Cycloaddition Chemistry of a Silylene‐Nickel Complex toward Organic π‐Systems: From Reversibility to C−H Activation

The versatile cycloaddition chemistry of the Si−Ni multiple bond in the acyclic (amido)(chloro)silylene→Ni0 complex 1, [(TMSL)ClSi→Ni(NHC)2] (TMSL=N(SiMe3)Dipp; Dipp=2,6‐iPr2C6H4; NHC=C[(iPr)NC(Me)]2), toward unsaturated organic substrates is reported, which is both reminiscent of and expanding on the reactivity patterns of classical Fischer and Schrock carbene–metal complexes. Thus, 1:1 reaction of 1 with aldehydes, imines, alkynes, and even alkenes proceed to yield [2+2] cycloaddition products, leading to a range of four‐membered metallasilacycles. This cycloaddition is in fact reversible for ethylene, whereas addition of an excess of this olefin leads to quantitative sp2‐CH bond activation, via a 1‐nickela‐4‐silacyclohexane intermediate. These results have been supported by DFT calculations giving insights into key mechanistic aspects.DFG, 390540038, EXC 2008: UniSysCatTU Berlin, Open-Access-Mittel - 202

Homocoupling of CO and isocyanide mediated by a C,C′-bis(silylenyl)-substituted ortho-carborane

The unexpected reactivity of the o-carborane supported bis-silylene [(LSi:)C]2B10H101 {L= PhC(tBuN)2} towards carbon monoxide and 2,6-dimethylphenyl isocyanide is reported. While the reaction of 1 with CO leads selectively to the novel head-to-head coupling and C–O cleavage product 2 from two molecules 1 and four molecules CO, the reaction of 1 with 2,6-dimethylphenyl isocyanide affords solely the 1 : 2 molar head-to-tail coupling product 3 with a Si[double bond, length as m-dash]C bond.TU Berlin, Open-Access-Mittel - 201

Atomic layer deposition on porous powders with in situ gravimetric monitoring in a modular fixed bed reactor setup

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Review of Scientific Instruments 88, 074102 (2017) and may be found at https://doi.org/10.1063/1.4992023.A modular setup for Atomic Layer Deposition (ALD) on high-surface powder substrates in fixed bed reactors with a gravimetric in situ monitoring was developed. The design and operation are described in detail. An integrated magnetically suspended balance records mass changes during ALD. The highly versatile setup consists of three modular main units: a dosing unit, a reactor unit, and a downstream unit. The reactor unit includes the balance, a large fixed bed reactor, and a quartz crystal microbalance. The dosing unit is equipped with a complex manifold to deliver gases and gaseous reagents including three different ALD precursors, five oxidizing or reducing agents, and two purge gas lines. The system employs reactor temperatures and pressures in the range of 25-600 °C and 10−3 to 1 bar, respectively. Typically, powder batches between 100 mg and 50 g can be coated. The capabilities of the setup are demonstrated by coating mesoporous SiO2 powder with a thin AlOx (submono) layer using three cycles with trimethylaluminium and H2O. The self-limiting nature of the deposition has been verified with the in situ gravimetric monitoring and full saturation curves are presented. The process parameters were used for a scale-up in a large fixed bed reactor. The samples were analyzed with established analytics such as X-ray diffraction, N2 adsorption, transmission electron microscopy, and inductively coupled plasma optical emission spectrometry.DFG, 53182490, EXC 314: Unifying Concepts in Catalysi

Synthesis and structure of the azidogermyliumylidene azide complex [L(N-3)Ge:]N-+(3)- with covalently and ionically bonded azide ligands at germanium(II) [L = bis(N-heterocyclic carbene)]

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Starting from the chlorogermyliumylidene chloride salt [L(Cl)Ge:]Cl (1) (L = 1,1′-methylene-3,3′-di-2,6-diisopropyl-phenylimidazole-2,2′-diylidene), the chloride ion can be easily substituted by BPh4 to yield [L(Cl)Ge:]BPh4 (3). Reaction of the latter with NaN3 furnishes [L(N3)Ge:]BPh4 (4). In contrast, the direct reaction of 1 with NaN3 affords exclusively the first azidogermyliumylidene azide salt [L(N3)Ge:]N3 (2). The latter represents the first isolable diazido Ge(II) complex with a covalently bonded azido ligand and a weakly coordinating azide anion as the counterion. All new compounds 2, 3, and 4 were fully characterized, including using X-ray diffraction analysis

Where silylene–silicon centres matter in the activation of small molecules

Small molecules such as H2, N2, CO, NH3, O2 are ubiquitous stable species and their activation and role in the formation of value-added products are of fundamental importance in nature and industry. The last few decades have witnessed significant advances in the chemistry of heavy low-coordinate main-group elements, with a plethora of newly synthesised functional compounds, behaving like transition-metal complexes with respect to facile activation of such small molecules. Among them, silylenes have received particular attention in this vivid area of research showing even metal-free bond activation and catalysis. Recent striking discoveries in the chemistry of silylenes take advantage of narrow HOMO–LUMO energy gap and Lewis acid–base bifunctionality of divalent Si centres. The review is devoted to recent advances of using isolable silylenes and corresponding silylene–metal complexes for the activation of fundamental but inert molecules such as H2, COx, N2O, O2, H2O, NH3, C2H4 and E4 (E = P, As).DFG, 390540038, EXC 2008: UniSysCatTU Berlin, Open-Access-Mittel - 202

Mechanistic studies of CO2 reduction to methanol mediated by an N-heterocyclic germylene hydride

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.The labile germylene hydride LCyGeH is capable of activating CO2 affording the corresponding formate LCyGeOCH([double bond, length as m-dash]O) (2) (LCy = cyclo-C6H8-1-NAr-2-C(Ph)NAr, Ar = 2,6-iPr2C6H3). Compound 2 and the previously reported LGeOCH([double bond, length as m-dash]O) (L = CH(MeC[double bond, length as m-dash]NAr)2, Ar = 2,6-iPr2C6H3) (2′) could be further converted to methanol with the AlH3·NMe3 alane-amine adduct as a hydrogen source upon workup with water. A plausible mechanism for the conversion of the formate complexes to methanol is proposed based on additional results from the conversion of 2′ with the milder hydride delivery agent LAlH2.DFG, EXC 314, Unifying Concepts in Catalysi

Taming the germyliumylidene [CIGe:](+) and germathionium [CIGe=S](+) ions by donor-acceptor stabilization using 1,8-bis(tributylphosphazenyl)naphthalene

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.The novel chlorogermyliumylidene complex L[ClGe:]+ (L = 1,8-bis(tri-n-butylphosphanzenyl)naphthalene) with a ‘naked’ Cl− as a counter anion was synthesized through reaction of L with Cl2Ge: and fully characterized. Its reaction with elemental sulfur afforded the first germathionium [ClGe[double bond, length as m-dash]S]+ cation containing species. The latter has also been fully characterized, including single-crystal X-ray diffraction analysis

Visible light driven non-sacrificial water oxidation and dye degradation with silver phosphates: multi-faceted morphology matters

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.The convenient synthesis of multi-faceted versusirregular shaped Ag3PO4microparticles for the visible light driven non-sacrificial water oxidation is reported. Strikingly, the multi-faceted particles are found to be more effective for oxygen evolution reaction (OER) by photocatalytic water oxidation in water and in phosphate buffer solutions as well as for dye degradation in comparison to the irregular shaped particles

Unprecedented silicon(II)-> calcium complexes with N-heterocyclic silylenes

The first N-heterocyclic silylene (NHSi) complexes of any s-block element to date are reported for calcium: [(eta(5)-C5Me5)(2)Ca<--:Si(O-C6H4-2-Bu-t){((NBu)-Bu-t)(2)CPh}] (6) and [(eta(5)-C5Me5)(2)Ca<--:Si((NBuCH)-Bu-t)(2)] (7). Complexes 6 and 7 are isolable in a facile way upon reaction of the corresponding free N-heterocyclic silylenes (NHSis) with [(eta(5)-C5Me5)(2)Ca] (2). Complexes 6 and 7 were fully characterised by spectroscopic means and the single crystal X-ray diffraction analysis of 6 is also reported. Analysis of the bonding situation by DFT methods including a Bader Atoms in molecules (AIM) analysis is also reported. The bonding interaction between the Si and Ca centres in complexes 6 and 7 can best be viewed as sigma-donor-acceptor interactions, with a considerable ionic contribution in the bond. The reactivity towards the oxygen containing substrates THF and benzophenone is also discussed.DFG, EXC 314, Unifying Concepts in Catalysi

Formation of N-heterocyclic, donor-stabilized borenium ions

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Cationic and zwitterionic boryl bromide species and a borenium–boryl bromide cation have been synthesised which represent new N-donor stabilised cationic boron compounds with β-diketiminate ligands. The unexpected borenium–boryl bromide results from a head-to-tail dimerisation of the corresponding zwitterionic boryl bromide accompanied by proton migration. The electronic nature of these new species was studied by DFT calculations