecting one end during growth gave rise to asymmetrical structures. </jats:p

The Anionic Polymerization of a tert-Butyl-Carboxylate-Activated Aziridine

N-Sulfonyl-activated aziridines are known to undergo anionic-ring-opening polymerizations (AROP) to form polysulfonyllaziridines. However, the post-polymerization deprotection of the sulfonyl groups from polysulfonyllaziridines remains challenging. In this report, the polymerization of tert-butyl aziridine-1-carboxylate (BocAz) is reported. BocAz has an electron-withdrawing tert-butyloxycarbonyl (BOC) group on the aziridine nitrogen. The BOC group activates the aziridine for AROP and allows the synthesis of low-molecular-weight poly(BocAz) chains. A 13C NMR spectroscopic analysis of poly(BocAz) suggested that the polymer is linear. The attainable molecular weight of poly(BocAz) is limited by the poor solubility of poly(BocAz) in AROP-compatible solvents. The deprotection of poly(BocAz) using trifluoroacetic acid (TFA) cleanly produces linear polyethyleneimine. Overall, these results suggest that carbonyl groups, such as BOC, can play a larger role in the in the activation of aziridines in anionic polymerization and in the synthesis of polyimines

Reversible Cross-Linking of Polyisoprene Coronas in Micelles, Block Comicelles, and Hierarchical Micelle Architectures Using Pt(0)–Olefin Coordination

Previous work has established that polyisoprene (PI) coronas in cylindrical block copolymer micelles with a poly(ferrocenyldimethylsilane) (PFS) core can be irreversibly cross-linked by hydrosilylation using (HSiMe₂)₂O in the presence of Karstedt’s catalyst. We now show that treatment of cylindrical PI-<i>b</i>-PFS micelles with Karstedt’s catalyst alone, in the absence of any silanes, leads to PI coronal cross-linking through Pt(0)–olefin coordination. The cross-linking can be reversed through the addition of 2-bis(diphenylphosphino)ethane (dppe), a strong bidentate ligand, which removes the platinum from the PI to form Pt(dppe)₂. The Pt(0) cross-linking of PI was studied with self-assembled cylindrical PI-<i>b</i>-PFS block copolymer micelles, where the cross-linking was found to dramatically increase the stability of the micellar structures. The Pt(0)–alkene coordination-induced cross-linking can be used to provide transmission electron microscopy contrast between PI and poly(dimethylsiloxane) (PDMS) corona domains in block comicelles as the process selectively increases the electron density of the PI regions. Moreover, following the assembly of a hierarchical scarf-shaped comicelle consisting of a PFS-<i>b</i>-PDMS platelet template with PI-<i>b</i>-PFS tassels, Pt(0)-induced cross-linking of the PI coronal regions allowed for the selective removal of the PFS-<i>b</i>-PDMS center, leaving behind an unprecedented hollowed-out scarf structure. The addition of Karstedt’s catalyst to PI or polybutadiene homopolymer toluene/xylene solutions resulted in the formation of polymer gels which underwent de-gelation upon the addition of dppe

Exploring the limits of 73Ge solid-state NMR spectroscopy at ultrahigh magnetic field

The ultrahigh field natural abundance \u2077\ub3Ge solid-state wide-line NMR study of germanium dichloride complexed with 1,4-dioxane and tetraphenylgermane yields the largest \u2077\ub3Ge quadrupolar coupling constant determined by NMR spectroscopy to date and the first direct observation of \u2077\ub3Ge chemical shift anisotropy.Peer reviewed: YesNRC publication: Ye

Bridged Difurans: Stabilizing Furan with p‑Block Elements

Thiophene is one of the most commonly used moieties in conjugated materials, whereas its oxygen congener, furan, is much less frequently encountered due to the susceptibility of furan toward light- and oxygen-induced degradation. In an effort to stabilize furans, three difurans, bridged by Ph₂Si, Ph₂Ge, and PhP­(O), were synthesized. Each bridged difuran has Me₃Si groups at the 2- and 6-positions. All of the bridged difurans were found to be stable under ambient conditions. Since it is known that electron-deficient furans exhibit improved stability, the stability of the bridged difurans is attributed, in part, to the p-block elements, which lower the LUMO levels of the molecules through σ*−π* conjugation. Single-crystal X-ray diffraction studies of the phosphorus-bridged species showed that the structure is similar to that of the known thiophene analogue, but with bond lengths consistent with the reduced aromaticity of furan. All of the p-block bridged difurans show strong absorption in the UV region and intense emissions with quantum yields ranging from 0.30 to 0.80. DFT calculations indicate that the frontier molecular orbitals of bridged difurans are slightly higher than those of their thiophene counterparts. In order to demonstrate the synthetic potential of bridged difurans, the phosphorus-bridged difuran was converted to its 2,6-dibromo derivative, which in turn was copolymerized with (9,9-dioctyl-9<i>H</i>-fluorene-2,7-diyl)­bis­(trimethylstannane) to form the stable conjugated polymer <b>PDFP-F</b>. The phosphorus-bridged difuran was also reduced from its phosphine oxide form and then quaternized with methyl triflate to produce the corresponding air-stable phosphonium salt