Synthesis of a Tungsten–Silylyne Complex via Stepwise Proton and Hydride Abstraction from a Hydrido Hydrosilylene Complex

Metal-silicon triple bonds: reactivity of the silylidyne complexes [Cp*(CO)2M[triple bond, length as m-dash]Si-Tbb] (M = Cr - W)

The different reactivity pattern of M[triple bond, length as m-dash]Si and M[triple bond, length as m-dash]C bonds (M = transition metal) is illustrated by a series of reactions of the silylidyne complexes [Cp*(CO)2M[triple bond, length as m-dash]Si-Tbb] (1-M) (M = Cr - W; Cp* = η 5-pentamethylcyclopentadienyl; Tbb = 4-tert-butyl-2,6-bis(bis(trimethylsilyl)methyl)phenyl)). Complexes 1-M were obtained selectively from Li[Cp*M(CO)3] and the 1,2-dibromodisilene (E)-Tbb(Br)Si[double bond, length as m-dash]Si(Br)Tbb. The reaction of 1-Mo and 1-W with two equivalents of mesityl isocyanate leads selectively to complex 2-Mo and 2-W, respectively, featuring a novel κ 2 O,O-imidocarbonatosilyl ligand. Ring opening of ethyloxirane occurs rapidly with 1-Mo and leads to the hydrido-enolatosilylidene complex 3-Mo illustrating the Si-centered electrophilicity of the silylidyne complex. Trimethylsilyldiazomethane induces a cleavage of the Mo[triple bond, length as m-dash]Si bond of 1-Mo after a rapid double [2 + 1] cycloaddition of the terminal N-atom, resulting in the first silaamidinato complex 4-Mo. In comparison, the reaction of 1-Mo with mesityl azide gives, after N2 elimination, the Mo-silaiminoacyl complex 5-Mo. All compounds were fully characterized and the isomerism and dynamics of 3-Mo in solution were analysed by a combination of spectroscopic and quantum-chemical studies.

Transition Metal Parent Alumylene Complexes: Synthesis, Structures, and XPS Characterization of Aluminum Oxidation State

The first isolation and characterization of transition metal complexes with the parent Al(I)-H unit were achieved in base-stabilized forms. W and Fe complexes, Cp*(CO)n(H)M←:AlH(NHC)2 (NHC = N-heterocyclic carbene, n = 1 or 2), were synthesized in 43-63% yields by the one-step reaction of Cp*M(CO)n(py)Me with H3Al·NHC. The characterization included 1H and 27Al nuclear magnetic resonance (NMR), and infrared (IR) spectroscopic analysis, as well as DFT calculations, which revealed the extremely strong σ-donating ability of the :AlH(NHC)2 ligand, and the highly polarized M(δ-)←:Al(δ+) coordination bonds. The monovalent oxidation state of the Al center of these complexes was confirmed by X-ray photoelectron spectroscopy (XPS). The hydroalumination of carbodiimide and the reduction of CO2 to CO were also demonstrated.

Neutral Chromium Complex with a Cr≡Si Triple Bond: Synthesis and Photoinduced H-H and Benzene C-H Bond Activation

A neutral silylyne complex with a Cr≡Si triple bond was prepared by dehydrogenation of a chromium silylene complex with Cr-H and Si-H bonds, and was isolated as monomeric crystals, unlike dimeric forms of its tungsten and molybdenum congeners. The strong Cr(δ-)-Si(δ+) bond polarity was revealed by the reaction with MeOH and DFT calculations. The chromium silylyne complex reacted with H2 under LED (365 nm) irradiation to reproduce the precursor silylene complex with a (H)Cr=Si(H) moiety, as a result of 1,2-H-H addition across the Cr≡Si triple bond. Similarly, the chromium silylyne complex reacted with benzene under irradiation to afford an 1,2-addition product with a (H)Cr=Si(Ph) moiety, via benzene C-H bond activation accompanied by Si-C bond forming.

Reactivity Analysis of the [2 + 2] Cycloaddition between Group-6 ≡ Group-14 Triple-Bonded Complexes and Acetylene: Insights from Theoretical Studies

Theoretical examinations of reactivity for the formal [2 + 2] cycloaddition of Me-C≡C-Ph to Group-6(G6)≡Group-14(G14) triple-bonded organometallic complexes have been carried out using the M06-2X-D3/def2-TZVP level of theory. Our theoretical findings suggest that Me-C≡C-Ph can undergo adduct formation with all G6≡Si complexes, resulting in the generation of four-membered ring structures. However, among the W≡Group-14 complex reactants, only W≡Si-based, W≡Ge-based, and W≡Sn-based organometallic molecules are capable of undergoing a [2 + 2] cycloaddition reaction with Me-C≡C-Ph. Based on energy decomposition analysis, our theoretical investigations demonstrate that the bonding mechanism in such [2 + 2] cycloaddition reactions involves the creation of two dative bonds between singlet fragments (the donor-acceptor model), as opposed to two electron-sharing bonds between triplet fragments. In addition, the examinations based on the activation strain model indicate that the activation barrier of the [2 + 2] cycloaddition reaction is predominantly governed by the geometric deformation energy of the two reactants (G6≡G14-Rea and Me-C≡C-Ph). Our research using the M06-2X method shows that the barrier heights of [2 + 2] cycloaddition reactions between Me-C≡C-Ph and G6≡Si-Rea are dependent on the geometric changes occurring in both fragments during the transition states, consistent with Hammond's postulate.

Synthesis of Cobalt-Tin and -Lead Tetrylidynes-Reactivity Study of the Triple Bond

Tetrylidynes [TbbSn≡Co(PMe3 )3 ] (1 a) and [TbbPb≡Co(PMe3 )3 ] (2) (Tbb=2,6-[CH(SiMe3 )2 ]2 -4-(t-Bu)C6 H2 ) are accessed for the first time via a substitution reaction between [Na(OEt2 )][Co(PMe3 )4 ] and [Li(thf)2 ][TbbEBr2 ] (E=Sn, Pb). Following an alternative procedure the stannylidyne [Ar*Sn≡Co(PMe3 )3 ] (1 b) was synthesized by hydrogen atom abstraction using AIBN from the paramagnetic hydride complex [Ar*SnH=Co(PMe3 )3 ] (4) (AIBN=azobis(isobutyronitrile)). The stannylidyne 1 a adds two equivalents of water to yield the dihydroxide [TbbSn(OH)2 CoH2 (PMe3 )3 ] (5). In reaction of the stannylidyne 1 a with CO2 a product of a redox reaction [TbbSn(CO3 )Co(CO)(PMe3 )3 ] (6) was isolated. Protonation of the tetrylidynes occurs at the cobalt atom to give the metalla-stanna vinyl cation [TbbSn=CoH(PMe3 )3 ][BArF 4 ] (7 a) [ArF =C6 H3 -3,5-(CF3 )2 ]. The analogous germanium and tin cations [Ar*E=CoH(PMe3 )3 ][BArF 4 ] (E=Ge 9, Sn 7 b) (Ar*=C6 H3 (2,6-Trip)2 , Trip=2,4,6-C6 H2 iPr3 ) were also obtained by oxidation of the paramagnetic complexes [Ar*EH=Co(PMe3 )3 ] (E=Ge 3, Sn 4), which were synthesized by substitution of a PMe3 ligand of [Co(PMe3 )4 ] by a hydridoylene (Ar*EH) unit.

The Electronic Nature of Cationic Group 10 Ylidyne Complexes

We report a broad theoretical study on [(PMe3)3MER]+ complexes, with M = Ni, Pd, Pt, E = C, Si, Ge, Sn, Pb, and R = ArMes, Tbb, (ArMes = 2,6-dimesitylphenyl; Tbb = C6H2-2,6-[CH(SiMe3)2]2-4-tBu). A few years ago, our group succeeded in obtaining heavier homologues of cationic group 10 carbyne complexes via halide abstraction of the tetrylidene complexes [(PMe3)3M=E(X)R] (X = Cl, Br) using a halide scavenger. The electronic structure and the M-E bonds of the [(PMe3)3MER]+ complexes were analyzed utilizing quantum-chemical tools, such as the Pipek–Mezey orbital localization method, the energy decomposition analysis (EDA), and the extended-transition state method with natural orbitals of chemical valence (ETS-NOCV). The carbyne, silylidyne complexes, and the germylidyne complex [(PMe3)3NiGeArMes]+ are suggested to be tetrylidyne complexes featuring donor–acceptor metal tetrel triple bonds, which are composed of two strong π(M→E) and one weaker σ(E→M) interaction. In comparison, the complexes with M = Pd, Pt; E = Sn, Pb; and R = ArMes are best described as metallotetrylenes and exhibit considerable M−E−C bending, a strong σ(M→E) bond, weakened M−E π-components, and lone pair density at the tetrel atoms. Furthermore, bond cleavage energy (BCE) and bond dissociation energy (BDE) reveal preferred splitting into [M(PMe3)3]+ and [ER] fragments for most complex cations in the range of 293.3–618.3 kJ·mol−1 and 230.4–461.6 kJ·mol−1, respectively. Finally, an extensive study of the potential energy hypersurface varying the M−E−C angle indicates the presence of isomers with M−E−C bond angles of around 95°. Interestingly, these isomers are energetically favored for M = Pd, Pt; E = Sn, Pb; and R = ArMes over the less-bent structures by 13–29 kJ·mol−1.

Heavy metalla vinyl-cations show metal-Lewis acid cooperativity in reaction with small molecules (NH3, N2H4, H2O, H2)

Halide abstraction from tetrylidene complexes [TbbE(Br)IrH(PMe3)3] [E = Ge (1), Sn (2)] and [Ar*E(Cl)IrH(PMe3)3] gives the salts [TbbEIrH(PMe3)3][BArF 4] [E = Ge (3), Sn (4)] and [Ar*EIrH(PMe3)3][BArF 4] [E = Ge (3'), E = Sn (4')] (Tbb = 2,6-[CH(SiMe3)2]2-4-(t-Bu)C6H2, Ar* = 2,6-Trip2C6H3, Trip = 2,4,6-triisopropylphenyl). Bonding analysis suggests their most suitable description as metalla-tetrela vinyl cations with an Ir[double bond, length as m-dash]E double bond and a near linear coordination at the Ge/Sn atoms. Cationic complexes 3 and 4 oxidatively add NH3, N2H4, H2O, HCl, and H2 selectively to give: [TbbGe(NH2)IrH2(PMe3)3][BArF 4] (5), [TbbE(NHNH2)IrH2(PMe3)3][BArF 4] [E = Ge (7), Sn (8)], [TbbE(OH)IrH2(PMe3)3][BArF 4] [E = Ge (9), Sn (10)], [TbbE(Cl)IrH2(PMe3)3][BArF 4] [E = Ge (11a), Sn (12a)], [TbbGe(H)IrH2(PMe3)3][BArF 4] (13), [TbbSn(μ-H3)Ir(PMe3)3][BArF 4] (14), and [TbbSn(H)IrH2(PMe3)3][BArF 4] (15). 14 isomerizes to give 15via an 1,2-H shift reaction. Hydride addition to cation 3 gives a mixture of products [TbbGeHIrH(PMe3)3] (16) and [TbbGeIrH2(PMe3)3] (17) and a reversible 1,2-H shift between 16 and 17 was studied. In the tin case 4 the dihydride [TbbSnIrH2(PMe3)3] (18) was isolated exclusively. The PMe3 and PEt3 derivatives, 18 and [TbbSnIrH2(PEt3)3] (19), respectively, could also be synthesized in reaction of [TbbSnH2]- with the respective chloride [(R3P) n IrCl] (R = Me, n = 4; R = Et, n = 3). Reaction of complex 19 with CO gives the substitution product [TbbSnIrH2(CO)(PEt3)2] (20). Further reaction with CO results in hydrogen transfer from the iridium to the tin atom to give [TbbSnH2Ir(CO)2(PEt3)2] (21). The reversibility of this ligand induced reductive elimination transferring 20 to 21 is shown.

Hydridotetrylene [Ar*EH] (E = Ge, Sn, Pb) coordination at tantalum, tungsten, and zirconium

In a reaction of tantalocene trihydride with the low valent aryl tin cation [Ar*Sn(C₆H₆)][Al(OC{CF₃}₃)₄] (1a) the hydridostannylene complex [Cp₂TaH₂–Sn(H)Ar*][Al(OC{CF₃}₃)₄] (2) was synthesized. Hydride bridged adducts [Cp₂WH₂EAr*][Al(OC{CF₃}₃)₄] (E = Sn 3a, Pb 3b) were isolated as products of the reaction between Cp₂WH₂ and cations [Ar*E(C₆H₆)][Al(OC{CF₃}₃)₄] (E = Sn 1a, Pb 1b). The tin adduct 3a exhibits a proton migration to give the hydridostannylene complex [Cp₂W(H) Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> Sn(H)Ar*][Al(OC{CF₃}₃)₄] 4a. The cationic complex 4a is deprotonated at the tin atom in reaction with base ^MeNHC at 80 °C to give a hydrido-tungstenostannylene [Cp₂W(H)SnAr*] 5a. Reprotonation of metallostannylene 5a with acid [H(Et₂O)₂][BAr^F] provides an alternative route to hydridotetrylene coordination. Complex 4a adds hydride to give the dihydrostannyl complex [Cp₂W(H)–SnH₂Ar*] (7). With styrene 4a shows formation of a hydrostannylation product [Cp₂W(H)Sn(CH₂CH₂Ph)Ar*][Al(OC{CF₃}₃)₄] (8). The lead adduct 3b was deprotonated with ^MeNHC to give plumbylene 5b [Cp₂W(H)PbAr*]. Protonation of 5b with [H(Et₂O)₂][Al(OC{CF₃}₃)₄] at −40 °C followed by low temperature NMR spectroscopy indicates a hydridoplumbylene intermediate [Cp₂W(H)Pb(H)Ar*]⁺ (4b). Hydrido-tungstenotetrylenes of elements Ge (5c), Sn (5a) and Pb (5b) were also synthesized reacting the salt [Cp₂W(H)Li]₄ with organotetrylene halides. The metallogermylene [Cp₂W(H)GeAr*] (5c) shows an isomerization via 1,2-H-migration to give the hydridogermylene [Cp₂WGe(H)Ar*] (9), which is accelerated by addition of AIBN. 9 is at rt photochemically transferred back to 5c under light of a mercury vapor lamp. Zirconocene dihydride [Cp₂ZrH₂]₂ reacts with tin cation 1a to give the trinuclear hydridostannylene adduct 10 [({Cp₂Zr}₂{μ-H})(μ-H)₂μ-Sn(H)Ar*][Al(OC{CF₃}₃)₄]. Deprotonation of 10 was carried out using benzyl potassium to give neutral [({Cp₂Zr}₂{μ-H})(μ-H)μ-Sn(H)Ar*] (11). 11 was also obtained from the reaction of low valent tin hydride [Ar*SnH]₂ with two equivalents of [Cp₂ZrH₂]₂. The trihydride Ar*SnH₃ reacts with half of an equivalent of [Cp₂ZrH₂]₂ under evolution of hydrogen and formation of a dihydrostannyl complex 13 [Cp₂Zr(μ-H)SnH₂Ar*]₂ and with further equivalents of Ar*SnH₃ to give bis(hydridostannylene) complex [Cp₂Zr{Sn(H)Ar*}₂].

Low valent cations of tin and lead were used to form hydridotetrylene coordination compounds. The mobility of the hydrogen substituent was investigated in deprotonation equilibria as well as in 1,2-H-shift reactions.

An NHC-Mediated Metal-Free Approach towards an NHC-Coordinated Endocyclic Disilene

A convenient metal-free approach towards an N-heterocyclic carbene (NHC)-coordinated disilene 2 is described. Compound 2, featuring the disilene incorporated in cyclopolysilane framework, was obtained in good yield and characterized using NMR spectroscopy and X-ray crystallography. Density functional theory (DFT) calculations of the reaction mechanism provide a rationale for the observed reactivity and give detailed information on the bonding situation of the base-stabilized disilene. Compound 2 undergoes thermal or light- induced (λ=456 nm) NHC loss, and a dimerization process to give a corresponding dimer with a Si10 skeleton. In order to shed light on the dimerization mechanism, DFT calculations were performed. Moreover, the reactivity of 2 was examined with selected examples of transition metal carbonyl compounds.

Accessing cationic tetrylene-nickel(0) systems featuring donor-acceptor E-Ni triple bonds (E = Ge, Sn)

We describe facile synthetic methods for accessing linear cationic tetrylene nickel(0) complexes [^SiiPDippE·Ni(PPh₃)₃]⁺ (E = Ge (4) and Sn (5); ^SiiPDipp = [(iPr₃Si)(Dipp)N]^-), which feature donor-acceptor E-Ni triple bonds. These species are readily accessed in a one-pot protocol, combining the bulky halo-tetrylenes ^SiiPDippECl (E = Ge (1) and Sn (2)), Ni(cod)₂, PPh₃, and Na[BAr^F₄]. Given the diamagnetic nature of 4 and 5, they each contain a formal zero-valent Ni centre, making the E-M triple bonds in these complexes unique compared to previously reported metal tetrylidyne complexes, which typically feature covalent/ionic bonding. In-depth computational analyses of these species further support triple bond character in their E-Ni interactions.

Molecular Main Group Metal Hydrides

This review serves to document advances in the synthesis, versatile bonding, and reactivity of molecular main group metal hydrides within Groups 1, 2, and 12-16. Particular attention will be given to the emerging use of said hydrides in the rapidly expanding field of Main Group element-mediated catalysis. While this review is comprehensive in nature, focus will be given to research appearing in the open literature since 2001.

Synthesis and Hydrogenation of Heavy Homologues of Rhodium Carbynes: [(Me3 P)2 (Ph3 P)Rh≡E-Ar*] (E=Sn, Pb)

Tetrylidynes [(Me3 P)2 (Ph3 P)Rh≡SnAr*] (10) and [(Me3 P)2 (Ph3 P)Rh≡PbAr*] (11) are accessed for the first time via dehydrogenation of dihydrides [(Ph3 P)2 RhH2 SnAr*] (3) and [(Ph3 P)2 RhH2 PbAr*] (7) (Ar*=2,6-Trip2 C6 H3 , Trip=2,4,6-triisopropylphenyl), respectively. Tin dihydride 3 was either synthesized in reaction of the dihydridostannate [Ar*SnH2 ]- with [(Ph3 P)3 RhCl] or via reaction between hydrides [(Ph3 P)3 RhH] and 1 / 2  [(Ar*SnH)2 ]. Homologous lead hydride [(Ph3 P)2 RhH2 PbAr*] (7) was synthesized analogously from [(Ph3 P)3 RhH] and 1 / 2  [(Ar*PbH)2 ]. Abstraction of hydrogen from 3 and 7 supported by styrene and trimethylphosphine addition yields tetrylidynes 10 and 11. Stannylidyne 10 was also characterized by 119 Sn Mössbauer spectroscopy. Hydrogenation of the triple bonds at room temperature with excess H2 gives the cis-dihydride [(Me3 P)2 (Ph3 P)RhH2 PbAr*] (12) and the tetrahydride [(Me3 P)2 (Ph3 P)RhH2 SnH2 Ar*] (14). Complex 14 eliminates spontaneously one equivalent of hydrogen at room temperature to give the dihydride [(Me3 P)2 (Ph3 P)RhH2 SnAr*] (13). Hydrogen addition and elimination at stannylene tin between complexes 13 and 14 is a reversible reaction at room temperature.

Thermochemistry of Tungsten-3p Elements for Density Functional Theory, Caveat Lector!

There are two primary foci in this research on WE (E = Si, P, and S) bonds: prediction of their bond dissociation enthalpies (BDEs), including σ- and π-bond energy components, and assessing the uncertainty of these BDE predictions for levels of theory commonly used in the literature. The internal standards for computational accuracy include metal-element bond lengths (mean absolute error = 1.8 ± 1.2%), main group homolog BDEs versus higher levels of ab initio theory (W1U and G4 BDEs, R² = 0.98), and DLPNO-CCSD(T)/def2-QZVPP calculations for metal-ligand BDEs (R² = 0.88). The W═Si first π-bond is underreported for density functional theory (DFT)/MP2 methods versus DLPNO-CCSD(T), while the latter shows negligible strength for the W;Si second π-bond, consistent with the literature. This research highlights clear issues with the underlying assumptions required for the use of perturbation theory methods for the fragments derived from W-P homolysis. The difficulties associated with modeling the metal thermochemistry with DFT (and MP2) levels of theory are manifest in the broad standard deviations observed. However, the average BDEs found using 48 popular DFT and MP2 levels of theory are reliable, 10.8 ± 6.8% mean absolute error (with W-P removed) versus DLPNO-CCSD(T), with the caveat that the individual basis set/pseudopotential/valence basis set combination can vary wildly. Analysis of the absolute error percentages with respect to the level of theory indicates little benefit to going higher on Jacob's Ladder, as simpler methods have lower error versus high-level ab initio techniques such as G4 and DLPNO-CCSD(T).

Planar Tetracoordinated Silicon (ptSi): Room-Temperature Stable Compounds Containing Anti-van't Hoff/Le Bel Silicon

While a variety of compounds containing planar tetracoordinated carbon (ptC), the so-called anti-van't Hoff/Le Bel carbon, are known experimentally, stable systems containing planar tetracoordinated silicon (ptSi) are barely known. As part of our studies on the application of stereoelectronically well-defined transition-metal fragments to stabilize silicon in unprecedented bonding modes, we report herein the synthesis and full characterization of a series of thermally stable complexes of the general formula [Tp'(CO)₂MSiC(R¹)C(R²)M(CO)₂Tp'] (M = Mo, W; R¹ = R² = Me or R¹ = H, R² = SiMe₃, Ph; Tp' = κ³-N,N',N″-hydridotris(3,5-dimethylpyrazolyl)borate), which incorporate a ptSi atom in addition to two ptC atoms. The complexes were obtained by reacting the metallasilylidyne complexes [Tp'(CO)₂M≡Si-M(CO)₂(PMe₃)Tp'] with alkynes R¹C≡CR² and were comprehensively analyzed by experimental studies and quantum chemical calculations. The analyses revealed that the ptSi atom is embedded in a tricyclic trapezoidal core featuring one internal SiC₂ and two outer M-Si-C three-membered rings, which are fused via two Si-C bonds. The structural peculiarities evoked by the presence of an anti-van't Hoff/Le Bel ptSi center, such as the short M-Si bonds, a nearly linear M-Si-M spine, long M-C bonds, and the presence of two planar tetracoordinated carbon atoms were elucidated by a detailed analysis of the electronic structure, suggesting that one factor for the stabilization of the ptSi geometry is the aromaticity of the central SiC₂ ring having two delocalized π electrons. Remarkably, the results further indicate the existence of both anti-van't Hoff/Le Bel carbon and silicon centers next to each other in the isolated complexes.

Transition metal chemistry of heavier group 14 congener triple-bonded complexes: syntheses and reactivity

The diversification and synthetic utility of carbyne complexes in organometallic chemistry and catalysis are well recognized, but the syntheses of related heavier group 14 alkylidyne complexes are a recent advancement. A wide range of metal-ylidyne M[triple bond, length as m-dash]E (E = Si-Pb) complexes were synthesized and characterized spectroscopically. The synthetic methodology generally involves elimination or substitution chemistry between metallates and suitable group 14 precursors. The reluctance in forming triple bonded complexes makes this field quite fascinating and challenging. This article gives a brief overview of the pioneering reports followed by detailed information on the latest developments of complexes having a triple bond between a metal and heavier group 14 elements (Si, Ge, Sn, and Pb). Their synthesis and chemistry of the earlier reports followed by recent progress in this field will be discussed. Furthermore, their unique structures and bonding properties will be described based on spectroscopic and theoretical studies.

An Air-Stable Heterobimetallic Si2 M2 Tetrahedral Cluster

Air- and moisture-stable heterobimetallic tetrahedral clusters [Cp(CO)2 MSiR]2 (M=Mo or W; R=SitBu3 ) were isolated from the reaction of N-heterocyclic carbene (NHC) stabilized silyl(silylidene) metal complexes Cp(CO)2 M=Si(SitBu3 )NHC with a mild Lewis acid (BPh3 ). Alternatively, treatment of the NHC-stabilized silylidene complex Cp(CO)2 W=Si(SitBu3 )NHC with stronger Lewis acids such as AlCl3 or B(C6 F5 )3 resulted in the reversible coordination of the Lewis acid to one of the carbonyl ligands. Computational investigations revealed that the dimerization of the intermediate metal silylidyne (M≡Si) complex to a tetrahedral cluster instead of a planar four-membered ring is due to steric bulk.

Techniques in the synthesis of organometallic compounds of tungsten

Tungsten is an elegant substance, and its compounds have great significance because of their extensive range of applications in diverse fields such as in gas sensors, photocatalysis, lithium ion batteries, H2production, electrochromic devices, dyed sensitized solar cells, microchip technology, and liquid crystal displays. Tungsten compounds exhibit a more efficient catalytic behavior, and tungsten-dependent enzymes generally catalyze the transfer of an oxygen atom to or from a physiological donor/acceptor with the metal center. Furthermore, tungsten has an n-type semiconductor band gap. Tungsten forms complexes by reacting with several elements such as H, C, N, O, and P as well as other numerous inorganic elements. Interestingly, all tungsten reactions occur at ambient temperature, usually with tetrahydrofuran and dichloromethane under vacuum. Tungsten has extraordinarily high-temperature properties, making it very useful for X-ray production and heating elements in furnaces. Tungsten coordinates with diverse nonmetallic elements and ligands and produces interesting compounds. This article describes an overview of the synthesis of various organometallic compounds of tungsten.

Cycloaddition Chemistry of a Silylene-Nickel Complex toward Organic π-Systems: From Reversibility to C-H Activation

The versatile cycloaddition chemistry of the Si-Ni multiple bond in the acyclic (amido)(chloro)silylene→Ni0 complex 1, [(TMS L)ClSi→Ni(NHC)2 ] (TMS L=N(SiMe3 )Dipp; Dipp=2,6-iPr2 C6 H4 ; NHC=C[(iPr)NC(Me)]2 ), toward unsaturated organic substrates is reported, which is both reminiscent of and expanding on the reactivity patterns of classical Fischer and Schrock carbene-metal complexes. Thus, 1:1 reaction of 1 with aldehydes, imines, alkynes, and even alkenes proceed to yield [2+2] cycloaddition products, leading to a range of four-membered metallasilacycles. This cycloaddition is in fact reversible for ethylene, whereas addition of an excess of this olefin leads to quantitative sp2 -CH bond activation, via a 1-nickela-4-silacyclohexane intermediate. These results have been supported by DFT calculations giving insights into key mechanistic aspects.

Electron acceptors promote proton–hydride tautomerism in low valent rhenium β-diketiminates

We report a series of β-diketiminate (BDI) complexes in which tautomeric rhenium(iii) hydride and rhenium(i) protio-BDI species readily interconvert between the solid and solution states.

Interconversion and reactivity of manganese silyl, silylene, and silene complexes

Interconversions between manganese silylene and silene complexes are reported, including those involving the first spectroscopically observed silene complexes with an SiH substituent, and their involvement in ethylene hydrosilylation is discussed.

Manganese disilyl hydride complexes [(dmpe)₂MnH(SiH₂R)₂] (4^Ph: R = Ph, 4^Bu: R = ⁿBu) reacted with ethylene to form silene hydride complexes [(dmpe)₂MnH(RHSi Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> CHMe)] (6^Ph,H: R = Ph, 6^Bu,H: R = ⁿBu). Compounds 6^R,H reacted with a second equivalent of ethylene to generate [(dmpe)₂MnH(REtSi Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> CHMe)] (6^Ph,Et: R = Ph, 6^Bu,Et: R = ⁿBu), resulting from apparent ethylene insertion into the silene Si–H bond. Furthermore, in the absence of ethylene, silene complex 6^Bu,H slowly isomerized to the silylene hydride complex [(dmpe)₂MnH( Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> SiEtⁿBu)] (3^Bu,Et). Reactions of 4^R with ethylene likely proceed via low-coordinate silyl {[(dmpe)₂Mn(SiH₂R)] (2^Ph: R = Ph, 2^Bu: R = ⁿBu)} or silylene hydride {[(dmpe)₂MnH( Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> SiHR)] (3^Ph,H: R = Ph, 3^Bu,H: R = ⁿBu)} intermediates accessed from 4^R by H₃SiR elimination. DFT calculations and high temperature NMR spectra support the accessibility of these intermediates, and reactions of 4^R with isonitriles or N-heterocyclic carbenes yielded the silyl isonitrile complexes [(dmpe)₂Mn(SiH₂R)(CNR′)] (7a–d: R = Ph or ⁿBu; R′ = o-xylyl or ^tBu), and NHC-stabilized silylene hydride complexes [(dmpe)₂MnH{ Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> SiHR(NHC)}] (8a–d: R = Ph or ⁿBu; NHC = 1,3-diisopropylimidazolin-2-ylidene or 1,3,4,5-tetramethyl-4-imidazolin-2-ylidene), respectively, all of which were crystallographically characterized. Silyl, silylene and silene complexes in this work were accessed via reactions of [(dmpe)₂MnH(C₂H₄)] (1) with hydrosilanes, in some cases followed by ethylene. Therefore, ethylene (C₂H₄ and C₂D₄) hydrosilylation was investigated using [(dmpe)₂MnH(C₂H₄)] (1) as a pre-catalyst, resulting in stepwise conversion of primary to secondary to tertiary hydrosilanes. Various catalytically active manganese-containing species were observed during catalysis, including silylene and silene complexes, and a catalytic cycle is proposed.

π-Electron systems containing Si=Si double bonds

Sterically large substituents can provide kinetic stabilization to various types of low-coordinate compounds. For example, regarding the chemistry of the group 14 elements, since West et al. introduced the concept of kinetic protection of the otherwise highly reactive Si=Si double bond by bulky mesityl (2,4,6-trimethylphenyl) groups in 1981, a number of unsaturated compounds of silicon and its group homologs have been successfully isolated by steric effects using the appropriate large substituents. However, the functions and applications of the Si-Si π-bonds consisting of the 3pπ electrons on the formally sp2-hybridized silicon atoms have rarely been explored until 10 years ago, when Scheschkewitz and Tamao independently reported the model systems of the oligo(p-phenylenedisilenylene)s (Si-OPVs) in 2007. This review focuses on the recent advances in the chemistry of π-electron systems containing Si=Si double bonds, mainly published in the last decade. The synthesis, characterization, and potential application of a variety of donor-free π-conjugated disilene compounds are described.

Triple bonds of niobium with silicon, germaniun and tin: the tetrylidyne complexes [(κ3-tmps)(CO)2Nb[triple bond, length as m-dash]E-R] (E = Si, Ge, Sn; tmps = MeSi(CH2PMe2)3; R = aryl)

A systematic, efficient approach to first complexes containing a triple bond between niobium and the elements silicon, germanium or tin is reported. The approach involves a metathetical exchange of the niobium-centered nucleophile (NMe4)[Nb(CO)4(κ2-tmps)] (1) (tmps = MeSi(CH2PMe2)3) with a suitable organotetrel(ii)halide. Compound 1 was obtained from (NMe4)[Nb(CO)6] and the triphosphane tmps by photodecarbonylation. Reaction of 1 with the disilene E-Tbb(Br)Si[double bond, length as m-dash]Si(Br)Tbb in the presence of 4-dimethylaminopyridine afforded selectively the red-brown silylidyne complex [(κ3-tmps)(CO)2Nb[triple bond, length as m-dash]Si-Tbb] (2-Si, Tbb = 4-tert-butyl-2,6-bis(bis(trimethylsilyl)methyl)phenyl). Similarly, treatment of 1 with E(ArMes)Cl (E = Ge, Sn; ArMes = 2,6-mesitylphenyl) afforded after elimination of (NMe4)Cl and two CO ligands the deep magenta colored germylidyne complex [(κ3-tmps)(CO)2Nb[triple bond, length as m-dash]Ge-ArMes] (3-Ge), and the deep violet, light-sensitive stannylidyne complex [(κ3-tmps)(CO)2Nb[triple bond, length as m-dash]Sn-ArMes] (3-Sn), respectively. Formation of 3-Sn proceeds via the niobiastannylene [(κ3-tmps)(CO)3Nb-SnArMes] (4-Sn), which was detected by IR and NMR spectroscopy. The niobium tetrylidyne complexes 2-Si, 3-Ge and 3-Sn were fully characterized and their solid-state structures determined by single-crystal X-ray diffraction studies. All complexes feature an almost linear tetrel coordination and the shortest Nb-E bond lengths (d(Nb-Si) = 232.7(2) pm; d(Nb-Ge) = 235.79(4) pm; d(Nb-Sn) = 253.3(1) pm) reported to date. Reaction of 3-Ge with a large excess of H2O afforded upon cleavage of the Nb-Ge triple bond the hydridogermanediol Ge(ArMes)H(OH)2. Photodecarbonylation of [CpNb(CO)4] (Cp = η5-C5H5) in the presence of Ge(ArMes)Cl afforded the red-orange chlorogermylidene complex [Cp(CO)3Nb[double bond, length as m-dash]Ge(ArMes)Cl] (5-Ge). The molecular structure of 5-Ge features an upright conformation of the germylidene ligand, a trigonal-planar coordinated Ge atom, and a Nb-Ge double bond length of 251.78(6) pm, which lies in-between the Nb-Ge triple bond length of 3-Ge (235.79(4) pm) and a Nb-Ge single bond length (267.3 pm). Cyclic voltammetric studies of 2-Si, 3-Ge, and 3-Sn reveal several electron-transfer steps. One-electron oxidation and reduction of the germylidyne complex of 3-Ge in THF are electrochemically reversible suggesting that both the radical cation and radical anion of 3-Ge are accessible species in solution.