Modulating Heavy Atom Effect in Germylene for Persistent Room Temperature Phosphorescence

It is worth but still challenging to develop the low-valent main group compounds with persistent room temperature phosphorescence (pRTP). Herein, we presented germylene-based persistent phosphors by introduction of low-valent Ge center into chromophore. A novel phosphors CzGe and its series of derivatives, namely CzGeS, CzGeSe, CzGeAu, and CzGeCu, were synthesized. Experiments and theoretical calculations reveal that the pRTP behavior were "turn on" due to the heavy atom effect of germylene. More importantly, the low-valent of oxidation state and structural traits propelled GeCz had a balance between the intersystem crossing and the shortening of lifetime caused by the heavy atoms, resulting the ultralong lifetime of 309 ms and phosphorescent quantum efficiency of 15.84 %, which is remarkable among heavy main group phosphors. This research provides valuable insights to the design of heavy atoms in phosphors and expand the applications of germylene chemistry.

Germylenes Exhibiting Solid-State Emissions that Extend to NIR

Low-valent main group compounds that fluoresce in the solid-state were previously unknown. To address this, we investigated room-temperature photoluminescence from a series of crystals of germylenes 3-8 in this article; they exhibited emissions nearly reaching the NIR. Germylene carboxylates (3-8) were synthesized by reacting dipyrromethene stabilized germylene pyrrolide (2) with carboxylic acids such as acetic acid, trifluoroacetic acid, benzoic acid, p-cyanobenzoic acid, p-nitrobenzoic acid, and acetylsalicylic acid.

Challenges and Prospects in the Catalytic Conversion of Carbon Dioxide to Formaldehyde

Formaldehyde (HCHO) is a crucial C₁ building block for daily-life commodities in a wide range of industrial processes. Industrial production of HCHO today is based on energy- and cost-intensive gas-phase catalytic oxidation of methanol, which calls for exploring other and more sustainable ways of carrying out this process. Utilization of carbon dioxide (CO₂ ) as precursor presents a promising strategy to simultaneously mitigate the carbon footprint and alleviate environmental issues. This Minireview summarizes recent progress in CO₂ -to-HCHO conversion using hydrogenation, hydroboration/hydrosilylation as well as photochemical, electrochemical, photoelectrochemical, and enzymatic approaches. The active species, reaction intermediates, and mechanistic pathways are discussed to deepen the understanding of HCHO selectivity issues. Finally, shortcomings and prospects of the various strategies for sustainable reduction of CO₂ to HCHO are discussed.

The Varied Frustrated Lewis Pair Reactivity of the Germylene Phosphaketene (CH{(CMe)(2,6‐ i Pr 2 C 6 H 3 N)} 2 )GePCO

The germylene species (CH{(CMe)(2,6‐iPr₂C₆H₃N)}₂)GePCO 1 is shown to react with the Lewis acids (E(C₆F₅)₃ E=B, Al). Nonetheless, 1 participates in FLP chemistry with electron deficient alkynes or olefins, acting as an intramolecular FLP. In contrast, in the presence of B(C₆F₅)₃ and an electron rich alkyne, 1 behaves as Ge‐based nucleophile to effect intermolecular FLP addition to the alkyne. This reactivity demonstrates that the reaction pathway is controlled by the nature of the electrophile and nucleophile generated in solution, as revealed by extensive DFT calculations.

Phosphine-Stabilized Pnictinidenes

The reaction of the intramolecular germylene‐phosphine Lewis pair (o‐PPh₂)C₆H₄GeAr* (1) with Group 15 element trichlorides ECl₃ (E=P, As, Sb) was investigated. After oxidative addition, the resulting compounds (o‐PPh₂)C₆H₄(Ar*)Ge(Cl)ECl₂ (2: E=P, 3: E=As, 4: E=Sb) were reduced by using sodium metal or LiHBEt₃. The molecular structures of the phosphine‐stabilized phosphinidene (o‐PPh₂)C₆H₄(Ar*)Ge(Cl)P (5), arsinidene (o‐PPh₂)C₆H₄(Ar*)Ge(Cl)As (6) and stibinidene (o‐PPh₂)C₆H₄(Ar*)Ge(Cl)Sb (7) are presented; they feature a two‐coordinate low‐valent Group 15 element. After chloride abstraction, a cyclic germaphosphene [(o‐PPh₂)C₆H₄(Ar*)GeP] [B(C₆H₃(CF₃)₂)₄] (8) was isolated. The ³¹P NMR data of the germaphosphene were compared with literature examples and analyzed by quantum chemical calculations. The phosphinidene was treated with [iBu₂AlH]₂, and the product of an Al−H addition to the low‐valent phosphorus atom (o‐PPh₂)C₆H₄(Ar*)Ge(H)P(H)Al(C₄H₉)₂ (9) was characterized.

Germyliumylidene: A Versatile Low Valent Group 14 Catalyst

Bis‐NHC stabilized germyliumylidenes [RGe(NHC)₂]⁺ are typically Lewis basic (LB) in nature, owing to their lone pair and coordination of two NHCs to the vacant p‐orbitals of the germanium center. However, they can also show Lewis acidity (LA) via Ge−C^NHC σ* orbital. Utilizing this unique electronic feature, we report the first example of bis‐NHC‐stabilized germyliumylidene [^MesTerGe(NHC)₂]Cl (1), (^MesTer=2,6‐(2,4,6‐Me₃C₆H₂)₂C₆H₃; NHC= IMe₄=1,3,4,5‐tetramethylimidazol‐2‐ylidene) catalyzed reduction of CO₂ with amines and arylsilane, which proceeds via its Lewis basic nature. In contrast, the Lewis acid nature of 1 is utilized in the catalyzed hydroboration and cyanosilylation of carbonyls, thus highlighting the versatile ambiphilic nature of bis‐NHC stabilized germyliumylidenes.

Partnering a Three-Coordinate Gallium Cation with a Hydroborate Counter-Ion for the Catalytic Hydrosilylation of CO2

A novel β-diketiminate stabilized gallium hydride, (^Dipp L)Ga(Ad)H (where (^Dipp L)={HC(MeCDippN)₂ }, Dipp=2,6-diisopropylphenyl and Ad=1-adamantyl), has been synthesized and shown to undergo insertion of carbon dioxide into the Ga-H bond under mild conditions. In this case, treatment of the resulting κ¹ -formate complex with triethylsilane does not lead to regeneration of the hydride precursor. However, when combined with B(C₆ F₅ )₃ , (^Dipp L)Ga(Ad)H catalyses the reductive hydrosilylation of CO₂ . Under stoichiometric conditions, the addition of one equivalent of B(C₆ F₅ )₃ to (^Dipp L)Ga(Ad)H leads to the formation of a 3-coordinate cationic gallane complex, partnered with a hydroborate anion, [(^Dipp L)Ga(Ad)][HB(C₆ F₅ )₃ ]. This complex rapidly hydrometallates carbon dioxide and catalyses the selective reduction of CO₂ to the formaldehyde oxidation level at 60 °C in the presence of Et₃ SiH (yielding H₂ C(OSiEt₃ )₂ ). When catalysis is undertaken in the presence of excess B(C₆ F₅ )₃ , appreciable enhancement of activity is observed, with a corresponding reduction in selectivity: the product distribution includes H₂ C(OSiEt₃ )₂ , CH₄ and O(SiEt₃ )₂ . While this system represents proof-of-concept in CO₂ hydrosilylation by a gallium hydride system, the TOF values obtained are relatively modest (max. 10 h^-1 ). This is attributed to the strength of binding of the formatoborate anion to the gallium centre in the catalytic intermediate (^Dipp L)Ga(Ad){OC(H)OB(C₆ F₅ )₃ }, and the correspondingly slow rate of the turnover-limiting hydrosilylation step. In turn, this strength of binding can be related to the relatively high Lewis acidity measured for the [(^Dipp L)Ga(Ad)]⁺ cation (AN=69.8).

Molecular Zinc Hydride Cations [ZnH]+ : Synthesis, Structure, and CO2 Hydrosilylation Catalysis

Protonolysis of [ZnH2 ]n with the conjugated Brønsted acid of the bidentate diamine TMEDA (N,N,N',N'-tetramethylethane-1,2-diamine) and TEEDA (N,N,N',N'-tetraethylethane-1,2-diamine) gave the zinc hydride cation [(L2 )ZnH]+ , isolable either as the mononuclear THF adduct [(L2 )ZnH(thf)]+ [BArF 4 ]- (L2 =TMEDA; BArF 4 - =[B(3,5-(CF3 )2 -C6 H3 )4 ]- ) or as the dimer [{(L2 )Zn)}2 (μ-H)2 ]2+ [BArF 4 ]- 2 (L2 =TEEDA). In contrast to [ZnH2 ]n , the cationic zinc hydrides are thermally stable and soluble in THF. [(L2 )ZnH]+ was also shown to form di- and trinuclear adducts of the elusive neutral [(L2 )ZnH2 ]. All hydride-containing cations readily inserted CO2 to give the corresponding formate complexes. [(TMEDA)ZnH]+ [BArF 4 ]- catalyzed the hydrosilylation of CO2 with tertiary hydrosilanes to give stepwise formoxy silane, methyl formate, and methoxy silane. The unexpected formation of methyl formate was shown to result from the zinc-catalyzed transesterification of methoxy silane with formoxy silane, which was eventually converted into methoxy silane as well.

Controlling the Product Platform of Carbon Dioxide Reduction: Adaptive Catalytic Hydrosilylation of CO2 Using a Molecular Cobalt(II) Triazine Complex

The catalytic reduction of carbon dioxide (CO2 ) is considered a major pillar of future sustainable energy systems and chemical industries based on renewable energy and raw materials. Typically, catalysts and catalytic systems are transforming CO2 preferentially or even exclusively to one of the possible reduction levels and are then optimized for this specific product. Here, we report a cobalt-based catalytic system that enables the adaptive and highly selective transformation of carbon dioxide individually to either the formic acid, the formaldehyde, or the methanol level, demonstrating the possibility of molecular control over the desired product platform.

Diverse Catalytic Systems and Mechanistic Pathways for Hydrosilylative Reduction of CO2

Catalytic hydrosilylation of carbon dioxide has emerged as a promising approach for carbon dioxide utilization. It allows the reductive transformation of carbon dioxide into value-added products at the levels of formate, formaldehyde, methanol, and methane. Tremendous progress has been made in the area of carbon dioxide hydrosilylation since the first reports in 1981. This focus review describes recent advances in the design and catalytic performance of leading catalyst systems, including transition-metal, main-group, and transition-metal/main-group and main-group/main-group tandem catalysts. Emphasis is placed on discussions of key mechanistic features of these systems and efforts towards the development of more selective, efficient, and sustainable carbon dioxide hydrosilylation processes.

Isolation of a Diylide-Stabilized Stannylene and Germylene: Enhanced Donor Strength through Coplanar Lone Pair Alignment

The preparation of the first stable diylide‐substituted stannylene and germylene (Y₂E, with E=Ge, Sn and Y=[PPh₃‐C‐SO₂Tol]⁻) is reported. The synthesis is easily accomplished in one step from the sulfonyl‐substituted metalated ylide YNa and the corresponding ECl₂ precursors. Y₂Ge and Y₂Sn exhibit unusual structures in the solid state and in solution, in which the three adjacent lone pairs in the C‐E‐C linkage are arranged coplanar to each other. As shown by DFT studies, this bonding situation is preferred over the typical π‐donation from the ligands into the empty p‐orbital at the metal due to the strong anion‐stabilizing ability of the sulfonyl groups in the ylide backbone and their additional coordination to the metal. The alignment of the three lone pairs leads to a remarkable boost of the HOMO energy and thus of the donor strengths of the tetrylenes. Hence, Y₂Ge and Y₂Sn become stronger donors than their diamino or diaryl congeners and comparable to cyclic alkyl(amino)carbenes. First reactivity studies confirm the high reactivity of Y₂Ge and Y₂Sn, which for example undergo an intramolecular C−H activation reaction via metal–ligand cooperation.

Borane-Catalyzed Cross-Metathesis Strategy for Facile Transformation of Cyclic (Alkyl)(Amino)Germylenes

A borane B(C₆ F₅ )₃ -catalyzed metathesis reaction between the Si-C bond in the cyclic (alkyl)(amino)germylene (CAAGe) 1 and the Si-H bond in a silane (R₃ SiH; 2) is reported. Mechanistic studies propose that the initial step of the reaction involves Si-H bond activation to furnish an ionic species [1-SiR₃ ]⁺ [HB(C₆ F₅ )₃ ]^- , from which [Me₃ Si]⁺ [HB(C₆ F₅ )₃ ]^- and an azagermole intermediate are generated. The former yields Me₃ SiH concomitant with the regeneration of B(C₆ F₅ )₃ whereas the latter undergoes isomerization to afford CAAGes bearing various silyl groups on the carbon atom next to the germylene center. This strategy allows the straightforward synthesis of eight new CAAGes starting from 1.