Observation of Transition-Metal-Boron Triple Bonds in IrB2 O- and ReB2 O. Angew Chem Int Ed Engl 2020;59:15260-15265. [PMID: 32424965 DOI: 10.1002/anie.202006652]

Infrared Photodissociation Spectroscopy of Mass-Selected Dinuclear Transition Metal Boride Carbonyl Cluster Cations

The transition-metal-boron bonding interactions and geometric structures of heterodinuclear transition metal carbonyl cluster cations BM(CO)n+ (M = Co, Ni, and Cu) are studied by a combination of the infrared photodissociation spectroscopy and density functional theory calculations at the B3LYP/def2-TZVP level. The BCu(CO)5+ and BCo(CO)6+ cations are characterized as an (CO)2B-M(CO)3/4+ structure involving an σ-type (OC)2B → M(CO)3,4+ dative bonding with end-on carbonyls, while for BNi(CO)5,6+ complexes with a bridged carbonyl, a 3c-2e bond involving the 5σ electrons of the bridged carbonyl and an electron-sharing bond between the B(CO)2 fragment and the Ni(CO)2,3+ subunits were revealed. Moreover, the fundamental driving force of the exclusive existence of a bridged carbonyl group in the boron-nickel complexes has been demonstrated to stem from the desire of the B and Ni centers for the favorable 8- and 18-electron structures.

Investigation of Pb-B Bonding in PbB2(BO)n- (n = 0-2): Transformation from Aromatic PbB2- to Pb[B2(BO)2]-/0 Complexes with BB Triple Bonds

Boron has been found to be able to form multiple bonds with lead. To probe Pb-B bonding, here we report an investigation of three Pb-doped boron clusters, PbB2-, PbB3O-, and PbB4O2-, which are produced by a laser ablation cluster source and characterized by photoelectron spectroscopy and ab initio calculations. The most stable structures of PbB2-, PbB3O-, and PbB4O2- are found to follow the formula, [PbB2(BO)n]- (n = 0-2), with zero, one, and two boronyl ligands coordinated to a triangular and aromatic PbB2 core, respectively. The PbB2- cluster contains a BB double bond and two Pb-B single bonds. The coordination of BO is observed to weaken Pb-B bonding but strengthen the BB bond in [PbB2(BO)n]- (n = 1, 2). The anionic [PbB2(BO)2]- and its corresponding neutral closed-shell [PbB2(BO)2] contain a BB triple bond. A low-lying Y-shaped isomer is also observed for PbB4O2-, consisting of a central sp2 hybridized B atom bonded to two boronyl ligands and a PbB unit.

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.

Boron-lead multiple bonds in the PbB2O- and PbB3O2- clusters

Despite its electron deficiency, boron can form multiple bonds with a variety of elements. However, multiple bonds between boron and main-group metal elements are relatively rare. Here we report the observation of boron-lead multiple bonds in PbB₂O^- and PbB₃O₂^-, which are produced and characterized in a cluster beam. PbB₂O^- is found to have an open-shell linear structure, in which the bond order of B☱Pb is 2.5, while the closed-shell [Pb≡B-B≡O]^2- contains a B≡Pb triple bond. PbB₃O₂^- is shown to have a Y-shaped structure with a terminal B = Pb double bond coordinated by two boronyl ligands. Comparison between [Pb≡B-B≡O]^2-/[Pb=B(B≡O)₂]^- and the isoelectronic [Pb≡B-C≡O]^-/[Pb=B(C≡O)₂]⁺ carbonyl counterparts further reveals transition-metal-like behaviors for the central B atoms. Additional theoretical studies show that Ge and Sn can form similar boron species as Pb, suggesting the possibilities to synthesize new compounds containing multiple boron bonds with heavy group-14 elements.

Probing the Nature of the Transition-Metal-Boron Bonds and Novel Aromaticity in Small Metal-Doped Boron Clusters Using Photoelectron Spectroscopy

Photoelectron spectroscopy combined with quantum chemistry has been a powerful approach to elucidate the structures and bonding of size-selected boron clusters (B_n^-), revealing a prevalent planar world that laid the foundation for borophenes. Investigations of metal-doped boron clusters not only lead to novel structures but also provide important information about the metal-boron bonds that are critical to understanding the properties of boride materials. The current review focuses on recent advances in transition-metal-doped boron clusters, including the discoveries of metal-boron multiple bonds and metal-doped novel aromatic boron clusters. The study of the RhB^- and RhB₂O^- clusters led to the discovery of the first quadruple bond between boron and a transition-metal atom, whereas a metal-boron triple bond was found in ReB₂O^- and IrB₂O^-. The ReB₄^- cluster was shown to be the first metallaborocycle with Möbius aromaticity, and the planar ReB₆^- cluster was found to exhibit aromaticity analogous to metallabenzenes. Expected final online publication date for the Annual Review of Physical Chemistry, Volume 73 is April 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Multiple d-d bonds between early transition metals in TM2Lin (TM = Sc, Ti) superatomic molecule clusters

The synthesis and application of compounds with Cr-Cr and V-V d-d quintuple bonds (σ, 2π, 2δ) have led to new thinking about whether d-d multiple bonds also exist between early transition metals such as Sc-Sc and Ti-Ti. In this study, by extensive unbiased global search at the density functional theory level, the low-energy structures of 26e and 30e TM2Lin clusters were obtained. Based on the super valence bond (SVB) theory, the prolate double-core structure of TM2Lin clusters was regarded as a superatomic molecule, of which each half was regarded as an open-shell superatom, and the electronic shell-closure was realized by forming multiple bonds between superatoms. Then, the quintuple super bonds (2δ, 2π, σ) of the Li18Ti2, Li20Sc2, [Li17V2]+, [Li17Ti2]- clusters and the triple super bonds (2π, σ) of the Li24Sc2 and Li24Y2 clusters were confirmed via chemical-bonding analysis. This way of forming multiple bonds between early transition metals through superatomic bonding has promoted the experimental synthesis and application of early transition metal multiple bond compounds.