Homogeneous catalysis employing gold compounds is a rapidly developing field. Au(III) catalysts in particular are interesting, since they exhibit catalytic properties unseen in other metals. In this ...study we report for the first time the complete mechanism of the nucleophilic addition of water to triple bonds that have not specifically been activated. The effect that the coordination of solvent molecules has on the course of the catalytic cycle is demonstrated, and the importance of hydrogen bonds to guide the substrate through the mechanism is highlighted. The influence of relativistic effects, which are particularly important for very heavy metals such as gold, is investigated, and it is concluded that the catalytic activity of gold could be seen as a relativistic effect.
The synthesis of a new potassium-indyl complex, KIn(NON
) (NON
= O(SiMe
NAr)
, Ar = 2,6-
Pr
C
H
) and its reactivity with organic azides RN
is reported. When R = 2,6-bis(diphenylmethyl)-4-
...Bu-phenyl, a dianionic alkyl-amide ligand is formed
C-H activation across a transient In-N
bond. Reducing the size of the R-group to 2,4,6-trimethylphenyl (mesityl, Mes) enables oxidation of the indium and elimination of dinitrogen to afford the imide species, KIn(NON
)(NMes). The anion contains a short In-N
bond, shown computationally to contain appreciable multiple bond character. Reaction of isolated imides with an additional equivalent of azide (R = Mes, SiMe
) generates tetrazenido-indium compounds KIn(NON
){κ-
,
'-N
(Mes)(R)-1,4}, shown by X-ray crystallography to contain planar InN
heterocycles in the anion.
Reaction of bismuth(II) compounds with sulfur gives mixtures of Bi(NONR)2(μ2-S n ) (NONR = O(SiMe2NR)22–). Examples for n = 1 and 3 have been crystallographically verified for R = 2,6-iPr2C6H3 ...(Dipp) and R = tBu, and the pentasulfide (n = 5) for R = Dipp. The corresponding product from reaction with the new Bi(II) radical Bi(NONAr‡)• (Ar‡ = C6H2(CHPh2)2-tBu-2,6,4) exists as the dimer Bi(NONAr‡)(S4)2, with π*(SOMO)−π*(SOMO) interactions linking the sulfur chains through trans-antarafacial pancake bonds.
More than 80 years after Paneth’s report of dimethyl bismuth, the first monomeric BiII radical that is stable in the solid state has been isolated and characterized. Reduction of the ...diamidobismuth(III) chloride Bi(NONAr)Cl (NONAr=O(SiMe2NAr)22−; Ar=2,6‐iPr2C6H3) with magnesium affords the BiII radical .Bi(NONAr). X‐ray crystallographic measurements are consistent with a two‐coordinate bismuth in the +2 oxidation state with no short intermolecular contacts, and solid‐state SQUID magnetic measurements indicate a paramagnetic compound with a single unpaired electron. EPR and density functional calculations show a metal‐centered radical with >90 % spin density in a p‐type orbital on bismuth.
Reduction of a BiIII compound affords the first isolable BiII radical (see scheme; Cl green, Si magenta, O red, N blue). X‐ray diffraction confirms a two‐coordinate metal with no short intermolecular contacts; SQUID measurements indicate a paramagnetic compound with a single unpaired electron. EPR and DFT results are consistent with a metal‐centered radical, with the unpaired electron predominantly in a p‐type orbital on Bi.
A comparison of the molecular structures of mono‐, di‐ and tetraborylated ferrocenes Fc{B(R1)(R2)} (R1/R2=Br/Br, Br/Fc, Br/Me, Me/Me, Me/OH, OMe/OMe), 1,1′‐fc{B(R1)(R2)}2 (R1/R2=Br/Br, Br/Me, ...OMe/OMe), and 1,1′,3,3′‐Fe{C5H3(BMe2)2}2 revealed the boryl substituent(s) to be bent out of the Cp ring plane towards the iron center. The corresponding dip angle α* decreases with decreasing Lewis acidity of the boron atom and with increasing degree of borylation at the ferrocene core. This trend is well reproduced by DFT calculations (including FcBH2, not yet accessible experimentally). A Bader analysis of the electron density topology of FcBH2 (α*=26.5°; BP86/TZVP) clearly showed that there is no direct iron–boron bonding in this compound. Instead, strongly delocalized orbital interactions have been identified that involve the boron p orbital, Cipso of the adjacent Cp ring, d orbitals at iron, and a through‐space interaction with the second Cp ring. A second important factor is attractive electrostatic interactions, which are enhanced upon ligand bending. Cyclic voltammetric measurements on the series FcBMe2, 1,1′‐fc(BMe2)2, and 1,1′,3,3′‐Fe{C5H3(BMe2)2}2 indicate a substantial anodic shift in the oxidation potential of the central iron atom upon introduction of BMe2 substituents. Addition of 4‐dimethylaminopyridine (DMAP) does not just counterbalance this effect, but leads to a cathodic shift of the FeII/FeIII redox transition far beyond the half‐wave potential of parent ferrocene. In the Mössbauer spectra, a continuous decrease in the quadrupole splitting (QS) is observed upon going from parent ferrocene to FcBMe2, to 1,1′‐fc(BMe2)2, and to 1,1′,3,3′‐Fe{C5H3(BMe2)2}2. In contrast, no significant differences are found between the QS values of ferrocene, Fc(BMe2DMAP), and 1,1′‐fc(BMe2−DMAP)2.
Ligand bending in selected mono‐, di‐, and tetraborylated ferrocenes was investigated by means of X‐ray crystallography, cyclic voltammetry, and Mössbauer spectroscopy. A detailed quantum chemical analysis of the subtle structural and electronic properties of these species is provided. The picture shows the DFT structure of model compound FcBH2 with dip angle α* defining the angle of bending (left) and a three‐center MO distributed over Fe, Cipso, and B (right).
We have investigated the double-layered carbon nano-onions (CNOs) C20@C60, C20@C80, C60@C180, C60@C240, C80@C240, and C240@C540 as well as their triple-layered analogues C60@C240@C540 and ...C80@C240@C540 with high-level electronic structure calculations. We were able to show that earlier work, which showed the free rotation of the inner fullerene in a CNO, does not extend to multilayered CNOs. We show that the likely reason for this immobility of the outer layers is the superadditivity of the interaction energies between individual shells, i.e., the total interaction energy of all shells is larger than the sum of all individual interaction energies between pairs of shells. We also show how the electronic states of individual fullerenes are polarized but essentially preserved in CNOs and how charge-transfer excitations between layers arise, which are significantly red-shifted to lower absorption energies compared to those of the free fullerenes. This allows CNOs to be utilized as photosensitizers in nanotechnology applications.
The potassium aluminyl complex KAl(NONAr) (NON=NONAr=O(SiMe2NAr)22−, Ar=2,6‐iPr2C6H3) reacts with 1,3,5,7‐cyclooctatetraene (COT) to give KAl(NONAr)(COT). The COT‐ligand is present in the asymmetric ...unit as a planar μ2‐η2:η8‐bridge between Al and K, with additional K⋅⋅⋅π‐aryl interactions to neighboring molecules that generate a helical chain. DFT calculations indicate significant aromatic character, consistent with reduction to COT2−. Addition of 18‐crown‐6 causes a rearrangement of the C8‐carbocycle to form the isomeric 9‐aluminabicyclo4.2.1nona‐2,4,7‐triene anion.
Uneasy lies the head that wears a crown: The initial product from the reaction of a two‐coordinate aluminyl anion with 1,3,5,7‐cyclooctatetraene (COT) contains the reduced COT‐ligand with pronounced aromatic character. Addition of 18‐crown‐6 to KAl(NONAr)(COT) promotes isomerization of the carbocycle to afford the 9‐aluminabicyclo4.2.1nona‐2,4,7‐triene anion.
Bismuth diphenylphosphanides Bi(NON
)(PPh
) (NON
=O(SiMe
NR)
, R=tBu, 2,6-iPr
C
H
, Aryl) undergo facile decomposition via single-electron processes to form reduced Bi and P species. The ...corresponding derivatives Bi(NON
)(PCy
) are stable. Reaction of the isolated Bi
radical
Bi(NON
) with white phosphorus (P
) proceeds with the reversible and selective activation of a single P-P bond to afford the bimetallic μ,η
-bicyclo1.1.0tetraphosphabutane compound.
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