Aluminum(III) Cations [(NHC) ⋅ AlMes2]+: Synthesis,Characterization, and Application in FLP-Chemistry

The three-coordinate aluminum cations ligated by N-heterocyclic carbenes (NHCs) [(NHC) ⋅ AlMes₂]⁺[B(C₆F₅)₄]⁻ (NHC=IMe^Me 4 , IiPr^Me 5 , IiPr 6 , Mes=2,4,6-trimethylphenyl) were prepared via hydride abstraction of the alanes (NHC) ⋅ AlHMes₂ (NHC=IMe^Me 1 , IiPr^Me 2 , IiPr 3 ) using [Ph₃C]⁺[B(C₆F₅)₄]⁻ in toluene as hydride acceptor. If this reaction was performed in diethyl ether, the corresponding four-coordinate aluminum etherate cations [(NHC) ⋅ AlMes₂(OEt₂)]⁺ [B(C₆F₅)₄]⁻ 7 – 9 (NHC=IMe^Me 7 , IiPr^Me 8 , IiPr 9 ) were isolated. According to a theoretical and experimental assessment of the Lewis-acidity of the [(IMe^Me) ⋅ AlMes₂]⁺ cation is the acidity larger than that of B(C₆F₅)₃ and of similar magnitude as reported for Al(C₆F₅)₃. The reaction of [(IMe^Me) ⋅ AlMes₂]⁺[B(C₆F₅)₄]⁻ 4 with the sterically less demanding, basic phosphine PMe₃ afforded a mixed NHC/phosphine stabilized cation [(IMe^Me) ⋅ AlMes₂(PMe₃)]⁺[B(C₆F₅)₄]⁻ 10 . Equimolar mixtures of 4 and the sterically more demanding PCy₃ gave a frustrated Lewis-pair (FLP), i.e., [(IMe^Me) ⋅ AlMes₂]⁺[B(C₆F₅)₄]⁻/PCy₃ FLP-11 , which reacts with small molecules such as CO₂, ethene, and 2-butyne.     

A Nickel Complex Containing a Pyramidalized,Ambiphilic Pincer Germylene Ligand

Reaction of N-heterocyclic carbene (NHC)-stabilized PGeP-type germylene Ge{o-(PiPr₂)C₆H₄}₂⋅^MeIiPr ( 1 ) (^MeIiPr=1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) with Ni(cod)₂ gave pincer germylene complex Ni[Ge{o-(PiPr₂)C₆H₄}₂](^MeIiPr) ( 2 ), in which the Ge center of 2 is significantly pyramidalized. Theoretical calculation on 2 predicted the ambiphilicity of the germanium center, which was confirmed by reactivity studies. Thus, complex 2 reacted with both Lewis base ^MeIMe (^MeIMe=1,3,4,5-tetramethylimidazol-2-ylidene) and Lewis acid BH₃⋅SMe₂ at the germanium center to afford the adducts Ni[Ge{o-(PiPr₂)C₆H₄}₂⋅^MeIMe](^MeIiPr) ( 3 ) and Ni[Ge{o-(PiPr₂)C₆H₄}₂⋅BH₃](^MeIiPr) ( 4 ), respectively. Furthermore, the former was slowly converted to dinuclear complex Ni₂[Ge{o-(PiPr₂)C₆H₄}₂]₂(^MeIMe)₂ ( 5 ) at room temperature. Complex 5 can be regarded as a dimer of the ^MeIMe analog of 2 with a Ni-Ge-Ge-Ni linkage.     

Expanded‐Ring N‐Heterocyclic Carbenes for the Stabilization of Highly Electrophilic Gold(I) Cations

Strategies for the synthesis of highly electrophilic Au^I complexes from either hydride‐ or chloride‐containing precursors have been investigated by employing sterically encumbered Dipp‐substituted expanded‐ring NHCs (Dipp=2,6‐iPr₂C₆H₃). Thus, complexes of the type (NHC)AuH have been synthesised (for NHC=6‐Dipp or 7‐Dipp) and shown to feature significantly more electron‐rich hydrides than those based on ancillary imidazolylidene donors. This finding is consistent with the stronger σ‐donor character of these NHCs, and allows for protonation of the hydride ligand. Such chemistry leads to the loss of dihydrogen and to the trapping of the [(NHC)Au]⁺ fragment within a dinuclear gold cation containing a bridging hydride. Activation of the hydride ligand in (NHC)AuH by B(C₆F₅)₃, by contrast, generates a species (at low temperatures) featuring a [HB(C₆F₅)₃]^? fragment with spectroscopic signatures similar to the “free” borate anion. Subsequent rearrangement involves B?C bond cleavage and aryl transfer to the carbophilic metal centre. Under halide abstraction conditions utilizing Na[BAr^f₄] (Ar^f=C₆H₃(CF₃)₂‐3,5), systems of the type [(NHC)AuCl] (NHC=6‐Dipp or 7‐Dipp) generate dinuclear complexes [{(NHC)Au}₂(μ‐Cl)]⁺ that are still electrophilic enough at gold to induce aryl abstraction from the [BAr^f₄]^? counterion.     

The Hydride‐Ion Affinity of Borenium Cations and Their Propensity to Activate H2 in Frustrated Lewis Pairs

A range of frustrated Lewis pairs (FLPs) containing borenium cations have been synthesised. The catechol (Cat)‐ligated borenium cation [CatB(PtBu₃)]⁺ has a lower hydride‐ion affinity (HIA) than B(C₆F₅)₃. This resulted in H₂ activation being energetically unfavourable in a FLP with the strong base PtBu₃. However, ligand disproportionation of CatBH(PtBu₃) at 100 °C enabled trapping of H₂ activation products. DFT calculations at the M06‐2X/6‐311G(d,p)/PCM (CH₂Cl₂) level revealed that replacing catechol with chlorides significantly increases the chloride‐ion affinity (CIA) and HIA. Dichloro–borenium cations, [Cl₂B(amine)]⁺, were calculated to have considerably greater HIA than B(C₆F₅)₃. Control reactions confirmed that the HIA calculations can be used to successfully predict hydride‐transfer reactivity between borenium cations and neutral boranes. The borenium cations [Y(Cl)B(2,6‐lutidine)]⁺ (Y=Cl or Ph) form FLPs with P(mesityl)₃ that undergo slow deprotonation of an ortho‐methyl of lutidine at 20 °C to form the four‐membered boracycles [(CH₂{NC₅H₃Me})B(Cl)Y] and [HPMes₃]⁺. When equimolar [Y(Cl)B(2,6‐lutidine)]⁺/P(mesityl)₃ was heated under H₂ (4 atm), heterolytic cleavage of dihydrogen was competitive with boracycle formation.     

Die Oxidation von Triisopropylphosphan mit Iod: Zur Rolle von trockenem und feuchtem Lösungsmittel

Oxidation of Triisopropylphosphane with Iodine: The Role of Dry or Moist Solvent i‐Pr₃P ( 1 ) and iodine give i‐Pr₃PI₂ ( 2 ). In crystals obtained from CH₂Cl₂ solution, ion pairs [i‐Pr₃PI⁺I^–] of 2 exhibiting I…I interactions are linked by CH₂Cl₂ molecules. With a second equivalent of iodine, i‐Pr₃PI⁺ I₃^– ( 3 ) is formed; the reaction of 2 with AgSbF₆ provides i‐Pr₃PI⁺SbF₆^– ( 6 ). The presence of moisture and air leads to the formation of i‐Pr₃POH⁺ salts. Solid i‐Pr₃POH⁺I^– ( 4 ) exhibits P–O–H…I cation‐anion contacts, solid (i‐Pr₃PO)₂H⁺I₃^– ( 5 ) contains a centrosymmetric P=O…H…O=P‐bridged cation. Distinguishing i‐Pr₃PI⁺ salts 2 , 3 from hydrolysis products 4 , 5 by ³¹P‐NMR in reaction mixtures is not trivial, because both kinds of cations exihibit similar ³¹P‐NMR shifts and both participate in interactions with their anions, and in equilibria with uncharged donors: rapid I⁺ transfer reactions and I…I soft‐soft interactions involving 1 , and rapid H⁺ transfer reactions and hydrogen bonds involving i‐Pr₃P=O ( 7 ).     

A Frustrated and Confused Lewis Pair

We report a new class of frustrated Lewis pairs (FLPs) by the hydroboration of bulky isocyanates ^iPr2ArNCO (^iPr2Ar=2,6‐iPr₂C₆H₃) and ^Ph2tBuArNCO (^Ph2tBuAr=2,6‐Ph₂‐4‐tBuC₆H₂) with Piers’ borane (HB(C₆F₅)₂). While hydroboration of smaller isocyanates such as ^iPr2ArNCO leads to isocyanate—N/B FLP adducts, hydroboration of the bulkier ^Ph2tBuArNCO allows isolation of the substrate‐free aminoborane with a short, covalent N?B bond. This confused FLP reversibly binds unsaturated substrates such as isocyanates and isocyanides, suggesting the intermediacy of a “normal” FLP along the reaction pathway, supported by high‐level DFT studies and variable‐temperature NMR spectroscopy. These results underscore the possibility of FLP behavior in systems that possess no obvious frustrated Lewis acid–base interaction.     

Reaction of an “Invisible” Frustrated N/B Lewis Pair with Dihydrogen

D ‐(+)‐Camphor forms the enamine 2 with piperidine. Compound 2 adds HB(C₆F₅)₂ at the enamine carbon atom C3 to form a Lewis acid/Lewis base adduct (exo‐/endo‐isomers of 3 ). Exposure of 3 to dihydrogen (2.5 bar, room temperature) leads to heterolytic splitting of H₂ to form the H⁺/H^? addition products ( 4 , two diastereoisomers) of the “invisible” frustrated Lewis pairs ( 5 , two diastereoisomers) that were apparently generated in situ by enamine hydroboration under equilibrium conditions.     

Fine‐Tuning of Lewis Acidity: The Case of Borenium Hydride Complexes Derived from Bis(phosphinimino)amide Boron Precursors

Reactions of bis(phosphinimino)amines LH and L′H with Me₂S ? BH₂Cl afforded chloroborane complexes LBHCl ( 1 ) and L′BHCl ( 2 ), and the reaction of L′H with BH₃ ? Me₂S gave a dihydridoborane complex L′BH₂ ( 3 ) (LH=[{(2,4,6‐Me₃C₆H₂N)P(Ph₂)}₂N]H and L′H=[{(2,6‐iPr₂C₆H₃N)P(Ph₂)}₂N]H). Furthermore, abstraction of a hydride ion from L′BH₂ ( 3 ) and LBH₂ ( 4 ) mediated by Lewis acid B(C₆F₅)₃ or the weakly coordinating ion pair [Ph₃C][B(C₆F₅)₄] smoothly yielded a series of borenium hydride cations: [L′BH]⁺[HB(C₆F₅)₃]^? ( 5 ), [L′BH]⁺[B(C₆F₅)₄]^? ( 6 ), [LBH]⁺[HB(C₆F₅)₃]^? ( 7 ), and [LBH]⁺[B(C₆F₅)₄]^? ( 8 ). Synthesis of a chloroborenium species [LBCl]⁺[BCl₄]^? ( 9 ) without involvement of a weakly coordinating anion was also demonstrated from a reaction of LBH₂ ( 4 ) with three equivalents of BCl₃. It is clear from this study that the sterically bulky strong donor bis(phosphinimino)amide ligand plays a crucial role in facilitating the synthesis and stabilization of these three‐coordinated cationic species of boron. Therefore, the present synthetic approach is not dependent on the requirement of weakly coordinating anions; even simple BCl₄^? can act as a counteranion with borenium cations. The high Lewis acidity of the boron atom in complex 8 enables the formation of an adduct with 4‐dimethylaminopyridine (DMAP), [LBH ? (DMAP)]⁺[B(C₆F₅)₄]^? ( 10 ). The solid‐state structures of complexes 1 , 5 , and 9 were investigated by means of single‐crystal X‐ray structural analysis.     

Homoleptic Two‐Coordinate Silylamido Complexes of Chromium(I), Manganese(I), and Cobalt(I)

Anionic two‐coordinate complexes of first‐row transition‐metal(I) centres are rare molecules that are expected to reveal new magnetic properties and reactivity. Recently, we demonstrated that a N(SiMe₃)₂^? ligand set, which is unable to prevent dimerisation or extraneous ligand coordination at the +2 oxidation state of iron, was nonetheless able to stabilise anionic two‐coordinate Fe^I complexes even in the presence of a Lewis base. We now report analogous Cr^I and Co^I complexes with exclusively this amido ligand and the isolation of a [Mn^I{N(SiMe₃)₂}₂]₂^2? dimer that features a Mn?Mn bond. Additionally, by increasing the steric hindrance of the ligand set, the two‐coordinate complex [Mn^I{N(Dipp)(SiMe₃)}₂]^? was isolated (Dipp=2,6‐iPr₂‐C₆H₃). Characterisation of these compounds by using X‐ray crystallography, NMR spectroscopy, and magnetic susceptibility measurements is provided along with ligand‐field analysis based on CASSCF/NEVPT2 ab initio calculations.     

Charge Effects in PCP Pincer Complexes of NiII bearing Phosphinite and Imidazol(i)ophosphine Coordinating Jaws: From Synthesis to Catalysis through Bonding Analysis

This contribution reports on a new family of Ni^II pincer complexes featuring phosphinite and functional imidazolyl arms. The proligands ^RPIMC^HOP^R′ react at room temperature with Ni^II precursors to give the corresponding complexes [(^RPIMCOP^R′)NiBr], where ^RPIMCOP^R=κ^P,κ^C,κ^P‐{2‐(R′₂PO),6‐(R₂PC₃H₂N₂)C₆H₃}, R=iPr, R′=iPr ( 3 b , 84 %) or Ph ( 3 c , 45 %). Selective N‐methylation of the imidazole imine moiety in 3 b by MeOTf (OTf=OSO₂CF₃) gave the corresponding imidazoliophosphine [(^iPrPIMIOCOP^iPr)NiBr][OTf], 4 b , in 89 % yield (^iPrPIMIOCOP^iPr=κ^P,κ^C,κ^P‐{2‐(iPr₂PO),6‐(iPr₂PC₄H₅N₂)C₆H₃}). Treating 4 b with NaOEt led to the NHC derivative [(NHCCOP^iPr)NiBr], 5 b , in 47 % yield (NHCCOP^iPr=κ^P,κ^C,κ^C‐{2‐(iPr₂PO),6‐(C₄H₅N₂)C₆H₃)}). The bromo derivatives 3–5 were then treated with AgOTf in acetonitrile to give the corresponding cationic species [(^RPIMCOP^R)Ni(MeCN)][OTf] [R=Ph, 6 a (89 %) or iPr, 6 b (90 %)], [(^RPIMIOCOP^R)Ni(MeCN)][OTf]₂ [R=Ph, 7 a (79 %) or iPr, 7 b (88 %)], and [(NHCCOP^R)Ni(MeCN)][OTf] [R=Ph, 8 a (85 %) or iPr, 8 b (84 %)]. All new complexes have been characterized by NMR and IR spectroscopy, whereas 3 b , 3 c , 5 b , 6 b , and 8 a were also subjected to X‐ray diffraction studies. The acetonitrile adducts 6 – 8 were further studied by using various theoretical analysis tools. In the presence of excess nitrile and amine, the cationic acetonitrile adducts 6 – 8 catalyze hydroamination of nitriles to give unsymmetrical amidines with catalytic turnover numbers of up to 95.     

Formation of Frustrated Lewis Pairs in Ptx‐Loaded Zeolite NaY

The formation of a frustrated Lewis pair consisting of sodium hydride (Na⁺H^?) and a framework‐bound hydroxy proton O(H⁺) is reported upon H₂ treatment of zeolite NaY loaded with Pt nanoparticles (Pt_x/NaY). Frustrated Lewis pair formation was confirmed using in situ neutron diffraction and spectroscopic measurements. The activity of the intrazeolite NaH as a size‐selective catalyst was verified by the efficient esterification of acetaldehyde (a small aldehyde) to form the corresponding ester ethyl acetate, whereas esterification of the larger molecule benzaldehyde was unsuccessful. The frustrated Lewis pair (consisting of Na⁺H^? and O(H⁺)) generated within zeolite NaY may be a useful catalyst for various catalytic reactions which require both H^? and H⁺ ions, such as catalytic hydrogenation or dehydrogenation of organic compounds and activation of small molecules.     

Trapping a Silicon(I) Radical with Carbenes: A Cationic cAAC–Silicon(I) Radical and an NHC–Parent‐Silyliumylidene Cation

The trapping of a silicon(I) radical with N‐heterocyclic carbenes is described. The reaction of the cyclic (alkyl)(amino) carbene [cAAC_Me] (cAAC_Me=:C(CMe₂)₂(CH₂)NAr, Ar=2,6‐i Pr₂C₆H₃) with H₂SiI₂ in a 3:1 molar ratio in DME afforded a mixture of the separated ion pair [(cAAC_Me)₂Si:^.]⁺I⁻ ( 1 ), which features a cationic cAAC–silicon(I) radical, and [cAAC_Me−H]⁺I⁻. In addition, the reaction of the NHC–iodosilicon(I) dimer [I_Ar(I)Si:]₂ (I_Ar=:C{N(Ar)CH}₂) with 4 equiv of I_Me (:C{N(Me)CMe}₂), which proceeded through the formation of a silicon(I) radical intermediate, afforded [(I_Me)₂SiH]⁺I⁻ ( 2 ) comprising the first NHC–parent‐silyliumylidene cation. Its further reaction with fluorobenzene afforded the C_Ar−H bond activation product [1‐F‐2‐I_Me‐C₆H₄]⁺I⁻ ( 3 ). The isolation of 2 and 3 confirmed the reaction mechanism for the formation of 1 . Compounds 1 – 3 were analyzed by EPR and NMR spectroscopy, DFT calculations, and X‐ray crystallography.     

A Facile Route to Backbone‐Tethered N‐Heterocyclic Carbene (NHC) Ligands via NHC to aNHC Rearrangement in NHC Silicon Halide Adducts

The reaction of 1,3‐diisopropylimidazolin‐2‐ylidene (iPr₂Im) with diphenyldichlorosilane (Ph₂SiCl₂) leads to the adduct (iPr₂Im)SiCl₂Ph₂ 1 . Prolonged heating of isolated 1 at 66 °C in THF affords the backbone‐tethered bis(imidazolium) salt [(^aHiPr₂Im)₂SiPh₂]²⁺ 2 Cl^? 2 (“^a” denotes “abnormal” coordination of the NHC), which can be synthesized in high yields in one step starting from two equivalents of iPr₂Im and Ph₂SiCl₂. Imidazolium salt 2 can be deprotonated in THF at room temperature using sodium hydride as a base and catalytic amounts of sodium tert‐butoxide to give the stable N‐heterocyclic dicarbene (^aiPr₂Im)₂SiPh₂ 3 , in which two NHCs are backbone‐tethered with a SiPh₂ group. This easy‐to‐synthesize dicarbene 3 can be used as a novel ligand type in transition metal chemistry for the preparation of dinuclear NHC complexes, as exemplified by the synthesis of the homodinuclear copper(I) complex [{^a(ClCu?iPr₂Im)}₂SiPh₂] 4 .     

[Ni(iPr2Im)2Br2]: A Convenient Entry into NHC Nickel ­Chemistry

The reaction of the NHC iPr₂Im [NHC=N‐heterocyclic carbene, iPr₂Im = 1, 3‐bis(isopropyl)imidazolin‐2‐ylidene] with freshly prepared NiBr₂ in thf or dme results in the formation of the air stable nickel(II) complex trans‐[Ni(iPr₂Im)₂Br₂] ( 2 ). Complex 2 was structurally characterized. Thermal analysis (DTA/TG) reveals a very high decomposition temperature of 298 °C. Reduction of 2 with sodium or C₈K in the presence of the olefins COD (cyclooctadiene) or COE (cyclooctene) affords the highly reactive compounds [Ni₂(iPr₂Im)₄(COD)] ( 1 ) and [Ni(iPr₂Im)₂(COE)] ( 4 ). Alkylation of 2 with organolithiums leads to the formation of trans‐[Ni(iPr₂Im)₂(R)₂] [R = Me ( 5 ), CH₂SiMe₃ ( 6 )], whereas the reaction of 2 with LiCp* [Cp* = (η⁵‐C₅(CH₃)₅)] at 80 °C causes the loss of one NHC ligand and affords [(η⁵‐C₅(CH₃)₅)Ni(iPr₂Im)Br] ( 7 ).     

Understanding the Subtleties of Frustrated Lewis Pair Activation of Carbonyl Compounds by N‐Heterocyclic Carbene/Alkyl Gallium Pairings

This study reports the use of the trisalkylgallium GaR₃ (R=CH₂SiMe₃), containing sterically demanding monosilyl groups, as an effective Lewis‐acid component for frustrated Lewis pair activation of carbonyl compounds, when combined with the bulky N‐heterocyclic carbene 1,3‐bis(tert‐butyl)imidazol‐2‐ylidene (ItBu) or 1,3‐bis(tert‐butyl)imidazolin‐2‐ylidene (SItBu). The reduction of aldehydes can be achieved by insertion into the C=O functionality at the C2 (so‐called normal) position of the carbene affording zwitterionic products [ItBuCH₂OGaR₃] ( 1 ) or [ItBuCH(p‐Br‐C₆H₄)OGaR₃] ( 2 ), or alternatively, at its abnormal (C4) site yielding [aItBuCH(p‐Br‐C₆H₄)OGaR₃] ( 3 ). As evidence of the cooperative behaviour of both components, ItBu and GaR₃, neither of them alone are able to activate any of the carbonyl‐containing substrates included in this study NMR spectroscopic studies of the new compounds point to complex equilibria involving the formation of kinetic and thermodynamic species as implicated through DFT calculations. Extension to ketones proved successful for electrophilic α,α,α‐trifluoroacetophenone, yielding [aItBuC(Ph)(CF₃)OGaR₃] ( 7 ). However, in the case of ketones and nitriles bearing acidic hydrogen atoms, C?H bond activation takes place preferentially, affording novel imidazolium gallate salts such as [{ItBuH}⁺{(p‐I‐C₆H₄)C(CH₂)OGaR₃}^?] ( 8 ) or [{ItBuH}⁺{Ph₂C=C=NGaR₃}^?] ( 12 ).     

Synthesis and Characterization of an Eclipsed Digermylene as a Building Block to Construct a Cyclic Octagermylene

The preparation of an unprecedented Ge^I‐Ge^I bonded digermylene [K₂{Ge₂(μ‐κ²:η²:η⁴‐2,6‐(2,6‐ⁱPr₂C₆H₃‐N)₂‐4‐CH₃C₅H₂N)₂}] in an eclipsed conformation stabilized by two bridging diamidopyridyl ligands is presented. Although it exhibits an eclipsed conformation, the Ge−Ge bond length is 2.5168(6) Å, which is shorter than those in the trans ‐bent and gauche digermylenes. In combination with two pendant amido groups, the Ge^I₂ motif is employed as a building block to assemble the first example of octagermylene [Ge₄(μ‐κ²:κ¹‐2,6‐(2,6‐ⁱPr₂C₆H₃‐N)₂‐4‐CH₃C₅H₂N)₂]₂ showing a cyclic configuration and containing three distinct types of Ge^I−Ge^I bonds.     

Planar N‐Heterocyclic Carbene Diarylborenium Ions: Synthesis by Cationic Borylation and Reactivity with Lewis Bases

The NHC–borane adduct (IBn)BH₃ ( 1 ) (NHC= N‐heterocyclic carbene; IBn=1,3‐dibenzylimidazol‐2ylidene) reacts with [Ph₃C][B(C₆F₅)₄] through sequential hydride abstraction and dehydrogenative cationic borylation(s) to give singly or doubly ring closed NHC–borenium salts 2 and 3 . The planar doubly ring closed product [C₃H₂(NCH₂C₆H₄)₂B][B(C₆F₅)₄] is resistant to quaternization at boron by Et₂O coordination, but forms classical Lewis acid–base adducts with the stronger donors Ph₃P, Et₃PO, or 1,4‐diazabicyclo[2.2.2]octane (DABCO). Treatment of 3 with tBu₃P selectively yields the unusual oligomeric borenium salt trans‐[(C₃H₂(NCH₂C₆H₄)₂B)₂(C₃H₂(NCHC₆H₄)₂B)][B(C₆F₅)₄] ( 7 ).     

A Capped Octahedral MHC6 Compound of a Platinum Group Metal

A MHC₆ complex of a platinum group metal with a capped octahedral arrangement of donor atoms around the metal center has been characterized. This osmium compound OsH{κ²‐C,C‐(PhBIm‐C₆H₄)}₃, which reacts with HBF₄ to afford the 14 e^? species [Os{κ²‐C,C‐(PhBIm‐C₆H₄)}(Ph₂BIm)₂]BF₄ stabilized by two agostic interactions, has been obtained by reaction of OsH₆(PiPr₃)₂ with N,N′‐diphenylbenzimidazolium chloride ([Ph₂BImH]Cl) in the presence of NEt₃. Its formation takes place through the C,C,C‐pincer compound OsH₂{κ³‐C,C,C‐(C₆H₄‐BIm‐C₆H₄)}(PiPr₃)₂, the dihydrogen derivative OsCl{κ²‐C,C‐(PhBIm‐C₆H₄)}(η²‐H₂)(PiPr₃)₂, and the five‐coordinate osmium(II) species OsCl{κ²‐C,C‐(PhBIm‐C₆H₄)}(PiPr₃)₂.     

Trapping a Silicon(I) Radical with Carbenes: A Cationic cAAC–Silicon(I) Radical and an NHC–Parent-Silyliumylidene Cation

The trapping of a silicon(I) radical with N-heterocyclic carbenes is described. The reaction of the cyclic (alkyl)(amino) carbene [cAAC_Me] (cAAC_Me=:C(CMe₂)₂(CH₂)NAr, Ar=2,6-iPr₂C₆H₃) with H₂SiI₂ in a 3:1 molar ratio in DME afforded a mixture of the separated ion pair [(cAAC_Me)₂Si:^.]⁺I⁻ ( 1 ), which features a cationic cAAC–silicon(I) radical, and [cAAC_Me−H]⁺I⁻. In addition, the reaction of the NHC–iodosilicon(I) dimer [I_Ar(I)Si:]₂ (I_Ar=:C{N(Ar)CH}₂) with 4 equiv of I_Me (:C{N(Me)CMe}₂), which proceeded through the formation of a silicon(I) radical intermediate, afforded [(I_Me)₂SiH]⁺I⁻ ( 2 ) comprising the first NHC–parent-silyliumylidene cation. Its further reaction with fluorobenzene afforded the C_Ar−H bond activation product [1-F-2-I_Me-C₆H₄]⁺I⁻ ( 3 ). The isolation of 2 and 3 confirmed the reaction mechanism for the formation of 1 . Compounds 1 – 3 were analyzed by EPR and NMR spectroscopy, DFT calculations, and X-ray crystallography.     

From Silylone to an Isolable Monomeric Silicon Disulfide Complex

The synthesis and characterization of the first bis‐N‐heterocyclic carbene stabilized monomeric silicon disulfide (bis‐NHC)SiS₂ 2 (bis‐NHC=H₂C[{NC(H)C(H)N(Dipp)}C:]₂, Dipp=2,6‐iPr₂C₆H₃) is reported. Compound 2 is prepared in 89 % yield from the reaction of the zero‐valent silicon complex (′silylone′) 1 [(bis‐NHC)Si] with elemental sulfur. Compound 2 can react with GaCl₃ in acetonitrile to give the corresponding (bis‐NHC)Si(S)S→GaCl₃ Lewis acid–base adduct 3 in 91 % yield. Compound 3 is also accessible through the reaction of the unprecedented silylone‐GaCl₃ adduct [(bis‐NHC)Si→GaCl₃] 4 with elemental sulfur. Compounds 2 , 3 , and 4 could be isolated and characterized by elemental analyses, HR‐MS, IR, ¹³C‐ and ²⁹Si‐NMR spectroscopy. The structures of 3 and 4 could be determined by single‐crystal X‐ray diffraction analyses. DFT‐derived bonding analyses of 2 and 3 exhibited highly polar Si S bonds with moderate p_π–p_π bonding character.