Substituent Effects on Boron–Bismuth Triple Bond: A New Target for Synthesis

Observation of an electron-precise metal boryne complex: [BiBH]. Chem Commun (Camb) 2023;59:12431-12434. [PMID: 37768059 DOI: 10.1039/d3cc04235a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Metal-boron triple bonds are rare due to the electron deficiency of boron. This study uncovers a simple electron-precise metal boryne complex, [BiBH]-, which is produced within an ion trap through chemical reactions of the open-shell BiB- anion with H2. Photoelectron imaging is used to investigate the electronic structure and chemical bonding of the BiBH- complex. The B atom in the linear closed-shell BiBH- is found to undergo sp hybridization, forming a B-H single bond and a BiB triple bond. Photoelectron imaging reveals three detachment transitions from the BiBH- (1Σ+) anion to the neutral BiBH, including the ground state (2Π3/2) and two excited states (2Σ+ and 2Π1/2). Strong vibronic coupling is observed between the 2Π3/2 and 2Σ+ states, evidenced by the appearance of bending vibrations and their unique photoelectron angular distributions. The BiBH- complex not only stands as the simplest metal boryne complex, but also serves as an ideal molecular system to investigate both spin-orbit and vibronic couplings.

Heavier group 13/15 multiple bond systems: synthesis, structure and chemical bond activation

Heavier group 13/15 multiple bonds have been under investigation since the late 80s and to date, several examples have been published, which shows the obsoleteness of the so-called double bond rule. Especially in the last few years, more and more group 13/15 multiple bonds became synthetically feasible and their application in terms of small molecule activation has been demonstrated. Our group has recently shown that the combination of the pnictinidene precursor ^DipTer-Pn(PMe₃) (Pn = P, As) in combination with Al(I) synthons afforded the first examples of phospha- and arsaalumenes as isolable and thermally robust compounds. This feature article is intended to show the recent developments in the field, to outline early synthetic approaches and to discuss strategies to unlock the synthetic potential of these elusive chemical bonds.

Theoretical investigations in the reactions of group 15 analogues of the monocationic five-membered N-heterocyclic carbenes: interplay of electrophilicity, basicity, and aromaticity governing the reactivity

The nature of the group 15 analogs of the five-membered N-heterocyclic carbenes (G15-Rea; G15 = N, P, As, Sb, and Bi) was investigated by using various methodologies.

Matrix infrared spectroscopy of F2BMF and FB[triple bond, length as m-dash]WF2 (M = Cr, Mo and W) complexes and quantum chemistry calculations

Laser-ablated group 6 transition metal atoms react with BF3 to yield typical transition metal inserted complexes F2B-MF (M = Cr, Mo, and W) and terminal borylene complex FB[triple bond, length as m-dash]WF2. These products are investigated by using infrared spectroscopy, isotopic substitution and theoretical frequency calculations. The inserted complexes F2B-MF (M = Cr, Mo, and W) were identified by antisymmetric and symmetric stretching modes of F-B-F. The FB[triple bond, length as m-dash]WF2 molecule has a 11B-F (10B-F) stretching frequency at 1453.2 (1505.0) cm-1 and the triple bond between boron and tungsten is confirmed by EDA-NOCV calculations, CASSCF calculation and NBO analysis. Furthermore, the bonding for tungsten complexes is compared with that of molybdenum and chromium complexes, which reveals interesting differences in their chemistries.

Investigation of the reactivity indices for the formation of substituted dinitroanilines and correlations to their dockings on α-tubulin of Plasmodium falciparum

The local and global reactivity descriptors of substituted dinitroaniline analogues were investigated using M06-2X/6-31 + G(d,p) method. It was observed that NH₂ (m = 3.53 eV; p = 3.70 eV) substituent conveyed the highest nucleophilic character on the benzene ring system than the other groups under study. For the substrates 4-substituted-1-chloro-2,6-dinitrobenzenes, the condensed to atom electrophilicity ([Formula: see text]) increases in the order COOCH₃ > NO₂ > F > SO₃H > CN > Cl > Br. The para substituted groups with the halogens follow the order of increasing electronegativity, F > Cl > Br. However, the nucleophilicity of the halo substituents of the products increases in the order, F > Br > Cl. Molecular docking simulations using the homology model with the crystallographic structure of zinc-induced bovine tubulin heterodimer (1JFF) as one of the templates reveal that the interactions between the tubulins of Plasmodium falciparum and dinitroaniline analogues are due to H-bonding. In general, the binding interaction is with the following residues: Met137, ARG64, Lys60, Glu183, Val4, His28, Cys171, Tyr224, Asn206, 228, Ile235, and Leu238. The pK_as of the residue decrease as the ring activating power of the substituents increases from strongly activating to weakly activating groups. There is no evidence of intra or intermolecular H-bonding between Arg64 and Cys171. Electronegativity (χ) gives a better generic description of the dinitroanilines than any other parameters considered. Short-range hydrophobic interaction contributes to reduced binding affinities of the ligands. Graphical abstractReaction of substituted 2,6-dinitro chlorobenzene with diisopropylamine. Orbital interaction between the substrates and diisopropylamine in the formation of the dinitroanilines.

Boron-Transition-Metal Triple-Bond FB≡MF2 Complexes

The boron-transition-metal triple-bond complexes FB≡MF₂ (M= Ir, Os, Re, W, Ta) were trapped in excess solid neon and argon through metal atom reactions with boron trifluoride and identified by matrix isolation infrared spectroscopy and quantum chemical calculations. The FB≡MF₂ molecule features very high ¹¹B-F stretching frequencies at 1586.6 cm^-1 (Ir), 1526.6 cm^-1 (Os), 1505.5 cm^-1 (Re), and 1453.2 cm^-1 (W), respectively. The very high strength of B≡M bonds with triple-bonding character is confirmed by EDA-NOCV calculations and the active molecular orbital and NBO analysis. The experimental observation of FB stabilization by heavy transition-metal atoms with triple bonds opens the door to design new boron-transition-metal complexes.

Non-classical covalent bonds

The possibility of multiple bond formation between Periodic Table Group 13 – 15 elements is considered. The ways of triple bond formation between these elements are discussed; particular attention is paid to the B≡B triple bonds. New non-linear compounds with triple bonds and their molecular structures are considered. The causes are given for the formation of compounds with unusually short distances between chemically non-bonded atoms. The grounds of the theory of two-centre three-electron bonds are presented and conditions of existence of isolated square planar carbon clusters are analyzed.

The bibliography includes 181 references.

A computational study to determine whether substituents make E13[triple bond, length as m-dash]nitrogen (E13 = B, Al, Ga, In, and Tl) triple bonds synthetically accessible

This study theoretically determines the effect of substituents on the stability of the triple-bonded L–E₁₃N–L (E₁₃ = B, Al, Ga, In, and Tl) compound using the M06-2X/Def2-TZVP, B3PW91/Def2-TZVP, and B3LYP/LANL2DZ+dp levels of theory. Five small substituents (F, OH, H, CH₃ and SiH₃) and four large substituents (SiMe(SitBu₃)₂, SiiPrDis₂, Tbt ( Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C₆H₂-2,4,6-{CH(SiMe₃)₂}₃) and Ar* (C₆H₃-2,6-(C₆H₂-2,4,6-i-Pr₃)₂)) are used. Unlike other triply bonded L–E₁₃P–L, L–E₁₃As–L, L–E₁₃Sb–L and L–E₁₃Bi–L molecules that have been studied, the theoretical findings for this study show that both small (but electropositive) ligands and bulky substituents can effectively stabilize the central E₁₃N triple bond. Nevertheless, these theoretical observations using the natural bond orbital and the natural resonance theory show that the central E₁₃N triple bond in these acetylene analogues must be weak, since these E₁₃N compounds with various ligands do not have a real triple bond.

This study theoretically determines the effect of substituents on the stability of the triple-bonded L–E₁₃N–L (E₁₃ = B, Al, Ga, In, and Tl) compound using the M06-2X/Def2-TZVP, B3PW91/Def2-TZVP, and B3LYP/LANL2DZ+dp levels of theory.

Probing the structures and bonding of size-selected boron and doped-boron clusters

Because of their interesting structures and bonding and potentials as motifs for new nanomaterials, size-selected boron clusters have received tremendous interest in recent years. In particular, boron cluster anions (Bn-) have allowed systematic joint photoelectron spectroscopy and theoretical studies, revealing predominantly two-dimensional structures. The discovery of the planar B36 cluster with a central hexagonal vacancy provided the first experimental evidence of the viability of 2D borons, giving rise to the concept of borophene. The finding of the B40 cage cluster unveiled the existence of fullerene-like boron clusters (borospherenes). Metal-doping can significantly extend the structural and bonding repertoire of boron clusters. Main-group metals interact with boron through s/p orbitals, resulting in either half-sandwich-type structures or substitutional structures. Transition metals are more versatile in bonding with boron, forming a variety of structures including half-sandwich structures, metal-centered boron rings, and metal-centered boron drums. Transition metal atoms have also been found to be able to be doped into the plane of 2D boron clusters, suggesting the possibility of metalloborophenes. Early studies of di-metal-doped boron clusters focused on gold, revealing ladder-like boron structures with terminal gold atoms. Recent observations of highly symmetric Ta2B6- and Ln2Bn- (n = 7-9) clusters have established a family of inverse sandwich structures with monocyclic boron rings stabilized by two metal atoms. The study of size-selected boron and doped-boron clusters is a burgeoning field of research. Further investigations will continue to reveal more interesting structures and novel chemical bonding, paving the foundation for new boron-based chemical compounds and nanomaterials.

Highly efficient electroluminescent PtII ppy-type complexes with monodentate ligands

Functional Pt^II ppy-type complexes (ppy = 2-phenylpyridine anion) with pyridine and chloride monodentate ligands are prepared, which show high electroluminescence efficiencies.