A lithium-aluminium heterobimetallic dimetallocene.

Homobimetallic dimetallocenes exhibiting two identical metal atoms sandwiched between two η5 bonded cyclopentadienyl rings is a narrow class of compounds, with representative examples being dizincocene and diberyllocene. Here we report the synthesis and structural characterization of a heterobimetallic dimetallocene, accessible through heterocoupling of lithium and aluminylene fragments with pentaisopropylcyclopentadienyl ligands. The Al-Li bond features a high ionic character and profits from attractive dispersion interactions between the isopropyl groups of the cyclopentadienyl ligands. A key synthetic step is the isolation of a cyclopentadienylaluminylene monomer, which also enables the structural characterization of this species. In addition to their structural authentication by single-crystal X-ray diffraction analysis, both compounds were characterized by multinuclear NMR spectroscopy in solution and in the solid state. Furthermore, reactivity studies of the lithium-aluminium heterobimetallic dimetallocene with an N-heterocyclic carbene and different heteroallenes were performed and show that the Al-Li bond is easily cleaved.

Merging the Energy Decomposition Analysis with the Interacting Quantum Atoms Approach.

Energy decomposition analysis (EDA) is a well-established approach to dissect the interaction energy into chemically sound components. Despite the inherent requirement of reference states has been a long-standing object of debate, the direct relation with the molecular orbital analysis helps in building up predictive models. The alternative molecular energy decomposition schemes that decompose the total energy into atomic and diatomic contributions, such as the interacting quantum atoms (IQA), has no external reference requirements and also the intra- and intermolecular interactions are treated on equal footing. However, a connection with heuristic chemical models are limited, bringing about a somewhat narrower predictive power. While efforts to reconcile the bonding picture obtained by both methodologies have been discussed in the past, a synergic combination of them has not been tackled yet. Herein, we present the use of IQA decomposition of the individual terms arising from the EDA in the context of intermolecular interactions, henceforth EDA-IQA. The method is applied to a molecular set covering a wide range of interaction types, including hydrogen bonding, charge-dipole, π-π and halogen interactions. We find that the electrostatic energy from EDA, entirely seen as intermolecular, leads to meaningful and non-negligible intra-fragment contributions upon IQA decomposition, originated from charge penetration. EDA-IQA also affords the decomposition of the Pauli repulsion term into intra- and inter-fragment contributions. The intra-fragment term is destabilizing, particularly for the moieties that are net acceptors of charge, while the inter-fragment Pauli term is actually stabilizing. In the case of the orbital interaction term, the sign and magnitude of the intra-fragment contribution at equilibrium geometries is largely driven by the amount of charge transfer, while the inter-fragment contribution is clearly stabilizing. EDA-IQA terms show a smooth behavior along the intermolecular dissociation path of selected systems. The new EDA-IQA methodology provides a richer energy decomposition scheme that aims at bridging the gap between the two main distinct real-space and Hilbert-space methodologies. Via this approach, the partitioning can be used directionally on all the EDA terms aiding in identifying the causal effects on geometries and/or reactivity.

Reply to the 'Comment on "The oxidation state in low-valent beryllium and magnesium compounds"' by S. Pan and G. Frenking, Chem. Sci., 2022, 13, DOI: 10.1039/D2SC04231B.

A recent article by Pan and Frenking challenges our assignment of the oxidation state of low valent group 2 compounds. With this reply, we show that our assignment of Be(+2) and Mg(+2) oxidation states in Be(cAACDip)2 and Mg(cAACDip)2 is fully consistent with our data. Some of the arguments exposed by Pan and Frenking were based on visual inspection of our figures, rather than a thorough numerical analysis. We discuss with numerical proof that some of the statements made by the authors concerning our reported data are erroneous. In addition, we provide further evidence that the criterion of the lowest orbital interaction energy in the energy decomposition analysis (EDA) method is unsuitable as a general tool to assess the valence state of the fragments. Other indicators based on natural orbitals for chemical valence (NOCV) deliver a more reliable bonding picture. We also emphasize the importance of using stable wavefunctions for any kind of analysis, including EDA.

The oxidation state in low-valent beryllium and magnesium compounds.

Low-valent group 2 (E = Be and Mg) stabilized compounds have been long synthetically pursued. Here we discuss the electronic structure of a series of Lewis base-stabilized Be and Mg compounds. Despite the accepted zero(0) oxidation state nature of the group 2 elements of some recent experimentally accomplished species, the analysis of multireference wavefunctions provides compelling evidence for a strong diradical character with an oxidation state of +2. Thus, we elaborate on the distinction between a description as a donor-acceptor interaction L(0) ⇆ E(0) ⇄ L(0) and the internally oxidized situation, better interpreted as a diradical L(-1) → E(+2) ← L(-1) species. The experimentally accomplished examples rely on the strengthened bonds by increasing the π-acidity of the ligand; avoiding this interaction could lead to an unprecedented low-oxidation state.

Unveiling the Electronic Structure of the Bi(+1)/Bi(+3) Redox Couple on NCN and NNN Pincer Complexes.

Low-valent group 15 compounds stabilized by pincer ligands have gained particular interest, given their direct access to fine-tune their reactivity by the coordination pattern. Recently, bismuth has been employed in a variety of catalytic transformations by taking advantage of the (+1/+3) redox couple. In this work, we present a detailed quantum-chemical study on the electronic structure of bismuth pincer complexes from two different families, namely, bis(ketimine)phenyl (NCN) and triamide bismuthinidene (NNN). The use of the so-called effective oxidation state analysis allows the unambiguous assignation of the bismuth oxidation state. In contrast to previous studies, our calculations suggest a Bi(+1) assignation for NCN pincer ligands, while Bi(+3) character is found for NNN pincer complexes. Notably, regardless of its oxidation state, the central bismuth atom disposes of up to two lone pairs for coordinating Lewis acids, as indicated by very high first and second proton affinity values. Besides, the Bi-NNN systems can also accommodate two Lewis base ligands, indicating also ambiphilic behavior. The effective fragment orbital analysis of Bi and the ligand allows monitoring of the intricate electron flow of these processes, revealing the noninnocent nature of the NNN ligand, in contrast with the NCN one. By the dissection of the electron density into effective fragment orbitals, we are able to quantify and rationalize the Lewis base/acid character.

Metalloradical Cations and Dications Based on Divinyldiphosphene and Divinyldiarsene Ligands.

Metalloradicals are key species in synthesis, catalysis, and bioinorganic chemistry. Herein, two iron radical cation complexes (3-E)GaCl4 [(3-E).+ = [{(IPr)C(Ph)E}2 Fe(CO)3 ].+ , E = P or As; IPr = C{(NDipp)CH}2 , Dipp = 2,6-iPr2 C6 H3 ] are reported as crystalline solids. Treatment of the divinyldipnictenes {(IPr)C(Ph)E}2 (1-E) with Fe2 (CO)9 affords [{(IPr)C(Ph)E}2 Fe(CO)3 ] (2-E), in which 1-E binds to the Fe atom in an allylic (η3 -EECvinyl ) fashion and functions as a 4e donor ligand. Complexes 2-E undergo 1e oxidation with GaCl3 to yield (3-E)GaCl4 . Spin density analysis revealed that the unpaired electron in (3-E).+ is mainly located on the Fe (52-64 %) and vinylic C (30-36 %) atoms. Further 1e oxidation of (3-E)GaCl4 leads to unprecedented η3 -EECvinyl to η3 -ECvinyl CPh coordination shuttling to form the dications (4-E)(GaCl4 )2 .

A theoretical study of the hydrolysis mechanism of A-234; the suspected novichok agent in the Skripal attack.

A-234, [EtO-P([double bond, length as m-dash]O)(F)-N[double bond, length as m-dash]C(Me)-N(Et)2], is the suspected A-type nerve agent used in the Skripal attack on the 4th of March 2018. Studies related to the structure and reactivity of this compound are limited. We, therefore, aimed at understanding the underlying hydrolysis mechanism of A-234 within the DFT framework. The attack of the water molecule can occur at the phosphinate and acetoamidine reactive centres. Our theoretical findings indicate that the hydrolysis at the acetoamidine centre is thermodynamically favoured compared to the hydrolysis at the phosphinate centre. The hydrolysis at the acetoamidine moiety may proceed via two pathways, depending on the nitrogen atom participating in the hydrolysis. The main pathway consists of four distinct channels to reach the final product, with the concerted 1,3-proton shift favoured kinetically and thermodynamically in the gas phase and water as solvent. The results are in good agreement with the literature, although some differences in the reaction mechanism were observed.