Trapping the Parent Inorganic Ethylenes H2SiGeH2 and H2SiSnH2 in the Form of Stable Adducts at Ambient Temperature

NHC-Stabilized Mixed Group 13/14/15 Element Hydrides

The syntheses of novel N-heterocyclic carbene (NHC) adducts of group 13, 14 and 15 element hydrides are reported. Salt metathesis reactions between NaPH2 and IDipp ⋅ GeH2 BH2 OTf (1) (IDipp=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) led to mixtures of the two isomers IDipp ⋅ GeH2 BH2 PH2 (2 a) and IDipp ⋅ BH2 GeH2 PH2 (2 b); by altering the reaction conditions an almost exclusive formation of 2 b was achieved. Attempts to purify mixtures of 2 a and 2 b by re-crystallization from THF afforded a salt [IDipp ⋅ GeH2 BH2  ⋅ IDipp][PHGeH2 BH2 PH2 BH2 GeH2 ] (4) that contains the novel anionic cyclohexyl-like inorganic heterocycle [PHGeH2 BH2 PH2 BH2 GeH2 ]- . In addition, the borane adducts IDipp ⋅ GeH2 BH2 PH2 BH3 (3 a) and IDipp ⋅ BH2 GeH2 PH2 BH3 (3 b) as even longer chain compounds were obtained from reactions of 2 a/2 b with H3 B ⋅ SMe2 and were studied by NMR spectroscopy. Accompanying DFT computations give insight into the mechanism and energetics associated with 2 a/2 b isomerization as well as their decomposition pathways.

Lewis Acid Stabilized Diatomic Molecules of Group 14: A Computational Study on [(CO)4Fe]2E2 (E = C, Si, Ge, Sn, Pb)

A Lewis base and acid combination has been effectively employed to stabilize and isolate the low-valent group 14 compounds. We report DFT studies on stabilizing low-valent group 14 diatomics as adducts of Lewis acids employing transition metal carbonyl fragment iron tetracarbonyl [Fe(CO)4] as Lewis acid. Computational studies on [(CO)4Fe]2E2, E = C, Si, Ge, Sn, and Pb, predict five plausible isomers on its potential energy surface: linear (E2_L), bent (E2_B), three-membered (E2_T), dibridged (E2_D), and four-membered (E2_F). For the carbon analogue, the lowest energy configuration is linear and has a typical cumulenic structure, while silicon and germanium analogues favor three-membered cyclic isomers. Four-membered cyclic isomers are the most stable for tin and lead analogues.

Structures and Stability of Mixed Main Group Hydrides [PBEH6]n (E = C, Si, Ge; n = 1-4) and Donor-Acceptor Stabilization of Monomeric Chain Isomers

Structures and stability of mixed group 13-14-15 element hydrides PBEH6 (E = C, Si, Ge), their oligomers, and complexes with Lewis acids and Lewis base are computationally studied at the B3LYP-D3/def2-TZVP level of theory. Unsubstituted chain hydrides are unstable and are expected to form cyclic oligomers. Cyclization can be prevented by the donor-acceptor complex formation. For complexes of chain hydrides with Lewis acid in many cases additional reactivity beyond the donor-acceptor complex formation is observed: cyclization and migration of terminal group from the group 13 Lewis acid to the boron or group 14 terminal atoms of the hydride. The most promising compounds for the experimental studies have been identified. Joint stabilization by both W(CO)5 and trimethylamine provides a synergetic effect, allowing stabilization of 13-14-15 chain compounds.

Calix[4]pyrrolato-germane-(thf)2: Unlocking the Anti-van't Hoff-Le Bel Reactivity of Germanium(IV) by Ligand Dissociation

Anti-van't Hoff-Le Bel configured p-block element species possess intrinsically high reactivity and are thus challenging to isolate. Consequently, numerous elements in this configuration, including square-planar germanium(IV), remain unexplored. Herein, we follow a concept to reach anti-van't Hoff-Le Bel reactivity by ligand dissociation from a rigid calix[4]pyrrole germane in its bis(thf) adduct. While the macrocyclic ligand assures square-planar coordination in the uncomplexed form, the labile thf donors provide robustness for isolation on a multigram scale. Unique properties of a low-lying acceptor orbital imparted to germanium(IV) can be verified, e.g., by isolating an elusive anionic hydrido germanate and exploiting it for challenging bond activations. Aldehydes, water, alcohol, and a CN triple bond are activated for the first time by germanium-ligand cooperativity. Unexpected behaviors against fluoride ion donors disclose critical interferences of a putative redox-coupled fluoride ion transfer during the experimental determination of Lewis acidity. Overall, we showcase how ligand lability grants access to the uncharted chemistry of anti-van't Hoff-Le Bel germanium(IV) and line up this element as a member in the emerging class of structurally constrained p-block elements.

Organogermanium Analogues of Alkenes, Alkynes, 1,3-Dienes, Allenes, and Vinylidenes

In this review, the latest achievements in the field of multiply bonded organogermanium derivatives, mostly reported within the last two decades, are presented. The isolable Ge-containing analogues of alkenes, alkynes, 1,3-dienes, allenes, and vinylidenes are discussed, and for each class of unsaturated organogermanium compounds, the most representative examples are given. The synthetic approaches toward homonuclear multiply bonded combinations solely consisting of germanium atoms, and their heteronuclear variants containing germanium and other group 14 elements, both acyclic and cyclic, are discussed. The peculiar structural features and nonclassical bonding nature of the abovementioned compounds are discussed based on their spectroscopic and structural characteristics, in particular their crystallographic parameters (double bond length, trans-bending at the doubly bonded centers, and twisting about the double bond). The prospects for the practical use of the title compounds in synthetic and catalytic fields are also briefly discussed.

Dope it with germanium: selective access to functionalized Si5Ge heterocycles

The Cl^- diadduct [nBu₄N]₂[A·2Cl] of the mixed cyclohexatetrelane (SiCl₂)₅(GeMe₂), A, is accessible from Me₂GeCl₂, 6 eq. Si₂Cl₆, and 2 eq. [nBu₄N]Cl in one step (96%). Free, tenfold functionalized A can be released from the primary product by decomplexation with AlCl₃ (78%). Insight into the assembly mechanism of [nBu₄N]₂[A·2Cl] and the reactivity of A is provided.

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.

Synthesis, structure and reactivity of μ3-SnH capped trinuclear nickel cluster

Treatment of the trichlorotin-capped trinuclear nickel cluster, [Ni₃(dppm)₃(μ₃-Cl)(μ₃-SnCl₃)], 1, with 4 eq. NaHB(Et)₃ yields a μ₃-SnH capped trinuclear nickel cluster, [Ni₃(dppm)₃(μ₃-H)(μ₃-SnH)], 2 [dppm = bis(diphenylphosphino)methane]. Single-crystal X-ray diffraction, nuclear magnetic resonance (NMR) spectroscopy, and computational studies together support that cluster 2 is a divalent tin hydride. Complex 2 displays a wide range of reactivity including oxidative addition of bromoethane across the Sn center. Addition of 1 eq. iodoethane to complex 2 releases H₂ (g) and generates an ethyltin-capped nickel cluster with a μ₃-iodide, [Ni₃(dppm)₃(μ₃-I)(μ₃-Sn(CH₂CH₃))], 4. Notably, insertion of alkynes into the Sn–H bond of 2 can be achieved via addition of 1 eq. 1-hexyne to generate the 1-hexen-2-yl-tin-capped nickel cluster, [Ni₃(dppm)₃(μ₃H)(μ₃-Sn(C₆H₁₁))], 5. Addition of H₂ (g) to 5 regenerates the starting material, 2, and hexane. The formally 44-electron cluster 2 also displays significant redox chemistry with two reversible one-electron oxidations (E = −1.3 V, −0.8 V vs. Fc^0/+) and one-electron reduction process (E = −2.7 V vs. Fc^0/+) observed by cyclic voltammetry.

The synthesis, structure, and reactivity of a μ₃-SnH capped trinuclear nickel cluster, [Ni₃(dppm)₃(μ₃-H)(μ₃-SnH)], is reported. This complex undergoes oxidative addition chemistry, alkyne insertion, and subsequent hydrogenation.

An NHC-Stabilized H2 GeBH2 Precursor for the Preparation of Cationic Group 13/14/15 Hydride Chains

The synthesis, characterization and reactivity studies of the NHC‐stabilized complex IDipp ⋅ GeH₂BH₂OTf (1) (IDipp=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene) are reported. Nucleophilic substitution of the triflate (OTf) group in 1 by phosphine or arsine donors provides access to the cationic group 13/14/15 chains [IDipp ⋅ GeH₂BH₂ERR¹R²]⁺ (2 E=P; R, R¹=H; R²=^tBu; 3 E=P; R=H; R¹, R²=Ph; 4 a E=P; R, R¹, R²=Ph; 4 b E=As; R, R¹, R²=Ph). These novel cationic chains were characterized by X‐ray crystallography, NMR spectroscopy and mass spectrometry. Moreover, the formation of the parent complexes [IDipp ⋅ GeH₂BH₂PH₃][OTf] (5) and [IDipp ⋅ GeH₃][OTf] (6) were achieved by reaction of 1 with PH₃. Accompanying DFT computations give insight into the stability of the formed chains with respect to their decomposition.

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.

Selective One-Pot Syntheses of Mixed Silicon-Germanium Heteroadamantane Clusters

Si x Ge y alloys are emerging materials for modern semiconductor technology. Well-defined model systems of the bulk structures aid in understanding their intrinsic characteristics. Three such model clusters have now been realized in the form of the Si x Ge y heteroadamantanes [0] , [1] , and [2] via selective one-pot syntheses starting from Me 2 GeCl 2 , Si 2 Cl 6 , and [nBu 4 N]Cl. Compound [0] contains 6 GeMe 2 and 4 SiSiCl 3 vertices, while one and two of the GeMe 2 groups are replaced by SiCl 2 moieties in compounds [1] and [2] , respectively. Chloride ion-mediated rearrangement quantitatively converts [2] into [1] at room temperature and finally into [0] at 60 °C, which is not only remarkable in view of the rigidity of these cage structures but also sheds light on the assembly mechanism.

Frustrated Lewis Pair Chelation as a Vehicle for Low-Temperature Semiconductor Element and Polymer Deposition

The stabilization of silicon(II) and germanium(II) dihydrides by an intramolecular Frustrated Lewis Pair (FLP) ligand, PB, ⁱ Pr₂ P(C₆ H₄ )BCy₂ (Cy=cyclohexyl) is reported. The resulting hydride complexes [PB{SiH₂ }] and [PB{GeH₂ }] are indefinitely stable at room temperature, yet can deposit films of silicon and germanium, respectively, upon mild thermolysis in solution. Hallmarks of this work include: 1) the ability to recycle the FLP phosphine-borane ligand (PB) after element deposition, and 2) the single-source precursor [PB{SiH₂ }] deposits Si films at a record low temperature from solution (110 °C). The dialkylsilicon(II) adduct [PB{SiMe₂ }] was also prepared, and shown to release poly(dimethylsilane) [SiMe₂ ]_n upon heating. Overall, this study introduces a "closed loop" deposition strategy for semiconductors that steers materials science away from the use of harsh reagents or high temperatures.

Insight into the Decomposition Mechanism of Donor-Acceptor Complexes of EH2 (E = Ge and Sn) and Access to Germanium Thin Films from Solution

Electron-donating N-heterocyclic carbenes (Lewis bases, LB) and electron-accepting Lewis acids (LA) have been used in tandem to yield donor-acceptor complexes of inorganic tetrelenes LB·EH₂·LA (E = Si, Ge, and Sn). Herein, we introduce the new germanium (II) dihydride adducts ImMe₂·GeH₂·BH₃ (ImMe₂ = (HCNMe)₂C:) and ImⁱPr₂Me₂·GeH₂·BH₃ (ImⁱPr₂Me₂ = (MeCNⁱPr)₂C:), with the former complex containing nearly 40 wt % germanium. The thermal release of bulk germanium from ImMe₂·GeH₂·BH₃ (and its deuterated isotopologue ImMe₂·GeD₂·BD₃) was examined in solution, and a combined kinetic and computational investigation was undertaken to probe the mechanism by which Ge is liberated. Moreover, the thermolysis of ImMe₂·GeH₂·BH₃ in solution cleanly affords conformal nanodimensional layers of germanium as thin films of variable thicknesses (20-70 nm) on silicon wafers. We also conducted a computational investigation into potential decomposition pathways for the germanium(II)- and tin(II)-dihydride complexes NHC·EH₂·BH₃ (NHC = [(HCNR)₂C:]; R = 2,6-ⁱPr₂C₆H₃ (Dipp), Me, and H; and E = Ge and Sn). Overall, this study introduces a mild and convenient solution-only protocol for the deposition of thin films of Ge, a widely used semiconductor in materials research and industry.

Organogermanium(II) Hydrides as a Source of Highly Soluble LiH

The reactions of monomeric C,N-chelated organogermanium(II) hydride L(H)Ge⋅BH₃ with organolithium salts RLi yielded lithium hydrogermanatoborates (Li(THF)₂ {BH₃ [L(H)GeR]})₂ . Compound (Li(THF)₂ {BH₃ [L(H)GePh]})₂ was used as a source of LiH for the reduction of organic C=O or C=N bonds in nonpolar solvents accompanied by the elimination of a neutral complex L(Ph)Ge⋅BH₃ . The interaction of (Li(THF)₂ {BH₃ [L(H)GePh]})₂ with the polar C=O bond was further investigated by computational studies revealing a plausible geometry of a pre-reactive intermediate. The experimental and theoretical studies suggest that, although the Li atom of (Li(THF)₂ {BH₃ [L(H)GePh]})₂ coordinates the C=O bond, the GeH fragment is the active species in the reduction reaction. Finally, benzaldehyde was reduced by a mixture of L(H)Ge⋅BH₃ with PhLi in nonpolar solvents.

NHC-Coordinated Diphosphene-Stabilized Gold(I) Hydride and Its Reversible Conversion to Gold(I) Formate with CO2

An NHC-coordinated diphosphene is employed as ligand for the synthesis of a hydrocarbon-soluble monomeric AuI hydride, which readily adds CO2 at room temperature yielding the corresponding AuI formate. The reversible reaction can be expedited by the addition of NHC, which induces β-hydride shift and the removal of CO2 from equilibrium through the formation of an NHC-CO2 adduct. The AuI formate is alternatively formed by dehydrogenative coupling of the AuI hydride with formic acid (HCO2 H), thus in total establishing a reaction sequence for the AuI hydride mediated dehydrogenation of HCO2 H as chemical hydrogen storage material.

N-Heterocyclic Carbene Adducts of Main Group Elements and Their Use as Ligands in Transition Metal Chemistry

N-Heterocyclic carbenes (NHC) are nowadays ubiquitous and indispensable in many research fields, and it is not possible to imagine modern transition metal and main group element chemistry without the plethora of available NHCs with tailor-made electronic and steric properties. While their suitability to act as strong ligands toward transition metals has led to numerous applications of NHC complexes in homogeneous catalysis, their strong σ-donating and adaptable π-accepting abilities have also contributed to an impressive vitalization of main group chemistry with the isolation and characterization of NHC adducts of almost any element. Formally, NHC coordination to Lewis acids affords a transfer of nucleophilicity from the carbene carbon atom to the attached exocyclic moiety, and low-valent and low-coordinate adducts of the p-block elements with available lone pairs and/or polarized carbon-element π-bonds are able to act themselves as Lewis basic donor ligands toward transition metals. Accordingly, the availability of a large number of novel NHC adducts has not only produced new varieties of already existing ligand classes but has also allowed establishment of numerous complexes with unusual and often unprecedented element-metal bonds. This review aims at summarizing this development comprehensively and covers the usage of N-heterocyclic carbene adducts of the p-block elements as ligands in transition metal chemistry.

Facile Access to an NHC-Coordinated Silicon Ring Compound with a Si=N Group and a Two-Coordinate Silicon Atom

Reaction of the bicyclo[1.1.0]tetrasilatetraamide Si₄ {N(SiMe₃ )Dipp}₄ 1 (Dipp=2,6-diisopropylphenyl) with 5 equiv of the N-heterocyclic carbene NHC^Me4 (1,3,4,5-tetramethylimidazol-2-ylidene) affords a bifunctional carbene-coordinated four-membered-ring compound with a Si=N group and a two-coordinate silicon atom Si₄ {N(SiMe₃ )Dipp}₂ (NHC^Me4 )₂ (NDipp) 2. When 2 reacts with 0.25 equiv sulfur (S₈ ), two sulfur atoms add to the divalent silicon atom in plane and perpendicular to the plane of the Si₄ ring, which confirms the silylone character of the two-coordinate silicon atom in 2.

Germylene stabilized group 12 metal complexes and their reactivity with chalcogens

This manuscript reports the first examples of germylene stabilized cadmium complexes 3, 6, and 7, and novel germylene zinc complexes 2 and 5.

NHCs in Main Group Chemistry

Since the discovery of the first stable N-heterocyclic carbene (NHC) in the beginning of the 1990s, these divalent carbon species have become a common and available class of compounds, which have found numerous applications in academic and industrial research. Their important role as two-electron donor ligands, especially in transition metal chemistry and catalysis, is difficult to overestimate. In the past decade, there has been tremendous research attention given to the chemistry of low-coordinate main group element compounds. Significant progress has been achieved in stabilization and isolation of such species as Lewis acid/base adducts with highly tunable NHC ligands. This has allowed investigation of numerous novel types of compounds with unique electronic structures and opened new opportunities in the rational design of novel organic catalysts and materials. This Review gives a general overview of this research, basic synthetic approaches, key features of NHC-main group element adducts, and might be useful for the broad research community.

Low-valent group 14 element hydride chemistry: towards catalysis

The chemistry of group 14 element(ii) hydride complexes has rapidly expanded since the first stable example of such a compound was reported in 2000. Since that time it has become apparent that these systems display remarkable reactivity patterns, in some cases mimicking those of late transition-metal (TM) hydride compounds. This is especially so for the hydroelementation of unsaturated organic substrates. Recently, this aspect of their reactivity has been extended to the use of group 14 element(ii) hydrides as efficient, "TM-like" catalysts in organic synthesis. This review will detail how the chemistry of these hydride compounds has advanced since their early development. Throughout, there is a focus on the importance of ligand effects in these systems, and how ligand design can greatly modify a coordinated complex's electronic structure, reactivity, and catalytic efficiency.

Silicon-fluorine chemistry: from the preparation of SiF2to C–F bond activation using silylenes and its heavier congeners

The feisty nature of silicon(ii) fluorides has been harnessed by two cyclic alkyl amino carbene (cAAC) ligands and (cAAC)₂SiF₂has been isolated at room temperature and structurally characterized.

Depolymerization of Poly(phosphinoboranes): From Polymers to Lewis Base Stabilized Monomers

We report on depolymerization reactions of poly(phosphinoboranes). The cleavage of the polymers [H₂ PBH₂ ]_n (2 a), [tBuHPBH₂ ]_n (2 c), [PhHPBH₂ ]_n (2 e) and the oligomer [Ph₂ PBH₂ ]_n (2 b), with strong Lewis bases (LBs), in particular with NHCs, leads to the corresponding monomeric phosphanylboranes R¹ R² PBH₂ LB. It is observed that the depolymerization depends on the strength and stability of the LBs as well as on the substitution pattern of the poly(phosphinoboranes). The solid state structures of the monomeric phosphinoboranes H₂ PBH₂ NHC^Me (NHC=N-heterocyclic carbene) (4 a), H₂ PBH₂ NHC^dipp (5 a) and tBuHPBH₂ NHC^Me (4 c) were determined. DFT calculations support the experimentally observed reaction behavior.

Pushing Chemical Boundaries with N-Heterocyclic Olefins (NHOs): From Catalysis to Main Group Element Chemistry

N-Heterocyclic olefins (NHOs) have gone from the topic of a few scattered (but important) reports in the early 1990s to very recently being a ligand/reagent of choice in the far-reaching research fields of organocatalysis, olefin and heterocycle polymerization, and low oxidation state main group element chemistry. NHOs are formally derived by appending an alkylidene (CR₂) unit onto an N-heterocyclic carbene (NHC), and their pronounced ylidic character leads to high nucleophilicity and soft Lewis basic character at the ligating carbon atom. These olefinic donors can also be structurally derived from imidazole, triazole, and thiazole-based heterocyclic carbenes and, as a result, have highly tunable electronic and steric properties. In this Account, we will focus on various synthetic routes to imidazole-2-ylidene derived NHOs (sometimes referred to as deoxy-Breslow intermediates) followed by a discussion of the electron-donor ability of this structurally tunable ligand group. It should be mentioned that NHOs have a close structural analogy with Breslow-type intermediates, N-heterocyclic ketene aminals, and β-azolium ylides; while these latter species play important roles in advancing synthetic organic chemistry, discussion in this Account will be confined mostly to imidazole-2-ylidene derived NHOs. In addition, we will cover selected examples from the literature where NHOs and their anionic counterparts, N-heterocyclic vinylenes, are used to access reactive main group species not attainable using traditional ligands. Added motivation for these studies comes from the emerging number of low coordinate main group element based compounds that display reactivity once reserved for precious metal complexes (such as H-H and C-H bond activation). Moreover, NHOs are versatile precursors to new mixed element (P/C and N/C), and potentially bidentate, ligand constructs of great potential in catalysis, where various metal oxidation states and coordination environments need to be stabilized during a catalytic cycle. The most active area of recent growth for NHOs is their use as nucleophiles to promote efficient organocatalytic transformations, including transesterification, carbonyl reduction, and the conversion of CO₂ into value added products. Polyesters have also been generated through the NHO-promoted ring-opening polymerization of lactones, and the highly tunable nature of NHO organocatalysts allows for the rapid screening and enhancement of catalytic performance. Therefore, the growing utility of NHOs in the realm of organic and polymer chemistry can be viewed as evidence of the widespread impact of N-heterocyclic olefins on the chemical community. It is hoped that through this Account others will join this flourishing research domain and that the rapid recent growth of NHO chemistry is sustained for the foreseeable future.

Reactivity of an amidinato silylene and germylene toward germanium(ii), tin(ii) and lead(ii) halides

The coordination chemistry of an amidinato silylene and germylene toward group 14 element(ii) halides is described. The reaction of the amidinato silicon(ii) amide [LSiN(SiMe₃)₂] (1, L = PhC(NtBu)₂) with SnCl₂ and PbBr₂ afforded the amidinato silylene-dichlorostannylene and -dibromoplumbylene adducts [L{(Me₃Si)₂N}SiEX₂] (E = Sn, X = Cl (2); E = Pb, X = Br (3)), respectively, in which there is a lone pair of electrons on the Sn(ii) and Pb(ii) atoms. X-ray crystallography, NMR spectroscopy and theoretical studies show conclusively that the Si(ii)-E(ii) bonds are donor-acceptor interactions. Similar electronic structures were found in the amidinato germylene-dichlorogermylene and -dichlorostannylene adducts [L{(Me₃Si)₂N}GeECl₂] (E = Ge (5), Sn (6)), which were prepared by treatment of the amidinato germanium(ii) amide [LGeN(SiMe₃)₂] (4) with GeCl₂·dioxane and SnCl₂, respectively.

Reactivity of a coordinated inorganic acetylene unit, HBNH, and the azidoborane cation [HB(N3)]. Chem Sci 2017;8:2337-2343. [PMID: 28451338 PMCID: PMC5365008 DOI: 10.1039/c6sc04893e]

A donor-acceptor complex of HBNH was prepared via thermolysis of a carbene-stabilized azidoborane. The reactivity of the fundamentally important HBNH unit (inorganic alkyne analogue) was explored in detail, including attempts to convert this species and related hydrido(azido)borane cations into molecular complexes of BN. This work provides added impetus for the development of molecular precursors that can release bulk boron nitride (a desirable insulator and thermal conductor) under mild conditions, and from solution.

Reductive Elimination of Hydrogen from Bis(trimethylsilyl)methyltin Trihydride and Mesityltin Trihydride

Alkyltin trihydride [(Me₃ Si)₂ CHSnH₃ ] was synthesized and the reductive elimination of hydrogen from this species was investigated. A methyl-substituted N-heterocyclic carbene reacts with the organotrihydride in dependence on stoichiometry and solvent to give a series of products of the reductive elimination and dehydrogenative tin-tin bond formation. Besides characterization of the carbene adduct of the alkyltin(II) hydride, a Sn₄ chain was also isolated, encompassing two stannyl-stannylene sites, which are stabilized each as NHC-adducts. Complete dehydrogenation resulted to give either a carbene-stabilized distannyne or a metalloid Sn₉ -cluster salt. Reductive elimination of hydrogen was also achieved with an excess of diethylmethylamine to give the alkyltin(II) hydride as a Lewis base free tetramer [(RSnH)₄ ]. The method of cluster formation at low temperatures by hydrogen elimination was also transferred to the mesityl-substituted tin trihydride MesSnH₃ . In this case [(MesSn)₁₀ ], showing a [5]prismane structure, was isolated in good yield and characterized. NMR spectroscopic features of the propellane-type cluster [Trip₆ Sn₆ ] are reported.

N-Heterocyclic carbene stabilized parent sulfenyl, selenenyl, and tellurenyl cations (XH+, X = S, Se, Te)

NHC-stabilized parent sulfenyl (H–S⁺), selenenyl (H–Se⁺) and tellurenyl (H–Te⁺) cations have been achieved by treatment of NHC chalcogen adducts with trifluoromethanesulfonic acid.

Azido- and amido-substituted gallium hydrides supported by N-heterocyclic carbenes

The synthesis of azido- and amido-gallanes supported by hindered N-heterocyclic carbene donors is reported.

The Structure of the Carbene Stabilized Si2H2 May Be Equally Well Described with Coordinate Bonds as with Classical Double Bonds

The cyclic alkyl(amino) carbene stabilized Si2H2 has been isolated in the molecular form of composition (Me-cAAC:)2Si2H2 (1) and (Cy-cAAC:)2Si2H2 (2) at room temperature. Compounds 1 and 2 were synthesized from the reduction of HSiCl3 using 3 equiv of KC8 in the presence of 1 equiv of Me-cAAC: and Cy-cAAC:, respectively. These are the first molecular examples of Si2H2 characterized by single crystal X-ray structural analysis. Moreover, electrospray ionization mass spectrometry and (1)H as well as (29)Si NMR data are reported. Furthermore, the structure of compound 1 has been investigated by theoretical methods. The theoretical analysis of 1 explains equally well its structure with coordinate bonds as with classical double bonds of a 2,3-disila-1,3-butadiene.

The Si2H radical supported by two N-heterocyclic carbenes

Cyclic voltammetric studies of the hydridodisilicon(0,II) borate [(Idipp)(H)SiII[double bond, length as m-dash]Si0(Idipp)][B(ArF)4] (1H[B(ArF)4], Idipp = C[N(C6H3-2,6-iPr2)CH]2, ArF = C6H3-3,5-(CF3)2) reveal a reversible one-electron reduction at a low redox potential (E 1/2 = -2.15 V vs. Fc+/Fc). Chemical reduction of 1H[B(ArF)4] with KC8 affords selectively the green, room-temperature stable mixed-valent disilicon(0,I) hydride Si2(H)(Idipp)2 (1H), in which the highly reactive Si2H molecule is trapped between two N-heterocyclic carbenes (NHCs). The molecular and electronic structure of 1H was investigated by a combination of experimental and theoretical methods and reveals the presence of a π-type radical featuring a terminal bonded H atom at a flattened trigonal pyramidal coordinated Si center, that is connected via a Si-Si bond to a bent two-coordinated Si center carrying a lone pair of electrons. The unpaired electron occupies the Si[double bond, length as m-dash]Si π* orbital leading to a formal Si-Si bond order of 1.5. Extensive delocalization of the spin density occurs via conjugation with the coplanar arranged NHC rings with the higher spin density lying on the site of the two-coordinated silicon atom.