Quintuple Bond Research Articles

Unusual coordination mode for 1,3-diphosphete ligands towards a Cr-Cr quintuple bond complex.

The reaction of LCr5̲CrL (L = N2C25H29, 1) with the phosphaalkynes R-C≡P (R = tBu, Me, Ad) yields the neutral dimerisation compounds [L2Cr2(μ,η1:η1:η2:η2-P2C2R2)] (R = tBu (2), Me (3)) and the tetrahedrane complex [L2Cr2(μ,η2:η2-PCAd)] (4). The 1,3-diphosphete ligands in complexes 2 and 3 are the first to possess this structural feature spanned over a metal-metal multiple bond, while the slightly bigger adamantyl phosphaalkyne remains a monomer in 4 with a side-on coordination mode.

Metal-Metal Bonding in Actinide Dimers: U2 and U2.

Understanding direct metal-metal bonding between actinide atoms has been an elusive goal in chemistry for years. We report for the first time the anion photoelectron spectrum of U2-. The threshold of the lowest electron binding energy (EBE) spectral band occurs at 1.0 eV, which corresponds to the electron affinity (EA) of U2, whereas the vertical detachment energy of U2- is found at EBE ∼ 1.2 eV. Electronic structure calculations on U2 and U2- were carried out with state-of-the-art theoretical methods. The computed values of EA(U2) and EA(U) and the difference between the computed dissociation energies of U2 and U2- are found to be internally consistent and consistent with experiment. Analysis of the bonds in U2 and U2- shows that while U2 has a formal quintuple bond, U2- has a quadruple bond, even if the effective bond orders differ only by 0.5 unit instead of one unit. The resulting experimental-computational synergy elucidates the nature of metal-metal bonding in U2 and U2-.

Comparison of RNC Coupling and CO Coupling Mediated by Cr-Cr Quintuple Bond and B-B Multiple Bonds: Main Group Metallomimetics.

A theoretical analysis of reductive coupling of isocyanide and CO mediated by a Cr-Cr quintuple bonded complex and B-B multiple bonded complexes shows how the difference in donor-acceptor capability of isocyanide and CO ligands controls the product distributions. In the case of CO, the Cr-Cr quintuple bonded complex is unable to show C-C coupling due to the high π- back bonding possibility of CO and the reaction follows the singlet potential energy surface throughout, whereas, in the case of isocyanide, less π- back bonding possibility allows the reactions to undergo a spin transition and gives a series of products with different spin multiplicities. Similarly, reactions of B-B multiple bonded complexes with CO and isocyanides are also controlled by donor-acceptor capabilities of ligands, and the C-C coupling takes place by changing the oxidation state of the boron centers from +I to +II, in contrast to the classical main group mediated reactions where stable oxidation states are always preserved. This part of the main group chemistry which is dominated by donor-acceptor bonding interaction is more likely to follow transition metal behavior.

Coordination Chemistry of Bulky Aminopryridinates with Main Group and Transition Metals.

The coordination chemistry of bidentate aminopyridinato ligands (ApH), in particular 2-aminopyridines, is a highly popular area of research. Due to easy accessibility and versatility, 2-aminopyridines have played a prominent role as alternatives to cyclopentadienyl ligands in coordination chemistry. Easily modifiable steric bulks and the ability for fine-tuning of electronic effects have allowed researchers to control not only the metal-to-ligand stoichiometry but also the properties of their metal complexes. Previously, ligand redistribution was frequently observed for ligands of small steric demands. Bulky aminopyridinato ligands refer to ligands that incorporate alkyl-substituted phenyl groups at the amine/amido nitrogen and at the sixth position of the pyridine ring. The steric crowding allowed the stabilization of transition metals in unusually low oxidation conditions. One of the remarkable developments, for example, is the stabilization of metal-metal quintuple bonds by these ligands, thus providing a diamagnetic platform to study such systems chemically. Application of metal aminopyridinates in homogeneous catalysis has also broadened considerably in recent years. This review provides a comprehensive account of advances made with such ligands since their development for main group and transition elements.

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.

Chromium to chromium quintuple bonds in a trigonal lantern configuration

AbstractA new family of the quintuply bonded dichromium complexes [Cr2{μ‐κ2‐HC(N‐2,6‐R2C6H3)2}2(μ‐κ2‐HC[NAr]2)] (R = iPr, Ar = 4‐MeC6H4 (5), Ar = 3,5‐Me2C6H3 (6), and Ar = 2,6‐Me2C6H3 (7); R = Et, Ar = 4‐MeC6H4 (8), Ar = 3,5‐Me2C6H3 [9], and Ar = 2,6‐Et2C6H3 (10)) with a heteroleptic lantern configuration was obtained upon the addition of one equivalent of amidinate to the quintuply bonded dichromium amidinates [Cr{μ‐κ2‐HC(N‐2,6‐R2C6H3)2}]2 (R = iPr, Et). Additionally, the same approach was applied to the preparation of the acetate derivative [Cr2{μ‐κ2‐HC(N‐2,6‐ iPr2C6H3)2}2(μ‐κ2‐CH3CO2)] (11), which represents the first example that the quintuply bonded dinuclear complex contains an oxygen‐containing ligand. Of particular interest is that the Cr‐Cr bond lengths in these new trigonal paddlewheel quintuple Cr‐Cr bond species are comparable with those in their precursor compounds. They show ultrashort Cr‐Cr bond lengths in a narrow range of 1.740–1.755 å on the basis of single‐crystal X‐ray crystallography. The small Mayer bond orders of the long Cr‐N bonds as well as divergent, C2v and D3h, structural conformations in 5–11 suggest that the metal–ligand interactions possess minor covalent character and the electrostatic interactions play a dominant role. As a result, these extremely short Cr‐Cr quintuple bonds are caused by the overlap between five pairs of d orbitals that do not involve much in metal–ligand bonding. Additionally, anionic lantern dichromium trisamidinates 5–10 can be chemically oxidized by one electron, supported by electrochemistry, and their ease to undergo oxidation is presumably associated with their neutral lantern dichromium trisamindinate products, whose structures inherently display a Jahn‐Teller distortion, exemplified by the structure of the homoleptic dichromium complex [Cr2{μ‐κ2‐HC(N‐2,6‐Et2C6H3)2}3] [12] determined by X‐ray crystallography. These results unambiguously support the Cr‐Cr quintuple bonding in these novel anionic lantern dichromium complexes.

Aromaticity analysis of fused heterometallacycles containing M[sbnd]M(M = Cr, Mo and W) quintuple bond

Transition-metal-containing aromatic compounds, which contain both aromatic properties and the characteristics of organometallic compounds, have attracted great attention due to their unique structure, electronic properties and fascinating reactivities. In this work, the aromaticity of the fused five-membered ring in M2[N(CH3)CHN(CH3)]2 containing MM (Cr, Mo and W) quintuple bond is analyzed. The calculated results show that aromaticity of Cr2[N(CH3)CHN(CH3)]2 is weak, the five-membered rings in M2[N(CH3)CHN(CH3)]2 (M = Cr, Mo, W) exhibit obvious π aromatic character. The contribution of σ aromaticity and δ aromaticity to the five-membered rings can be neglected.

Trapping of CO2 by Cr–Cr quintuple bonds. A theoretical approach

The reaction of CO2 with quintuple Cr–Cr bond organometallic compounds is investigated using Density Functional Theory calculations. In these organometallic compounds, the electronic density is localized at the multiple Cr–Cr bonds. As expected, there is an electron transfer from this multiple bond to the Lowest Unoccupied Molecular Orbital (LUMO) of CO2, yielding a reaction with the carbon atom of the CO2 molecule. A posterior reaction of NH2− with the captured CO2 is also investigated and it is possible to see that CO2 interacts with the amine anion generating carbamate ion, which is one of the main products of the natural photosynthesis process. The whole reaction is considered a homogenous catalysis procedure since this ion is released allowing the complex to return to its initial geometry.

Uranium dimer loses a bond

Thirteen years ago, chemists determined that the U2 molecule has 10 bonding electrons, formally a quintuple bond (Nature 2005, DOI: 10.1038/nature03249). Now, a group led by Stefan Knecht of ETH Zurich has updated the quantum calculations used to model the dimer, taking into account the relativistic effects of electrons in motion. The results suggest the molecule has only a quadruple bond (Nat. Chem. 2018, DOI: 10.1038/s41557-018-0158-9). Knecht says understanding actinides is challenging. Lab experiments are difficult, and theoretical modeling is complicated by the actinides’ byzantine electronic structures and the relativistic, or near light-speed, motion of their electrons, which affects the energy levels of orbitals. Knecht and his collaborators worked on and off since 2006 writing new computer code to fully account for relativistic effects that the previous work approximated. He believes the earlier work unintentionally evaluated a low-lying excited state rather than the dimer’s ground state. The new model led

Spin-dependent transport properties of a graphene electrode-single quintuple bond [PhCrCrPh] molecule junction

ABSTRACTWe apply a first-principle computational approach to study the spin-dependent electron transport properties of a single-quintuple bond [PhCrCrPh] molecule with the -bent and linear configurations sandwiched between two ferromagnetic zigzag graphene nanoribbon electrodes. Theoretical results suggest that the current through the -bent configuration is significantly larger than the corresponding linear one. The device shows a perfect two-state molecular conformational switch, and a maximum predicted ON/OFF ratio of currents can be up to around for majority-spin (α)/minority-spin (β) state. Interestingly, the device shows an obvious spin-polarisation behaviour and negative differential resistance effect. The spin filtering efficiency can reach up to 100, and the maximum value of the peak-to-valley ratio of NDR is up to about 46. These results suggest that our proposed device has attractive potential in molecular switch as well as spin-filtering.

Yi‐Chou Tsai

Angewandte Chemie International EditionVolume 57, Issue 30 p. 9215-9215 Author ProfileFree Access Yi-Chou Tsai First published: 26 March 2018 https://doi.org/10.1002/anie.201802927AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract “If I were not a scientist, I would be a baseball commentator. My favorite place on earth is Melbourne, because of the atmosphere and the food ...” This and more about Yi-Chou Tsai can be found on page 9215. Yi-Chou Tsai The author presented on this page has published more than 10 articles in Angewandte Chemie in the last 10 years, most recently: “Reversible Cleavage/Formation of the Chromium–Chromium Quintuple Bond in the Highly Regioselective Alkyne Cyclotrimerization”: Y.-S. Huang, G.-T. Huang, Y.-L. Liu, J.-S. K. Yu, Y.-C. Tsai, Angew. Chem. Int. Ed. 2017, 56, 15427; Angew. Chem. 2017, 129, 15629. The work of Y.-C. Tsai has been featured on the back cover of Angewandte Chemie: “The Mo–Mo Quintuple Bond as a Ligand to Stabilize Transition-Metal Complexes”: D.-Y. Lu, P. P.-Y. Chen, T.-S. Kuo, Y.-C. Tsai, Angew. Chem. Int. Ed. 2015, 54, 9106; Angew. Chem. 2015, 127, 9234. Date of birth: July 19, 1969 Position: Professor of Chemistry, National Tsing Hua University E-mail: yictsai@mx.nthu.edu.tw Homepage: http://chem.web.nthu.edu.tw/files/13-1078-32021.php?Lang=zh-tw ORCID: 0000-0002-0857-6448 Education: 1991 BS, National Taiwan Normal University, Taipei 2001 PhD supervised by Christopher C. Cummins, Massachusetts Institute of Technology 2001–2003 Postdoc with Robert H. Grubbs, Caltech Awards: 2014 Outstanding Research Award, Ministry of Science and Technology, Taiwan Research: Synthetic inorganic and organometallic chemistry; metal catalysis; main-group chemistry Hobbies: Watching how pitchers face batters in baseball games, cycling, solving math problems with kids If I were not a scientist, I would be a baseball commentator. My favorite place on earth is Melbourne, because of the atmosphere and the food. My top three films of all time are The Shawshank Redemption, Forrest Gump, and The Lord of the Rings: The Return of the King. My favorite piece of music is Beethoven's 6th Symphony; it is simply beautiful. My favorite motto is “less is more”. What I look for first in a publication are the schemes, the abstract, and the conclusion. When I'm frustrated, I usually go for a bike ride in the countryside. The most significant scientific advance of the last 100 years has been without a doubt the development of computers. The most important thing I learned from my parents is to think well, do well, and feel well. If I could have dinner with three famous scientists from history, they would be Niels Bohr, Dmitri Mendeleev, and Charles Darwin. And I would ask them what scientists should do in the second half of the 21st century. I can never resist adding another new molecule to my collection. I celebrate success by going to a karaoke bar with co-workers and friends. My 5 top papers: 1“A Three-Coordinate and Quadruply-Bonded Mo–Mo Complex”: Y.-C. Tsai, Y.-M. Lin, J.-S. K. Yu, J.-K. Hwang, J. Am. Chem. Soc. 2006, 128, 13980. (A quadruply bonded dimolybdenum unit is supported by only two bridging bidentate ligands.) 2“Remarkably Short Metal–Metal Bonds: A Lantern-Type Quintuply Bonded Dichromium(I) Complex”: Y.-C. Tsai, C.-W. Hsu, J.-S. K. Yu, G.-H. Lee, Y. Wang, T.-S. Kuo, Angew. Chem. Int. Ed. 2008, 47, 7250; Angew. Chem. 2008, 120, 7360. (Consistent with the theoretical prediction, the metal–metal quintuple bond can be stabilized in the lantern geometry.) 3“Theory-Guided Experiments on the Mechanistic Elucidation of the Reduction of Dinuclear Zinc, Manganese, and Cadmium”: D.-Y. Lu, J.-S. K. Yu, T.-S. Kuo, G.-H. Lee, Y. Wang, Y.-C. Tsai, Angew. Chem. Int. Ed. 2011, 50, 7611; Angew. Chem. 2011, 123, 7753. (The similarity between manganese, zinc, and cadmium was found in their low-valent metal–metal bond formation.) 4“The Mo–Mo Quintuple Bond as a Ligand to Stabilize Transition Metal Complexes”: D.-Y. Lu, P. P.-Y. Chen, T.-S. Kuo, Y.-C. Tsai, Angew. Chem. Int. Ed. 2015, 54, 9106; Angew. Chem. 2015, 127, 9234. (Like C–C multiple bonds, metal–metal quintuple bonds can be utilized as a ligand to stabilize a transition-metal complex.) 5“Synthesis and Characterization of an Eclipsed Digermylene as a Building Block to Construct a Cyclic Octagermylene”: Y.-T. Wey, F.-S. Yang, H.-C. Yu, T.-S. Kuo, Y.-C. Tsai, Angew. Chem. Int. Ed. 2017, 56, 15108; Angew. Chem. 2017, 129, 15304. (The GeI–GeI bonded digermylene can exist in an eclipsed conformation and serve as a building block to construct a cyclic oligogermylene.) Volume57, Issue30July 20, 2018Pages 9215-9215 ReferencesRelatedInformation

Identifying Strong Covalent Interactions with Pauli Energy.

As one of the most widely used chemical concepts whose origin can be traced back to Lewis theory of bonding a century ago, a covalent bond involves sharing one or more pairs of electrons between atoms. A strong covalent interaction (SCI) is such a covalent bond that two or more electron pairs are shared, yielding a double, triple, quadruple, or even higher bond order. Despite its ubiquity and usefulness, a robust and generally applicable approach to accurately identify strong covalent interactions and determine their bond orders is still lacking. In this work, an SCI index is proposed from density functional theory using the Pauli energy, which is the contribution of the Pauli exclusion principle to the kinetic energy. Illustrative examples from organic, inorganic, and organometallic systems were provided. Its close relationship with the electron localization function (ELF) was elucidated. Both ELF and SCI generate similar results. Two complexes with a quintuple metal-metal bond have been confirmed. A stronger than quintuple bond has been showcased. This work should provide a robust approach to determine bond orders for strong covalent interactions in complex systems, pinpoint the physiochemical origin of strong covalent interactions, and rationalize the usefulness of both SCI and ELF. These tools should be able to be applied to other systems in different fields to effectively appreciate strong covalent interactions.

U2@ I h(7)-C80: Crystallographic Characterization of a Long-Sought Dimetallic Actinide Endohedral Fullerene.

The nature of actinide-actinide bonds has attracted considerable attention for a long time, especially since recent theoretical studies suggest that triple and up to quintuple bonds should be possible, but little is known experimentally. Actinide-actinide bonds inside fullerene cages have also been proposed, but their existence has been debated intensively by theoreticians. Despite all the theoretical arguments, critical experimental data for a dimetallic actinide endohedral fullerene have never been obtained. Herein, we report the synthesis and isolation of a dimetallic actinide endohedral metallofullerene (EMF), U2@C80. This compound was fully characterized by mass spectrometry, single crystal X-ray crystallography, UV-vis-NIR spectroscopy, Raman spectroscopy, cyclic voltammetry, and X-ray absorption spectroscopy (XAS). The single crystal X-ray crystallographic analysis unambiguously assigned the molecular structure to U2@ I h(7)-C80. In particular, the crystallographic data revealed that the U-U distance is within the range of 3.46-3.79 Å, which is shorter than the 3.9 Å previously predicted for an elongated weak U-U bond inside the C80 cage. The XAS results reveal that the formal charge of the U atoms trapped inside the fullerene cage is +3, which agrees with the computational and crystallographic studies that assign a hexaanionic carbon cage, ( I h-C80)6-. Theoretical studies confirm the presence of a U-U bonding interaction and suggest that the weak U-U bond in U2@ I h(7)-C80 is strengthened upon reduction and weakened upon oxidation. The comprehensive characterization of U2@ I h(7)-C80 and the overall agreement between the experimental data and theoretical investigations provide experimental proof and deeper understanding for actinide metal-metal bonding interactions inside a fullerene cage.

Reversible Cleavage/Formation of the Chromium–Chromium Quintuple Bond in the Highly Regioselective Alkyne Cyclotrimerization

AbstractHerein we report the employment of the quintuply bonded dichromium amidinates [Cr{κ2‐HC(N‐2,6‐iPr2C6H3)(N‐2,6‐R2C6H3)}]2 (R=iPr (1), Me (7)) as catalysts to mediate the [2+2+2] cyclotrimerization of terminal alkynes giving 1,3,5‐trisubstituted benzenes. During the catalysis, the ultrashort Cr−Cr quintuple bond underwent reversible cleavage/formation, corroborated by the characterization of two inverted arene sandwich dichromium complexes (μ‐η6:η6‐1,3,5‐(Me3Si)3C6H3)[Cr{κ2‐HC(N‐2,6‐iPr2C6H3)(N‐2,6‐R2C6H3)}]2 (R=iPr (5), Me (8)). In the presence of σ donors, such as THF and 2,4,6‐Me3C6H2CN, the bridging arene 1,3,5‐(Me3Si)3C6H3 in 5 and 8 was extruded and 1 and 7 were regenerated. Theoretical calculations were employed to disclose the reaction pathways of these highly regioselective [2+2+2] cylcotrimerization reactions of terminal alkynes.

Reversible Cleavage/Formation of the Chromium-Chromium Quintuple Bond in the Highly Regioselective Alkyne Cyclotrimerization.

Herein we report the employment of the quintuply bonded dichromium amidinates [Cr{κ2 -HC(N-2,6-i Pr2 C6 H3 )(N-2,6-R2 C6 H3 )}]2 (R=iPr (1), Me (7)) as catalysts to mediate the [2+2+2] cyclotrimerization of terminal alkynes giving 1,3,5-trisubstituted benzenes. During the catalysis, the ultrashort Cr-Cr quintuple bond underwent reversible cleavage/formation, corroborated by the characterization of two inverted arene sandwich dichromium complexes (μ-η6 :η6 -1,3,5-(Me3 Si)3 C6 H3 )[Cr{κ2 -HC(N-2,6-i Pr2 C6 H3 )(N-2,6-R2 C6 H3 )}]2 (R=i Pr (5), Me (8)). In the presence of σ donors, such as THF and 2,4,6-Me3 C6 H2 CN, the bridging arene 1,3,5-(Me3 Si)3 C6 H3 in 5 and 8 was extruded and 1 and 7 were regenerated. Theoretical calculations were employed to disclose the reaction pathways of these highly regioselective [2+2+2] cylcotrimerization reactions of terminal alkynes.

Mo-Mo Quintuple Bond is Highly Reactive in H-H, C-H, and O-H σ-Bond Cleavages Because of the Polarized Electronic Structure in Transition State.

The recently reported high reactivity of the Mo-Mo quintuple bond of Mo2(N∧N)2 (1) {N∧N = μ-κ2-CH[N(2,6-iPr2C6H3)]2} in the H-H σ-bond cleavage was investigated. DFT calculations disclosed that the H-H σ-bond cleavage by 1 occurs with nearly no barrier to afford the cis-dihydride species followed by cis-trans isomerization to form the trans-dihydride product, which is consistent with the experimental result. The O-H and C-H bond cleavages by 1 were computationally predicted to occur with moderate (ΔG°⧧ = 9.0 kcal/mol) and acceptable activation energies (ΔG°⧧ = 22.5 kcal/mol), respectively, suggesting that the Mo-Mo quintuple bond can be applied to various σ-bond cleavages. In these σ-bond cleavage reactions, the charge-transfer (CTMo→XH) from the Mo-Mo quintuple bond to the X-H (X = H, C, or O) bond and that (CTXH→Mo) from the X-H bond to the Mo-Mo bond play crucial roles. Though the HOMO (dδ-MO) of 1 is at lower energy and the LUMO + 2 (dδ*-MO) of 1 is at higher energy than those of RhCl(PMe3)2 (LUMO and LUMO + 1 of 1 are not frontier MO), the H-H σ-bond cleavage by 1 more easily occurs than that by the Rh complex. Hence, the frontier MO energies are not the reason for the high reactivity of 1. The high reactivity of 1 arises from the polarization of dδ-type MOs of the Mo-Mo quintuple bond in the transition state. Such a polarized electronic structure enhances the bonding overlap between the dδ-MO of the Mo-Mo bond and the σ*-antibonding MO of the X-H bond to facilitate the CTMo→XH and reduce the exchange repulsion between the Mo-Mo bond and the X-H bond. This polarized electronic structure of the transition state is similar to that of a frustrated Lewis pair. The easy polarization of the dδ-type MOs is one of the advantages of the metal-metal multiple bond, because such polarization is impossible in the mononuclear metal complex.

Metal-metal multiple bonds with “half-bond” components in paramagnetic organometallics of f-block metals: Cyclopentadienyluranium carbonyls as molecular relatives of diuranium

The experimentally observed reductive CO coupling in organouranium systems observed by Cloke and co-workers makes of interest the exploration of the structures and thermochemistry of simple Cp2U2(CO)n (n = 5, 4, 3, 2) derivatives. In this connection, the low-energy Cp2U2(CO)n (n = 2, 3, 4) structures contain two to four bridging η2-μ-CO groups supplemented, in some cases, by one or two terminal CO groups. No examples of CO coupling to form C2O2 ligands are found in any of these Cp2U2(CO)n structures in contrast to the previously studied Cp2Th2(CO)4 system in which CO coupling to form C2O2 ligands is observed. The retention of uranium valence electrons in low-energy Cp2U2(CO)n (n = 3, 4) structures, even after partial donation of uranium electrons to reduce Cp to Cp– and CO to CO2-, leads to a rich and complicated variety of UU bonding modes as well as spin states from singlet to quintet. Of particular interest are uranium-uranium multiple bonds containing multiple single electron half-bond components in triplet and quintet spin state Cp2U2(CO)n structures. The formal uranium-uranium multiple bonds in such Cp2U2(CO)n structures exhibit some of the features of the quintuple bond of diuranium, U2, in which a typical σ + 2π triple bond similar to the CC triple bond of acetylene is supplemented by no less than four separate one-electron half-bonds. Thus the UU bonds in the lowest energy Cp2U2(CO)n (n = 2, 3) structures can be interpreted as formal triple bonds of various types with unusually short bond distances of ∼2.5 Å and Wiberg bond indices of ∼3.

Cleavage of P-X bond of phosphines by a dichromium complex containing a quintuple bond

The reactivity of formally quintuply bonded bimetallic aminopyridinato chromium complex (1) towards various phosphines was investigated. Oxidative additions were observed in which the CrCr quintuple bond is inserted into P-X bond of the used phosphines to give the corresponding [Ap2Cr2(μ-PR2)(μ-X)] complexes (2a-2c) {where Ap=(2,6-diisopropylphenyl)-[6-(2,6-dimethylphenyl)pyridin-2-yl]amide, 2a: R = C6H5, X = H; 2b: R = C6H5, X = Cl; 2c: R = C2H5, X = Cl)}. The synthesized compounds are diamagnetic and 2a and 2c have been characterized by X-ray crystal structure analysis. The structures indicate a reduction of the bond order of the Cr2 moiety to four. The bimetallic CrII complexes 2a and 2c feature metal-metal distances of 1.856(11) and 1.867(7) Å, respectively.

The accurate wavefunction of the active space of the rhenium dimer resolved using the ab initio Brueckner coupled-cluster method

Rhenium is a unique metal in the 5d-series of transition metals having the highest boiling point in the periodic table. It is also known to exist in poly-coordinated states with other rhenium atoms. Based on the existence of strikingly unusual states of elements in astrophysical bodies of nebulae, interstellar debris, exoplanets and other part of the universe, a set of ab initio calculations of the rhenium dimer has been conducted to provide detailed description of its molecular properties that are applicable to the astrochemical research. Ab initio calculations and NBO analysis revealed that rhenium forms quintuple bond in its diatomic state and that it displays preferred state of triplet configuration with high-lying electrons. Calculations also revealed that the two states of rhenium dimer vary in their bonding nature. The singlet spin space is composed of five single bonds, while the triplet state comprises four bonds and two additional lone pairs. Interestingly, while these two states vary in subdivision of electrons at the highest d-level, they share the same frequencies while having different zero-point energies. The calculations reveal intrinsic synergy between the atoms composed of natural bond orbitals, the bonding pattern and the thermochemical properties of Re2, all features being of significant importance to physical and chemical sciences.

ChemInform Abstract: Configuring Bonds Between First‐Row Transition Metals

AbstractReview: 47 refs.