Synthesis of an [(NHC)2 Pd(SiMe3 )2 ] Complex and Catalytic cis-Bis(silyl)ations of Alkynes with Unactivated Disilanes

Advances in disilylation reactions to access cis/trans-1,2-disilylated and gem-disilylated alkenes

Organosilane compounds are widely used in both organic synthesis and materials science. Particularly, 1,2-disilylated and gem-disilylated alkenes, characterized by a carbon-carbon double bond and multiple silyl groups, exhibit significant potential for subsequently diverse transformations. The versatility of these compounds renders them highly promising for applications in materials, enabling them to be valuable and versatile building blocks in organic synthesis. This review provides a comprehensive summary of methods for the preparation of cis/trans-1,2-disilylated and gem-disilylated alkenes. Despite notable advancements in this field, certain limitations persist, including challenges related to regioselectivity in the incorporation and chemoselectivity in the transformation of two nearly identical silyl groups. The primary objective of this review is to outline synthetic methodologies for the generation of these alkenes through disilylation reactions, employing silicon reagents, specifically disilanes, hydrosilanes, and silylborane reagents. The review places particular emphasis on investigating the practical applications of the C-Si bond of disilylalkenes and delves into an in-depth discussion of reaction mechanisms, particularly those reactions involving the activation of Si-Si, Si-H, and Si-B bonds, as well as the C-Si bond formation.

Ca(II) and Yb(II) complexes featuring M(C≡C)4 structural motif: enforced proximity or genuine η2 -bonding?

Bis(carbazolide) complexes M[3,6-tBu2 -1,8-(RC≡C)2 Carb]2 (THF)n (R=SiMe3 , n=0, M=Ca, Yb; R=Ph, n=1, M=Ca, Yb; n=0, M=Yb) were synthesized through transamination reaction of M[N(SiMe3 )2 ]2 (THF)2 with two molar equivalents of carbazoles. The complexes feature M(η2 -C≡C)4 structural motif composed of M(II) ions encapsulated by four acetylene fragments due to atypical for alkaline- and rare-earth metals η2 -interactions with triple C≡C bond. This interaction is evidenced experimentally by X-ray diffraction, Raman spectroscopy in the solid state and by NMR-spectroscopy in the solution. According to QTAIM analysis there are 4 bond critical points (3;-1) between the metal atom and each of the triple bonds, which are connected by a strongly curved, almost T-shaped bond pathway.

Carbene Complexes of Plutonium: Structure, Bonding, and Divergent Reactivity to Lanthanide Analogs

Organoplutonium chemistry was established in 1965, yet structurally authenticated plutonium-carbon bonds remain rare being limited to π-bonded carbocycle and σ-bonded isonitrile and hydrocarbyl derivatives. Thus, plutonium-carbenes, including alkylidenes and N-heterocyclic carbenes (NHCs), are unknown. Here, we report the preparation and characterization of the diphosphoniomethanide-plutonium complex [Pu(BIPMTMSH)(I)(μ-I)]2 (1Pu, BIPMTMSH = (Me3SiNPPh2)2CH) and the diphosphonioalkylidene-plutonium complexes [Pu(BIPMTMS)(I)(DME)] (2Pu, BIPMTMS = (Me3SiNPPh2)2C) and [Pu(BIPMTMS)(I)(IMe4)2] (3Pu, IMe4 = C(NMeCMe)2), thus disclosing non-actinyl transneptunium multiple bonds and transneptunium NHC complexes. These Pu-C double and dative bonds, along with cerium, praseodymium, samarium, uranium, and neptunium congeners, enable lanthanide-actinide and actinide-actinide comparisons between metals with similar ionic radii and isoelectronic 4f5 vs 5f5 electron-counts within conserved ligand fields over 12 complexes. Quantum chemical calculations reveal that the orbital-energy and spatial-overlap terms increase from uranium to neptunium; however, on moving to plutonium the orbital-energy matching improves but the spatial overlap decreases. The bonding picture that emerges is more complex than the traditional picture of the bonding of lanthanides being ionic and early actinides being more covalent but becoming more ionic left to right. Multiconfigurational calculations on 2M and 3M (M = Pu, Sm) account for the considerably more complex UV/vis/NIR spectra for 5f5 2Pu and 3Pu compared to 4f5 2Sm and 3Sm. Supporting the presence of Pu═C double bonds in 2Pu and 3Pu, 2Pu exhibits metallo-Wittig bond metathesis involving the highest atomic number element to date, reacting with benzaldehyde to produce the alkene PhC(H)═C(PPh2NSiMe3)2 (4) and "PuOI". In contrast, 2Ce and 2Pr do not react with benzaldehyde to produce 4.

Pd Nanoparticle-Catalyzed Stereospecific Mizoroki-Heck Arylation of cis-1,2-Disilylarylethylenes

In the presence of catalytic amounts of Pd nanoparticles, generated from Pd2dba3/Ag(I), cis-1,2-ditrimethylsilylarylethylenes undergo with aryl iodides a stereospecific Mizoroki-Heck arylation leading to trans-ditrimethylsilyldiarylethylenes. This chemoselectivity is in contrast to that of their trimethylgermyl analogues, which are arylated at the position of the C-Ge bonds. trans-1,2-Ditrimethylsilylarylethylenes are completely unreactive under the standard reaction conditions. The reaction tolerates the presence of boryl, silyl, or bromine substituents on the aryl iodides. From a mechanistic point of view, the process involves syn-arylpalladation followed by syn-dehydropalladation.

Synergistic Palladium/Lewis Acid-Catalyzed Regio- and Stereo-divergent Bissilylation of Alkynoates: Scope, Mechanism, and Origin of Selectivity

Transition metal-catalyzed bissilylation reactions of alkynes with disilane reagents have become one of the most straightforward and efficient protocols to rapidly produce structurally diverse alkenyl silicon derivatives. In these reactions, the utilization of unsymmetrical disilane reagents provided the possibilities for reactivity enhancement as well as the synthetic merits in contrast to symmetrical disilane reagents. However, a major yet challenging objective is achieving precise control over the selectivity including the regioselectivity and the cis/trans-selectivity. Herein we realized the first divergent bissilylation of alkynoates with our developed air-stable disilane reagent 8-(2-substituted-1,1,2,2-tetramethyldisilanyl)quinoline (TMDQ) by means of synergistic Pd/Lewis acid catalytic system. The catalytic system precisely dictates the selectivity, resulting in the divergent synthesis of 1,2-bissilyl alkenes. The power of these 1,2-bissilyl alkenes serving as the key synthetic intermediates has been clearly demonstrated by rapid construction of diverse motifs and densely functionalized biologically active compounds. In addition, the origins of the switchable selectivities were well elucidated by experimental and computational studies on the reaction mechanism and were mainly attributed to different ligand steric effects, the use of the specific disilane reagent TMDQ and the different coordination modes of different Lewis acid with alkynoates.

Dinuclear and tetranuclear group 10 metal complexes constructed from linear tetrasilane comprising both Si-H and Si-Si moieties

The activation of Si-H bonds and/or Si-Si bonds in organosilicon compounds by transition-metal species plays a crucial role for the production of functional organosilicon compounds. Although group-10-metal species are frequently used to activate Si-H and/or Si-Si bonds, so far, systematic investigation to clarify the preferences of these metal species with respect to the activation of Si-H and/or Si-Si bonds remain elusive. Here, we report that platinum(0) species that bear isocyanide or N-heterocyclic-carbene (NHC) ligands selectively activates the terminal Si-H bonds of the linear tetrasilane Ph₂(H)SiSiPh₂SiPh₂Si(H)Ph₂ in a stepwise manner, whereby the Si-Si bonds remain intact. In contrast, analogous palladium(0) species are preferably inserted into the Si-Si bonds of the same linear tetrasilane, whereby the terminal Si-H bonds remain intact. Substitution of the terminal hydride groups in Ph₂(H)SiSiPh₂SiPh₂Si(H)Ph₂ with chloride groups leads to the insertion of platinum(0) isocyanide into all Si-Si bonds to afford an unprecedented zig-zag Pt₄ cluster.

Palladium-catalyzed disilylation of ortho-halophenylethylenes enabled by 2-pyridone ligand

A palladium-catalyzed disilylation reaction applicable for a variety of non-, α-, or β-substituted and α,β-disubstituted ortho-halophenylethylenes has been developed. This reaction proceeds with high yields and very low catalyst loadings. The two C-Si bonds of the disilylated products could be well-differentiated chemoselectively in the reaction with various electrophiles.

Rhodium-Catalyzed Trans-Bis-Silylation Reactions of 2-Ethynyl-3-pentamethyldisilanylpyridines

Rhodium-catalyzed reactions of 2-ethynyl-3-pentamethyldisilanylpyridine derivatives (1 and 2) are reported. The reactions of compounds 1 and 2 in the presence of catalytic amounts of rhodium complexes at 110 °C gave the corresponding pyridine-fused siloles (3) and (4) through intramolecular trans-bis-silylation cyclization. The reaction of 2-bromo-3-(1,1,2,2,2-pentamethyldisilanyl)pyridine with 3-phenyl-1-propyne in the presence of PdCl₂(PPh₃)₂-CuI catalysts afforded 1:2 bis-silylation adduct 6. DFT calculations were also performed to understand the reaction mechanism for the production of compound 3 from compound 1.

A Hydride-Substituted Homoleptic Silylborate: How Similar is it to its Diborane(6)-Dianion Isostere?

The B-nucleophilic 9H-9-borafluorene dianion reacts with 9-chloro-9-silafluorene to afford air- and moisture-stable silylborate salts M[Ar₂ (H)B-Si(H)Ar₂ ] (M[HBSiH], M=Li, Na). Li[HBSiH] and Me₃ SiCl give the B-pyridine adduct Ar₂ (py)B-Si(H)Ar₂ ((py)BSiH) or the chlorosilane Li[Ar₂ (H)B-Si(Cl)Ar₂ ] (Li[HBSiCl]) in C₆ H₆ -pyridine or THF. In both cases, the first step is H^- abstraction at the B center. The resulting free borane subsequently binds a py or thf ligand. While the py adduct is stable at room temperature, the thf adduct undergoes a 1,2-H shift via the cyclic B(μ-H)Si intermediate BHSi, which is afterwards attacked at the Si atom by a Cl^- ion to give Li[HBSiCl]. DFT calculations were employed to support the proposed reaction mechanism and to characterize the electronic structure of BHSi. Treatment of Li[HBSiCl] with the N-heterocyclic carbene IMe introduces the neutral donor at the Si atom and leads to Ar₂ (H)B-Si(IMe)Ar₂ (HBSi(IMe)), a donor-acceptor-stabilized silylene.

Structure and Reactivity of [Ru–Al] and [Ru–Sn] Heterobimetallic PPh3-Based Complexes

Treatment of [Ru(PPh₃)(C₆H₄PPh₂)₂H][Li(THF)₂] with AlMe₂Cl and SnMe₃Cl leads to elimination of LiCl and CH₄ and formation of the heterobimetallic complexes [Ru(C₆H₄PPh₂)₂{PPh₂C₆H₄AlMe(THF)}H] 5 and [Ru(PPh₃)(C₆H₄PPh₂)(PPh₂C₆H₄SnMe₂)] 6, respectively. The pathways to 5 and 6 have been probed by variable temperature NMR studies, together with input from DFT calculations. Complete reaction of H₂ occurs with 5 at 60 °C and with 6 at room temperature to yield the spectroscopically characterized trihydride complexes [Ru(PPh₂)₂{PPh₂C₆H₄AlMe}H₃] 7 and [Ru(PPh₂)₂{PPh₂C₆H₄SnMe₂}H₃] 8. In the presence of CO, 6 forms the acylated phosphine complex, [Ru(CO)₂(C(O)C₆H₄PPh₂)(PPh₂C₆H₄SnMe₂)] 9, through a series of intermediates that were identified by NMR spectroscopy in conjunction with ¹³CO labeling. Complex 6 undergoes addition and substitution reactions with the N-heterocyclic carbene 1,3,4,5-tetramethylimidazol-2-ylidene (IMe₄) to give [Ru(IMe₄)₂(PPh₂C₆H₄)(PPh₂C₆H₄SnMe₂)] 10, which converted via rare N-Me group C–H activation to [Ru(IMe₄)(PPh₃)(IMe₄)′(PPh₂C₆H₄SnMe₂)] 11 upon heating at 60 °C and to a mixture of [Ru(IMe₄)₂(IMe₄)′(PPh₂C₆H₄SnMe₂)] 12 and [Ru(PPh₃)(PPh₂C₆H₄)(IMe₄-SnMe₂)′] 13 at 120 °C.

Synthesis of Pyridine-Fused Siloles by Palladium-Catalyzed Intramolecular Bis-Silylation

Silole derivatives are attracting significant attention as new functional materials with excellent electronic and photophysical properties. Thus, the development of synthesis methods to afford such derivatives is highly desirable. Herein, the synthesis of pyridine-fused siloles under the conditions of the Sonogashira coupling reaction is described. The reactions of 2-bromo-3-(pentamethyldisilanyl)pyridine (1) with ethynylbenzene derivatives in the presence of PdCl2(PPh3)2-CuI as a catalyst afforded the corresponding pyridine-fused siloles (2a-2c) through intramolecular trans-bis-silylation. DFT calculations were also performed to understand the reaction mechanism. This paper is the first to report on the successful use of palladium catalysts in the trans-bis-silylation of alkynes with disilanes.

Carbene Complexes of Neptunium

Since the advent of organotransuranium chemistry six decades ago, structurally verified complexes remain restricted to π-bonded carbocycle and σ-bonded hydrocarbyl derivatives. Thus, transuranium-carbon multiple or dative bonds are yet to be reported. Here, utilizing diphosphoniomethanide precursors we report the synthesis and characterization of transuranium-carbene derivatives, namely, diphosphonio-alkylidene- and N-heterocyclic carbene–neptunium(III) complexes that exhibit polarized-covalent σ²π² multiple and dative σ² single transuranium-carbon bond interactions, respectively. The reaction of [Np^IIII₃(THF)₄] with [Rb(BIPM^TMSH)] (BIPM^TMSH = {HC(PPh₂NSiMe₃)₂}^1–) affords [(BIPM^TMSH)Np^III(I)₂(THF)] (3Np) in situ, and subsequent treatment with the N-heterocyclic carbene {C(NMeCMe)₂} (I^Me4) allows isolation of [(BIPM^TMSH)Np^III(I)₂(I^Me4)] (4Np). Separate treatment of in situ prepared 3Np with benzyl potassium in 1,2-dimethoxyethane (DME) affords [(BIPM^TMS)Np^III(I)(DME)] (5Np, BIPM^TMS = {C(PPh₂NSiMe₃)₂}^2–). Analogously, addition of benzyl potassium and I^Me4 to 4Np gives [(BIPM^TMS)Np^III(I)(I^Me4)₂] (6Np). The synthesis of 3Np–6Np was facilitated by adopting a scaled-down prechoreographed approach using cerium synthetic surrogates. The thorium(III) and uranium(III) analogues of these neptunium(III) complexes are currently unavailable, meaning that the synthesis of 4Np–6Np provides an example of experimental grounding of 5f- vs 5f- and 5f- vs 4f-element bonding and reactivity comparisons being led by nonaqueous transuranium chemistry rather than thorium and uranium congeners. Computational analysis suggests that these Np^III=C bonds are more covalent than U^III=C, Ce^III=C, and Pm^III=C congeners but comparable to analogous U^IV=C bonds in terms of bond orders and total metal contributions to the M=C bonds. A preliminary assessment of Np^III=C reactivity has introduced multiple bond metathesis to transuranium chemistry, extending the range of known metallo-Wittig reactions to encompass actinide oxidation states III-VI.

Inorganometallics (Transition Metal-Metalloid Complexes) and Catalysis

While the formation and breaking of transition metal (TM)-carbon bonds plays a pivotal role in the catalysis of organic compounds, the reactivity of inorganometallic species, that is, those involving the transition metal (TM)-metalloid (E) bond, is of key importance in most conversions of metalloid derivatives catalyzed by TM complexes. This Review presents the background of inorganometallic catalysis and its development over the last 15 years. The results of mechanistic studies presented in the Review are related to the occurrence of TM-E and TM-H compounds as reactive intermediates in the catalytic transformations of selected metalloids (E = B, Si, Ge, Sn, As, Sb, or Te). The Review illustrates the significance of inorganometallics in catalysis of the following processes: addition of metalloid-hydrogen and metalloid-metalloid bonds to unsaturated compounds; activation and functionalization of C-H bonds and C-X bonds with hydrometalloids and bismetalloids; activation and functionalization of C-H bonds with vinylmetalloids, metalloid halides, and sulfonates; and dehydrocoupling of hydrometalloids. This first Review on inorganometallic catalysis sums up the developments in the catalytic methods for the synthesis of organometalloid compounds and their applications in advanced organic synthesis as a part of tandem reactions.

Palladium-Catalyzed Silylation of 2,3-Allenols with Unactivated Disilanes: Access to 2-Silyl-1,3-butadienes and α-Silyl-β-hydroxy Vinylsilanes

Regioselective silylation of 2,3-allenols with disilanes was carried out under catalysis of Pd₂dba₃/P(o-MeOC₆H₄)₃. In the presence of Cs₂CO₃, the reaction achieved 2-silyl-1,3-dienes. Reaction of 1-aryl-2,3-allenols gave the products with excellent Z/E selectivity and E-isomers as the major species. Reaction of α-alkylallenols or α-alkyl-α-aryl-allenols resulted in products with moderate Z/E selectivity and E-isomers are also major. Without a base, the reaction produced α-silyl-β-hydroxyl vinylsilanes, which were converted to 2-silyl-1,3-dienes upon treatment with Cs₂CO₃.

Theoretical investigation on the effect of the ligand on bis-silylation of C(sp)–C(sp) by Ni complexes

Density functional theory is used to study the bis-silylation of alkyne catalysed by a transition metal nickel–organic complex. The active catalyst, organic ligand, reaction mechanism, and rate-determining step were discussed with regard to dynamics and thermodynamics. COD or SIPr (COD = cyclooctadiene, SIPr = 1,3-bis(2,6-diisopropyl-phenyl)-4,5-dihydroimidazol-2-ylidene) coordination with Ni will greatly reduce the energy barrier of the Si–Si insertion step, that is, ΔΔG reaches 15.5 kcal mol⁻¹. Furthermore, the structure of alkynes will change the energy barrier of the alkyne insertion step.

Density functional theory (DFT) is used to study the bis-silylation of alkynes catalyzed by a transition metal nickel–organic complex; the active catalyst, the organic ligand, the reaction mechanism, and rate-determining step are discussed in this paper.

Zintl cluster supported low coordinate Rh(i) centers for catalytic H/D exchange between H2 and D2

We describe the synthesis of the coordinatively unsaturated Zintl clusters [Rh(L){η3-Ge9(Hyp)3}] (where L = PMe3, PPh3, IMe4 or [W(Cp)2H2]). These species are active catalysts in H/D exchange and C–H bond activation reactions.

Me3SiSiMe2(O n Bu): a disilane reagent for the synthesis of diverse silacycles via Brook- and retro-Brook-type rearrangement

Herein, a readily available disilane Me₃SiSiMe₂(OⁿBu) has been developed for the synthesis of diverse silacycles via Brook- and retro-Brook-type rearrangement. This protocol enables the incorporation of a silylene into different starting materials, including acrylamides, alkene-tethered 2-(2-iodophenyl)-1H-indoles, and 2-iodobiaryls, via the cleavage of Si–Si, Si–C, and Si–O bonds, leading to the formation of spirobenzosiloles, fused benzosiloles, and π-conjugated dibenzosiloles in moderate to good yields. Preliminary mechanistic studies indicate that this transformation is realized by successive palladium-catalyzed bis-silylation and Brook- and retro-Brook-type rearrangement of silane-tethered silanols.

A readily available disilane Me₃SiSiMe₂(OⁿBu) as a silylene source has been developed for the synthesis of diverse silacycles via Brook- and retro-Brook-type rearrangement.

Synthesis of trans-Mono(silyl)palladium(II) Bromide Complexes

The stoichiometric reaction of cis-[Pd(ITMe)₂(SiR₃)₂], where (SiR₃ = SiMe₃ and SiMe₂Ph and ITMe = 1,3,4,5-tetramethylimidazol-2-ylidene) with allyl bromide affords the corresponding allylsilanes along with complexes of the type trans-[Pd(ITMe)₂(SiR₃)(Br)]. The structure of trans-[Pd(ITMe)₂(SiMe₂Ph)Br] 2b has been determined in the solid state and displays a slightly distorted square-planar geometry with the two N-heterocyclic carbene ligands in a trans-configuration.

Bis-silylation of internal alkynes enabled by Ni(0) catalysis

1,2-Bis-silyl alkenes have exciting synthetic potential for programmable sequential synthesis via manipulation of the two vicinal silyl groups. Transition metal-catalyzed bis-silylation of alkynes with disilanes is the most straightforward strategy to access such useful building blocks. However, this process has some limitations: (1) symmetric disilanes are frequently employed in most of the reactions to assemble two identical silyl groups, which makes chemoselective differentiation for stepwise downstream transformations difficult; (2) the main catalysts are low-valent platinum group transition metal complexes, which are expensive; and (3) internal alkynes remain challenging substrates with low inherent reactivity. Thus, the development of abundant metal-catalyzed bis-silylation of internal alkynes with unsymmetrical disilanes is of significance. Herein, we solve most of the aforementioned limitations in bis-silylation of unsaturated bonds by developing a strongly coordinating disilane reagent and a Ni(0) catalytic system. Importantly, we sufficiently realize the stepwise recognition of the two silyl groups, making this synthetic protocol of wide potential utility.

Bis-silylated alkenes offer the advantage of two functional handles with distinguished reactivity for downstream functionalization. Here, the authors report a nickel-catalyzed bis-silylation of internal alkynes to versatile silylated alkene intermediates which can be chemoselectively manipulated.

Recent advances in NHC–palladium catalysis for alkyne chemistry: versatile synthesis and applications

This review summarizes the recent developments in NHC–palladium catalysis for alkyne chemistry: versatile synthesis and applications.

N-Heterocyclic Carbene Analogues of Nucleophilic Phosphinidene Transition Metal Complexes

Chloride abstraction from the complexes [(η6 -p-cymene){(IDipp)P}MCl] (2 a, M=Ru; 2 b, M=Os) and [(η5 -C5 Me5 ){(IDipp)P}IrCl] (3 b, IDipp=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) with sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaBArF ) in the presence of trimethylphosphine (PMe3 ), 1,3,4,5-tetramethylimidazolin-2-ylidene (Me IMe) or carbon monoxide (CO) afforded the complexes [(η6 -p-cymene){(IDipp)P}M(PMe3 )]BArF ] (4 a, M=Ru; 4 b, M=Os), [(η6 -p-cymene){(IDipp)P}Os(Me IMe)]BArF ] (5) and [(η5 -C5 Me5 ){(IDipp)P}IrL][BArF ] (6, L=PMe3 ; 7, L=Me IMe; 8, L=CO). These cationic N-heterocyclic carbene-phosphinidene complexes feature very similar structural and spectroscopic properties as prototypic nucleophilic arylphosphinidene complexes such as low-field 31 P NMR resonances and short metal-phosphorus double bonds. Density functional theory (DFT) calculations reveal that the metal-phosphorus bond can be described in terms of an interaction between a triplet [(IDipp)P]+ cation and a triplet metal complex fragment ligand with highly covalent σ- and π-contributions. Crystals of the C-H activated complex 9 were isolated from solutions containing the PMe3 complex, and its formation can be rationalized by PMe3 dissociation and formation of a putative 16-electron intermediate [(η5 -C5 Me5 )Ir{P(IDipp)}I][BArF ], which undergoes C-H activation at one of the Dipp isopropyl groups and addition along the iridium-phosphorus bond to afford an unusual η3 -benzyl coordination mode.

Impact of the Novel Z-Acceptor Ligand Bis{(ortho-diphenylphosphino)phenyl}zinc (ZnPhos) on the Formation and Reactivity of Low-Coordinate Ru(0) Centers

The preparation and reactivity with H₂ of two Ru complexes of the novel ZnPhos ligand (ZnPhos = Zn(o-C₆H₄PPh₂)₂) are described. Ru(ZnPhos)(CO)₃ (2) and Ru(ZnPhos)(IMe₄)₂ (4; IMe₄ = 1,3,4,5-tetramethylimidazol-2-ylidene) are formed directly from the reaction of Ru(PPh₃)(C₆H₄PPh₂)₂(ZnMe)₂ (1) or Ru(PPh₃)₃HCl/LiCH₂TMS/ZnMe₂ with CO and IMe₄, respectively. Structural and electronic structure analyses characterize both 2 and 4 as Ru(0) species in which Ru donates to the Z-type Zn center of the ZnPhos ligand; in 2, Ru adopts an octahedral coordination, while 4 displays square-pyramidal coordination with Zn in the axial position. Under photolytic conditions, 2 loses CO to give Ru(ZnPhos)(CO)₂ that then adds H₂ over the Ru-Zn bond to form Ru(ZnPhos)(CO)₂(μ-H)₂ (3). In contrast, 4 reacts directly with H₂ to set up an equilibrium with Ru(ZnPhos)(IMe₄)₂H₂ (5), the product of oxidative addition at the Ru center. DFT calculations rationalize these different outcomes in terms of the energies of the square-pyramidal Ru(ZnPhos)L₂ intermediates in which Zn sits in a basal site: for L = CO, this is readily accessed and allows H₂ to add across the Ru-Zn bond, but for L = IMe₄, this species is kinetically inaccessible and reaction can only occur at the Ru center. This difference is related to the strong π-acceptor ability of CO compared to IMe₄. Steric effects associated with the larger IMe₄ ligands are not significant. Species 4 can be considered as a Ru(0)L₄ species that is stabilized by the Ru→Zn interaction. As such, it is a rare example of a stable Ru(0)L₄ species devoid of strong π-acceptor ligands.

Building up Strain in One Step: Synthesis of an Edge-Fused Double Silacyclobutene from an Extensively Trichlorosilylated Butadiene Dianion

The exhaustive trichlorosilylation of hexachloro‐1,3‐butadiene was achieved in one step by using a mixture of Si₂Cl₆ and [nBu₄N]Cl (7:2 equiv) as the silylation reagent. The corresponding butadiene dianion salt [nBu₄N]₂[1] was isolated in 36 % yield after recrystallization. The negative charges of [1]²⁻ are mainly delocalized across its two carbanionic (Cl₃Si)₂C termini (α‐effect of silicon) such that the central bond possesses largely C=C double‐bond character. Upon treatment with 4 equiv of HCl, [1]²⁻ is converted into neutral 1,2,3,4‐tetrakis(trichlorosilyl)but‐2‐ene, 3. The Cl⁻ acceptor AlCl₃, induces a twofold ring‐closure reaction of [1]²⁻ to form a six‐membered bicycle 4 in which two silacyclobutene rings are fused along a shared C=C double bond (84 %). Compound 4, which was structurally characterized by X‐ray crystallography, undergoes partial ring opening to a monocyclic silacyclobutene 2 in the presence of HCl, but is thermally stable up to at least 180 °C.

Insertion of Ni(0) and Pd(0) precursors into the Si-Si bond of a disilane with two hypercoordinate silicon atoms

The activation of the silicon-silicon bond in disilane Ph2Si(μ-PzMe2)2SiPh2 (1), which possesses two five-coordinate silicon centers, was achieved by a reaction with Pd(0) or Ni(0) precursors of modest steric demand to afford a dinuclear Pd complex (2) or two types of mononuclear Ni complexes (3 and 4), respectively.

π-Complexes of Diborynes with Main Group Atoms

We present herein an in-depth study of complexes in which a molecule containing a boron-boron triple bond is bound to tellurate cations. The analysis allows the description of these salts as true π complexes between the B-B triple bond and the tellurium center. These complexes thus extend the well-known Dewar-Chatt-Duncanson model of bonding to compounds made up solely of p block elements. Structural, spectroscopic and computational evidence is offered to argue that a set of recently reported heterocycles consisting of phenyltellurium cations complexed to diborynes bear all the hallmarks of π-complexes in the π-complex/metallacycle continuum envisioned by Joseph Chatt. Described as such, these compounds are unique in representing the extreme of a metal-free continuum with conventional unsaturated three-membered rings (cyclopropenes, azirenes, borirenes) occupying the opposite end.

Palladium-catalyzed Suzuki-Miyaura coupling of thioureas or thioamides

Cross-coupling reactions involving metal carbene intermediates play an increasingly important role in C-C bond formation. Expanding the carbene precursors to a broader range of starting materials and more diverse products is an ongoing challenge in synthetic organic chemistry. Herein, we report a Suzuki-Miyaura coupling reaction of in situ-generated Pd-carbene complexes via desulfurization of thioureas or thioamides. This strategy enables the preparation of a broad array of substituted amidinium salts and unsymmetrical diaryl ketones. The reaction is readily scalable, compatible with bromo groups on aromatic rings, tolerant to moisture and air and has a broad substrate scope. Furthermore, a single crystal structure of Pd-diaminocarbene complex is obtained and proven to be the key intermediate in both catalytic and stoichiometric reactions. Preliminary mechanistic studies demonstrate the dual role of the silver salt as a desulfurating reagent assisting the elimination of sulfur and as oxidant facilitating the Pd^II/Pd⁰/Pd^II catalytic cycle.

Catalytic Difunctionalization of Unactivated Alkenes with Unreactive Hexamethyldisilane through Regeneration of Silylium Ions

A metal-free, intermolecular syn-addition of hexamethyldisilane across simple alkenes is reported. The catalytic cycle is initiated and propagated by the transfer of a methyl group from the disilane to a silylium-ion-like intermediate, corresponding to the (re)generation of the silylium-ion catalyst. The key feature of the reaction sequence is the cleavage of the Si-Si bond in a 1,3-silyl shift from silicon to carbon. A central intermediate of the catalysis was structurally characterized by X-ray diffraction, and the computed reaction mechanism is fully consistent with the experimental findings.

Mild synthesis of silyl ethers via potassium carbonate catalyzed reactions between alcohols and hydrosilanes

A method has been developed for the silanolysis of alcohols using an abundant and non-corrosive base K₂CO₃ as a catalyst.

Silicon chemistry in zero to three dimensions: from dichlorosilylene to silafullerane

As one of the simplest examples of functionalized Si(ii) species, the SiCl₂/[SiCl₃]⁻ system is not only fundamentally interesting, but also an important starting point for the assembly of oligosilane chains, rings, and clusters.

Insights into disilylation and distannation: sequence influence and ligand/steric effects on Pd-catalyzed difunctionalization of carbenes

Density functional theory (DFT) calculation has been used to reveal the mechanism of Pd-catalyzed disilylation of carbene, which is a pathway to construct disilylmethane derivatives.