A voltammetric study of some tris(trimethylsilyl)-methyltin derivatives

Classical d.c. polarography, supplemented by other voltammetric techniques, is used to elucidate the mechanism of reduction of di- and tri-halide derivatives of tris(trimethylsilyl) methyltm, despite the difficulties encountered in work at very negative potentials in ethanolic solutions. The dihalides are reduced in two irreversible one-electron steps; the trihalides are reduced in three one-electron steps, the first of which is quasi-reversible, the other two being irreversible. The first step in each case is adsorption-controlled while the others are diffusion-controlled. D.c. polarography is suitable for the determination of these compounds down to 5 × lO^-5 M.     

Tris(trimethylsilyl)silyl versus tris(trimethylsilyl)germyl: Radical reactivity and oxidation ability

A comparison of the tris(trimethylsilyl)silyl I and tris(trimethylsilyl)germyl II radical reactivity is provided. Their formation as well as their reactivity encountered in a large variety of chemical processes (addition to double bond, halogen abstraction, peroxyl radical formation…) is examined by laser flash photolysis, quantum mechanical calculations and electron spin resonance (ESR) experiments. The starting compound (TMS)₃GeH is more reactive than (TMS)₃SiH toward the t-butoxyl, the t-butylperoxyl and the phosphinoyl radicals. A similar behavior is noted for an aromatic ketone triplet state. II exhibits a lower absolute electronegativity: accordingly, the addition to electron rich alkenes is less efficient than for I. Radical II is also found less reactive for both the peroxylation and the halogen abstraction reactions. The rearrangement of is slower than for ; this is related to the respective exothermicity of the processes.     

The mass spectra of some tris(trimethylsilyl)acylsilanes and tris(trimethylsilyl)silanes

While tris(trimethylsilyl) alkanoylsilanes fragment in the acylsilane form yielding [(Me₃Si)₃SiCO]⁺ by α-cleavage, the molecular ions of their aryl counterparts rearrange to ionized silaethenes prior to cleavage, paralleling known photochemical behaviour. Sila-allyl type structures are attributed to the stable [M? Me˙]⁺ ions obtained by subsequent cleavage. Metastable ion characteristics reveal the identity of the structures of the monomeric silaethene ions obtained from one of the aroylsilanes and a 1,2-disilacyclobutane. The non-compliance of the alkanoylsilanes with their photochemical behaviour is attributed to a preferred elimination of the stable alkyl radical (R˙) from the molecular ions. Several polysilanes display abundant odd-electron ions which may possess a disilene structure.     

Preparation of tris(trimethylsilyl)methyl (“trisyl”) derivatives of silicon

Treatment of (Me₃Si)₃CLi (“trisyl”lithium, TsiLi) with appropriate silicon halides has given a range of compounds of the type (Me₃Si)₃CSiRR′X; e.g., TsiSiCl₃, TsiSiMeCl₂, TsiSiMe₂X (X = Cl, OMe), TsiSiPh₂X (X = F, Cl, OMe), and TsiSiPhMeH. The trisyl group causes very large steric hindrance to nucleophilic displacements at the silicon to which it is attached, so that (unless one or more hydride ligands are present) most of the common displacements at silicon do not occur. However, halides can be reduced to hydrides by LiAlH₄, and the hydrides can be converted into halides in electrophilic displacements by hallogens. The presence of even one hydride ligand markedly reduces the hindrance, so that, for example, TsiSiPhHI reacts with refluxing methanol to give TsiSiPhH(OMe).     

Synthesis of some tris(trimethylsilyl)germyl compounds

A variety of compounds containing the tris(trimethylsilyl)germyl group were prepared and characterized spectroscopically. Photolysis of adamantoyltris(trimethylsilyl)germane failed to yield the isomeric germene: in CCl₄ the photolysis appeared to occur by a Norrish type 1 process.     

The molecular structure of [dimethyl(phenyl)silyl]tris(trimethylsilyl)methane

The structure of the crowded molecule (Me₃Si)₃C(SiMe₂Ph) has been determined by single crystal X-ray diffraction. The steric strain manifest itself mainly in lengthening of the Me₃SiC and Me₂PhSiC bonds (average length 1.920(6) $\text{,ac>A}\text{?}$) and closing up of the CSiC angles within the Me₃Si and Me₂PhSi groups (average 105.2(10)°), with correspondingly large C(1)SiC angles (113.5(13)°; C(1) is the central carbon atom).     

Reaktionen von Zink- und Cadmiumhalogeniden mit Tris(trimethylsilyl)phosphan und Tris(trimethylsilyl)arsan

Reactions of Zinc and Cadmium Halides with Tris(trimethylsilyl)phosphane and Tris(trimethylsilyl)arsane ZnCl₂ reacts with E(SiMe₃)₃ (E = P, As) in toluene in the presence of PⁿPr₃ to give the binuclear complexes [Zn₂Cl₂{E(SiMe₃)₂}₂(PⁿPr₃)₂] · C₇H₈ (E = P 1 , As 2 ). Therefore by the use of PⁱPr₃ clusters consisting of ten metal atoms are obtained, [Zn₁₀Cl₁₂(ESiMe₃)₄(PⁱPr₃)₄] (E = P 3 , As 4 ). As a result of the reaction of CdBr₂ with P(SiMe₃)₃ the compound [CdBr₂{P(SiMe₃)₃}]₂ ( 5 ) can be isolated at –40 °C. In the presence of PⁿPr₃ CdBr₂ reacts with P(SiMe₃)₃ forming the binuclear complex [Cd₂Br₂{P(SiMe₃)₂}₂(PⁿPr₃)₂] · thf ( 6 ). The same reaction with PⁱPr₃ yields to the cluster [Cd₁₀Br₁₂(PSiMe₃)₄{P(SiMe₃)₃}₄] · 2 C₇H₈ ( 7 ). ZnI₂ and CdI₂ react with As(SiMe₃)₃ to yield the complexes [MI₂{As(SiMe₃)₃}]₂ (M = Zn 8 , Cd 9 ). In the case of CdI₂ additionally the cluster [Cd₁₀I₁₂(AsSiMe₃)₄ · {As(SiMe₃)₃}₄] · 4,5 C₇H₈ ( 10 ) is formed which is analogous to the compounds 3 , 4 and 7 . In the presence of [PⁿBu₄]I 8  reacts in THF to give the ionic compound [PⁿBu₄]₂[Zn₆I₆(AsSiMe₃)₄(thf)₂] · C₆H₆ ( 11 ).     

Derivatization of Tris(trimethylsilyl)heptaphosphane

Through SiP bond cleavage, the reaction of P₇(SiMe₃)₃ with one equivalent of KO^tBu or LiO^tBu afforded different isomers of the heptaphosphanide anion [P₇(SiMe₃)₂]⁻. With LiO^tBu, concomitant inversion at an equatorial (silylated) phosphorus atom occurred and the C_s symmetric isomer characterized by a mirror plane formed. With KO^tBu, inversion did not occur and the resulting asymmetric anion with C₁ symmetry formed. With NaO^tBu, a mixture of both isomers was obtained. The symmetries and structures of the anions were elucidated with ³¹P{¹H} and ²⁹Si{¹H} NMR spectroscopy, and relative stabilities were calculated employing the B3LYP/6-31+G* method.The reaction of KP₇(SiMe₃)₂ or LiP₇(SiMe₃)₂ with 1,2-dichlorotetramethyldisilane led to (SiMe₃)₂P₇SiMe₂SiMe₂P₇(SiMe₃)₂, a molecule composed of two P₇-cages connected by a disilane bridge. It can also be obtained through silyl exchange using P₇(SiMe₃)₃ and ClMe₂SiSiMe₂Cl. The compound was characterized with ³¹P and ²⁹Si-NMR spectroscopy and elemental analysis. Treatment of P₇(SiMe₃)₃ with HypCl (Hyp = hypersilyl = Si(SiMe₃)₃) in DME led to the quantitative formation of Hyp₂P₇SiMe₃. Single crystal X-ray diffraction as well as ³¹P and ²⁹Si-NMR spectroscopy proves the presence of a heteroleptically substituted heptaphosphane cage.Quantum chemical HF and B3LYP/6-31G* calculations of equilibrium structures for the two possible isomers of P₇(SiMe₃)₃ (sym and asym) reveal that asym is destabilized by about 30-40 kJ mol⁻¹, which explains why its formation could not be observed. The phosphorus inversion barrier for the sym → asym transition is calculated as 60-70 kJ mol⁻¹.     

Preparation and reactions of some sterically hindered silanols, including [tris(trimethylsilyl)methyl]silanetriol

The silanol TsiSiMe₂OH (Tsi = (Me₃Si)₃C) has been made by hydrolysis of the iodide TsiSiMe₂I in H₂O/dioxane or H₂O/Me₂SO. It has been shown to react with some acid chlorides RCOCl (R=Me, Et, CICH₂ Ph, 4-O₂NC₆H₄, and 3,5- (O₂N)₂C₆H₃) and anhydrides (RCO)₂O (R = Me, CF₃, or Ph) to give the carboxylates TsiSiMe₂OCOR, and with SO₂Cl₂ to give TsiSiMe₂OSO₂Cl. The triol TsiSi(OH)₃ has been made by treatment of TsiSiH(OH)I with H₂O/Me₂SO at 150°C or with a mixture of aqueous AgClO₄ and an organic solvent. The triol has been shown to react with RCOCl (R = Me, Et, or Ph) or (RCO)₂O (R = Ph) to give the corresponding TsiSi(OCOR)₃, with (CF₃CO)₂O to give TsiSi(OH)₂(OCOCF₃), and with a mixture of Me₃SiCl and AgClO₄ in benzene or one of Me₃Sil and (Me₃Si)NH to give TsiSi(OSiMe₃)₃. The triol is unusually stable, but decomposes at its m.p. of 285–290°C.     

Tris(trimethylsilyl)methane is not an effective mediator of radical reactions

The reductive dehalogenation of organohalides by tris(trimethylsilyl)methane has been re-investigated. Contrary to claims made in a recent publication (Tetrahedron Lett.2006, 47, 5163-5165), (TMS)₃CH does not reduce organohalides. In competition experiments between (TMS)₃CH and the poor chain mediator Et₃SiH, the latter performed the reduction. Computational investigations support these experimental findings and indicate that the C-H bond of (TMS)₃CH is too strong for this compound to serve as an effective mediator of radical reactions.     

Tris(trimethylsilyl)methanselenenylhalogenide und -chalkogenide

Tris(trimethylsilyl)methaneselenenyl Halides and Chalcogenides . Ditrisyldiselenide ( 1 ) (trisyl = TSi = (Me₃Si)₃C) reacts with SOCl₂, Br₂ and I₂ to provide trisylselenenyl halides TSiSeX ( 2 : X = Cl; 3 : X = Br, 4 : X = I). Insertion of S and Se into the Se? Se bond of 1 to yield (TSiSe)₂S_n ( 5 : n = 1; 6 : n = 2) and (TSiSe)₂Se_n ( 7 : n = 1; 8 : n = 2) was catalysed by iodine. 5 was isolated in pure state and examined by X-ray diffraction. Triselenide 7 can be cleaved by I₂ in CS₂ to give 4 and Se₂I₂ ( 9 ). From 2 with Me₃SiCN and Me₃SiNCS, the new selenenyl pseudohalides TSiSeCN ( 10 ) and TSiSeSCN ( 11 ) were prepared. The compounds were characterised by ¹H, ¹³C- and ⁷⁷Se n.m.r. spectra.     

Preparation and lithiation of tris(o-tolyldimethylsilyl)methane

The compound (o-MeC₆H₄Me₂Si)₃CH has been prepared and shown to be metallated slowly by MeLi in refluxing THF to give the lithium reagent (o-MeC₆H₄Me₂Si)₃CLi. This reacts with MeI to give (o-MeC₆H₄Me₂Si)₃CMe, but not with Me₂SiHCl nor with a range of other organosilicon halides.