The diagonal relationship between beryllium and aluminum and the isoelectronic relationship between BeH unit and Al atom were utilized to design nine new planar and quasi-planar pentacoordinate ...carbon (ppC) species CAl
n
Be
m
H
x
q
(
n
+
m
= 5,
q
= 0, ±1,
x
=
q
+
m
− 1) (
1a-9a
) by attaching H atoms onto the Be atoms in CAl
4
Be, CAl
3
Be
2
−
, CAl
2
Be
3
2−
, and CAlBe
4
3−
. These ppC species are σ and π double aromatic. In comparison with their parents, these H-attached molecules are more stable electronically, as can be reflected by the more favourable alternative negative-positive-negative charge-arranging pattern and the less dispersed peripheral orbitals. Remarkably, seven of these nine molecules are global energy minima, in which four of them are kinetically stable, including CAl
3
Be
2
H (
2a
), CAl
2
Be
3
H
−
(
4a
), CAl
2
Be
3
H
2
(
5a
), and CAlBe
4
H
4
+
(
9a
). They are the promising target for the experimental realization of species with a ppC.
The destabilization issues, like high charges, small HOMO-LUMO gaps, and dispersed MOs,
etc.
can be eliminated
via
attaching hydrogen atoms.
Neutral nano-polygons with ultrashort Be-Be distances Tong, Wen-Yan; Zhao, Tao-Tao; Zhao, Xue-Feng ...
Dalton transactions : an international journal of inorganic chemistry,
11/2019, Letnik:
48, Številka:
42
Journal Article
Recenzirano
Ultrashort metal-metal distances (USMMDs,
d
M-M
< 1.900 Å) have been realized computationally between the main group metal beryllium. However, due to their ionic charge state and the insufficient ...stability of their electronic structures and/or thermodynamic stabilities, the known species with ultrashort Be-Be distances are unsuitable for synthesis in the condensed phase, which deters the applications of these interesting structures from being explored. In the present study, using our previously reported global minima species XH
3
-Be
2
H
3
-XH
3
+
(X = N and P) with ultrashort Be-Be distances and well-defined electronic structures as their parent molecules, we designed a series of neutral polygons retaining ultrashort Be-Be distances. These polygons also possess well-defined electronic structures and good thermodynamic stabilities, which are demonstrated by their large HOMO-LUMO gaps of 6.20-7.68 eV, very high vertical detachment energies (VDEs) of 8.96-11.29 eV, rather low vertical electron affinities (VEAs) of −1.21 to +1.78 eV, and unexpectedly high formation energies relative to the building blocks of E
−
and Be
2
H
3
+
(−105.2 to −153.2 kcal mol
−1
for the formation of an E-Be bond). The good stability with regard to their electronic structures and thermochemistry reveal their high feasibility to be synthesized in the condensed phase. Thus, we anticipate experimental studies on these interesting nano-polygons to realize structures with USMMDs between main group metals and explore their possible application.
DFT calculations revealed that neutral polygons (E-Be
2
H
3
)
n
are the viable targets for realizing ultrashort metal-metal distances between main group metals.
A current project in metal-metal bonding chemistry is to achieve ultrashort metal-metal distances (USMMDs, denoted by
d
M-M
< 1.900 Å) between main group metal beryllium atoms. A valid way for ...achieving such USMMDs is the substitution of a carbon atom in a planar pentacoordinate environment with the isoelectronic Be
2
moiety. In the present work, we report our recent findings that a similar substitution can be applied to the carbon atom in a planar hexacoordinate environment. Using species CN
3
Be
3
+
and CO
3
Li
3
+
and related analogues as the templates, the Be
2
N
3
M
3
+
(M = Be, Mg, Ca) and Be
2
O
3
M
3
+
(M = Li, Na, K) species with axial ultrashort Be-Be distances of 1.627-1.870 Å were designed computationally. The ultrashort Be-Be distances in these species represent a balance between the lengthening effect of axial Be-Be electrostatic interactions and the shortening effects of the strong X-Be bonding and repulsive X-X-X electrostatic interactions. In addition, the shorter axial Be-Be distances were determined firstly by the smaller size of the bridging electronegative X atoms and secondly by the lower electronegativity of the peripheral M atoms, while the stabilities of the newly designed species were closely related to the types of valence electron pairs, whereby the localized two-center two-electron bonds were better for stabilization than the non-bonding valence lone pairs. Among the newly designed species, Be
2
N
3
Be
3
+
and Be
2
N
3
Mg
3
+
were characterized to be the kinetically stable global minima, thereby providing promising targets for the experimental realization of species with USMMDs between main group metals.
Replacing the planar hexacoordinate carbon in CX
3
M
3
+
species with the Be
2
moiety leads to isoelectronic species with ultrashort Be-Be distances.
The subject of metal-metal bonding interactions in molecular systems continues to attract research interest. Chromium heretofore has been the only element known to afford metal-metal distances ...shorter than 1.700 Å in the form of Cr-Cr multiple bonds. In this computational study, the effect of a triple bond on reducing interatomic distances is simulated through forming three non-classical bonding orbitals between two beryllium atoms, thereby realizing the remarkably short Be-Be distances (1.692-1.735 Å) in kinetically stable global minimum species L → Be2H3 ← L+ (L = NH3, PH3, and noble gases Ne-Xe). Such diberyllium complexes make promising candidates for experimental realization. In particular, the Be-Be distance of 1.692 Å in Ne → Be2H3 ← Ne+ represents the first example of global minimum having a main group metal-metal distance under 1.700 Å. TEA → Be2H3 ← TEA+, which contains the bulky triethylamine (TEA) ligands, is designed as a more promising target for synthesis and isolation in condensed states.
Density functional theory calculations (B3LYP and B2PLYP-D2) have been utilized to design and characterize novel homoatomic lithium(0) organometallic complexes of the NHC→Li–Li←NHC type ...(NHC=N-heterocyclic carbenes). The computed Li–Li bond length and energy are consistent with those experimentally observed for Li2(g). These and other structural and energetic data suggest that such organolithium compounds should be viable targets for synthesis. These compounds would represent a new class of molecular “allotropes” and could have novel reactivities.
Display omitted
A ruthenium monothiolate carbene complex (2cat) readily derived from the Grubbs–Hoveyda system is among the newly developed catalysts for Z-selective olefin metathesis reactions. We have performed ...density functional theory calculations (B3LYP and M06) to elucidate the detailed mechanism of 2cat-catalyzed homometathesis of terminal olefins. The five-coordinate 2cat dissociates to a tetrahedral intermediate, from which two consecutive metathesis events via the bottom-bound olefin attack mechanism lead to (Z)-olefins as major products. The Z selectivity stems from the bulky thiolate ligand, which sterically forces both olefinic substituents to the far side of the metallacyclobutane ring to achieve a Z geometry in the resulting olefin product.
DFT B3LYP/6-31G(d) calculations were performed to examine the feasibility of graphene-like C
42
H
18
and starbenzene C
6
(BeH)
6
(SBz) polymers as ligands of 3D-extensible sandwich compounds ...(3D-ESCs) with uninterrupted sandwich arrays. The results revealed that sandwich compounds with three or more C
42
H
18
ligands were not feasible. The possible reason may be the localization of π electrons on certain C
6
hexagons due to π-metal interactions, which makes the whole ligand lose its electronic structure basis (higher degree of π electron delocalization) to maintain the planar structure. For comparison, with the aid of benzene (Bz) molecules, the SBz polymers can be feasible ligands for designing 3D-ESCs because the C-Be interactions in individual SBz are largely ionic, which will deter the π electrons on one C
6
ring from connecting to those on neighbouring C
6
rings. This means that high degree of π electron delocalization is not necessary for maintaining the planarity of SBz polymers. Such a locally delocalized π electron structure is desirable for the ligands of 3D-ESCs. Remarkably, the formation of a sandwich compound with SBz is thermodynamically more favourable than that found for bis(Bz)chromium. The assembly of 3D-ESCs is largely exothermic, which will facilitate future experimental synthesis. The different variation trends on the HOMO-LUMO gaps in different directions (relative to the sandwich axes) suggest that they can be developed to form directional conductors or semiconductors, which may be useful in the production of electronic devices.
DFT calculations suggest that the feasible ligands of a 3D sandwich complex should have locally delocalized π electrons.
DFT B3LYP/6-31G(d) calculations were performed to examine the feasibility of graphene-like C42H18 and starbenzene C6(BeH)6 (SBz) polymers as ligands of 3D-extensible sandwich compounds (3D-ESCs) with ...uninterrupted sandwich arrays. The results revealed that sandwich compounds with three or more C42H18 ligands were not feasible. The possible reason may be the localization of π electrons on certain C6 hexagons due to π-metal interactions, which makes the whole ligand lose its electronic structure basis (higher degree of π electron delocalization) to maintain the planar structure. For comparison, with the aid of benzene (Bz) molecules, the SBz polymers can be feasible ligands for designing 3D-ESCs because the C-Be interactions in individual SBz are largely ionic, which will deter the π electrons on one C6 ring from connecting to those on neighbouring C6 rings. This means that high degree of π electron delocalization is not necessary for maintaining the planarity of SBz polymers. Such a locally delocalized π electron structure is desirable for the ligands of 3D-ESCs. Remarkably, the formation of a sandwich compound with SBz is thermodynamically more favourable than that found for bis(Bz)chromium. The assembly of 3D-ESCs is largely exothermic, which will facilitate future experimental synthesis. The different variation trends on the HOMO-LUMO gaps in different directions (relative to the sandwich axes) suggest that they can be developed to form directional conductors or semiconductors, which may be useful in the production of electronic devices.
We report the first computational study on a nickel hydride HAT-initiated catalytic reaction, a novel hydrodefluorination of CF
3
-substituted aryl alkenes to afford
gem
-difluoroalkenes. This study ...provides detailed mechanistic insights into the reaction, including HAT from NiH to C&z.dbd;C, a carbon radical rebound to nickel to facilitate chemoselective defluorination, and a two-state reactivity of Ni(
ii
) enabling σ-bond metathesis with PhSiH
3
to regenerate the catalyst. The findings can have implications for developing new metal hydride HAT-initiated reactions.
We report the first computational study on a nickel hydride HAT-initiated catalytic reaction, a novel hydrodefluorination of CF
3
-substituted aryl alkenes to afford
gem
-difluoroalkenes.
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