Synthesis and Reactivity of Base-Stabilized and Base-Free Silaimidoyl Bromides.

The reactivity of the base-free bromosilylene dtbpCbzSiBr (dtbpCbz = 1,8-bis(3,5-di-tert-butylphenyl)-3,6-di-tert-butylcarbazolyl) toward carbodiimides and azides was studied in order to generate base-stabilized and base-free silaimidoyl bromides, respectively. The steric bulk of carbodiimides and azides allows control over the reactivity. While with small substituents such as tert-butyl or adamantyl, the reactions cannot be stopped at the Si═N stage, with large substituents, they lead to C-H activation in the product. The Dipp substituent (Dipp = 2,6-diisopropylphenyl) allowed the isolation of the silaimidoyl bromide dtbpCbzSi(Br)NDipp and its CNDipp-coordinated analogue. The reactivity of the Si═N double bond species was studied with respect to cycloaddition and donor exchange reactions.

Synthesis and properties of cyclic sandwich compounds.

Cyclic nanometre-scale sandwich complexes assembled from individual building blocks were synthesized. Sandwich complexes, in which a metal ion is π-coordinated by two planar aromatic organic rings belong to the foundations of organometallic chemistry. They have been successfully used in a wide variety of applications ranging from catalysis, synthesis and electrochemistry to nanotechnology, materials science and medicine1,2. Extending the sandwich structural motif leads to linear multidecker compounds, in which aromatic organic rings and metal atoms are arranged in an alternating fashion. However, the extension to a cyclic multidecker scaffold is unprecedented. Here we show the design, synthesis and characterization of an isomorphous series of circular sandwich compounds, for which the term 'cyclocenes' is suggested. These cyclocenes consist of 18 repeating units, forming almost ideally circular, closed rings in the solid state, that can be described by the general formula [cyclo-MII(µ-η8:η8-CotTIPS)]18 (M = Sr, Sm, Eu; CotTIPS = 1,4-(iPr3Si)2C8H62-). Quantum chemical calculations lead to the conclusion that a unique interplay between the ionic metal-to-ligand bonds, the bulkiness of the ligand system and the energy gain on ring closure, which is crucially influenced by dispersion interactions, facilitate the formation of these cyclic systems. Up to now, only linear one-dimensional multidecker sandwich compounds have been investigated for possible applications such as nanowires3-10. This textbook example of cyclic sandwich compounds is expected to open the door for further innovations towards new functional organometallic materials.

Reactivity of Pt(0) bromosilylene complexes towards ethylene.

The base-free carbazolyl bromosilylene RSiBr (R = 1,8-bis(3,5-di-tert-butyl-phenyl)-3,6-di-tert-butyl-carbazolyl) reacts with (η2-C2H4)Pt(PPh3)2 and Pt(PCy3)2 to form platinasilacyclobutane R(Br)Si(C2H4)Pt(PPh3)2 (1) and silylene platinum complex R(Br)SiPt(PCy3)2 (2), respectively. When silylene complex 2 is treated with C2H4, the six-membered metallasilacycle R(Br)Si(C2H4)2Pt(PCy3)2 (3) is obtained. All compounds are characterised by XRD and multinuclear NMR spectroscopy.

The Archetypal Homoleptic Lanthanide Quadruple-Decker-Synthesis, Mechanistic Studies, and Quantum Chemical Investigations.

Reduction of [SmIII (COT1,4-SiiPr3 )(BH4 )(thf)] (COT1,4-SiiPr3 =1,4-(i Pr3 Si)3 C8 H6 ) with KC8 resulted in [SmIII/II/III (COT1,4-SiiPr3 )4 ], the first example of a homoleptic lanthanide quadruple-decker. As indicated by an analysis of the bond metrics in the solid-state, the inner Sm ion is present in the divalent oxidation state, while the outer ones are trivalent. This observation could be confirmed by quantum chemical calculations. Mechanistic studies revealed not only insight into possible formation pathways of [SmIII/II/III (COT1,4-SiiPr3 )4 ] but also resulted in the transformation to other mixed metal sandwich complexes with unique structural properties. These are the 1D-polymeric chain structured [KSmIII (COT1,4-SiiPr3 )]n and the hexametallic species [(tol)K(COT1,4-SiiPr3 )SmII (COT1,4-SiiPr3 )K]2 which were initially envisioned as possible building blocks as part of different retrosynthetically guided pathways that we developed.

Sustainable Fatty Acid Modification of Cellulose in a CO2-Based Switchable Solvent and Subsequent Thiol-Ene Modification.

Searching for more sustainable materials as an alternative to petroleum-based products is of increasing interest due to different environmental issues. Cellulose and fatty acids are two very promising candidates for biobased material design. Herein, we report a sustainable synthesis of fatty acid cellulose esters (FACEs) via transesterification of cellulose with methyl-10-undecenoate in a CO2-based switchable solvent system. FACEs with a degree of substitution between 0.70 and 1.97 were synthesized by simple variation of reaction parameters and characterized in detail. Subsequently, a FACE with a degree of substitution (DS) of 0.70 was modified via thiol-ene reaction, demonstrating an efficient and versatile method to tune the structure and properties of the new cellulose derivatives. Films were produced from each sample via solvent casting, and their mechanical properties were examined using tensile tests. Elastic moduli (E) ranging from 90 to 635 MPa and elongations at break between 2 and 23% were observed, depending on the DS of the FACE and the type of thiol employed for the modification. Finally, contact angle measurements confirmed an increase in the surface hydrophobicity (75-91°) for the thiol-ene-modified samples.