1,2-Dihalodigermenes bearing bulky Eind groups: synthesis, characterization, and conversion to halogermylenoids

Approach to the "Missing" Diarylsilylene: Formation, Characterization, and Intramolecular C-H Bond Activation of Blue Diarylsilylenes with Bulky Rind Groups

The treatment of the bulky Rind-based dibromosilanes, (Rind)2SiBr2 (2) [Rind = 1,1,7,7-tetra-R1-3,3,5,5-tetra-R2-s-hydrindacen-4-yl: EMind (a: R1 = Et, R2 = Me) and Eind (b: R1 = R2 = Et)], with two equivalents of tBuLi in Et2O at low temperatures resulted in the formation of blue solutions derived from the diarylsilylenes, (Rind)2Si: (3). Upon warming the solutions above -20 °C, the blue color gradually faded, accompanying the decomposition of 3 and yielding cyclic hydrosilanes (4) via intramolecular C-H bond insertion at the Si(II) center. The molecular structures of the bulky Eind-based 3b and 4b were confirmed by X-ray crystallography. Thus, at -20 °C, blue crystals were formed (Crystal-A), which were identified as mixed crystals of 3b and 4b. Additionally, colorless crystals of 4b as a singular component were isolated (Crystal-B), whose structure was also determined by an X-ray diffraction analysis. Although the isolation of 3 was difficult due to their thermally labile nature, their structural characteristics and electronic properties were discussed based on the experimental findings complemented by computational results. We also examined the hydrolysis of 3b to afford the silanol, (Eind)2SiH(OH) (5b).

Stretched Central Double Bonds in Dialumene and Disilene by Amino Substituents: A Case of Lone Pair Repulsion

There have been remarkable advances in the syntheses and applications of groups 13 and 14 homonuclear ethene analogues. However, successes are largely limited to aryl- and/or silyl-substituted species. Analogues bearing two or more heteroatoms are still scarce. In this work, the block-localized wavefunction (BLW) method at the density functional theory (DFT) level was employed to study dialumene and disilene bearing two amino substituents whose optimal geometries exhibit significantly stretched central M=M (M=Al or Si) double bonds compared with aryl- and/or silyl-substituted species. Computational analyses showed that the repulsion between the lone electron pairs of amino substituents and M=M π bond plays a critical role in the elongation of the M=M bonds. Evidently, replacing the substituent groups -NH2 with -BH2 can enhance the planarity and shorten the central double bonds due to the absence of lone pair electrons in BH2 .

Unusual nuclear exchange within a germanium-containing aromatic ring that results in germanium atom transfer

The delivery of single atoms is highly desirable for the straightforward synthesis of complex molecules, however this approach is limited by a lack of suitable atomic transfer reagents. Here, we report a germanium atom transfer reaction employing a germanium analogue of the phenyl anion. The reaction yields a germanium-substituted benzene, along with a germanium atom which can be transferred to other chemical species. The transfer of atomic germanium is demonstrated by the formation of well-defined germanium doped molecules. Furthermore, computational studies reveal that the reaction mechanism proceeds via the first example of an aromatic-to-aromatic nuclear germanium replacement reaction on the germabenzene ring. This unusual reaction pathway was further probed by the reaction of our aromatic germanium anion with a molecular silicon species, which selectively yielded the corresponding silicon-substituted benzene derivative.

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.

A series of (E)-1,2-diaryldigermenes incorporating bulky Eind groups: structural characteristics and absorption properties

A series of (E)-1,2-diaryldigermenes, (Eind)ArGeGeAr(Eind) [Ar = phenyl (2), thiophen-2-yl (3), 9,9-dimethyl-2-fluorenyl (4) and 2,2'-bithiophen-5-yl (5)], supported by the fused-ring bulky 1,1,3,3,5,5,7,7-octaethyl-s-hydrindacen-4-yl (Eind) groups, have been obtained as yellow-orange to red crystalline solids by the reaction of 1,2-dibromodigermene, (Eind)BrGeGeBr(Eind) (1), with ArLi. In the crystals of 2-5, the digermene cores show a flexible nature adopting a trans-bent geometry with the trans-bent angles (θ) between the Ge-Ge vector and the C_Eind-Ge-C_Ar plane of 34.04(12)° (2), 38.3(3)° and 38.8(3)° (3), 33.69(12)° (4) and 39.30(13)° (5). In the UV-vis spectra, strong π-π* absorptions have been observed with an absorption maximum at 451 nm (ε = 1.3 × 10⁴) (2), 455 nm (ε = 9.7 × 10³) (3), 480 nm (ε = 1.3 × 10⁴) (4) and 497 nm (ε = 1.4 × 10⁴) (5), retaining the GeGe double bond in solution. The absorption data and DFT calculations provide evidence for the intrinsic π-conjugation between the GeGe chromophore and aromatic rings involving the narrowing of the HOMO-LUMO gaps (ΔE) with the extension of the carbon π-electron systems.

Spontaneous Decomposition of an Extraordinarily Twisted and Trans-Bent Fully-Phosphanyl-Substituted Digermene to an Unusual GeI Cluster

Ditetrelenes R₂ E=ER₂ (E=Si, Ge, Sn, Pb) substituted by multiple N/P/O/S-donor groups are extremely rare due to their propensity to disaggregate into their tetrylene monomers R₂ E. We report the synthesis of the first fully phosphanyl-substituted digermene {(Mes)₂ P}₂ Ge=Ge{P(Mes)₂ }₂ (3, Mes=2,4,6-Me₃ C₆ H₂ ), which adopts a highly unusual structure in the solid state, that is both strongly trans-bent and highly twisted. Variable-temperature ³¹ P{¹ H} NMR spectroscopy suggests that 3 persists in solution, but is subject to a dynamic equilibrium between two conformations, which have different geometries about the Ge=Ge bond (twisted/non-twisted) due to a difference in the nature of their π-stacking interactions. Compound 3 undergoes unprecedented, spontaneous decomposition in solution to give a unique Ge^I cluster {(Mes)₂ P}₄ Ge₄ ⋅5 CyMe (7).

Reversible metathesis of ammonia in an acyclic germylene-Ni0 complex

Carbenes, a class of low-valent group 14 ligand, have shifted the paradigm in our understanding of the effects of supporting ligands in transition-metal reactivity and catalysis. We now seek to move towards utilizing the heavier group 14 elements in effective ligand systems, which can potentially surpass carbon in their ability to operate via 'non-innocent' bond activation processes. Herein we describe our initial results towards the development of scalable acyclic chelating germylene ligands (viz. 1a/b), and their utilization in the stabilization of Ni0 complexes (viz. 4a/b), which can readily and reversibly undergo metathesis with ammonia with no net change of oxidation state at the GeII and Ni0 centres, through ammonia bonding at the germylene ligand as opposed to the Ni0 centre. The DFT-derived metathesis mechanism, which surprisingly demonstrates the need for three molecules of ammonia to achieve N-H bond activation, supports reversible ammonia binding at GeII, as well as the observed reversibility in the overall reaction.

Synthesis of Low-Valent Dinuclear Group 14 Compounds with Element-Element Bonds by Transylidation

Dinuclear low-valent compounds of the heavy main group elements are rare species owing to their intrinsic reactivity. However, they represent desirable target molecules due to their unusual bonding situations as well as applications in bond activations and materials synthesis. The isolation of such compounds usually requires the use of substituents that provide sufficient stability and synthetic access. Herein, we report on the use of strongly donating ylide-substituents to access low-valent dinuclear group 14 compounds. The ylides not only impart steric and electronic stabilization, but also allow facile synthesis via transfer of an ylide from tetrylene precursors of type R Y2 E to ECl2 (E=Ge, Sn; R Y=TolSO2 (PR3 )C with R=Ph, Cy). This method allowed the isolation of dinuclear complexes amongst a germanium analogue of a vinyl cation, [(Ph Y)2 GeGe(Ph Y)]+ with an electronic structure best described as a germylene-stabilized GeII cation and a ylide(chloro)digermene [Cy Y(Cl)GeGe(Cl)Cy Y] with an unusually unsymmetrical structure.

Bonding Relationship between Silicon and Germanium with Group 13 and Heavier Elements of Groups 14-16

The topic of heavier main group compounds possessing multiple bonds is the subject of momentous interest in modern organometallic chemistry. Importantly, there is an excitement involving the discovery of unprecedented compounds with unique bonding modes. The research in this area is still expanding, particularly the reactivity aspects of these compounds. This article aims to describe the overall developments reported on the stable derivatives of silicon and germanium involved in multiple bond formation with other group 13, and heavier groups 14, 15, and 16 elements. The synthetic strategies, structural features, and their reactivity towards different nucleophiles, unsaturated organic substrates, and in small molecule activation are discussed. Further, their physical and chemical properties are described based on their spectroscopic and theoretical studies.

Ferrocenyl-substituted low-coordinated heavier group 14 elements

Several examples of stable low-coordinated species of heavier group 14 elements (Si, Ge, Sb, Pb) such as divalent species and multiple-bond compounds have been reported. With the goal in mind to create unprecedented low-coordinated species of heavier group 14 elements that exhibit considerably increased redox stability, ferrocenyl (Fc)-substituted low-coordinated species of heavier group 14 elements were designed. In this short account article, recent progress on the synthesis of Fc-based low-coordinated species of heavier group 14 elements is summarized.

1,2-Insertion reactions of alkynes into Ge-C bonds of arylbromogermylene

1,2-Insertion reactions of alkynes into the Ge-C bonds in dibromodigermenes afford stable crystalline bromovinylgermylenes. In contrast to previously reported Lewis-base-supported vinylgermylenes, the bromovinylgermylene obtained from reaction of the bromogermylene with 3-hexyne via such an 1,2-insertion is a donor-free monomer. A feasible reaction mechanism, proposed on the basis of the observed experimental results in combination with theoretical calculations, suggests that the [1+2]-cycloadduct and the insertion product are the kinetic and thermodynamic product, respectively.

A stable free tetragermacyclobutadiene incorporating fused-ring bulky EMind groups

The first free cyclobutadiene (CBD) germanium analogue was obtained as room-temperature stable dark red crystals via the reaction of the bulky EMind-substituted 1,2-dichlorodigermene with lithium naphthalenide. The cyclic 4π-electron antiaromaticity is essentially stabilized by the polar Jahn-Teller distortion in the germanium CBD producing a planar rhombic-shaped charge-separated structure.