Stabilisation of a Strontium Hydride with a Monodentate Carbazolyl Ligand and its Reactivity.

The molecular strontium hydride 2 [(Cbz)SrH(L)] (L=benzene, toluene) was isolated and stabilized by employing a sterically demanding carbazole ligand (Cbz=1,8-bis(3,5-ditertbutylphenyl)-3,6-ditertbutylcarbazolyl). Compound 2 was synthesized via phenylsilane metathesis with the corresponding amide (Cbz)SrN(SiMe) and characterized by H NMR, XRD and vibrational spectroscopy methods. We further investigated the stoichiometric reactivity of 2 towards carbon monoxide, azobenzene and trimethylsilylacetylene, showing three distinct reactivity pathways: addition, reduction and deprotonation.

Unconventional Insertions of Internal Alkynes into a Mixed-Valent Silaiminyl-Silylene.

The reactivity of a mixed-valent silaiminyl-silylene [LSi-Si(NDipp)L] (L = PhC(NBu), Dipp = 2,6-Pr-CH) toward various substituted internal alkynes was investigated. In contrast to previous reports that primarily yield [Si(μ-C)Si]-modified rings via 1,2-addition of two silylenes in the center of the molecule, our study reveals a novel reaction pathway. The introduction of [R-C≡C-R] (R = Ph or SiMe, R = Ph or C≡CSiMe) gave unconventional insertion into one of the amidinate ligands, followed by migration of the {NBu} group to bridge two Si atoms.

CO reduction by calcium and ytterbium hydride complexes with a bulky monodentate carbazolyl ligand.

The bulky monodentate carbazolyl ligand 1,8-bis(3,5-dibutylphenyl)-3,6-dibutylcarbazole (Cbz) was employed in the synthesis of monomeric heteroleptic amido carbazolyl complexes of Ca and Yb. For both central metal atoms, dimeric hydride complexes [(Cbz)Ca(benzene)H], [(Cbz)Ca(THF)H], [(Cbz)Yb(benzene)H] and [(Cbz)Yb(THF)H] were obtained, which show remarkably poor solubility in organic solvents. The characteristic hydride H NMR resonance of [(Cbz)Ca(benzene)H] was observed at 2.

De- and Rearomatisation of Pyridine in Silylene Chemistry.

Traditional methods relying on metal-ligand cooperation for activating pyridine bonds in de- and rearomatisation are being challenged by the abundant metal-free element species as alternatives. Here, we investigated the de/re-aromatisation of pyridine facilitated by pyridylamino-functionalised silylene reactions with ketones and ketene. The reactivity outcome is highly dependent on the substituents on the ketones.

III-Nitride Magnetron Sputter Epitaxy on Si: Controlling Morphology, Crystal Quality, and Polarity Using Al Seed Layers.

Group III-nitride semiconductors have been subject of intensive research, resulting in the maturing of the material system and adoption of III-nitrides in modern optoelectronics and power electronic devices. Defined film polarity is an important aspect of III-nitride epitaxy as the polarity affects the design of electronic devices. Magnetron sputtering is a novel approach for cost-effective epitaxy of III-nitrides nearing the technological maturity needed for device production; therefore, control of film polarity is an important technological milestone.

Reactivities of phosphaalkynes towards diverse bis-silylenes.

Bis-silylenes do not only act as strong chelating σ-donor ligands, but also exhibit cooperative behaviour in the activation of small molecules. Three different P-Si containing molecules were prepared from the reaction between BuCP and different bis-silylenes, which are bridged by ferrocenediyl, diaminobenzene, or -carborane.

Silylenes with a Small Chalcogenide Substituent: Tuning Frontier Orbital Energies from O to Te.

The general synthesis of heteroleptic acyclic silylenes with a bulky carbazolyl substituent (Cbz) is detailed and a series of compounds with a chalcogenide substituent of the type [(Cbz)SiER] (ER=OBu, SEt, SePh, TePh) is reported. With the bulky carbazolyl substituent present, the chalcogenide moiety can be very small, as is shown by incorporating groups as small as ethyl, phenyl or tert-butyl. For the first time, the electronic properties of the silylene can be tuned along a complete series of chalcogenide substituents.

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

The reactivity of the base-free bromosilylene CbzSiBr (Cbz = 1,8-bis(3,5-di-butylphenyl)-3,6-di--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 -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.

Photolysis of Phosphaketenyltetrylenes with a Carbazolyl Substituent.

Phosphaketenes of divalent group 14 compounds can potentially serve as precursors for the synthesis of heavy multiple-bond systems. We have employed the Cbz substituent ( Cbz=1,8-bis(3,5-ditertbutylphenyl)-3,6-ditertbutylcarbazolyl) to prepare such phosphaketenyltetrylenes [( Cbz)EPCO] (E=Ge, Sn, Pb). While the phosphaketenyltetrylenes are stable at ambient conditions, they can be readily decarbonylated photolytically.

Monitoring of the Initial Stages of Diamond Growth on Aluminum Nitride Using In Situ Spectroscopic Ellipsometry.

The high thermal conductivity of polycrystalline diamond makes it ideally suited for thermal management solutions for gallium nitride (GaN) devices, with a diamond layer grown on an aluminum nitride (AlN) interlayer atop the GaN stack. However, this application is limited by the thermal barrier at the interface between diamond and substrate, which has been associated with the transition region formed in the initial phases of growth. In this work, in situ spectroscopic ellipsometry (SE) is employed to monitor early-stage microwave plasma-enhanced chemical vapor deposition diamond growth on AlN.

Heteroatom-Based Diradical(oid)s.

Heteroatom-centered diradical(oid)s have been in the focus of molecular main group chemistry for nearly 30 years. During this time, the diradical concept has evolved and the focus has shifted to the rational design of diradical(oid)s for specific applications. This review article begins with some important theoretical considerations of the diradical and tetraradical concept.

Strain-Driven, Non-Catalysed Ring Expansion of Silicon Heterocycles.

Silacycles are ubiquitous building blocks. Small silacycles can typically be expanded catalytically. A silirane, silirene and phosphasilirene as well as a siletane and a silolene were prepared starting from the base-free bromosilylene [( Cbz)SiBr] ( Cbz=1,8-bis(3,5-ditertbutylphenyl)-3,6-ditertbutylcarbazolyl).

A Barium Complex of the Silanide SiH: Hydride Surrogate and Source of Silicon.

The silanide SiH is an archetypical anion. Its metathesis chemistry is, however, still underdeveloped. We have conveniently prepared the barium silanide complex [(Cbz)BaSiH] with a bulky carbazolide ligand by reaction of the corresponding barium amide with phenyl silane in a good yield.

Snapshots of sequential polyphosphide rearrangement upon metallatetrylene addition.

Insertion and functionalization of gallasilylenes [LSi-Ga(Cl)L] (L = PhC(NBu); L = [{2,6-iPrCHNCMe}CH]) into the -E rings of [Cp*Fe(-E)] (Cp* = -CMe; E = P, As) are reported. Reactions of [Cp*Fe(-E)] with gallasilylene result in E-E/Si-Ga bond cleavage and the insertion of the silylene in the -E rings. [(LSi-Ga(Cl)L){(-P)FeCp*}], in which the Si atom binds to the bent -P ring, was identified as a reaction intermediate.

Effects of silylene ligands on the performance of carbonyl hydrosilylation catalyzed by cobalt phosphine complexes.

In order to study the effects of silylene ligands on the catalytic activity of carbonyl hydrosilylation catalyzed by cobalt phosphine complexes, readily available model catalysts are required. In this contribution, a comparative study of the hydrosilylation of aldehydes and ketones catalyzed by tris(trimethylphosphine) cobalt chloride, CoCl(PMe) (1), and bis(silylene) cobalt chloride, Co(LSi:)(PMe)Cl (2, LSi: = {PhC(NBu)}SiCl), is presented. It was found that both complexes 1 and 2 are good catalysts for the hydrosilylation of aldehydes and ketones under mild conditions.

Reactivity of Pt(0) bromosilylene complexes towards ethylene.

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

Control over Selectivity in Alkene Hydrosilylation Catalyzed by Cobalt(III) Hydride Complexes.

Two new bisphosphine [PCP] pincer cobalt(III) hydrides, [(L)Co(PMe)(H)(Cl)] (, = 2,6-((PhP)(Et)N)CH) and [(L)Co(PMe)(H)(Cl)] (, = 2,6-((PrP)(Et)N)CH), as well as one new bissilylene [SiCSi] pincer cobalt(III) hydride, [(L)Co(PMe)(H)(Cl)] (, = 1,3-((PhC(BuN)Si)(Et)N)CH), were synthesized by reaction of the corresponding protic [PCP] or [SiCSi] pincer ligands , and with CoCl(PMe). Despite the similarities in the ligand scaffolds, the three cobalt(III) hydrides show remarkably different performance as catalysts in alkene hydrosilylation. Among the PCP pincer complexes, has higher catalytic activity than complex , and both catalysts afford -Markovnikov selectivity for both aliphatic and aromatic alkenes.

Stereoselective Activation of Small Molecules by a Stable Chiral Silene.

The reaction of the dilithium salt of the enantiopure (S)-BINOL (1,1'-bi-2-naphthol) with two equivalents of the amidinate-stabilized chlorosilylene [L SiCl] (L =PhC(NtBu) ) led to the formation of the first example of a chiral cyclic silene species comprising an (S)-BINOL ligand. The reactivity of the Si=C bond was investigated by reaction with elemental sulfur, CO and HCl. The reaction with S led to a Si=C bond cleavage and concomitantly to a ring-opened product with imine and silanethione functional groups.

Cyclopenta-fused polyaromatic hydrocarbons: synthesis and characterisation of a stable, carbon-centred helical radical.

An air- and moisture-stable helical radical with seven six- and five-membered rings arranged alternately was synthesized by cyclizations in a suitably ,'-substituted terphenyl and re-establishment of its conjugation. Mesityl groups at the five-membered rings prevent radical reactions. This cyclopenta-fused polyaromatic hydrocarbon (CP-PAH) was characterized by X-ray crystallographic analysis, EPR and UV/Vis spectroscopy, and by cyclic voltammetry.

Rare-earth metal complexes with redox-active formazanate ligands.

The synthesis and characterisation of rare-earth metal complexes with redox-active formazanate ligands are described. Deprotonation of the neutral formazan ligand LH (L = PhNNC(Ph)NNPh) with [Ln{N(SiMe)}] (Ln = Y, Sm, Dy) resulted in homoleptic tris(formazanate) complexes with the general formula [(L)Ln] (Ln = Y (1), Sm (2), Dy (3)), in which the central metal atom is coordinated by six N atoms, revealing a propeller-type structure. To generate heteroleptic complexes, a novel formazan ligand LH (L = {PhNNC(4-BuPh)NNPh}) was employed.

Accessing Cationic α-Silylated and α-Germylated Phosphorus Ylides.

The synthesis and full characterization of α-silylated (α-SiCPs; 1-7) and α-germylated (α-GeCPs; 11-13) phosphorus ylides bearing one chloride substituent R PC(R )E(Cl)R (R=Ph; R =Me, Et, Ph; R =Me, Et, iPr, Mes; E=Si, Ge) is presented. The molecular structures were determined by X-ray diffraction studies. The title compounds were applied in halide abstraction studies in order to access cationic species.

Attempted reduction of a carbazolyl-diiodoalane.

We report details of our attempts to reduce the bulky carbazolyl diiodoalane [R-AlI]. The reducing agents employed include KC, Cp*Co and the Mg(I) compound [(BDI)Mg]. The use of KC allowed the spectroscopic observation of the alanediyl [R-Al].

Revealing the growth of copper on polystyrene--poly(ethylene oxide) diblock copolymer thin films with GISAXS.

Copper (Cu) as an excellent electrical conductor and the amphiphilic diblock copolymer polystyrene-block-poly(ethylene oxide) (PS-b-PEO) as a polymer electrolyte and ionic conductor can be combined with an active material in composite electrodes for polymer lithium-ion batteries (LIBs). As interfaces are a key issue in LIBs, sputter deposition of Cu contacts on PS-b-PEO thin films with high PEO fraction is investigated with in situ grazing-incidence small-angle X-ray scattering (GISAXS) to follow the formation of the Cu layer in real-time. We observe a hierarchical morphology of Cu clusters building larger Cu agglomerates.

Towards Heteroleptic Dicoordinate Cu Complexes.

In this work we detail our efforts to systematically generate stable dicoordinate Cu complexes. Initial experiments via metathesis reactions of a bulky potassium carbazolide (RK) with copper(II) salts indeed yielded a stable product, RCuOTf (1). However, subsequent attempts to grasp systematic synthetic access to complexes of the type RCuX (X=monoanionic ligand) proved difficult as many of the complexes rapidly decomposed in solution.

Origin(s) of Anomalous Substrate Conduction in MOVPE-Grown GaN HEMTs on Highly Resistive Silicon.

The performance of transistors designed specifically for high-frequency applications is critically reliant upon the semi-insulating electrical properties of the substrate. The suspected formation of a conductive path for radio frequency (RF) signals in the highly resistive (HR) silicon substrate itself has been long held responsible for the suboptimal efficiency of as-grown GaN high electron mobility transistors (HEMTs) at higher operating frequencies. Here, we reveal that not one but two discrete channels distinguishable by their carrier type, spatial extent, and origin within the metal-organic vapor phase epitaxy (MOVPE) growth process participate in such parasitic substrate conduction.