Synthesis and Reactivity of a Hypersilylsilylene

Stabilization of an amidinatosilylene with a bulky tris(trimethylsilyl)silyl substituent was realized with the preparation of PhC(NtBu)₂Si{Si(SiMe₃)₃} (1) from PhC(NtBu)₂SiHCl₂ with K{Si(SiMe₃)₃} in more than 90% yield. The highly deshielded ²⁹Si NMR resonance (δ = 76.91 ppm) can be attributed to the absence of a π-donating substituent. The molecular structure of 1 shows a trigonal-planar geometry around the Si^II center with a Si^II-Si^IV bond length of 2.4339(13) Å. A series of reactions of 1 with Me₃NO, S, Se, and Te were performed. While siloxane derivatives (2 and 3) are obtained from reactions with Me₃NO, silachalcogenones (4-6) are formed with other chalcogens. The presence of Si═E (E = S, Se, and Te) bonds in 4-6 have been confirmed by single-crystal X-ray studies. Silaoxirane (7) formation was observed when 1 was treated with acetone, demonstrating the importance of the tris(trimethylsilyl)silyl group to kinetically and thermodynamically protect the silaoxirane derivative with less bulky substituents on the C atom.

Acyclic 1,2-dimagnesioethanes/-ethene derived from magnesium(i) compounds: multipurpose reagents for organometallic synthesis

Reactions of three magnesium(i) dimers, [{(ArNacnac)Mg-}2] (ArNacnac = [(ArNCMe)2CH]-; Ar = xylyl (Xyl), mesityl (Mes) or 2,6-diethylphenyl (Dep)), with either 1,1-diphenylethylene (DPE), α-methylstyrene (MS), trans-stilbene (TS) or diphenylacetylene (DPA) led to the 1,2-addition of the Mg-Mg bond across the substrate, giving rise to the 1,2-dimagnesioethanes, [{(XylNacnac)Mg}2(μ-DPE)], [{(DepNacnac)Mg}2(μ-MS)], [{(ArNacnac)Mg}2(μ-TS)] (Ar = Mes or Dep); and a 1,2-dimagnesioethene, [{(MesNacnac)Mg}2(μ-DPA)]. The reactions involving the 1,1-substituted alkenes are shown to be readily redox reversible, in that the reaction products are in equilibrium with a significant proportion of the starting materials at room temperature. Variable temperature NMR spectroscopy and a van't Hoff analysis point to low kinetic barriers to these weakly exergonic reactions. [{(MesNacnac)Mg}2(μ-DPE)] and [{(MesNacnac)Mg}2(μ-DPA)] behave as 1,2-di-Grignard reagents in their reactions with very bulky amido-zinc bromides, yielding the first examples of a 1,2-dizincioethane, [(L*Zn)2(μ-DPE)] (L* = -N(Ar*)(SiPri 3); Ar* = C6H2Me{C(H)Ph2}2-4,2,6), and a 1,2-dizincioethene, [(TBoLZn)2(μ-DPA)] (TBoL = -N(SiMe3){B(DipNCH)2}, Dip = 2,6-diisopropylphenyl), respectively. Divergent reactivity is shown for [{(MesNacnac)Mg}2(μ-DPE)], which behaves as a two-electron reducing agent when treated with amido-cadmium and amido-magnesium halide precursors, yielding the cadmium(i) and magnesium(i) dimers, [PhBoLCdCdPhBoL] (PhBoL = -N(SiPh3){B(DipNCH)2}) and [L†MgMgL†] (L† = -N(Ar†)(SiMe3); Ar† = C6H2Pri{C(H)Ph2}2-4,2,6), respectively. A further class of reactivity for [{(MesNacnac)Mg}2(μ-DPE)] derives from its reaction with the bulky amido-germanium chloride, L*GeCl, which gives a magnesio-germane, presumably via intramolecular C-H activation of a highly reactive magnesiogermylene intermediate, [:Ge(L*){Mg(MesNacnac)}]. [{(MesNacnac)Mg}2(μ-DPE)] can be considered as acting as a two-electron reducing, magnesium transfer reagent in this reaction.

Reduction of Carbon Oxides by an Acyclic Silylene: Reductive Coupling of CO

Reactions of a boryl-substituted acyclic silylene with carbon dioxide and monoxide are reported. The former proceeds through oxygen atom abstraction, generating CO (with rearrangement of the putative silanone product through silyl-group transfer). The latter is characterized by reductive coupling of CO to give an ethynediolate fragment, which undergoes formal insertion into the Si-B bond. The net conversion of carbon dioxide with two equivalents of silylene offers a route for the three-electron reduction of CO₂ to [C₂ O₂ ]^2- .

Synthesis and Reactivity Studies of Amido-Substituted Germanium(I)/Tin(I) Dimers and Clusters

Three amide ligands of varying steric bulk and electronic properties were utilized to prepare a series of amido-germanium(II)/tin(II) halide compounds, (LEX)_n , (L= -N{B(DipNCH)₂ }(SiMe₃ ), ^TBo L; -N{B(DipNCH)₂ }(SiPh₃ ), ^PhBo L; -N(Dip)(tBu), ^DBu L; Dip=C₆ H₃ iPr₂ -2,6; E=Ge or Sn; X=Cl or Br; n=1 or 2). Reductions of these with a magnesium(I) dimer, {(^Mes Nacnac)Mg}₂ (^Mes Nacnac=[(MesNCMe)₂ CH]^- , Mes=mesityl), afforded singly bonded amido-digermynes (^TBo LGe-Ge^TBo L and ^PhBo LGe-Ge^PhBo L), and an amido-distannyne (^PhBo LSn-Sn^PhBo L), in addition to several low-valent, amido stabilized tetrel-tetrel bonded cluster compounds, (^DBu LGe)₄ , (^DBu LSn)₆ and Sn₅ (^TBo L)₄ . The nature of the products resulting from these reactions was largely dependent on the steric bulk of the amide ligand employed. Cluster (^DBu LGe)₄ possessed an unusual folded butterfly structure, the bonding and electronic of which were examined using DFT calculations. Reactions of the amido-germanium(I) compounds with H₂ were explored, and gave rise to the amido-digermene, ^TBo L(H)Ge=Ge(H)^TBo L and the cyclotetragermane, {^DBu L(H)Ge}₄ . Reactions of (^DBu LGe)₄ with a series of unsaturated small molecule substrates yielded ^DBu LGeOGe^DBu L, ^DBu LGe(μ-C₂ H₄ )₂ Ge^DBu L and ^DBu LGe(μ-1,4-C₆ H₈ )(μ-1,2-C₆ H₈ )Ge^DBu L. The latter results imply that (^DBu LGe)₄ can act as a masked source of the digermyne ^DBu LGeGe^DBu L in these reactions. All further reactivity studies indicated that the germanium(I) compounds exhibit a "transition-metal-like" behavior, which is closely related to that previously described for bulky digermynes and related compounds.

Synthesis of N-Heterocycle Substituted Silyl Ligands within the Coordination Sphere of Iron

N-Heterocycle-substituted silyl iron complexes have been synthesized by nucleophilic substitution at trichlorosilyl ligands bound to iron. The homoleptic (tripyrrolyl)- and tris(3-methylindolyl)silyl groups were accessed from (Cl₃Si)CpFe(CO)₂ (Cl₃SiFp) by substitution of chloride with pyrrolide or 3-methylindolide, respectively. Analogously, nucleophilic substitution of Cl with pyrrolide on the anionic Fe(0) synthon Cl₃SiFe(CO)₄ ^- generates the (tripyrrolyl)silyl ligand, bound to the iron tetracarbonyl fragment. The bulkier 2-mesitylpyrrolide substitutes a maximum of 2 chlorides on Cl₃SiFp under the same conditions. The tridentate, trianionic nucleophile tmim (tmimH₃ = tris(3-methylindol-2-yl)methane) proves reluctant to perform the substitution in a straightforward manner; instead, ring-opening and incorporation of THF occurs to form the tris-THF adduct tmim(C₄H₈O)₃SiFe(CO)₄ ^-. The bidentate, monoanionic nucleophile 2-(dipp-iminomethyl)pyrrolide (^DippIMP, dipp = 2,6-diisopropylphenyl) shows chloride displacement and addition of a second ^DippIMP moiety on the imine backbone. The heterocycle-based silyl ligands were shown to be sterically and electronically tunable, moderately electron-donating ligands. The presented approach to new silyl ligands avoids strongly reducing conditions and potentially reactive hydrosilane intermediates.

Isolation and Characterization of Crystalline, Neutral Diborane(4) Radicals

Diaryldihalodiboranes(4) were reacted with bis(amidinato)- and bis(guanidinato)silylenes to generate the first neutral diborane-centered radicals. These formally non-aromatic 5π electron systems are stable in the solid state as well as in solution and were characterized by solid-state structure determination, high-resolution mass spectrometry, and EPR spectroscopy. The reactivity of one of these radicals with the oxidant 1,4-benzoquinone led to ring-opening and B-O bond formation.

Cyclic amino(carboranyl) silylene: synthesis, structure and reactivity

A carbene-stabilized cyclic amino(carboranyl) silylene has been prepared and structurally characterized, which can form a Lewis acid–base adduct with borane and undergo cycloaddition reactions with unsaturated molecules such as diphenylacetylene and benzophenone.

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.

Silicon-fluorine chemistry: from the preparation of SiF2to C–F bond activation using silylenes and its heavier congeners

The feisty nature of silicon(ii) fluorides has been harnessed by two cyclic alkyl amino carbene (cAAC) ligands and (cAAC)₂SiF₂has been isolated at room temperature and structurally characterized.

Facile Conversion of Bis-Silylene to Cyclic Silylene Isomers: Unexpected C-N and C-H Bond Cleavage

Reaction of thiolate 1 with carbene-stabilized diiodo-bis-silylene (2) (in a 2:1 ratio) in THF unexpectedly gives both the first five-membered, sulfur-containing, zwitterionic silylene ring (3) via insertion of the "Si^I₂" unit of 2 into the olefinic C-H bond of the imidazole ring of 1 and four-membered cyclic silylene (4) via insertion of a silicon(I) atom of 2 into the C_phenyl-N bond of the carbene ligand. The parallel reaction in toluene only gives 3 as the major product. The nature of the bonding in isomeric 3 and 4 was probed by experimental and theoretical methods.

Accessing Low-Valent Inorganic Cations by Using an Extremely Bulky N-Heterocyclic Carbene

The extremely bulky N-heterocyclic carbene (NHC), ITr (ITr=[(HCNCPh₃ )₂ C:]) featuring sterically shielding umbrella-shaped trityl (CPh₃ ) substituents was prepared. This NHC features the highest percent buried volume (%V_bur ) to date, and was used to form a thermally stable quasi one-coordinate thallium(I) cation [ITr-Tl]⁺ . This Tl^I adduct and the corresponding lithium complex [ITr⋅Li(OEt₂ )]⁺ are versatile "all-in-one" transmetalation/ligation reagents for preparing low-coordinate inorganic species inaccessible by pre-existing routes.

Iron(II), Cobalt(II), Nickel(II), and Zinc(II) Silylene Complexes: Reaction of the Silylene [iPrNC(NiPr2 )NiPr]2 Si with FeBr2 , CoBr2 , NiBr2 ⋅MeOCH2 CH2 OMe, ZnCl2 , and ZnBr2

Reaction of the donor-stabilized silylene [iPrNC(NiPr₂ )NiPr]₂ Si (1) with FeBr₂ , CoBr₂ , NiBr₂ ⋅MeOCH₂ CH₂ OMe, ZnCl₂ , and ZnBr₂ afforded the respective transition-metal silylene complexes 4-8, the formation of which can be described in terms of a Lewis acid/base reaction (4, 5, 7, 8) or a nucleophilic substitution reaction (6). However, the reactivity profile of silylene 1 is not only based on its strong Lewis base character; the different coordination modes of the two guanidinato ligands (4-6 vs. 7 and 8) add an additional reactivity facet. The paramagnetic compounds 4 and 5 and the diamagnetic compounds 6⋅THF, 7, and 8⋅0.5 Et₂ O were structurally characterized by single-crystal X-ray diffraction. In addition, compound 6⋅THF was studied by ¹⁵ N and ²⁹ Si solid-state NMR spectroscopy, and 7 and 8 were characterized by NMR spectroscopic studies in the solid state (¹⁵ N, ²⁹ Si) and in solution (¹ H, ¹³ C, ²⁹ Si). Compounds 4-8 represent very rare examples of Fe^II , Co^II , Ni^II , and Zn^II silylene complexes. Four-coordinate silicon(II) compounds with an SiN₃ M skeleton (M=Fe, Co, Ni) and M in the formal oxidation state +2 (4-6) have not yet been reported, and five-coordinate silicon(II) compounds with an SiN₄ Zn skeleton (7, 8) are also unprecedented.

Strikingly diverse reactivity of structurally identical silylene and stannylene

The divergent reactivity of structurally similar silylene and stannylene was observed with coinage metal halides. While the former tends to form an adduct, the latter undergoes ligand exchange reaction.

Bis(amidinato)- and bis(guanidinato)silylenes and silylenes with one sterically demanding amidinato or guanidinato ligand: synthesis and reactivity

Silylenes 1–4 have great synthetic potential for the synthesis of higher coordinate silicon(ii) and silicon(iv) complexes with unprecedented structural motifs.

C(sp3)–F, C(sp2)–F and C(sp3)–H bond activation at silicon(ii) centers

Silylene, [PhC(NtBu)₂SiN(SiMe₃)₂] (1) underwent C(sp³)–F, C(sp²)–F and C(sp³)–H bond activation with trifluoroacetophenone, octafluorotoluene, and acetophenone, respectively, under ambient conditions.

PNacPNacE: (E = Ga, In, Tl) – monomeric group 13 metal(i) heterocycles stabilized by a sterically demanding bis(iminophosphoranyl)methanide

Monomeric group 13 metal(i) complexes of gallium, indium and thallium stabilised by a sterically demanding bis(iminophosphoranyl)methanide ligand have been prepared and characterised.

Cationic Five-Coordinate Bis(guanidinato)silicon(IV) Complexes with SiN4 El Skeletons (El=S, Se): "Heterolytic Activation" of S-S and Se-Se Bonds

The donor-stabilized silylene [iPrNC(NiPr2 )NiPr]2 Si (2) reacts with PhEl-ElPh (El=S, Se) to form the respective cationic five-coordinate bis(guanidinato)silicon(IV) complexes {[iPrNC(NiPr2 )NiPr]2 SiSPh}(+) PhS(-) (4) and {[iPrNC (NiPr2 )NiPr]2 SiSePh}(+) PhSe(-) (5). Compounds 4 and 5 were characterized by crystal structure analyses and NMR spectroscopic studies in the solid state.

Stabilization of a two-coordinate, acyclic diaminosilylene (ADASi): completion of the series of isolable diaminotetrylenes, :E(NR2)2(E = group 14 element)

An extremely bulky boryl-amide ligand, [N(SiMe₃){B(DAB)}]⁻(TBoN; DAB = (DipNCH)₂, Dip = C₆H₃Prⁱ₂-2,6), has been developed and utilised in the preparation of the first isolable, two-coordinate acyclic diaminosilylene (ADASi),viz.:Si(TBoN)₂.

Group 14 inorganic hydrocarbon analogues

This Review article deals with the synthesis and properties of inorganic hydrocarbon analogues: binary chemical species that contain heavier Group 14 elements (Si, Ge, Sn or Pb) and hydrogen as components. Rapid advances in our general knowledge of these species have enabled the development of industrially relevant processes such as the hydrosilylation of unsaturated substrates and the chemical vapor deposition of semi-conducting films.

Carbon-based two electron σ-donor ligands beyond classical N-heterocyclic carbenes

Recent advances in N-heterocyclic carbene-derived carbon-based two electron σ-donor ligands are presented in this perspective.