Chemical Bonding in Silicon Carbonyl Complexes

Although silylene-carbonyl complexes are known for decades, only recently isolable examples have been accomplished. In this work, the bonding situation is re-evaluated to explain the origins of their remarkable stability within the Kohn-Sham molecular orbital theory framework. It is shown that the chemical bond can be understood as CO interaction with the silylene via a donor-acceptor interaction: a σ-donation from the σCO into the empty p-orbital of silicon, and a π-back donation from the sp2 lone pair of silicon into the π*CO antibonding orbitals. Notably, it was established that the driving force behind the surprisingly stable Si−CO compounds, however, is another π-back donation from a perpendicular bonding R−Si σ-orbital into the π*CO antibonding orbitals. Consequently, the pyramidalization of the central silicon atom cannot be associated with the strength of the π-back donation, in sharp contrast to the established chemical bonding model. Considering this additional bonding interaction not only shed light on the bonding situation, but is also an indispensable key for broadening the scope of silylene-carbonyl chemistry

Evidence of AlII Radical Addition to Benzene

Electrophilic AlIII species have long dominated the aluminum reactivity towards arenes. Recently, nucleophilic low-valent AlI aluminyl anions have showcased oxidative additions towards arenes C−C and/or C−H bonds. Herein, we communicate compelling evidence of an AlII radical addition reaction to the benzene ring. The electron reduction of a ligand stabilized precursor with KC8 in benzene furnishes a double addition to the benzene ring instead of a C−H bond activation, producing the corresponding cyclohexa-1,3(orl,4)-dienes as Birch-type reduction product. X-ray crystallographic analysis, EPR spectroscopy, and DFT results suggest this reactivity proceeds through a stable AlII radical intermediate, whose stability is a consequence of a rigid scaffold in combination with strong steric protection

Evidence of AlII Radical Addition to Benzene

Electrophilic AlIII species have long dominated the aluminum reactivity towards arenes. Recently, nucleophilic low-valent AlI aluminyl anions have showcased oxidative additions towards arenes C-C and/or C-H bonds. Herein, we communicate compelling evidence of an AlII radical addition reaction to the benzene ring. The electron reduction of a ligand stabilized precursor with KC8 in benzene furnishes a double addition to the benzene ring instead of a C-H bond activation, producing the corresponding cyclohexa-1,3(orl,4)-dienes as Birch-type reduction product. X-ray crystallographic analysis, EPR spectroscopy, and DFT results suggest this reactivity proceeds through a stable AlII radical intermediate, whose stability is a consequence of a rigid scaffold in combination with strong steric protection

Revisiting the origin of the bending in group 2 metallocenes AeCp2 (Ae = Be–Ba)

Metallocenes are well-established compounds in organometallic chemistry, and can exhibit either a coplanar structure or a bent structure according to the nature of the metal center (E) and the cyclopentadienyl ligands (Cp). Herein, we re-examine the chemical bonding to underline the origins of the geometry and stability observed experimentally. To this end, we have analysed a series of group 2 metallocenes [Ae(C5R5)2] (Ae = Be–Ba and R = H, Me, F, Cl, Br, and I) with a combination of computational methods, namely energy decomposition analysis (EDA), polarizability model (PM), and dispersion interaction densities (DIDs). Although the metal–ligand bonding nature is mainly an electrostatic interaction (65–78%), the covalent character is not negligible (33–22%). Notably, the heavier the metal center, the stronger the d-orbital interaction with a 50% contribution to the total covalent interaction. The dispersion interaction between the Cp ligands counts only for 1% of the interaction. Despite that orbital contributions become stronger for heavier metals, they never represent the energy main term. Instead, given the electrostatic nature of the metallocene bonds, we propose a model based on polarizability, which faithfully predicts the bending angle. Although dispersion interactions have a fair contribution to strengthen the bending angle, the polarizability plays a major role

Evidence of AlII Radical Addition to Benzene

Electrophilic AlIII species have long dominated the aluminum reactivity towards arenes. Recently, nucleophilic low-valent AlI aluminyl anions have showcased oxidative additions towards arenes C C and/or C H bonds. Herein, we communicate compelling evidence of an AlII radical addition reaction to the benzene ring. The electron reduction of a ligand stabilized precursor with KC8 in benzene furnishes a double addition to the benzene ring instead of a C H bond activation, producing the corresponding cyclohexa-1,3 (orl,4)-dienes as Birch-type reduction product. X-ray crystallographic analysis, EPR spectroscopy, and DFT results suggest this reactivity proceeds through a stable AlII radical intermediate, whose stability is a consequence of a rigid scaffold in combination with strong steric protection

Quality Control Modelling of Competitive Professionals’ Training at Vocational Education Institutions

The most important condition that provides the opportunity for the professionalism of professionals is their competitiveness. The current task of institutions of professional (vocational technical) education (IP(VT)E) is to prepare a qualified and competitive specialist who not only has a certain level of knowledge, skills and abilities but can practically apply them in their professional activities. Future specialists’ training quality is based on the ability to adapt to rapidly changing production conditions. It is due both to the prospect of Ukraine’s accession to the European Union and to the internal situation in the country, where a large number of applicants in IP(VT)E and institutions of professional higher education (IPHE) do not always meet the requirements of the labour market. It requires resetting educational goals and objectives of vocational education, considering global changes in society, production, and technology. This article aims to substantiate the quality management model of training competitive specialists in IP(VT)E, considering the factors affecting the quality of training and contradictions that need to be resolved in the training process and experimental verification of its effectiveness. A set of theoretical and empirical methods was used to create a model and test its effectiveness, identifying the components that have become key in creating a model of quality management training for future competitive professionals in vocational education institutions. To determine the effectiveness, a set of questionnaires was developed, and within the framework of the pedagogical experiment, a section was conducted among entrants, applicants, graduates, pedagogical workers, heads of IP(VT)E regions of Ukraine, and employers, the results were analysed

Ligand-Mediated Regioselective Rhodium-Catalyzed Benzotriazole–Allene Coupling:Mechanistic Exploration and Quantum Chemical Analysis

Contains fulltext : 228437.pdf (publisher's version ) (Open Access

Isolation of a 16pi-Electrons 1,4-Diphosphinine-1,4-diide with a Planar C4P2 Ring

Rottschäfer D, Neumann B, Stammler H-G, Andrada D, Sergeieva T, Ghadwal R. Isolation of a 16pi-Electrons 1,4-Diphosphinine-1,4-diide with a Planar C4P2 Ring. Chemistry - A European Journal. 2021;27(9):3055-3064.Herein, we report the first 1,4-diphosphinine-1,4-diide compound [(ADC Ph )P] 2 ( 5-Ph ) (ADC Ph = PhC{(NDipp)C} 2 ; Dipp = 2,6-iPr 2 C 6 H 3 ) derived from an anionic dicarbene (ADC Ph ) as a red crystalline solid. Compound 5-Ph containing a 16pi-electron planar fused-tricyclic ring system was obtained by the 4e reduction of [(ADC Ph )PCl 2 ] 2 ( 4-Ph ) with Mg (or KC 8 ) in a quantitative yield. Experimental and computational results imply that the central 8pi-electrons C 4 P 2 ring of 5-Ph , which is fused between two 6pi-electrons C 3 N 2 aromatic rings, is antiaromatic. Thus, each of the phosphorus atoms of 5-Ph has two electron-lone-pairs, one in a p-type orbital is in conjugation with the C=C bonds of the C 4 P 2 ring, while the second resides in a sigma-symmetric orbital. This can be shown with the gold complex [(ADC Ph )P(AuCl) 2 ] 2 ( 6-Ph ) obtained by reacting 5-Ph with (Me 2 S)AuCl. A mixture of 5-Ph and 4-Ph undergoes comproportionation in the presence of MgCl 2 to form the intermediate oxidation state compound [(ADC Ar )P] 2 (MgCl 4 ) ( 7-Ph ), which is an aromatic species. © 2020 Wiley-VCH GmbH