Dispersion, rehybridization, and pentacoordination: keys to understand clustering of boron and aluminum hydrides and halides

The structure, stability, and bonding characteristics of dimers and trimers involving BX3 and AlX3 (X = H, F, Cl) in the gas phase, many of them explored for the first time, were investigated using different DFT (B3LYP, B3LYP/D3BJ, and M06-2X) and ab initio (MP2 and G4) methods together with different energy decomposition formalisms, namely, many-body interaction-energy and localized molecular orbital energy decomposition analysis. The electron density of the clusters investigated was analyzed with QTAIM, electron localization function, NCIPLOT, and adaptive natural density partitioning approaches. Our results for triel hydride dimers and Al2X6 (X = F, Cl) clusters are in good agreement with previous studies in the literature, but in contrast with the general accepted idea that B2F6 and B2Cl6 do not exist, we have found that they are predicted to be weakly bound systems if dispersion interactions are conveniently accounted for in the theoretical schemes used. Dispersion interactions are also dominant in both homo- and heterotrimers involving boron halide monomers. Surprisingly, B3F9 and B3Cl9 C3v cyclic trimers, in spite of exhibiting rather strong B-X (X = F, Cl) interactions, were found to be unstable with respect to the isolated monomers due to the high energetic cost of the rehybridization of the B atom, which is larger than the two- and three-body stabilization contributions when the cyclic is formed. Another important feature is the enhanced stability of both homo- and heterotrimers in which Al is the central atom because Al is systematically pentacoordinated, whereas this is not the case when the central atom is B, which is only tri- or tetra-coordinatedPID2021-125207NB-C31, PID2021-125207NB-C32, PID2019-110091GB-I0

Experimental realisation of elusive multiple-bonded aluminium compounds : a new horizon in the aluminium chemistry

The synthesis and isolation of stable main group compounds featuring multiple bonds has been of great interest for several decades. A plethora of such multiply bonded complexes have been obtained by using sterically demanding substituents that provide both kinetic and thermodynamic stability. Most of these compounds have unusual structural and electronic properties that challenge the classical concept of covalent multiple bonding. In contrast, analogous aluminium compounds are scarce in spite of its high natural abundance. The parent dialumene (Al2H2) has been calculated to be extremely unstable, thus making compounds containing Al multiple bonds a challenging synthetic target. This Review provides an overview of the recent advances in the cutting edge synthetic approaches and the careful ligand design used to obtain aluminium homo‐ and heterodiatomic multiply bonded complexes. In addition, the reactivity of these novel compounds towards various small molecules and reagents will be discussed herein

Investigations of bridged bis(cyclopentadienyl)- and pnictogenyl-substituted aluminum compounds

The present work demonstrates the findings on the synthesis and characterization of the first bis(aluminocenophane), which has two 5-bonded cyclopentadienyl rings and the shortest Al-Al single bond of all acyclic dialanes. Furthermore, the results of donor stabilized aluminocenophane derivatives with different donor ligands as well as different ansa-bridging motifs such as sila[2] and carba[1] are presented. The new complexes are characterized in the solid state and in solution. In addition, quantum chemical studies were carried out on these new molecules. The synthesis of bis(aluminocenophane) as well as donor stabilized aluminocenophane derivatives started from the corresponding magnesocenophanes as powerful cyclopentadienyl transfer agents with aluminum(III)halide. Furthermore, the synthesis of monomeric, dimeric and trimeric pnictogenylalanes and their reactivity towards carbon dioxide is presented. The bonding situations of the monomeric and oligomeric as well as donor-stabilized aminoalane and phosphanylalane could be illuminated by NBO and EDA analysis. Furthermore, the mechanism of the carbon dioxide insertion reaction into the Al-N-, Al-P- and Al-D-bonds could be illustrated. Since the popular synthesis strategy for ferrocene-containing polymers (ring-opening polymerization) starts from the isolation of the monomer precursor (ferrocenophane), polyferrocenylmethylene (PFM) was previously unknown because carba[1]ferrocenophanes have not been reported. In this thesis, a new synthesis route of polyferrocenylmethylene (PFM) starting from carba[1]magnesocenophane is described. In addition to the characterization of the polymer, a crystal structure of a cyclic hexamer of polyferrocenylmethylene was obtained.Die vorliegende Arbeit befasst sich mit der Synthese und Charakterisierung des ersten Bis(aluminocenophans), welches zwei 5-gebundene Cyclopentadienyl-ringe und die kürzeste Al-Al-Einfachbindung aller acyclischen Dialane aufweist. Darüber hinaus werden donor-stabilisierte Aluminocenophan-Derivate mit unterschiedlichen Donor-Liganden sowie unterschiedlichen ansa-Verbrückungsmotiven wie Sila[2] und Carba[1] vorgestellt. Die neuen Komplexe wurden sowohl im Festkörper als auch in Lösung charakterisiert. Darüber hinaus, wurden quantenchemische Untersuchungen zu diesen neuen Molekülen angestellt. Die Synthese des Bis(aluminocenophans) sowie der donor-stabilizierten Aluminocenophan-Derivate gingen von den entsprechenden Magnesocenophanen als gute Cylopentadienyl-transferreagenzien und Aluminium(III)halogeniden aus. Außerdem wird die Synthese von monomeren, dimeren und trimeren Pnictogenylalanen und deren Reaktivität gegenüber Kohlenstoffdioxid beschrieben. Quantenchemische Untersuchungen an diesen neuen Molekülstrukturen wurden angestellt. Durch NBO und EDA-Analyse konnten die Bindungssituationen der monomeren und oligomeren sowie donor-stabilizierten Aminoalane und Phosphanylalane beleuchtet werden. Des Weiteren, konnte der Mechanismus der Kohlenstoffdioxid-Insertionsreaktion in die Al-N-, Al-P- und Al-D-Bindungen aufgeklärt werden. Da die bekannte Synthesestrategie ferrocenhaltiger Polymere (Ringöffnungs-polymerisation) von der Isolierung des Monomersprecursors (Ferrocenophan) ausgeht, war die Synthese von Polyferrocenylmethylen bisher unbekannt, da Carba[1]ferrocenophane nicht beschrieben sind. In dieser Arbeit wird ein neuer Syntheseweg für Polyferrocenylmethylens ausgehend von Carba[1]magnesocenophan beschrieben. Neben der Charakterisierung des Polymers wurde auch die Kristallstruktur eines cyclischen Hexamers von Polyferrocenylmethylen erhalten

Synthesis and Reactivity of a Dialane-Bridged Diradical

Radicals of the lightest group 13 element, boron, are well established and observed in numerous forms. In contrast to boron, radical chemistry involving the heavier group 13 elements (aluminum, gallium, indium, and thallium) remains exceedingly underexplored, primarily attributed to the formidable synthetic challenges associated with these elements. Herein, we report the synthesis and isolation of planar and twisted conformers of a doubly CAAC (cyclic alkyl(amino)carbene)-radical-substituted dialane. Extensive characterization through spectroscopic analyses and X-ray crystallography confirms their identity, while quantum chemical calculations support their open-shell nature and provide further insights into their electronic structures. The dialane-connected diradicals exhibit high susceptibility to oxidation, as evidenced by electrochemical measurements and reactions with o-chloranil and a variety of organic azides. This study opens a previously uncharted class of dialuminum systems to study, broadening the scope of diradical chemistry and its potential applications

Synthesis, characterization, and computational analysis of the dialanate dianion, [H3Al-AlH3]2− : a valence isoelectronic analogue of ethane

C.J. and A.S. gratefully acknowledge financial support from the Australian Research Council, while C.J. thanks the U.S. Air Force Asian Office of Aerospace Research and Development (FA2386-14-1-4043) for funding. G.F. acknowledges financial support from the Deutsche Forschungsgemeinschaft.The first example of a well-defined binary, low-oxidation-state aluminum hydride species that is stable at ambient temperature, namely the dianion in [{(DepNacnac)Mg}2(μ-H)]2[H3Al-AlH3] (DepNacnac=[(DepNCMe)2CH]−, Dep=2,6-diethylphenyl), has been prepared via a magnesium(I) reduction of the alanate complex, (DepNacnac)Mg(μ-H)3AlH(NEt3). An X-ray crystallographic analysis has shown the compound to be a contact ion complex, which computational studies have revealed to be the source of the stability of the aluminum(II) dianion.PostprintPeer reviewe

Quantum computational chemical calculations to estimate the necessary energy for hydrogen storage in the metal hydrides AlH3ScH3 and Al2H6

Hydrogen storage describes the methods of storing H2 for subsequent use. Hydrogen storage is the main issue that needs to be solved before the technology can be implemented into key areas such as transport. The high energy density, good stability and reversibility of metal hydrides make them appealing as hydrogen storage materials. Metal hydrides have the potential for reversible on‐board hydrogen storage and release at low temperatures and pressures. The aim of this thesis is to describe, document and carry out the previous theoretical quantum chemical calculations by density functional theory (DFT) at B3LYP level of theory with 6‐311++G(3df,3pd) basis set for aluminium and hydrogen, and a SDD pseudopotential for scandium in order to; first of all, optimize the molecular structures; secondly, predict the vibrational frequencies of the optimized structures and finally estimate the energies needed to absorb and release hydrogen from both metal hydrides AlH3ScH3 and Al2H6. Our calculated results show that the hydrogen absorption energy value for the formation of AlH3ScH3 (‐47,479kcal/mol) is higher than the value for the formation of Al2H6 (‐33,481 kcal/mol). These were not the expected results because the energy has been increased, and thus the operation temperatures are also higher. The transition metal scandium in the hydride does not decrease the hydrogenation energy due to cation matrix that seems to be the responsible for the thermal stability.Outgoin

Synthesis Of Volatile And Thermally Stable Aluminum Hydride Complexes And Their Use In Atomic Layer Deposition Of Metal Thin Films

The research discussed in this dissertation spans both synthetic inorganic and nanomaterials chemistry. Aluminum hydride complexes have been synthesized and characterized which are highly volatile and thermally stable and their potential as reducing agents for ALD of electropositive metal and metal-containing films was evaluated. A major discovery has been the deposition of aluminum metal films by thermal ALD using an aluminum dihydride complex supported by a simple amido-amine ligand (Chapters 2). Aluminum is the most electropositive element deposited by purely thermal ALD to date and represents a significant breakthrough for this field. This process may have important industrial applications and the aluminum hydride reducing agents should enable a variety of novel ALD processes for metals and elements. The deposition of titanium metal films by ALD was attempted using the aluminum hydride reducing agents (Chapter 3). Rather than pure titanium films, highly thermodynamically stable titanium carbonitride (TiCxNy) films were deposited instead. Chapter 4 explored the ubiquitous ALD precursor trimethylaluminum (AlMe3) as a potential reducing agent and high quality tungsten carbide films were deposited using AlMe3 and WCl6. Tungsten-rich tungsten carbide films were deposited using WCl¬6 and an aluminum hydride reducing agent instead of AlMe3 (Chapter 5). While exploring the chemistry and properties of N-heterocyclic carbene aluminum hydride complexes, a structurally unusual dialane complex was synthesized which displayed good volatility and thermal stability and it was used to deposit aluminum metal by a thermal ALD process (Chapter 6)

Reversible Dissociation of a Dialumene

Dialumenes are neutral Al(I) compounds with Al=Al multiple bonds. We report the isolation of an amidophosphine‐supported dialumene. Our X‐ray crystallographic, spectroscopic, and computational DFT analyses reveal a long and extreme trans‐bent Al=Al bond with a low dissociation energy and bond order. In solution, the dialumene can dissociate into monomeric Al(I) species. Reactivity studies reveal two modes of reaction: as dialumene or as aluminyl monomers