Ethyl-Zinc(II)-Cation Equivalents: Synthesis and Hydroamination Catalysis

Zinc Ammonio-dodecaborates: Synthesis, Lewis Acid Strength, and Reactivity

Two series of zinc salts, [EtZn][A] and Zn[A]₂, with weakly coordinating anions [A]^- as counterions have been prepared, and their activities as catalysts for hydrosilylation reactions of 1-hexene, benzophenone, and acetophenone have been investigated. The counterions and per- and partially chlorinated 1-ammonio-closo-dodecaborate anions [Me₃NB₁₂Cl₁₁]^- [1]^-, [Pr₃NB₁₂H₅Cl₆]^- [2]^-, [Bu₃NB₁₂H₄Cl₇]^- [3]^-, and [Hex₃NB₁₂H₅Cl₆]^- [4]^- were chosen as potential and more readily available alternatives to carborate anions such as [CHB₁₁Cl₁₁]^- and [HexCB₁₁Cl₁₁]^-. The basicity of anion [4]^- was determined as being close to that of the triflimide anion [N(SO₂CF₃)₂]^-, and the fluoride ion affinities (FIAs) of compounds [EtZn][2] and Zn[2]₂ are lower than those of the Lewis acids B(C₆F₅)₃ and Zn[HexCB₁₁Cl₁₁]₂. The higher anion basicity and the resulting lower Lewis acidity of the zinc centers result in low activity in 1-hexene hydrosilylation catalysis and only moderate activity in the hydrosilylation catalysis of benzophenone and acetophenone.

Heterometallic Al6Zn12 nano-plate with π-conjugated ligand: synthesis and nonlinear absorption properties

Presented herein is the synthesis, structure, and optical properties of the aluminum(III)-zinc(II) heterometallic compound AlOC-57. This compound was found to form a large unit cell (approximately sixteen thousand atoms) and a three-shell nano-plate structure. Based on the Z-scan patterns, the third-order nonlinear optical response of the heterometallic nano-plate was mainly attributed to its nonlinear absorption (reverse saturable absorption).

Towards Naked Zinc(II) in the Condensed Phase: A Highly Lewis Acidic ZnII Dication Stabilized by Weakly Coordinating Carborate Anions

The employment of the hexyl-substituted anion [HexCB₁₁ Cl₁₁ ]^- allowed the synthesis of a Zn^II species, Zn[HexCB₁₁ Cl₁₁ ]₂ , 3, in which the Zn²⁺ cation is only weakly coordinated to two carborate counterions and that is soluble in low polarity organic solvents such as bromobenzene. DOSY NMR studies show the facile displacement of at least one of the counterions, and this near nakedness of the cation results in high catalytic activity in the hydrosilylation of 1-hexene and 1-methyl-1cyclohexene. Fluoride ion affinity (FIA) calculations reveal a solution Lewis acidity of 3 (FIA=262.1 kJ mol^-1 ) that is higher than that of the landmark Lewis acid B(C₆ F₅ )₃ (FIA=220.5 kJ mol^-1 ). This high Lewis acidity leads to a high activity in catalytic CO₂ and Ph₂ CO reduction by Et₃ SiH and hydrogenation of 1,1-diphenylethylene using 1,4-cyclohexadiene as the hydrogen source. Compound 3 was characterized by multinuclear NMR spectroscopy, mass spectrometry, single crystal X-ray diffraction, and DFT studies.

Facile and systematic access to the least-coordinating WCA [(RFO)3Al-F-Al(ORF)3]- and its more Lewis-basic brother [F-Al(ORF)3]- (RF = C(CF3)3)

By reaction of the Lewis acid Me3Si-F-Al(ORF)3 with a series of [PF6]- salts, gaseous PF5 and Me3Si-F are liberated and salts of the anion [F-Al(ORF)3]- ([f-al]-; RF = C(CF3)3) can be obtained. By addition of another equivalent of Me3Si-F-Al(ORF)3 to [f-al]-, gaseous Me3Si-F is released and salts of the least coordinating anion [(RFO)3Al-F-Al(ORF)3]- ([al-f-al]-) are formed. Both procedures work for a series of synthetically useful cations including Ag+, [NO]+, [Ph3C]+ and in very clean reactions with 5 g batch sizes giving excellent yields typically exceeding 90%. In addition, the synthesis of Me3Si-F-Al(ORF)3 has been optimized and scaled up to 85 g batches in an one-pot procedure. These anions could previously only be obtained by difficult to control decomposition reactions of [Al(ORF)4]- or by halide abstraction reactions with Me3Si-F-Al(ORF)3, generating relatively large countercations that are unsuited for further use as universal starting materials. Especially [al-f-al]- is of interest for the stabilization of reactive cations, since it is even weaker coordinating than [Al(ORF)4]- and more stable against strong electrophiles. This bridged anion can be seen as an adduct of [f-al]- and Al(ORF)3. Thus, it is similarly Lewis acidic as BF3 and eventually reacts with nucleophiles (Nu) from the reaction environment to yield Nu-Al(ORF)3 and [f-al]-. This prevents working with [al-f-al]- salts in ethereal or other donor solvents. By contrast, the [f-al]- anion is no longer Lewis acidic and may therefore be used for reactions involving stronger nucleophiles than the [al-f-al]- anion can withstand. Subsequently it may be transformed into the [al-f-al]- salt by simple addition of one equivalent of Me3Si-F-Al(ORF)3.

Are homoleptic complexes of ethylene with group 12 metals isolable in solution? A DFT study

Ethylene efficiently binds late transition metals of groups 10 and 11. In spite of their reactivity, homoleptic compounds of formula [M-(η²-C₂H₄)₃]ⁿ⁺ (with n = 0,1) have been isolated in solution and solid state and characterized spectroscopically throughout the last 50 years with metals from groups 10 and 11. X-ray diffraction studies proved that such homoleptic adducts adopt planar "wheel" structures where ethylene moieties lies flat in the same plane both in group 10 and 11. These experimental findings were also confirmed by several in-depth computational investigations carried out to understand the bond pattern of such peculiar structures. Homoleptic complexes of group 10 and 11 metals with ethylene are normally obtained in poorly coordinating solvents (like CH₂Cl₂ or light petroleum) saturated with ethylene to increase the stability of such species in solution. In the case of coinage metals, Cu(I), Ag(I) and Au(I), weakly coordinating fluorinated counter-ions (like SbF₆^-) succeeded in stabilize the ethylene adducts, but, curiously, no analogous success has been reported for Zn(II), Cd(II), and Hg(II). Isoelectronic congeners along group 12 are still elusive, however, and, to our knowledge, full experimental and theoretical characterizations are still missing. This manuscript focuses on the theoretical study of the thermodynamic stability and properties of homoleptic complexes of ethylene with metals from group 12 in comparison with those from groups 10 and 11.