Reaction Mechanism of the Symmetry-Forbidden [2+2] Addition of Ethylene and Acetylene to Amido-Substituted Digermynes and Distannynes Ph2NEENPh2, (E=Ge, Sn): A Theoretical Study

Widening the Landscape of Small Molecule Activation with Gold-Aluminyl Complexes: A Systematic Study of E-H (E=O, N) Bonds, SO2 and N2 O Activation

The electronic features of gold-aluminyl complexes have been thoroughly explored. Their similarity with Group 14 dimetallenes and other metal-aluminyl complexes suggests that their reactivity with small molecules beyond carbon dioxide could be accessed. In this work, the reactivity of the [^t Bu₃ PAuAl(NON)] (NON=4,5-bis(2,6 diisopropylanilido)-2,7-ditert-butyl-9,9-dimethylxanthene) complex towards water, ammonia, sulfur dioxide and nitrous oxide is computationally explored. The reaction mechanisms computed for each substrate strongly suggest that all activation processes are in principle experimentally feasible. Electronic structure analysis highlights that, in all cases, the reactivity is driven by the presence of the poorly polarized electron-sharing gold-aluminyl bond, which induces a radical-like reactivity of the complex towards all the substrates. A flat topology of the potential energy surface (PES) has been found for the reaction with N₂ O, where two almost isoenergetic transition states can be located along the same reaction coordinate with different geometries, suggesting that the N₂ O binding mode may not be a good indicator of the nature of N₂ O activation in a cooperative bimetallic reactivity. In addition, the catalytic potentialities of these complexes have been explored in the framework of nitrous oxide reduction. The study reveals that the [^t Bu₃ PAuAl(NON)] complex might be an efficient catalyst towards oxidation of phosphines (and boranes) via N₂ O reduction. These findings underline recurring trends in the novel chemistry of gold-aluminyl complexes and call for experimental feedbacks.

Energy decomposition analysis of cationic carbene analogues with groups 13 and 16 elements as a central atom: A comparative study

Decomposition of the molecular interaction energies into physically intuitive components provides insights to the chemical bonding between fragments. The extended transition state-natural orbital for chemical valence (ETS-NOCV) and natural energy...

Disila- and digermabenzenes

Reactions of isolable disilynes and digermynes with alkynes can result in the formation of the corresponding disila- (DSBs) and digermabenzenes (DGBs), wherein two carbon atoms of the benzene ring are replaced by silicon or germanium atoms. Detailed structural and spectroscopic analyses of these DSBs and DGBs have revealed that they exhibit considerable aromaticity, comparable to that of benzene. However, in contrast to the all-carbon system benzene, these DSBs and DGBs are highly reactive toward small molecules such as oxygen, hydrogen, 1,3-dienes, and water. During the investigation of their reactivity, we discovered that a 1,2-DGB works as a catalyst for the cyclotrimerization of arylalkynes, which provides access to the corresponding 1,2,4-triarylbenzenes. In this perspective article, our recent progress in the area of DSB and DGB chemistry is summarized.

Reactivity of dicationic N-heterocyclic chalcogen carbene analogues with methane and ethene: a theoretical investigation

The reactions of chalcogen N-heterocyclic carbenic (NHC) dications [(Dipp2DAB)M2+, M = O, S, Se, and Te, and Dipp2DAB = 1,4-(2,6-diisopropyl)phenyl-1,4-diaza-1,3-butadiene] with methane and ethene are investigated by the density functional theory. The activation energies and reaction enthalpies are analyzed by the energy decomposition analysis (EDA) to understand the reactivity of the reactions. Calculations show that the oxide carbenic dication (Dipp2DAB)O2+ reactant has a pair of rather unbalanced O-N bonds due to the combined effects of the smallness of the central O atom and the bulkiness of the two Dipp ligands surrounding the DAB ring, suggesting the oxide reactant is much less stable than the chalcogenide ones. Because of its unique characteristics, the oxide carbenic dication distinguishes itself from the rest of the chalcogen family. The differences between oxides and chalcogenides of the chalcogen family complexes well known in inorganic chemistry are also observed in this theoretical investigation. This work further reveals that the reasons for the distinctive characteristics between oxide and chalcogenide complexes are due to the fundamental fact that the 2s and 2p atomic orbitals are more amenable to hybridization than those of higher valences, and the mixing of the former valence orbitals results in much smaller atoms than the latter.

A theoretical study of the reactivity of ethene and benzophenone with a hyper-coordinated alkene containing a so-called E=E (E = C, Si, Ge, Sn, and Pb) unit

The reactivity of a reported hyper-coordinated alkene (Rea-E; Rea = reactant; E = group 14 element) featuring a central E[double bond, length as m-dash]E moiety was theoretically analyzed using DFT (density functional theory) and the EDA-NOCV (energy decomposition analysis-natural orbitals for chemical valence) method. M06-2X/def2-SVP and B3LYP-D3/def2-SVP results demonstrate that five Rea-E molecules have an energy minimum as their structures have no imaginary frequency. Theoretical examinations based on three types of bond order calculations (Wiberg, Mayer, and Fuzzy), the LOL (localized orbital locator) analyses, Lewis structures and the NBO (natural bond orbital) analyses suggest that a very weak central Si-Si single bond and an extremely weak central Ge-Ge single bond, rather than a double bond, are present in the Rea-Si and Rea-Ge molecules, respectively. On the other hand, no bond is found between the two central group 14 atoms in Rea-C, Rea-Sn, and Rea-Pb. The theoretical investigation demonstrates that the reactivity of the Rea-E compound decreases in the order Rea-Si > Rea-Ge > Rea-C, a trend that results from the differences in the atomic radii of the group 14 elements. Carbon has the smallest atomic radius in the group 14 family, causing steric crowding between Rea-C and other attacking species. This circumstance, in turn, increases the activation energies of its addition reactions and renders these reactions energetically infeasible. For the cyclic product of Rea-Ge, the theoretical evidence reveals that the comparatively large atomic radius of Ge induces the weakest Pauli repulsions and the smallest overlap integrals between Rea-Ge and the other doubly bonded molecules. This situation, in turn, makes the overall cyclization reaction of Rea-Ge endothermic. As a result, only the silicon-centered molecule, Rea-Si, can undergo the [2 + 2] cycloaddition reactions with doubly bonded molecules without kinetic or thermodynamic difficulty, which agrees well with the available experimental findings.

Recent advances of group 14 dimetallenes and dimetallynes in bond activation and catalysis

Since the first heavy alkene analogues of germanium and tin were isolated in 1976, followed by West's disilene in 1981, the chemistry of stable group 14 dimetallenes and dimetallynes has advanced immensely. Recent developments in this field veered the focus from the isolation of novel bonding motifs to mimicking transition metals in their ability to activate small molecules and perform catalysis. The potential of these homonuclear multiply bonded compounds has been demonstrated numerous times in the activation of H2, NH3, CO2 and other small molecules. Hereby, the strong relationship between structure and reactivity warrants close attention towards rational ligand design. This minireview provides an overview on recent developments in regard to bond activation with group 14 dimetallenes and dimetallynes with the perspective of potential catalytic applications of these compounds.

Understanding the reactivity of carbene-analogous phosphane complexes with group 13 elements as a central atom: a theoretical investigation

The reactions of carbenic cations (PtBu₃)₂M⁺ (M = B, Al, Ga, In, and Tl) with methane and ethene are studied using density functional theory.

A mechanistic study of the activation of small molecules (H2 and C2H2) by group 14 analogues of selenophene

In this study, the reactivity influenced by group 14 elements (E = C, Si, Ge, Sn, and Pb), which are used as substituents in heterocyclic five-membered rings, was theoretically examined by using density functional theory (B3PW91/def2-SVP).

The interplay and strength of the π⋯HF, C⋯HF, F⋯HF and F⋯HC hydrogen bonds upon the formation of multimolecular complexes based on C2H2⋯HF and C2H4⋯HF small dimers

The conception of this theoretical research was idealized aiming to unveil the intermolecular structures of complexes formed by acetylene or ethylene and hydrofluoric acid. At light of computational calculations by using the B3LYP/6-311++G(d,p) method, the geometries of the C₂H₂⋯(HF), C₂H₂⋯2(HF), C₂H₂⋯4(HF), C₂H₄⋯(HF), C₂H₄⋯2(HF) and C₂H₄⋯4(HF) hydrogen-bonded complexes were fully optimized. Moreover, the Post-Hartree-Fock calculations MP2/6-311++G(d,p), MP2/aug-cc-pVTZ, MP4(SDQ)/6-311++G(d,p) and CCSD/6-311++G(d,p) also were also used. The infrared spectra were analyzed in order to identify the new vibrational modes and frequencies of the proton donors shifted to red region. Through the modeling of charge-fluxes on the basis of the Quantum Theory of Atoms In Molecules (QTAIM) and, by contradicting the expectation of the hydrofluorination mechanisms of acetylene or ethylene, C⋯HF was recognized as a new type of hydrogen bond instead of the already well known π⋯H. The calculations of the Natural Bonding Orbital (NBO) and Charges derived from the Electrostatic Potential Grid-based (ChElPG) were also applied to interpret the shifting frequencies as well as measuring of the punctual charge-transfer after the formation of the complexes. Finally, the determination of the stabilization energy was carried out through the arguments of the Fock matrix in NBO basis and through the supermolecule approach. Also it is worthwhile to notice that some algebraic formulations were used for determining the electronic cooperative effect (CE).

A Theoretical Study on the Stability of PtL2 Complexes of Endohedral Fullerenes: The Influence of Encapsulated Ions, Cage Sizes, and Ligands

The {η²-(X@C _n )}PtL₂ complexes possessing three kinds of encapsulated ions (X = F^-, Ø, Li⁺), three various ligands (L = CO, PPh₃, NHC^Me), and twelve cage sizes (C₆₀, C₇₀, C₇₂, C₇₄, C₇₆, C₇₈, C₈₀, C₈₄, C₈₆, C₉₀, C₉₆, C₁₀₀) are theoretically examined by using the density functional theory (M06/LANL2DZ). The present computational results demonstrate that the backward-bonding orbital interactions, rather than the forward-bonding orbital interactions, play a dominant role in the stability of {η²-(X@C _n )}PtL₂ complexes. Additionally, our theoretical study shows that the presence of the encapsulated Li⁺ ion can greatly improve the stability of {η²-(X@C _n )}PtL₂ complexes, whereas the existence of the encapsulated F^- ion can heavily reduce the stability of {η²-(X@C _n )}PtL₂ complexes. Moreover, the theoretical evidence strongly suggests that the backward-bonding orbital interactions as well as the stability increase in the order {η²-(X@C _n )}Pt(CO)₂ < {η²-(X@C _n )}Pt(PPh₃)₂ < {η²-(X@C _n )}Pt(NHC^Me)₂. As a result, these theoretical observations can provide experimental chemists a promising synthetic direction.

Facile insertion of ethylene into a group 14 element-carbon bond: effects of the HOMO-LUMO energy gap on reactivity

The diarylstannylenes, Sn(AriPr4)2 and Sn(AriPr6)2, (AriPr4 = C6H3-2,6-(C6H3-2,6-iPr2)2, AriPr6 = C6H3-2,6-(C6H2-2,4,6-iPr3)2), undergo a facile migratory insertion reaction with ethylene at 60 °C to afford the alkyl aryl stannylenes AriPr4SnCH2CH2AriPr4 and AriPr6SnCH2CH2AriPr6 which were characterized via1H, 13C and 119Sn NMR, UV-vis and IR spectroscopy, as well as by X-ray crystallography. Quantum mechanical calculations were performed, and two potential mechanisms were identified, with a migratory insertion reaction pathyway being energetically preferred.

Theoretical investigations of the reactivity of neutral molecules that feature an MM (M = B, Al, Ga, In, and Tl) double bond

The geometry, the electronic structure and the reactivity of compounds that feature a central MM (M = group 13 element) double bond with two sterically bulky ligands (L₁ = ^tBu₂MeSi and L₂ = NHC^iPr), L₁L₂MML₁L₂ (Rea-MM) are studied at the B3LYP-D3(BJ)/def2-SVP level of theory.

Synthesis and Reactivity Studies of Amido-Substituted Germanium(I)/Tin(I) Dimers and Clusters

Three amide ligands of varying steric bulk and electronic properties were utilized to prepare a series of amido-germanium(II)/tin(II) halide compounds, (LEX)_n , (L= -N{B(DipNCH)₂ }(SiMe₃ ), ^TBo L; -N{B(DipNCH)₂ }(SiPh₃ ), ^PhBo L; -N(Dip)(tBu), ^DBu L; Dip=C₆ H₃ iPr₂ -2,6; E=Ge or Sn; X=Cl or Br; n=1 or 2). Reductions of these with a magnesium(I) dimer, {(^Mes Nacnac)Mg}₂ (^Mes Nacnac=[(MesNCMe)₂ CH]^- , Mes=mesityl), afforded singly bonded amido-digermynes (^TBo LGe-Ge^TBo L and ^PhBo LGe-Ge^PhBo L), and an amido-distannyne (^PhBo LSn-Sn^PhBo L), in addition to several low-valent, amido stabilized tetrel-tetrel bonded cluster compounds, (^DBu LGe)₄ , (^DBu LSn)₆ and Sn₅ (^TBo L)₄ . The nature of the products resulting from these reactions was largely dependent on the steric bulk of the amide ligand employed. Cluster (^DBu LGe)₄ possessed an unusual folded butterfly structure, the bonding and electronic of which were examined using DFT calculations. Reactions of the amido-germanium(I) compounds with H₂ were explored, and gave rise to the amido-digermene, ^TBo L(H)Ge=Ge(H)^TBo L and the cyclotetragermane, {^DBu L(H)Ge}₄ . Reactions of (^DBu LGe)₄ with a series of unsaturated small molecule substrates yielded ^DBu LGeOGe^DBu L, ^DBu LGe(μ-C₂ H₄ )₂ Ge^DBu L and ^DBu LGe(μ-1,4-C₆ H₈ )(μ-1,2-C₆ H₈ )Ge^DBu L. The latter results imply that (^DBu LGe)₄ can act as a masked source of the digermyne ^DBu LGeGe^DBu L in these reactions. All further reactivity studies indicated that the germanium(I) compounds exhibit a "transition-metal-like" behavior, which is closely related to that previously described for bulky digermynes and related compounds.

The selective formation of a 1,2-disilabenzene from the reaction of a disilyne with phenylacetylene

A stable 3,5-diphenyl-1,2-disilabenzene was selectively synthesized by the reaction between the isolabe disilyne TbbSiSiTbb (Tbb = 2,6-[CH(SiMe₃)₂]₂-4-t-Bu-phenyl) with phenylacetylenes.

Facile activation of alkynes with a boraguanidinato-stabilized germylene: a combined experimental and theoretical study

A boraguanidinato-stabilized germylene, [(i-Pr)₂NB(N-2,6-Me₂C₆H₃)₂]Ge, reacts with alkynes RC[triple bond, length as m-dash]CR selectively in a 2 : 1 molar ratio to afford 3,4-R,R'-1,2-digermacyclobut-3-enes 1a-e as the products of formal [2 + 2 + 2] cyclization [R/R' = Me/Me (1a), Ph/Ph (1b), Ph/H (1c), t-Bu/H (1d) and Cy/H (1e)]. Ferrocenyl-substituted alkynes react similarly, yielding the corresponding ferrocenylated 3,4-R,R'-1,2-digermacyclobut-3-enes 2a-d [where R/R' = Fc/H (2a), Fc/Me (2b), Fc/Ph (2c), and Fc/Fc (2d); Fc = ferrocenyl]. By contrast, only one of the triple bonds available in conjugated diynes RC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CR is activated with the germylene, while the second one remains intact even in the presence of an excess of the germylene. The exclusive formation of 3,4-R,(C[triple bond, length as m-dash]CR)-1,2-digermacyclobut-3-enes 3a-c [R = Ph (3a), t-Bu(3b), and Fc (3c)] was ascribed to a steric repulsion around the second triple bond. On the other hand, the reaction of the germylene with more flexible dialkyne fc(C[triple bond, length as m-dash]CPh)₂ (fc = ferrocene-1,1'-diyl) proceeded in the expected manner, producing compound 4, where both triple bonds are transformed into 1,2-digermacyclobut-3-ene rings by reaction with four equivalents of the germylene. All compounds were characterized by multinuclear NMR spectroscopy, Raman and IR spectroscopy, and in the case of 1a-c, 2a, 2c, 3a, 3b and 4, also by single-crystal X-ray diffraction analysis. The ferrocenyl substituted compounds were studied by cyclic voltammetry (CV). Finally, the plausible reaction pathway was studied for a model reaction of [(i-Pr)₂NB(N-2,6-Me₂C₆H₃)₂]Ge with MeC[triple bond, length as m-dash]CMe using DFT computations.

Phosphaborenes: Accessible Reagents for the Synthesis of C-C/P-B Isosteres

Formal exchange of C=C units with isoelectronic B=N or B=P units can provide access to molecules with unique electronic or chemical properties. Herein, we report the simple solution-phase generation of highly reactive phosphaborenes, RP=BR, and demonstrate their use for the introduction of P=B units into organic systems. Ring opening of a P-B-containing cyclobutene isostere provided access to unique 1,4-boraphosphabutadiene systems with conjugated main-group multiple bonds.

NHC-Stabilised Acetylene-How Far Can the Analogy Be Pushed?

Experimental studies suggest that the compound (NHC^bz )₂ C₂ H₂ can be considered as a complex of a distorted acetylene fragment which is stabilised by benzoannelated N-heterocyclic carbene ligands (NHC^bz )→(C₂ H₂ )←(NHC^bz ). A quantum chemical analysis of the electronic structures shows that the description with dative bonds is more favourable than with electron-sharing double bonds (NHC^bz )=(C₂ H₂ )=(NHC^bz ).

Reaction Mechanism of the Hydrogermylation/Hydrostannylation of Unactivated Alkenes with Two-Coordinate E(II) Hydrides (E=Ge, Sn): A Theoretical Study

Quantum chemical calculations using density functional theory with the TPSS+D3(BJ) and M06-2X+D3(ABC) functionals have been carried out to understand the mechanisms of catalyst-free hydrogermylation/hydrostannylation reactions between the two-coordinate hydrido-tetrylenes :E(H)(L(+) ) (E=Ge or Sn, L(+) =N(Ar(+) )(SiiPr3 ); Ar(+) =C6 H2 {C(H)Ph2 }2 iPr-2,6,4) and a range of unactivated terminal (C2 H3 R, R=H, Ph, or tBu) and cyclic [(CH)2 (CH2 )2 (CH2 )n , n=1, 2, or 4] alkenes. The calculations suggest that the addition reactions of the germylenes and stannylenes to the cyclic and acyclic alkenes occur as one-step processes through formal [2+2] addition of the E-H fragment across the C-C π bond. The reactions have moderate barriers and are weakly exergonic. The steric bulk of the tetrylene amido groups has little influence on the activation barriers and on the reaction energies of the anti-Markovnikov pathway, but the Markovnikov addition is clearly disfavored by the size of the substituents. The addition of the tetrylenes to the cyclic alkenes is less exergonic than the addition to the terminal alkenes, which agrees with the experimentally observed reversibility of the former reactions. The hydrogermylation reactions have lower activation energies and are more exergonic than the stannylene addition. An energy decomposition analysis of the transition state for the hydrogermylation of cyclohexene shows that the reaction takes place with simultaneous formation of the Ge-C and (Ge)H-C' bonds. The dominant orbitals of the germylene are the σ-type lone pair MO of Ge, which serves as a donor orbital, and the vacant p(π) MO of Ge, which acts as acceptor orbital for the π* and π MOs of the olefin. Inspection of the transition states of some selected reactions suggests that the differences between the activation energies come from a delicate balance between the deformation energies of the interacting species and their interaction energies.

Addition of alkynes to digermynes: experimental insight into the reaction pathway

The reaction pathway for the addition of alkynes to digermynes has been investigated using a mechanistic probe approach.