A nitrogen-base catalyzed generation of organotin(ii) hydride from an organotin trihydride under reductive dihydrogen elimination

Characterization of Germanium Nanoparticles from Arylgermanium Trihydrides

Germanium is a promising basis for nanomaterials due to its low toxicity and valuable optical and electronic properties. However, germanium nanomaterials have seen little research compared to other group 14 elements due to unpredictable chemical behavior and high costs. Here, we report the dehydrocoupling of o-tolylgermanium trihydride to amorphous nanoparticles. The reaction is facilitated through reflux at 162 °C and can be accelerated with an amine base catalyst. Through cleavage of both H2 and toluene, new Ge-Ge bonds form. This results in nanoparticles consisting of crosslinked germanium with o-tolyl termination. The particles are 2-6 nm in size and have masses above approximately 3500 Da. The organic substituents are promising for further functionalization. Combined with strong absorption up to 600 nm and moderate solubility and air stability, there are numerous possibilities for future applications.

Recent advances in the chemistry of isolable carbene analogues with group 13-15 elements

Carbenes (R2C:), compounds with a divalent carbon atom containing only six valence shell electrons, have evolved into a broader class with the replacement of the carbene carbon or the RC moiety with main group elements, leading to the creation of main group carbene analogues. These analogues, mirroring the electronic structure of carbenes (a lone pair of electrons and an empty orbital), demonstrate unique reactivity. Over the last three decades, this area has seen substantial advancements, paralleling the innovations in carbene chemistry. Recent studies have revealed a spectrum of unique carbene analogues, such as monocoordinate aluminylenes, nitrenes, and bismuthinidenes, notable for their extraordinary properties and diverse reactivity, offering promising applications in small molecule activation. This review delves into the isolable main group carbene analogues that are in the forefront from 2010 and beyond, spanning elements from group 13 (B, Al, Ga, In, and Tl), group 14 (Si, Ge, Sn, and Pb) and group 15 (N, P, As, Sb, and Bi). Specifically, this review focuses on the potential amphiphilic species that possess both lone pairs of electrons and vacant orbitals. We detail their comprehensive synthesis and stabilization strategies, outlining the reactivity arising from their distinct structural characteristics.

Divergent Reactivity of a Cyclic Bis-Hydridostannylene: A Masked Sn(I) Diradicaloid

Herein, reactivity studies of a cyclic bis-hydridostannylene [(ADC)SnH]2 (1-H2) (ADC=PhC{(NDipp)C}2; Dipp=2,6-iPr2C6H3) with various unsaturated organic substrates are reported. Reactions of terminal alkynes (RC≡CH) with 1-H2 afford mixed acetylide-vinyl-functionalized bis-stannylenes via dehydrogenation and hydrostannylation. Treatment of 1-H2 with PhC≡CCH3 gives a unique distannabarrelene via dehydrogenative C(sp3)-H stannylation and hydrostannylation of the C≡CCH3 moiety. 1-H2 undergoes dehydrogenative [2+2]-cycloaddition reactions with diphenylacetylene, azobenzene, acetone, benzophenone, and benzaldehyde to form the 1,4-distannabarrelene derivatives. The elimination of H2 in these reactions suggests the masked-diradical property of 1-H2. In fact, these [2+2]-cycloaddition products are also accessible on treatments of the Sn(I) diradicaloid [(ADC)Sn]2 (1) with appropriate reagents. All compounds have been characterized by multinuclear NMR spectroscopy and single crystal X-ray diffraction. Moreover, the catalytic activity of 1-H2 has been shown for the hydroboration of unsaturated substrates.

Phosphanyl-substituted tin half-sandwich complexes†

Phosphanyl-substituted tin(ii) half sandwich complexes are reported. Due to the Lewis acidic tin center and Lewis basic phosphorous atom they form head-to-tail dimers. Their properties and reactivities were investigated both experimentally and theoretically. Furthermore, related transition metal complexes of these species are presented.

Phosphanyl-substituted tin(ii) half sandwich complexes are reported, which exhibit Lewis acidic tin atoms and Lewis basic phosphorous atoms and form head-to-tail dimers.

Reactivity of organogermanium and organotin trihydrides

The organogermanium and organotin trihydrides (TbbEH₃) [E = Ge (3), Sn (7)] with the Tbb substituent were synthesized by hydride substitution (Tbb = 2,6-[CH(SiMe₃)₂]₂-4-(t-Bu)C₆H₂). Deprotonation of the organoelement trihydrides 3 and 7 was studied in reaction with bases MeLi, BnK and LDA (Bn = benzyl, LDA = lithium diisopropylamide) to yield the deprotonation products (8-11) as lithium or potassium salts. Hydride abstraction from TbbSnH₃ using the trityl salt [Ph₃C][Al(OC{CF₃}₃)₄] gives the salt [TbbSnH₂][Al(OC{CF₃}₃)₄] (12) which was stabilized by thf donor ligands [TbbSnH₂(thf)₂][Al(OC{CF₃}₃)₄] (13). Tintrihydride 7 reacts with trialkylamine Et₂MeN to give as the product of a reductive elimination of hydrogen the distannane (TbbSnH₂)₂ (14). Transfer of hydrogen was observed in reaction of trihydrides TbbEH₃ (E = Ge, Sn) and Ar*GeH₃ with N-heterocyclic carbene (NHC). The NHC adduct TbbSnH(^iPrNHC) (15) was synthesized at rt and the germanium hydrides exhibit hydrogen transfer at higher temperatures to give Ar*GeH(^MeNHC) (16) and TbbGeH(^MeNHC) (17).

Isolable Tin(II) Hydrides Featuring Sterically Undemanding Pincer-Type Ligands and Their Dehydrogenative Sn-Sn Bond Forming Reactions to Distannynes Promoted by Lewis Acidic Tri-sec-butylborane

Unlike isolable tin(II) hydrides supported by bulky ligands reported in the literature, this research describes the synthesis and characterization of thermally stable tin(II) hydrides L^PhSnH (1-H) and ^MeLSnH (2-H) stabilized by sterically undemanding N,N,N-coordinating pincer-type ligands (L^Ph = 2,5-dipyridyl-3,4-diphenylpyrrolato; ^MeL = 2,5-bis(6-methylpyridyl)pyrrolato). The results from previous reports reveal that attempts to access tin(II) hydrides containing less-bulky ligands have had limited success, and decomposition to tin(I) distannynes often occurs. The key to the successful isolation of 1-H and 2-H is the identification of the role of Lewis acidic B^sBu₃, generated upon delivering hydride from commonly used hydride reagents M[B^sBu₃H] ("selectrides", M = Li or K). This study details compelling experimental evidence and theoretical results of the role played by B^sBu₃, which catalyzes the dehydrocoupling reactions of 1-H and 2-H to yield tin(I) distannynes L^PhSn-SnL^Ph (1₂) and ^MeLSn-Sn^MeL (2₂) with the liberation of H₂. To avoid the interference of B^sBu₃, 1-H and 2-H can be isolated in pure forms using pinacolborane as the hydride donor with L^PhSnOMe (1-OMe) and ^MeLSnOMe (2-OMe) as reactants, respectively. DFT calculations and experimental observations indicate that the coordination of the Sn-H bond of 1-H to B^sBu₃ leaves an electrophilic tin center, rendering the nucleophilic attack by the second equivalent of 1-H forming a Sn-Sn bond.

Benchmark Study on the Calculation of 119Sn NMR Chemical Shifts

A new benchmark set termed SnS51 for assessing quantum chemical methods for the computation of ¹¹⁹Sn NMR chemical shifts is presented. It covers 51 unique ¹¹⁹Sn NMR chemical shifts for a selection of 50 tin compounds with diverse bonding motifs and ligands. The experimental reference data are in the spectral range of ±2500 ppm measured in seven different solvents. Fifteen common density functional approximations, two scalar- and one spin-orbit relativistic approach are assessed based on conformer ensembles generated using the CREST/CENSO scheme and state-of-the-art semiempirical (GFN2-xTB), force field (GFN-FF), and composite DFT methods (r²SCAN-3c). Based on the results of this study, the spin-orbit relativistic method combinations of SO-ZORA with PBE0 or revPBE functionals are generally recommended. Both yield mean absolute deviations from experimental data below 100 ppm and excellent linear regression determination coefficients of ≤0.99. If spin-orbit calculations are not affordable, the use of SR-ZORA with B3LYP or X2C with ωB97X or M06 may be considered to obtain qualitative predictions if no severe spin-orbit effects, for example, due to heavy nuclei containing ligands, are expected. An empirical linear scaling correction is demonstrated to be applicable for further improvement, and respective empirical parameters are given. Conformational effects on chemical shifts are studied in detail but are mostly found to be small. However, in specific cases when the ligand sphere differs substantially between conformers, chemical shifts can change by up to several hundred ppm.

A Brønsted Acidic Gallium Hydride: Facile Interconversion of NNNN-Macrocycle Supported [GaI]+ and [GaIIIH]2

Protonolysis of [Cp*M] (M=Ga, In, Tl) with [(Me₄TACD)H][BAr₄^Me] (Me₄TACD=N,N′,N′′,N′′′‐tetramethyl‐1,4,7,10‐tetraazacyclododecane; [BAr₄^Me]⁻=[B{C₆H₃‐3,5‐(CH₃)₂}₄]⁻) provided monovalent salts [(Me₄TACD)M][BAr₄^Me], whereas [Cp*Al]₄ yielded trivalent [(Me₄TACD)AlH][BAr₄^Me]₂. Protonation of [(Me₄TACD)Ga][BAr₄^Me] with [Et₃NH][BAr₄^Me] gave an unusually acidic (pK_a(CH₃CN)=24.5) gallium(III) hydride dication [(Me₄TACD)GaH][BAr₄^Me]₂. Deprotonation with IMe₄ (1,3,4,5‐tetramethyl‐imidazol‐ylidene) returned [(Me₄TACD)Ga][BAr₄^Me]. These reversible processes occur with formal two‐electron oxidation and reduction of gallium. DFT calculations suggest that gallium(I) protonation is facilitated by strong coordination of the tetradentate ligand, which raises the HOMO energy. High nuclear charge of [(Me₄TACD)GaH]²⁺ facilitates hydride‐to‐metal charge transfer during deprotonation. Attempts to prepare a gallium(III) dihydride cation resulted in spontaneous dehydrogenation to [(Me₄TACD)Ga]⁺.

Controlling Oxidative Addition and Reductive Elimination at Tin(I) via Hemi-Lability

We report on the synthesis of a distannyne supported by a pincer ligand bearing pendant amine donors that is capable of reversibly activating E-H bonds at one or both of the tin centres through dissociation of the hemi-labile N-Sn donor/acceptor interactions. This chemistry can be exploited to sequentially (and reversibly) assemble mixed-valence chains of tin atoms of the type ArSn{Sn(Ar)H}_n SnAr (n=1, 2). The experimentally observed (decreasing) propensity towards chain growth with increasing chain length can be rationalized both thermodynamically and kinetically by the electron- withdrawing properties of the -Sn(Ar)H- backbone units generated via oxidative addition.

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.

Hydrostannylation of carbon dioxide by a hydridostannylene molybdenum complex

Reaction of the aryltin(II) hydrides {Ar^iPr₄Sn(μ-H)}₂ or {Ar^iPr₆Sn(μ-H)}₂ (Ar^iPr₄ = -C₆H₃-2,6-(C₆H₃-2,6-ⁱPr₂)₂, Ar^iPr₆ = -C₆H₃-2,6-(C₆H₂-2,4,6-ⁱPr₃)₂) with two equivalents of the molybdenum carbonyl [Mo(CO)₅(THF)] afforded the divalent tin hydride transition metal complexes, Mo(CO)₅{Sn(Ar^iPr₆)H}, (1), or Mo(CO)₅{Sn(Ar^iPr₄)(THF)H} (2), respectively. Complex 1 effects the facile hydrostannylation of carbon dioxide, to yield Mo(CO)₅{Sn(Ar^iPr₆)(κ²-O,O'-O₂CH)}, (3), which features a bidentate formate ligand coordinating the tin atom. Reaction of 3 with the pinacolborane, HBpin (pin = pinacolato) in benzene regenerated 1 in quantitative yield. All complexes were characterized by X-ray crystallography, as well as UV-visible, IR, and multinuclear NMR spectroscopies. The isolation of 1 and 2 is consistent with the existence of monomeric forms of {Ar^iPr₄Sn(μ-H)}₂ and {Ar^iPr₆Sn(μ-H)}₂ in solution. Regeneration of 1 from 3via reaction with pinacolborane as the hydrogen source shows the catalytic potential of 1 in the hydrogenation of CO₂.

Tetryl-Tetrylene Addition to Phenylacetylene

Phenylacetylene adds [Ar*GeH2 -SnAr'], [Ar*GeH2 -PbAr'] and [Ar'SnH2 -PbAr*] at rt in a regioselective and stereoselective reaction. The highest reactivity was found for the stannylene, which reacts immediately upon addition of one equivalent of alkyne. However, the plumbylenes exhibit addition to the alkyne only in reaction with an excess of phenylacetylene. The product of the germylplumbylene addition reacts with a second equivalent of alkyne and the product of a CH-activation, a dimeric lead acetylide, were isolated. In the case of the stannylplumbylene the trans-addition product was characterized as the kinetically controlled product which isomerizes at rt to yield the cis-addition product, which is stabilized by an intramolecular Sn-H-Pb interaction. NMR chemical shifts of the olefins were investigated using two- and four-component relativistic DFT calculations, as spin-orbit effects can be large. Hydride abstraction was carried out by treating [Ar'SnPhC=CHGeH2 Ar*] with the trityl salt [Ph3 C][Al(OC{CF3 })4 ] to yield a four membered ring cation.

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.

Transition-Metal-Like Catalysis with a Main-Group Element: Bismuth-Catalyzed C-F Coupling of Aryl Boronic Esters

The main-group age: The past decade has revealed main-group-element compounds that display transition-metal-like reactivity in stoichiometric and even catalytic transformations. Cornella and co-workers have now reported a bismuth complex that catalyzes fluoroarene formation from aryl boronate esters, a reaction that is almost unprecedented in transition-metal catalysis.

Diaryltin Dihydrides and Aryltin Trihydrides with Intriguing Stability

In the last few decades, organotin hydrides have proven their potential as building blocks for a great variety of organometallic compounds. In this context, organotin hydrides with sterically shielding aryl substituents have attracted special interest, as these ligands can kinetically stabilize metastable products. The selective synthesis of aryltin halide compounds Ar*₂SnCl₂ and Ar*SnI₃ featuring the highly sterically encumbered aryl ligand Ar* (^iPrAr* = 2,6-(Ph₂CH)₂-4-iPrC₆H₂; ^MeAr* = 2,6-(Ph₂CH)₂-4-MeC₆H₂) is presented. These aryltin halides were converted into corresponding aryltin hydrides Ar*₂SnH₂ and Ar*SnH₃, which exhibit a surprisingly high thermal stability and oxygen tolerance.

Reductive dehydrocoupling of diphenyltin dihydride with LiAlH4: selective synthesis and structures of the first bicyclo[2.2.1]heptastannane-1,4-diide and bicyclo[2.2.2]octastannane-1,4-diide

The reaction of diphenyltin dihydride with LiAlH4 gives access to a set of charged tin cages as their lithium salts. Variation in the ratio of reactants provides a perstannabicyclooctane dianion and a perstannanorbornane as the di- and monoanions. These compounds can be synthesised selectively by careful stoichiometric control and have been characterised by single crystal X-ray diffractometry, NMR and UV-vis spectroscopy. Computational exploration of the electronic structures of these compounds was undertaken and, in agreement with structural and spectroscopic features, indicated significant σ-delocalisation in the tin skeletons.

Hydridoorganostannylene Coordination: Group 4 Metallocene Dichloride Reduction in Reaction with Organodihydridostannate Anions

Organodihydridoelement anions of germanium and tin were reacted with metallocene dichlorides of Group 4 metals Ti, Zr and Hf. The germate anion [Ar*GeH2 ]- reacts with hafnocene dichloride under formation of the substitution product [Cp2 Hf(GeH2 Ar*)2 ]. Reaction of the organodihydridostannate with metallocene dichlorides affords the reduction products [Cp2 M(SnHAr*)2 ] (M=Ti, Zr, Hf). Abstraction of a hydride substituent from the titanium bis(hydridoorganostannylene) complex results in formation of cation [Cp2 M(SnAr*)(SnHAr*)]+ exhibiting a short Ti-Sn interaction. (Ar*=2,6-Trip2 C6 H3 , Trip=2,4,6-triisopropylphenyl).

Deprotonation of Organogermanium and Organotin Trihydrides

Terphenyltin and terphenylgermanium trihydrides were deprotonated in reaction with strong bases, such as LiMe, LDA, or KBn. In the solid state, the Li salts of the germate anion 4 and 4a exhibit a Li-Ge contact. In the Li salt of the dihydridostannate anion 6a, the Li cation is not coordinated at the tin atom instead an interaction of the Li cation with the hydride substituents was found. Evidenced by ¹H-⁷Li-HOESY NMR spectroscopy the Li-salt of the deprotonated tin hydride 6a exhibits in toluene solution a contact between Li cation and hydride substituents, whereas in the ¹H-⁷Li-HOESY NMR spectrum of the homologous germate salt 4a, no crosspeak between hydride and Li signals was found. The organodihydridogermate and -stannate react as nucleophiles with low-valent Group 14 electrophiles. Thus, three compounds were synthesized: Ar-Ë'-EH₂-Ar (E', E = Sn, Ge; Pb, Ge; Pb, Sn; Ar = Ar', Ar*). Following an alternative synthesis Ar'SnH₂PbAr* was synthesized in reaction between [(Ar*PbH)₂] and [(Ar'SnH)₄] generated in situ. In reaction between low-valent organotin hydride [(Ar*SnH)₂] and organdihydridostannate [Ar*SnH₂]^- formation of distannate [Ar*₂Sn₂H₃]^- was found.

Base-induced reversible H2 addition to a single Sn(ii) centre

A range of amines catalyse the oxidative addition (OA) of H2 to [(Me3Si)2CH]2Sn (1), forming [(Me3Si)2CH]2SnH2 (2). Experimental and computational studies point to 'frustrated Lewis pair' mechanisms in which 1 acts as a Lewis acid and involve unusual late transition states; this is supported by the observation of a kinetic isotope effect for Et3N. When DBU is used the energetics of H2 activation are altered, allowing an equilibrium between 1, 2 and adduct [1·DBU] to be established, thus demonstrating reversible oxidative addition/reductive elimination (RE) of H2 at a single main group centre.

Fast kinetics studies of the Lewis acid-base complexation of transient stannylenes with σ- and π-donors in solution

The Lewis acid-base complexation chemistry of dimethyl- and diphenylstannylene (SnMe2 and SnPh2, respectively) in hexanes solution has been studied by laser photolysis methods. Complexation of the two stannylenes with a series of nine O-, S-, and N-donors (including cyclic and acyclic dialkyl ethers and sulfides, a primary, secondary, and tertiary amine, ethyl acetate and acetone), two alkenes, and an alkyne proceeds rapidly and reversibly to generate the corresponding stannylene-donor Lewis pairs, which have been detected in each case by time-resolved UV-vis absorption spectroscopy. The complexes exhibit UV-vis absorption maxima in the range of λmax ∼ 310-405 nm depending on the donor and substitution at tin. Bimolecular rate constants for complexation (kC), which could be determined for 14 of the 24 Lewis pairs that were studied, were found to fall within a factor of four of the diffusional limit in all cases, with SnMe2 showing consistently higher reactivity than SnPh2. Equilibrium constants for complexation (KC) could be measured for all but one of the stannylene-π- and O-donor pairs, the values corresponding to (gas phase) binding free energies in the range of +1.1 to -3.9 kcal mol-1. Comparison of the experimental equilibrium constants for complexation of SnMe2 and SnPh2 with methanol and diethyl ether to those measured previously for the homologous silylenes and germylenes indicates that Lewis acidity decreases in the order SiR2 > SnR2 > GeR2 for both the dimethyl- and diphenyltetrylene series, the diphenyl derivatives exhibiting significantly stronger Lewis acidity in all three cases. The experimental trends in the binding energies and UV-vis spectra of the complexes are reproduced well by density functional theory (DFT) calculations, which have been carried out at the (TD)ωB97XD/def2-TZVP level of theory. The experimental data also show evidence of a reaction between tetramethyldistannene (Me2Sn[double bond, length as m-dash]SnMe2, 4a) and amine donors, which is suggested to afford the corresponding amine-stabilized stannylidenestannylene structure. The mechanistic proposal is supported by DFT calculations of the complexation of 4a and SnMe2 with model O-, S- and N-donors.

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.

Reversible Coordination of H2 by a Distannyne

The terphenyl tin(II) hydride [Ar^iPr₄Sn(μ-H)]₂ (1) (Ar^iPr₄ = C₆H₃-2,6(C₆H₃-2,6-ⁱPr₂)₂) was shown to form an equilibrium with the distannyne Ar^iPr₄SnSnAr^iPr₄ (2) and H₂ in toluene at 80 °C. The equilibrium constant and Gibbs free energy for the dissociation of H₂ are 2.23 × 10^-4 ± 4.9% and 5.89 kcal/mol ± 0.68%, respectively, by ¹H NMR spectroscopy and 2.33 × 10^-4 ± 6.2% and 5.86 kcal/mol ± 0.73%, respectively, by UV-vis spectroscopy, indicating that the hydride 1 is strongly favored. Further heating of 2 at ca. 100 °C afforded the known pentagonal-bipyramidal Sn₇ cluster Sn₅(SnAr^iPr₄)₂ (3). Mechanistic studies show that 3 is formed from distannyne 2, which is generated from 1. The order of the reaction for the conversion of 2 into 3 was found to be zero, and the rate constant is 1.77 × 10^-5 M s^-1 at 100 °C. Hydride 1 was further characterized by cyclic voltammetry, and its pK_a was found to be 18.8(2) via titration with 1,8-diazabicyclo[5.4.0]undec-7-ene. The bond dissociation free energy was estimated to be 51.1 kcal/mol ± 3.4% on the basis of its pK_a and reduction potential. Studies with deuterium indicate ready exchange of D₂ with the hydrides in 1.

Evidence for single metal two electron oxidative addition and reductive elimination at uranium

Reversible single-metal two-electron oxidative addition and reductive elimination are common fundamental reactions for transition metals that underpin major catalytic transformations. However, these reactions have never been observed together in the f-block because these metals exhibit irreversible one- or multi-electron oxidation or reduction reactions. Here we report that azobenzene oxidises sterically and electronically unsaturated uranium(III) complexes to afford a uranium(V)-imido complex in a reaction that satisfies all criteria of a single-metal two-electron oxidative addition. Thermolysis of this complex promotes extrusion of azobenzene, where H-/D-isotopic labelling finds no isotopomer cross-over and the non-reactivity of a nitrene-trap suggests that nitrenes are not generated and thus a reductive elimination has occurred. Though not optimally balanced in this case, this work presents evidence that classical d-block redox chemistry can be performed reversibly by f-block metals, and that uranium can thus mimic elementary transition metal reactivity, which may lead to the discovery of new f-block catalysis.

The reactivity of f-block complexes is primarily defined by single-electron oxidations and σ-bond metathesis. Here, Liddle and co-workers provide evidence that a uranium complex can undergo reversible oxidative addition and reductive elimination, demonstrating transition metal-like reactivity within f-block chemistry.

Reaction of stannylene phosphorus Lewis pairs with dichlorides of germanium, tin and lead - the formation of base stabilized stannyl stannylenes/germylenes and redox reaction with PbCl2

The reaction of intramolecular stannylene phosphorus Lewis pairs with heavier dichlorides of group 14 (GeCl2, SnCl2, PbCl2) is reported. Phosphine base stabilized stannyl germylenes/stannylenes were formed by the oxidative addition of an E-Cl bond to the stannylene tin atom (E = Ge, Sn). In solution, a dynamic equilibrium between two diastereomeric configurations was observed. With PbCl2 a redox reaction towards elemental lead and the dichlorinated tin(iv) compound was found. All compounds were characterized by X-ray diffraction, NMR spectroscopy and elemental analysis.

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.

Ligand coordination modulates reductive elimination from aluminium(iii)

Oxidative addition to low-valent main-group centres is a major class of reactivity for these species. Here, we present a mechanistic study of the much rarer reverse process – reductive elimination – in Al(iii) systems, and unravel ligand effects in this process.