Bis(2,4,6-trimethyl­phen­yl)zinc(II)

The title compound, [Zn(C9H11)2] or Mes2Zn (Mes = mesityl = 2,4,6-trimethyl­phen­yl), crystallizes with a quarter of a mol­ecule in the asymmetric unit. The ZnII atom is in a strictly linear environment with a Zn—C bond length of 1.951 (5) Å. Due to the imposed 2/m symmetry, both aromatic rings are coplanar. One of the methyl groups is disordered over two equally occupied positions

Resonance Raman Spectro-Electrochemistry to Illuminate Photo-Induced Molecular Reaction Pathways

Electron transfer reactions play a key role for artificial solar energy conversion, however, the underlying reaction mechanisms and the interplay with the molecular structure are still poorly understood due to the complexity of the reaction pathways and ultrafast timescales. In order to investigate such light-induced reaction pathways, a new spectroscopic tool has been applied, which combines UV-vis and resonance Raman spectroscopy at multiple excitation wavelengths with electrochemistry in a thin-layer electrochemical cell to study [RuII(tbtpy)2]2+ (tbtpy = tri-tert-butyl-2,2′:6′,2′′-terpyridine) as a model compound for the photo-activated electron donor in structurally related molecular and supramolecular assemblies. The new spectroscopic method substantiates previous suggestions regarding the reduction mechanism of this complex by localizing photo-electrons and identifying structural changes of metastable intermediates along the reaction cascade. This has been realized by monitoring selective enhancement of Raman-active vibrations associated with structural changes upon electronic absorption when tuning the excitation wavelength into new UV-vis absorption bands of intermediate structures. Additional interpretation of shifts in Raman band positions upon reduction with the help of quantum chemical calculations provides a consistent picture of the sequential reduction of the individual terpyridine ligands, i.e., the first reduction results in the monocation [(tbtpy)Ru(tbtpy•)]+, while the second reduction generates [(tbtpy•)Ru(tbtpy•)]0 of triplet multiplicity. Therefore, the combination of this versatile spectro-electrochemical tool allows us to deepen the fundamental understanding of light-induced charge transfer processes in more relevant and complex systems

Synthesis, Structure, and Stability of Lithium Arylphosphanidyl‐diarylphosphane Oxide

The reaction of LiP(H)Tipp ( 2a ) and KP(H)Tipp ( 2b , Tipp = C 6 H 2 ‐2,4,6‐ i Pr 3 ), which are accessible via metalation of Tipp‐PH 2 ( 1 ), with bis(4‐ tert ‐butylphenyl)phosphinic chloride yields Tipp‐P=P(OM)Ar 2 [M = Li ( 3a ) and K ( 3b )]. These complexes show characteristic chemical 31 P shifts and large 1 J PP coupling constants. These compounds degrade with elimination of the phosphinidene Tipp‐P: and the alkali metal diarylphosphinites M–O–PAr 2 [M = Li ( 4a ) and K ( 4b )]. The phosphinidene forms secondary degradation products (like the meso and R,R/S,S ‐isomers of diphosphane Tipp‐P(H)–P(H)Tipp ( 5 ) via insertion into a P–H bond of newly formed Tipp‐PH 2 ), whereas the crystallization of [Tipp‐P=P(OLi)Ar 2 · LiOPAr 2 · LiCl · 2Et 2 O] 2 (i.e. [ 3a·4a· LiCl · 2Et 2 O] 2 ) succeeds from diethyl ether. The metathesis reactions of LiP(Si i Pr 3 )Tipp and LiP(Si i Pr 3 )Mes (Mes = C 6 H 2 ‐2,4,6‐Me 3 ) with Ar 2 P(O)Cl yield Ar*‐P=P(OSi i Pr 3 )Ar 2 (Ar* = Mes, Tipp) which degrade to Ar 2 POSi i Pr 3 and other secondary products.image John Wiley & Sons, Ltd

One‐Step Synthesis and Schlenk‐Type Equilibrium of Cyclopentadienylmagnesium Bromides

Abstract In the in situ Grignard metalation method (iGMM), the addition of bromoethane to a suspension of magnesium turnings and cyclopentadienes [C 5 H 6 (HCp), C 5 H 5 ‐Si( i Pr) 3 (HCp TIPS )] in diethyl ether smoothly yields heteroleptic [(Et 2 O)Mg(Cp R )(μ‐Br)] 2 (Cp R =Cp ( 1 ), Cp TIPS ( 2 )). The Schlenk equilibrium of 2 in toluene leads to ligand exchange and formation of homoleptic [Mg(Cp R ) 2 ] ( 3 ) and [(Et 2 O)MgBr(μ‐Br)] 2 ( 4 ). Interfering solvation and aggregation as well as ligand redistribution equilibria hamper a quantitative elucidation of thermodynamic data for the Schlenk equilibrium of 2 in toluene. In ethereal solvents, mononuclear species [(Et 2 O) 2 Mg(Cp TIPS )Br] ( 2’ ), [(Et 2 O) n Mg(Cp TIPS ) 2 ] ( 3’ ), and [(Et 2 O) 2 MgBr 2 ] ( 4’ ) coexist. Larger coordination numbers can be realized with cyclic ethers like tetrahydropyran allowing crystallization of [(thp) 4 MgBr 2 ] ( 5 ). The interpretation of the temperature‐dependency of the Schlenk equilibrium constant in diethyl ether gives a reaction enthalpy ΔH and reaction entropy ΔS of −11.5 kJ mol −1 and 60 J mol −1 , respectively.Cyclopentadienylmagnesium bromides are accessible with high yields by a fast and smooth one‐pot synthesis. In hydrocarbons and in ethereal solvents a dissociative Schlenk equilibrium is operative interconverting heteroleptic compounds into homoleptic congeners. imag

In situ Grignard Metalation Method, Part II: Scope of the One‐Pot Synthesis of Organocalcium Compounds

The in situ Grignard Metalation Method ( i GMM) is a straightforward one‐pot strategy to synthesize alkaline‐earth metal amides in multi‐gram scale with high yields via addition of bromoethane to an ethereal suspension of a primary or secondary amine and magnesium (Part I) or calcium (Part II). This method is highly advantageous because no activation of calcium is required prior to the reaction. Contrary to the magnesium‐based i GMM, there are some limitations, the most conspicuous one is the large influence of steric factors. The preparation of Ca(hmds) 2 succeeds smoothly within a few hours with excellent yields opening the opportunity to prepare large amounts of this reagent. Side reactions and transfer of the i GMM to substituted anilines and N‐heterocycles as well as other H‐acidic substrates such as cyclopentadienes are studied. Bulky amidines cannot be converted directly to calcium amidinates via the i GMM but stoichiometric calciation with Ca(hmds) 2 enables their preparation

In Situ Grignard Metalation Method for the Synthesis of Hauser Bases

The in situ Grignard Metalation Method ( i GMM) is a straightforward one‐pot procedure to quickly produce multigram amounts of Hauser bases R 2 N‐MgBr which are valuable and vastly used metalation reagents and novel electrolytes for magnesium batteries. During addition of bromoethane to a suspension of Mg metal and secondary amine at room temperature in an ethereal solvent, a smooth reaction yields R 2 N‐MgBr under evolution of ethane within a few hours. A Schlenk equilibrium is operative, interconverting the Hauser bases into their solvated homoleptic congeners Mg(NR 2 ) 2 and MgBr 2 depending on the solvent. Scope and preconditions are studied, and side reactions limiting the yield have been investigated. DOSY NMR experiments and X‐ray crystal structures of characteristic examples clarify aggregation in solution and the solid state

Structural Diversity of Lithium N ‐Mesityl‐ P , P ‐diphenylphosphinimidate of the type [(L)Li{O−PPh 2 =N−Mes] n Depending on Lewis Base L

Abstract Metalation of N ‐mesityl‐ P,P ‐diphenylphosphinic amide with n BuLi in toluene yields tetranuclear lithium N ‐mesityl‐ P , P ‐diphenylphosphinimidate ([Ph 2 P(OLi)=N−Mes] 4 , 1 ). Metalation of Ph 2 P(O)−N(H)Mes with a mixture of dibutylmagnesium and butyllithium in DME leads to formation of dinuclear [Ph 2 P{OLi(dme)}=N−Mes] 2 ( 2 ). Excess of Ph 2 P(O)−N(H)Mes gives dinuclear [Li(O−PPh 2 =N−Mes){Ph 2 P(=O)−N(H)−Mes}] 2 ( 3 ) with three‐coordinate alkali ions. The metathetical approach via reaction of 1 with anhydrous magnesium bromide in ethereal solution yields [{(thf)LiBr} 2 {(thf)Li(O−PPh 2 =NMes)(Et 2 O)Li(O−PPh 2 =NMes)}] ( 4 ). Heterobimetallic Li/Mg compounds are not accessible by these protocols. Reactions of 1 with DME, with excess of Ph 2 P(O)−N(H)Mes or with LiBr allows the straightforward conversion to compounds 2 , 3 and 4 .imag

Suitability of Carbazolyl Hauser and Turbo‐Hauser Bases as Magnesium‐Based Electrolytes

Lithium-ion batteries pose certain drawbacks and alternatives are highly demanded. Requirements such as low corrosiveness, electrochemical stability and suitable electrolytes can be met by magnesium-ion batteries. Metalation of carbazole with Mg in THF in the presence of ethyl bromide yields the sparingly soluble Hauser base [(thf)$_{3}$Mg(Carb)Br] (1) which shows a Schlenk-type equilibrium with formation of [(thf)$_{3}$Mg(Carb)$_{2}$] and [(thf)4MgBr2]. A THF solution of 1 shows a low over-potential and a good cyclability of electrodeposition/-stripping of Mg on a Cu current collector. An improved performance is achieved with the turbo-Hauser bases [(thf)(Carb)Mg(μ-Br/X)$_{2}$Li(thf)$_{2}$] (X=Br (2) and Cl (3)) which show a significantly higher solubility in ethereal solvents. The THF solvation energies increase from (thf)$_{x}$MgBr$_{2}$ over (thf)$_{x}$Mg(Carb)Br to (thf)$_{x}$Mg(Carb)$_{2}$ for an equal number x of ligated THF molecules

7. Experiment (10.07.2020): Cobalt

Inhalt: hydratisierte Cobald(II)-Verbindungen; Cobald(III)-Amin-Komplexe; Haftatom-/Bindungsisomerie; Ligandeneinfluss; Cobalthydroxide; Cobalt-Amin-Komplexe; Cobalt-Thiocyanat-Komplex