Transition Metal Fragments Research Articles

Affecting Charges and Structures of {Bi6} Architectures by 12-Electron Transition Metal Fragments.

Molecules based on polyatomic bismuth substructures are currently attracting a lot of attention owing to this heavy and essentially non-toxic element's uncommon chemical and physical properties, which include unprecedented bonding properties. Hexaatomic {Bi6} substructures that underly more complex cluster structures were recently reported to adopt different structures or exhibit different structural details as a consequence of the charge of the {Bi6} unit. This leads to either crown-shaped cycles for a nominal Bi66- or differently distorted trigonal prisms for compositions close to Bi62-. It was predicted by quantum chemistry that Bi64- should adopt a distinctly distorted boat-like shape, yet a corresponding compound has remained elusive. Here, we report a proof of this assumption by the synthesis and isolation of [K(crypt-222)]2[Bi6{Zn(hmds)}2]∙1.5THF (1), comprising a bimetallic [Bi6{Zn(hmds)}2]2- cluster that fulfils the prediction for the geometric and electronic structure of the missing link (crypt-222 = 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo-[8.8.8]hexa-cosane, hmds = hexamethyldisilazanid). A detailed quantum chemical study shows how the nature of Lewis-acidic transition metal complexes - in particular, 12-electron fragments - control and fine-tune the resulting {Bi6} architectures in accordance with the degree of electron-withdrawal from the polybismuthide core.

A Phosphorus-Centred, Zirconocene-Bridged Tetraradical: Synthesis, Structure and Application as Molecular Double Switch.

Biradicals are important intermediates in the formation and breaking of a chemical bond. Their use as molecular switches is of particular interest. Much less is known about tetraradicals, which can, for example, consist of two biradical(oid) units. Here we report the synthesis of the first persistent phosphorus-centred tetraradical bound to a transition metal fragment. Starting from a zirconocene complex, rac-(ebthi)ZrCl2 (rac-(ebthi)=1,2-ethylene-1,10-bis(η5-tetrahydroindenyl), two cyclo-1,3-diphospha-pentane-1,3-diyls were successfully introduced, which finally led to the isolation of a deep green zirconcene-bridged bis(biradicaloid) complex (5) that can act as a double molecular switch. Under the influence of light (570 nm), this tetraradical forms a transannular bond in each of the two five-membered biradical units, leading to the formation of housane 5 h. Upon irradiation at 415 nm, the reverse reaction is observed, fully recovering tetraradical 5. Through single-crystal-to-single-crystal transformation, both stable species of the molecular switch could be structurally characterised using SCXRD. The switching under the influence of light and the activation of molecular hydrogen were analysed in solution using NMR and UV spectroscopy. It was found that the addition of one or two equivalents of molecular hydrogen can be switched on and off by light.

Isolation and Crystallographic Characterization of an Octavalent Co2O2 Diamond Core.

High-valent cobalt oxides play a pivotal role in alternative energy technology as catalysts for water splitting and as cathodes in lithium-ion batteries. Despite this importance, the properties governing the stability of high-valent cobalt oxides and specifically possible oxygen evolution pathways are not clear. One root of this limited understanding is the scarcity of high-valent Co(IV)-containing model complexes; there are no reports of stable, well-defined complexes with multiple Co(IV) centers. Here, an oxidatively robust fluorinated ligand scaffold enables the isolation and crystallographic characterization of a Co(IV)2-bis-μ-oxo complex. This complex is remarkably stable, in stark contrast with previously reported Co(IV)2 species that are highly reactive, which demonstrates that oxy-Co(IV)2 species are not necessarily unstable with respect to oxygen evolution. This example underscores a new design strategy for highly oxidizing transition-metal fragments and provides detailed data on a previously inaccessible chemical unit of relevance to O-O bond formation and oxygen evolution.

Germaborene reactivity study - addition of carbon nucleophiles, cycloaddition reactions, coordination chemistry.

MeNHC substituted germaborenium cation 2 was synthesized directly in reaction of bromo-substituted germaborene 1b with MeNHC. The adamantyl isonitrile substituted germaborenium cation 4 was obtained stepwise: substitution of the chloride atom against adamantyl isonitrile at the B-Cl unit in 1a, simultaneous migration of the chloride to the germanium atom followed by chloride abstraction using Na[BArF 4] gives the germaborenium cation 4. Substitution of the bromide atom in 1b against carbon monoxide followed by bromide abstraction using Ag[Al(OtBuF)4] leads to compound 6 exhibiting a B[double bond, length as m-dash]C double bond substituted at the boron atom by a germylium cation. Treating the germaborene [Ge[double bond, length as m-dash]B-Ph] (1c) with selenium, a cycloaddition product 7 was characterised featuring a GeBSe heterocycle. Carbon dioxide reacts with 1b to give a four membered ring molecule 8 as the product of a B-C and Ge-O bond formation. In reaction of 1b with dimethylbutadiene, a product 9 of a [2 + 4] cycloaddition was isolated. Transition metal fragments [Fe(CO)4 (10), CuBr (11), AuCl (12)] show coordination at the germaborene double bond. Molecular structures of the germaborene coordination compounds 10-12 are presented and the ligand properties are discussed. After treating the germaborene [Ge[double bond, length as m-dash]B-Br] (1b) with [Cp*Al]4, insertion of a Cp*Al moiety into the B-Br bond was found (13).

Reactions of (mesityl)n(methyl)2-nsilylene complexes with pyridine-N-oxide (n = 1 and 0): formation of silanone complexes and a disiloxanyloxy complex.

Silanones (OSiR2), a heavier congener of ketones (R2CO), are highly reactive species that are readily converted to oligomeric siloxane (O-SiR2)n. Coordination of silanones to the transition-metal fragments to afford silanone-coordinated complexes is a reliable silanone stabilization method. Recently, our group reported the synthesis, structures, and reactivity of dimesityl-substituted silanone complexes Cp*(OC)2M{OSiMes2(L)}(SiMe3) (M = W, Mo, L: Lewis base, Cp*: η5-C5Me5, Mes: 2,4,6-Me3C6H2). Herein, to investigate the effect of substituents on the silicon atom during the formation of a silanone complex, we demonstrated the use of Mes and smaller Me groups. As a result, the formation of Mes(Me)-substituted silanone molybdenum complex Cp*(OC)2Mo{OSiMes(Me)(py)}(SiMe3) (5b, py: pyridine) was suggested, the silanone tungsten complex Cp*(OC)2W{OSiMes(Me)(DMAP)}(SiMe3) (4a, DMAP: 4-(dimethylamino)pyridine) was obtained, and a dimethyl-substituted disiloxanyloxy(dioxo) complex Cp*(O)2W(OSiMe2OSiMe3) (9) was formed. The reaction of 4a with PMe3 proceeded via the elimination of DMAP and migration of the SiMe3 group to the oxygen atom of the silanone ligand to afford Cp*(OC)2W(SiMes(Me)OSiMe3)(PMe3) (11a). The Mo complex Cp*(OC)2Mo(SiMes(Me)OSiMe3)(PMe3) (11b) was produced by the reaction of Cp*(OC)2Mo{SiMes(Me)}(SiMe3) (7b) with pyridine-N-oxide in the presence of PMe3.

Electroactive Prussian Blue Analogues/TiO2 Nanocomposites Obtained through SILAR Assembly in Mesoporous Nanoarchitectures

AbstractThe preparation of nanomaterials for energy applications such as intercalation batteries and materials that can act as substrates for water oxidation is a subject of major interest nowadays. In this work, we report the deposition of Prussian blue (PB) and its cobalt analogue (CoPBA) on mesoporous titania thin films (MTTF) using the successive ionic layer adsorption reaction (SILAR) technique under soft conditions. A bifunctional ligand, 1,10‐phenanthroline‐5,6‐dione (pd), was used to functionalize the titania surface and promote the growth of PB and CoPBA. The resulting PB@MTTF and CoPBA@MTTF nanocomposites were characterized using several techniques and it was determined that PB and CoPBA grow in a controlled and sequential manner, maintaining the mesoporous architecture. Both PB@MTTF and CoPBA@MTTF demonstrated very good electroactive properties, while CoPBA@MTTF exhibited water oxidation capabilities. The flexibility of this PBA@MTTF platform allows the incorporation of any labile transition metal ion or fragment into the structure of the coordination polymer embedded into a mesoporous matrix, opening the door for (photo)electrochemical devices and catalysts.

Half‐Sandwich, Bent‐Sandwich and Triple‐Decker Molybdenum Complexes of S2N2 – Fluxionality and Metal‐Metal Bond

AbstractThe instability of the π‐complexes of electron‐rich inorganic aromatics with transition metal fragments, contrary to their conventional aromatic analogues, was investigated by taking the four‐membered 6π‐electron S2N2. Our theoretical investigation based on fragment molecular orbitals and Energy Decomposition Analysis with Natural Orbitals for Chemical Valence (EDA‐NOCV) on the bonding nature of different types of π‐complexes of S2N2 viz. half‐sandwich, bent‐sandwich and triple‐decker type complexes with molybdenum fragment reveals that S2N2 can potentially act as a six π‐electron donor. However, due to the lower energy π* MOs the π‐back donation from metal fragment is stronger than the π‐donation, which might lead to weaking of the overall ring structure and low dissociation energy. The dissociation energy for dissociation of one S2N2 ring increases with the increasing number of S2N2 in the complex. The smaller size of the ring leads to fluxional behaviour in order to attain orbital compatibility between the π‐MOs and the metal orbitals. Also, the triple decker complex depicts an unsymmetric middle deck, where the middle S2N2 ring has been fragmented into two SN units along with a Mo−Mo bond. The higher dissociation energy of triple‐decker complexes can be corroborated well with the report of an isoelectronic triple‐decker complex [Mo2Te12]6+.

Four-Membered Bimetallic Carbon Complex [(MCp*)2(μ-NPh)(μ-C)] (M = Fe, Ru, Os) - An Ambiphilic Carbene with Lone Pair and σ-Hole Reactivity.

Singlet carbenes are extensively studied compounds capable of electrophilic, nucleophilic or ambiphillic behaviour. The ambiphilic reactivity of singlet carbenes have been conventionally observed in orthogonal planes. Here, we report a detailed bonding and reactivity study of a homobimetallic carbon complex [(MCp*)2(μ-NPh)(μ-C)] (1M, M = Fe, Ru, Os) that shows ambiphilicity in the same direction. The structure of this complex can be considered as two fused three-membered M-C-M and M-N-M rings. The bonding analysis suggests that these 17VE homobimetallic complexes have one formal M-M bond with a bridging carbene centre featuring a high lying spn-hybridised lone pair. Accordingly, the carbene centre shows high proton affinity and act as a good 2e- donor to Lewis acids and transition metal fragment. Apart from the transition metal non-bonding electrons, the π-framework of M-C-M and M-N-M arms can be best described as 3c-2e- bonds. The two transition metals in the four-membered skeleton generate many low-lying, virtual orbitals. These low-lying virtual orbitals induces electron excitation from the spn-hybrid orbital in presence of H- and other 2e- donor ligands such as PMe3, NHC and CO. Hence, the spn-hybrid lone pair orbital shows σ-hole reactivity in presence of Lewis bases.

Pyridine‐Stabilized Cationic Silanethione Tungsten Complexes: Synthesis, Structures, and Reactivity

AbstractSilanethione compounds, R2Si=S, have been recognized as highly reactive species. One reliable way to stabilize silanethione is its coordination to transition metal fragments to convert silanethione‐coordinated transition metal complexes. Herein, we report the synthesis, structure, and reactivity of a second cationic silanethione tungsten complex [Cp*(OC)3W{S=SiR2(py)}]TFPB (R=Me (5 a), Ph (5 b), Cp*: η5‐C5Me5, py: pyridine, and TFPB−: [B{3,5‐(CF3)2C6H3}4]−). Complex 5 was obtained by H− abstraction from the Si atom in the corresponding silylsulfanyl complex Cp*(OC)3W(SSiR2H) (4) with Ph3CTFPB, followed by the addition of pyridine. The reaction of 5 with PhNCS and PMe3 produced [Cp*(OC)3W{SSiR2N(Ph)C(PMe3)2}]TFPB (R=Me (6 a), Ph (6 b)) via the elimination of pyridine and the addition of the 1,3‐dipolar species PhNC(PMe3)2 (A) to the Si atom.

Dative quadruple bonds between d10 transition metals and beryllium in BeM(PMe3)2 and BeM(CO)2 (M = Ni, Pd, and Pt) complexes: Transition metal fragments as six‐electron donor and two‐electron acceptor

AbstractThe structure, chemical bonding, and reactivity of neutral 16 valence electrons (VE) transition metal complexes of beryllium, BeM(PMe3)2 (1M‐Be) and BeM(CO)2 (2M‐Be, M = Ni, Pd, and Pt) were studied. The molecular orbital and EDA‐NOCV analysis suggest dative quadruple bonds between the transition metal and beryllium, viz., one Be→M σ bond, one Be←M σ bond, and two Be←M π bonds. The strength of these bonding interactions varies based on the ligands coordinated to the transition metal. The Be←M σ bond is stronger than the Be→M σ bond when the ligand is PMe3, whereas the reverse order is observed when the ligand is CO. This is attributed to the higher π acceptor strength of CO as compared to PMe3. Since these complexes have M–Be dative quadruple bonds, the beryllium center is susceptible to ambiphilic reactivity, as indicated by high proton and hydride affinity values.

Synthesis, structure and properties of coordination complexes of tin(ii) phthalocyanine and naphthalocyanine with transition metal fragments

Tin(ii) phthalocyanine and naphthalocyanine form stable M–Sn bonds yielding coordination complexes with transition metal fragments. In this review, we discuss the syntheses, structures and properties of such complexes.

η6 -Metalated Aryl Iodides in Diels-Alder Cycloaddition Reactions: Mode of Activation and Catalysis.

The potential application of η6 -metalated aryl iodides as organocatalyst has been explored by means of computational methods. It is found that the enhanced halogen bonding donor ability of these species, in comparison with their demetalated counterparts, translates into a significant acceleration of the Diels-Alder cycloaddition reaction involving cyclohexadiene and methyl vinyl ketone. The factors behind this acceleration, the endo-exo selectivity of the process and the influence of the nature of the transition metal fragment in the activity of these species are quantitatively explored in detail by means of the combination of the Activation Strain Model of reaction and the Energy Decomposition Analysis methods.

Synthesis and Characterization of Ir-(κ2-NSi) Species Active toward the Solventless Hydrolysis of HSiMe(OSiMe3)2.

The reaction of [IrH(Cl)(κ2-NSitBu2)(coe)] (1) with 1 equiv of PCy3 (or PHtBu2) gives the species [IrH(Cl)(κ2-NSitBu2)(L)] (L = PCy3, 2a; PHtBu2, 2b), which reacts with 1 equiv of AgOTf to afford [IrH(OTf)(κ2-NSitBu2)(L)] (L = PCy3, 3a and PHtBu2, 3b). Complexes 2a, 2b, 3a, and 3b have been characterized by means of NMR spectroscopy and HR-MS. The solid-state structures of complexes 2a, 2b, and 3a have been determined by X-ray diffraction studies. The reversible coordination of water to 3a, 3b, and 4 to afford the corresponding adduct [IrH(OTf)(κ2-NSitBu2)(L)(H2O)] (L = PCy3, 3a-H2O; PHtBu2, 3b-H2O; coe, 4-H2O) has been demonstrated spectroscopically by NMR studies. The structure of complexes 3b-H2O and 4-H2O have been determined by X-ray diffraction studies. Computational analyses of the interaction between neutral [NSitBu2]• and [Ir(H)L(X)]• fragments in Ir-NSitBu2 species confirm the electron-sharing nature of the Ir-Si bond and the significant role of electrostatics in the interaction between the transition metal fragment and the κ2-NSitBu2 ligand. The activity of Ir-(κ2-NSitBu2) species as catalysts for the hydrolysis of HSiMe(OSiMe3)2 depends on the nature of the ancillary ligands. Thus, while the triflate derivatives are active, the related chloride species show no activity. The best catalytic performance has been obtained when using complexes 3a, with triflate and PCy3 ligands, as a catalyst precursor, which allows the selective obtention of the corresponding silanol.

Kenneth Wade. 13 October 1932—16 March 2014

Much of Ken Wade's scientific career was devoted to developing and exploiting the chemistries of boron, aluminium, gallium and indium (the Group 13 elements). He made significant contributions to both experimental and theoretical aspects of the subject and was a highly regarded teacher and attentive research supervisor. Ken was a modest and self-critical man who had a rare ability to recognize patterns in large chemical and molecular structure data sets and express the resulting generalizations in the form of simple rules that experimental chemists could appreciate and use to predict new compounds. Ken was fascinated by the structures of cluster compounds that are based on regular polyhedral shapes. Cluster molecules generally contain groups of metal atoms linked by metal–metal bonds and located on one or more spherical shells. Since the 1960s they have attracted the attention of both academic and industrial chemists. Understanding and predicting their three-dimensional shapes raised a significant intellectual challenge for chemists. The clusters also attracted attention because they occupy an intermediate position between co-ordination compounds based on a single metal atom and the parent metal, which has an infinite number of linked metal atoms. This provided chemists with a unique opportunity to explore the evolution of their electronic and chemical properties as the cluster size increases. Ken was the first to recognize the electronic relationships connecting closo- , nido- , arachno- and hypho - clusters. These clusters are inter-related by the successive removal of vertices from a regular closo- deltahedron, i.e. a polyhedron with all the faces triangular. His ability to connect the structures of these molecules to the number of valence electrons involved in skeletal bonding represented a significant contribution to chemical bonding theories. Ken communicated his conclusions in very clearly written papers and books. This made the complexities of cluster chemistry amenable to many and especially those who did not have a strong background in quantum chemistry. The skeletal electron counting rules, or Wade's Rules, which Ken pioneered, are now very much part of the fabric of modern cluster chemistry and form an important component of modern undergraduate inorganic chemistry courses. Wade's Rules may be applied to main group and transition metal carbonyl clusters as well as clusters containing both main group and transition metal fragments. Besides providing an accessible entry into cluster chemistry for students, the rules have been used creatively by many leading synthetic chemists to discover new classes of compounds.

Stabilizing a 20-Electron Metallaazulyne by Aromaticity.

The 18-electron rule states that metal complexes with 18 valence electron metal centers are thermodynamically stable because nine valence orbitals of transition metals including one s orbital, three p orbitals, and five d orbitals can collectively accommodate 18 electrons, achieving the same electron configuration as the noble gas in the period. Thus, 20-electron compounds are extremely rare due to a violation of such a rule. Here, we demonstrate a 20-electron metallaazulyne via density functional theory calculations stabilized by aromaticity, which was supported by various aromaticity indices including nucleus-independent chemical shift, anisotropy of the induced current density, the isochemical shielding surface, and electron density of delocalized bonds. Interestingly, when a transition metal fragment is first introduced into the aromatic azulyne molecule, the resulting osmaazulyne becomes antiaromatic, in sharp contrast to the previous transformation from pentalyne to metallapentalyne. More interestingly, when osmaazulyne is reduced by two electrons, the resulting 20e osmaazulyne becomes aromatic. Our findings highlight an important application of aromaticity in stabilizing 20e species, inviting experimental verification.

Back Cover: Atom Swapping on Aromatic Rings: Conversion from Phosphinine Pincer Metal Complexes to Metallabenzenes Triggered by O2 Oxidation (Angew. Chem. Int. Ed. 21/2022)

An atom-swapping method for the synthesis of metallabenzenes, where a phosphorus atom on phosphinine is replaced by a transition-metal fragment, is reported by Kyoko Nozaki and co-workers in their Research Article (e202117096). Swapping of the P atom for Rh or Ir proceeded by oxidation of the phosphorus atom and subsequent reductive cleavage of the C−P bond of the phosphinine ring.

Atom Swapping on Aromatic Rings: Conversion from Phosphinine Pincer Metal Complexes to Metallabenzenes Triggered by O2 Oxidation

AbstractHerein, we report a novel method for the synthesis of metallabenzenes by swapping the phosphorus atom in an aromatic phosphinine ring with transition metal fragments. The oxidation of a phosphine‐phosphinine‐phosphine pincer iridium complex by O2 triggered the replacement of the phosphorus atom of the phosphinine ring by an iridium fragment to afford iridabenzene. Dianionic rhodabenzene was also synthesized from a phosphinine rhodium complex by oxidation of the phosphorus atom, followed by subsequent reduction using metallic potassium. The aromaticity of the newly synthesized irida‐ and rhoda‐benzenes was evaluated both experimentally and theoretically.

Atom Swapping on Aromatic Rings: Conversion from Phosphinine Pincer Metal Complexes to Metallabenzenes Triggered by O2 Oxidation.

Herein, we report a novel method for the synthesis of metallabenzenes by swapping the phosphorus atom in an aromatic phosphinine ring with transition metal fragments. The oxidation of a phosphine-phosphinine-phosphine pincer iridium complex by O2 triggered the replacement of the phosphorus atom of the phosphinine ring by an iridium fragment to afford iridabenzene. Dianionic rhodabenzene was also synthesized from a phosphinine rhodium complex by oxidation of the phosphorus atom, followed by subsequent reduction using metallic potassium. The aromaticity of the newly synthesized irida- and rhoda-benzenes was evaluated both experimentally and theoretically.

Synthesis and structure of a pyridine-stabilized silanone molybdenum complex and its reactions with PMe3 and acetone.

Silanones (OSiR2) are highly reactive species that readily convert to oligomeric siloxane (O-SiR2)n. The coordination of silanones to transition metal fragments to afford silanone-coordinated complexes is a reliable silanone stabilization method. Herein, a pyridine-stabilized silanone molybdenum complex Cp*(OC)2Mo{OSiMes2(py)}(SiMe3) (2b, Cp*: η5-C5Me5, Mes: 2,4,6-Me3C6H2, and py: pyridine) was synthesized by reacting the silyl(silylene) complex Cp*(OC)2Mo(SiMes2)(SiMe3) (4b) with pyridine-N-oxide in pyridine. X-ray crystal structure analysis revealed that the geometry of complex 2b is similar to those of the previously synthesized DMAP-stabilized analogue Cp*(OC)2Mo{OSiMes2(DMAP)}(SiMe3) (2a, DMAP: 4-(dimethylamino)pyridine). The SiO and Mo-O bond distances in 2b are similar to those observed in 2a, but the N-Si coordination bond of 2b is slightly longer (approximately 0.05 Å) than that of 2a, indicating weaker pyridine coordination than that of DMAP. The reaction of 2a with excess PMe3 in C6D6 at room temperature for 28 h afforded Cp*(OC)2Mo(PMe3)(SiMe3) (5c) in a 43% NMR yield. In contrast, reacting 2b with excess PMe3 in C6D6 at room temperature for 9 h afforded 5c and the five-membered metallacyclic carbene complex Cp*(OC)Mo(C(SiMe3)OSiMes2O)(PMe3) (6) in 10% and 41% NMR yields, respectively. The reactions of pyridine-stabilized silanone complexes Cp*(OC)2M(OSiMes2(py))(SiMe3) (M = Mo (2b) and W (1b)) with acetone proceeded via pyridine elimination, coordination of acetone to the Si center in the silanone ligand, and elimination of HSiMe3 to give Cp*(OC)2M{OSiMes2OC(Me)CH2} (M = Mo (8) and W (9)) in high yields.

Releasing Antiaromaticity in Metal-Bridgehead Naphthalene.

As a fundamental chemical property, aromaticity guides the synthesis of novel structures and materials. Replacing the carbon moieties of aromatic hydrocarbons with transition metal fragments is a promising strategy to synthesize intriguing organometallic counterparts with a similar aromaticity to their organic parents. However, since antiaromaticity will endow compound instability, it is a great challenge to obtain an antiaromatic organometallic counterpart based on such transition metal replacement in aromatic hydrocarbons. Here, we report an efficient aromaticity transformation on aromatic naphthalene through the bridgehead replacement of an osmium fragment, leading to the unprecedented synthesis of metal-bridgehead naphthalene featuring a highly twisted structure as confirmed by X-ray crystallography characterization. Such a twisted conformation works together with its phosphonium substituents to release the antiaromaticity in the planar conformation of the metal-bridgehead naphthalene. Our findings prove the bridgehead involvement of transition metals in unexpected aromaticity modifications and open an avenue for novel metal-bridgehead complexes.