Insertion reactions of thermally generated stannylenes R2Sn into Sn-X (X = Cl,Br, SPh) and Sn-Sn bonds

Thermally generated stannylenes R₂Sn insert efficiently into Sn-X bonds (X  Cl, 3r, SPh) as well as into electron deficient SnSn bonds e.g. in Me₂(Hal)SnSn(Hal)Me₂, but not into hexaalkyldistannanes R₆Sn₂ under the same conditions; stannylenes R₂Sn always behave as nucleophiles here.     

Benzyl-tris(trimethylsilyl)methylzinndihalogenide, {(CH3)3Si}3C(C6H5–CH2)SnHal2 mit Hal = Cl,Br, I

Benzyl-tris(trimethylsilyl)methyl Tin Dihalides, {(CH₃)₃Si}₃C(C₆H₅–CH₂)SnHal₂ with Hal = Cl, Br, I The tin tetrahalides SnHal₄ (Hal = Cl, Br, I) react with base-free tris(trimethylsilyl)methyllithium (Tsi–Li) solved in toluene to form the trihalides Tsi–SnHal₃. But when the reaction is carried out in a 1 : 2 molar ratio at 60 °C in toluene, Tsi–H, Tsi–Hal and benzyl-trisyl tin-dihalides are formed in good yields, respectively. The nmr (¹H, ¹³C, ²⁹Si, ¹¹⁹Sn) and the Raman spectra are discussed, the X-ray structure analyses of the dibromide as well as the diiodide have been measured.     

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 einiger Methylmetallhalogenide des Aluminiums,Galliums und Indiums mit Hexamethyldisilazan

Reactions of some Methylmetal Halides of Aluminium, Gallium, and Indium with Hexamethyldisilazane MeAlCl₂ or MeGaBr₂, and bis(trimethylsilyl)amine form the dimeric, mixed-substituted ring molecules (Me(Hal)M^III–N(H)SiMe₃)₂ and one equivalent Me₃SiHal. The NMR (¹H, ¹³C, ²⁹Si) and vibrational spectra (IR, Raman) are measured and the X-ray structure analysis of the compound with M^III = Al and Hal = Cl, has been done as well. Me₂AlCl with an excess of HN(SiMe₃)₂ forms the expected amide (Me₂Al–N(H)SiMe₃)₂, the homologue Me₂GaCl with HMDS, however, gives at 50–55 °C only the cyclic (1 : 1) adduct (Me₂Ga–N(H)SiMe₃) · (Me₂GaCl). This complex crystallizes in the space group Cmc2₁, the unit cell consists of four binucleate molecules with folded Ga–N–Ga–Cl-ring skeletons.     

Über die Si---N-bindung : XLIV. Die umsetzung von benzophenon mit bis- und tris(trimethylsilyl)amin

The thermal LiHal elimination of

- and

functional compounds provides a simple synthetic route to four-membered SiC and SiN rings. In attempts to inhibit dimerisation sterically, bulky silylmethyl and silylamino substituents were introduced (I–III). (Me₃Si)₃CSiF₂R reacts with LiNHR′, 1,3- migration of a silyl group from carbon to the nitrogen (I, R′= 2,4,6-Me₃C₆H₂) taking place. Substitution occurs for R′ = SiMe₂CMe₂, (II, III) only.Dichloro-bis(trimethylsilyl)methane reacts with halogenosilanes and lithium in THF to give bis(trimethylsilyl)-halogenosilaethanes (Me₃Si)₂CHSi(Hal)RR′; R= Me, R′ = N(SiMe₃)₂, IV, Hal = F; V, Hal = Cl. However a reductive THF cleavage accompanied by a silyl group migration to the oxygen occurs and 1-halogenosilyl-1- trimethylsilyl-5-trimethylsiloxi-pent-1-ene,(Me₃Si)(RR′SiHal)CCH(CH₂)₃OSiMe₃, Are The main products (VII–X) of these reactions. Disubstitution occurs with F₃Si-i-Pr (VI). (Me₃Si)₃CSiFNHSiMe₂CMe₃ (II) reacts with C₄H₉Li in a molar ratio $\text{1}\text{2}$ to give an 1-aza-2,3-disilacyclobutane (XI), involving substitution, LiF elimination, and nucleophilic migration of a methanide ion of the unsaturated precusor.(Me₃Si)₂CHSiFMeN (2,4,6-Me₃C₆H₂)SiMe₃ cyclizes under comparable conditions in the reaction with MeLi via a methylene group of the mesityl group (XII).     

Contributions to the chemistry of halosilane adducts: XVIII. On the nature of compounds of trimethylhalosilanes with 1,1,3,3-tetramethylguanidine and 2-trimethylsilyl-1,1,3,3-tetramethylguanidine: preparation and characterization of mono- and bis-(2-trimethylsilyl)-1,1,3,3-tetramethylguanidinium halides

1,1,3,3-Tetramethylguanidine (TMG) and 2-(trimethylsilyl)-1,1,3,3-tetramethylguanidine (TMSTMG) react with trimethylhalosilanes Me₃SiHal in equimolar ratio with ionization of the Sihalogen bond to give the stable guanidinium salts [(Me₂N)₂CNHSiMe₃]Hal (Hal  Cl (1), Br (2)) and [(Me₂N)₂CN(SiMe₃)₂]Hal (Hal  Cl (3), Br (4), I (5)), respectively, involving tetracoordinate silicon. No reaction occurs with Me₃SiF. The same ionic species are present in CHCl₃ or CH₃CN solutions (IR, ¹H, ²⁹Si NMR), thus establishing for the first time, the formation of an ionic solid derivative of Me₃SiCl stable towards dissociation. Reaction with an excess of TMG gives an equilibrium mixture of TMSTMG and TMG · HHal. The bis(silyl)guanidinium salts are less stable towards dissociation than the mono(silyl) derivatives, the stability sequence being Cl⁻ < Br⁻ < I⁻ within the series. The reactions of both types of compound have been investigated. The implications of the present and earlier results for the mechanisms of racemization and nucleophilic substitution at silicon are discussed.     

The crystal structure of triphenyltin isothiocyanate

The crystal structure of Ph₃SnNCS has been determined by single crystal X-ray diffraction. The crystals are monoclinic, P2₁, a = 19.02(3), b = 11.67(2), c = 15.49(2)Å;, β = 95.64(10)°, Z = 8. The molecules are arranged in infinite zig-zag S…SnNCS…Sn&.sbnd; chains similar to those in Me₃SnNCS, but with slightly longer SnN, shorter SnS bonds, and almost planar SnC₃ units. Principal mean bond lengths and angles are: SnN, 2.22(5); NC, 1.17(8); CS, 1.58(7); SSn, 2.92(1); SnC, 2.09(3); CC, 1.38(2)Å; SnNCm 161(4); CSSn, 97(3); SSnN, 175(3) and CSnC, 119.8(1.5)°.     

Clˉ as the halogen bond acceptor: studies on strong halogen bonds

The Clˉ anion as the halogen bond acceptor, the diiodotetrafluoroethane I(CF₂)₂I and its derivatives I(MF₂)_nI (M = C, Si, Ge, Sn) as the halogen bond donor, and the strong halogen bonds could be formed. The halogen bonds between I(MF₂)_nI and Clˉ have been designed and investigated by Moller–Plesset perturbation/aug-cc-pVDZ calculations together with the aug-cc-pVDZ-pp basis set for iodine and stannum. The halogen bonds in the I(MF₂)_nI???Clˉ complexes are strong, which are apparently related to the group IV elements, becoming stronger along the sequence of M = Si, C, Ge, Sn. Accompanied with increasing number (n) of MF₂ unit, the halogen bonds (M = Si, Ge, Sn) also become stronger. The energy decomposition analyses reveal that the exchange energy contributes most in forming these halogen-bonded interactions. In the meantime, the electrostatic energy is also a significant factor for the I???Clˉ interactions. The halogen bonds of I(MF₂)nI???Clˉ(M = C, Ge, Sn) belong to partial-covalent interactions, while they are noncovalent interactions when M = Si.     

Molecular structures of (SiCl3)2CH2 and (SiCl3)2CCl2 as studied by electron diffraction

An electron diffraction analysis of the molecular structures of 1,1,1,3,3,3-hexachloro-1,3-disilapropane and octachloro-1,3-disilapropane has been carried out. Deviations from the staggered conformation are indicated. The data may be approximated by models with C₂ symmetry and a small tilt of the SiCl₃ groups. The main bond lengths (r_g) and bond angles obtained for (SiCl₃)₂ CH₂ are: SiCl, 202.7(4); SiC, 186.6(6); CH, 109.8(24) pm, ClSiCl, 107.9(1); SiCSi, 118.3(7)°; and for (SiCl₃)₂CCl₂: SiCl, 202.0(4); SiC, 190.2(9); CCl, 179.6(9) pm; ClSiCl, 109.5(1); SiCSi, 120.6(9); ClCCl, 110.9(16); SiCCl, 106.3(3)°.     

Matrix Isolation and IR spectroscopy of stannylenes (CH3)2Sn and (CD3)2Sn

Free stannylenes Me₂Sn and (CD₃)₂Sn, generated thermally from the cyclic hexamers or by microwave discharge from Me₂SnH₂, are isolated by Argon matrix technique. All IR bands could be attributed to the important molecular vibrations by normal coordinate analysis. As shown by ab initio SCF calculations, Me₂Sn has a singlet groud state, the angle CSnC is 95.3°, the CSn bond length is 2.203 Å.     

Übergangsmetall-substituierte phosphane,arsane und stibane : XXIX. Metallierte arsane und stibane mit chiralem eisen-substituenten

The reaction of Cp(CO)₂FeEMe₂ (E  As, Sb, Bi) with Me₃P, Et₃P, Me₂PhP and (MeO)₃P leads to a CO/R₃P exchange and formation of the chiral derivatives Cp(CO)(R₃P)FeEMe₂. Cp(CO)[(MeO)₃P]FeEMe₂ rearranges already at room temperature to Cp(CO)[(Me₃E]FeP(O)(OMe)₂ which is transformed by (MeO)₃P to Cp(CO)[(MeO)₃P]FeP(O)(OMe)₂. The high nucleophilicity of the new organometallic Lewis bases is established by the easy conversion of Cp(CO)(Me₃P)FeSbMe₂ to [Cp(CO)(Me₃P)Fe(SbMe₃)]I with MeI, or to [Cp(CO)(Me₃P)FeSbMe₂Fe(CO)LCp]Hal (L  CO, Hal  Cl; L  Me₃P, Hal  Br) with Cp(CO)LFe-Hal, respectively. The new compounds are characterized by spectroscopy and elementary analyses.     

Thermolysis of [tris(trimethylsilyl)methyl](diphenyl)fluorosilane. Isomerization of a sila-olefin intermediate

The compound (Me₃Si)₃CSiPh₂F loses Me₃SiF under reflux or on passage through a tube at 450°C to give three products, A, B, and C, in approximately 20/20/60 ratio. Products A and B, which are solids, were shown by X-ray crystallographic analysis to be the diastereoisomeric forms of 1-dimethylsila-2-trimethylsilyl-3-[(methyl)(phenyl)sila]indane. From its mass and ¹H NMR spectra, C (a liquid) was tentatively identified as 1,3-bis(dimethylsila)-2-[(dimethyl)(phenyl)silyl]indane. All three products are isomers of the sila-olefin (Me₃Si)₂CSiPh₂, and it is suggested that the latter is first formed by loss of Me₃SiF from (MeSi)₃CSiPh₂F, and the equilibrium (Me₃Si)₂CSiPh₂ ? (Me₃Si)(Ph₂MeSi)CSiMe₂ ? (Me₃Si)(PhMe₂Si)CSiMePh ? (Me₂PhSi)₂CSiMe₂ is then rapidly established; internal cyclizations involving addition of aryl CH bonds across SiC bonds then occur to give the observed products. Consistent with this is the observation that a mixture of silicon alkoxides, thought to be (Me₃Si)₂CHSiPh₂OMe and its isomers (which would be formed by addition of methanol across the SiC bonds of the four sila-olefins) is produced when methanol is passed through the hot tube with the (Me₃Si)₃CSiPh₂F.Full structural details are given for compounds A and B. Some features of interest are: (a) the conformation of the 5-membered ring is different in the two diastereoisomers; (b) the exocyclic SiCSiMe₃ bond angles, of ca. 120° are unusually large; and (c) there is a little distortion of the fused benzene ring, which is attributed to the effect of silicon substituents on the hybridization of carbon atoms to which they are attached.     

Rate constants for the reactions of CCl(X2II) with a series of silanes

Rate constants for the gas phase reactions of CCl generated by the flash photolysis of CHBr₂Cl with a series of silanes have been obtained by kinetic absorption spectroscopy. In general, the rate constants are very high, and range from (4.8 ± 0.5) × 10⁸ (SiH₄) to (6.4 ± 0.34) × 10⁹ for Si₂H₆. CCl does not insert into the SiC or primary CH bonds of silanes and its rate of reaction with tertiary SiH bonds is 600 times greater than with tertiary CH bonds. CCl reacts slowly with the SiSi bond. k_H/k_D varies from 1.9 to 1.0 on going from primary to tertiary SiH bonds. The electrophilic character of CCl is manifested, on a per SiH bond basis, by excellent correlations between the rate constants and the hydrilic character of the SiH bond, and between log k and the ionization potential.     

Molecular structure and conformation of gaseous vinyldimethylchlorosilane as determined by electron diffraction

The molecular structure of vinyldimethylchlorosilane has been determined by gas phase electron diffraction at room temperature. The least squares values of the bond lengths (r_g) and bond angles (∠_α) are : r(CH) = 1.086(6) Å, r(CC) = 1.347(5) Å, r(SiC=) = 1.838(6) Å, r(SiC) = 1.876(3) Å, r(SiCl) = 2.078(2) Å, ∠CCSi = 127.8° (1.2) and ∠=CSiCl = 107° (1). Models with pure syn form and a mixture of syn and gauche gave equally good agreement with the diffraction data.     

Etude structurale de composes organosilicies par diffusion rayleigh depolarisee: VI. Effets electroniques dans les systemes Cz.dbnd;CSi,PhSi,SiCC, SiNSi Et Si3N

Depolarised Rayleigh scattering is sensitive to conjugated electronic effects. The proper effect of silicon bonded to an sp² carbon atom in Me₃SiPh and Me₃SiCHCHΣ (Σ = H, Me, t-Bu, SiMe₃) has been illustrated by comparison of the systems containing a C_sp²M bond with the corresponding systems containing a C_sp³M bond for M = C, Si. To be able to make this comparison it was necessary to study the additivity of the bond and group optical anisotropies in alkenes with Me, CMe₃, SiMe₃ groups by means of a more approximate model assuming axial symmetry for the CC bond but of more convenient and more general use than a more realistic model without axial symmetry. Contrary to the NSi (from monosilylamines), SiOC and SiOSi systems, silicon adjacent to an unsaturated system, causes an exaltation of the optical anisotropy which mainly results from increase of the longitudinal optical polarisability. This exaltation is consistent with electron delocalisation in an orbital obviously longer than the basic π orbital. Such an effect seems strengthened in (Me₃Si)₂NΣ if the donating ability of Σ increases, Σ = H, Me, t-Bu. For Me₃SiCHCHSiMe₃ and if the molecules Me₃SiNHΣ¹ (Σ¹ = Me, t-Bu), (Me₃Si)₂NH and (Me₃Si)₃N are compared, a compensation is observed between the effect of the new lengthening of the π orbital and the π electronic density fall by CSi or NSi bonds.     

Electron diffraction and vibrational spectroscopic investigation of the molecular structure of (chloromethyl)trichlorosilane

An electron diffraction analysis of the molecular structure of the title compound has been carried out, and related vibrational spectroscopic measurements and calculations have been made. The main bond lengths (r_g and bond angles r_α) are as follows: SiCl, 202.8(2); SiC, 185.1(10); CCl, 179.4(11); CH, 111.2(18) pm; SiCCl, 111.7(4);l ClSiC, 109.95(21)°. The conformation of the molecule is staggered. The barrier to internal rotation is estimated to be around 10 kJ mol^?1.     

CIDNP 1H study of the photolysis of 7-sila- and 7-germa-norbornadienes

The photochemical decomposition of 7-sila- and 7-germa-norbornadienes (Ia,b) was studied by the CIDNP ¹H technique. The reactions proceeds by a two-step mechanism via the reversible formation of singlet biradicals, II. The triplet biradical (II), formed as a result of S-T conversion of (II)(S), irreversibly decomposes giving Me₂E (E = Si, Ge). The insertion of Me₂E into the CBr bond of PhCH₂Br and the SnCl bond of Me₃SnCl occurs via a radical mechanism, as deduced from the CIDNP effects observed in these reactions.     

Neue Synthesen von Me2SbX (X = Cl,I) und Kristallstrukturen von Me2SbI und [(Me3Si)2CH]2SbCl

Novel Syntheses of Me₂SbX (X = Cl, I) and Crystal Structures of Me₂SbI and [(Me₃Si)₂CH]₂SbCl The crystal structures of Me₂SbI (Me = CH₃) and [(Me₃Si)₂CH]₂SbCl have been determined by X‐ray methods. Both molecules are pyramidal. The Me₂SbI molecules are associated to chains through short intermolecular Sb…I distances (366,7(1) pm) with linear I–Sb…I units (171,87(4)°) and bent Sb–I…Sb bridges (116,83(3)°).     

The crystal and molecular structure of tris[(triphenylstannyl)methyl]methane

The title compound, C₅₈H₅₂Sn₃, belongs to the triclinic space group P$\text{1}$, with a 10.165, b 13.365, c 18.670 Å, α 96.28, β 93.88, γ 103.15°, V = 2443.8 ų, f_w = 1105.1, Z = 2, D_calc 1.501 g cm^?3, m.p. 206.5–208°C, λ(Mo-K_$\text{α}$) 0.71069 Å. The structure was refined on 2684 nonzero reflections to an R factor of 0.044. The crystal contains molecules in which the (SnCH₂)₃CH core possesses an approximate C₃ symmetry. The three SnC(H₂) bonds are gauche to the C(4)-H bond. Repulsive interactions involving the bulky Ph₃Sn substituents lead to large SnC(H₂)C(H) angles (av. 117.3°), whereas the C(H₂)C(H)C(H₂) angles at the tertiary carbon average 111.3°. Little distortion of the Ph₃Sn groups themselves is present, since the PhSnPh angles (av. 109.8°) are almost equal to the C(H₂)SnPh angles (av. 109.9°). The molecule as a whole has no symmetry because the aromatic rings in the three Ph₃Sn groups have different orientations. The phenyl groups create a pocket in the middle of the molecule which encloses and shields the tertiary hydrogen atom. The resulting inaccessibility of this hydrogen accounts in part for the low reactivity of the title compound in redox reactions.     

Synthesis,molecular structure and stereoisomerization of 2-phosphinyl and 2-phosphonylethyl diorganotin halides

Functionally substituted triorganotin halides V–IX of type R₂Sn(X)(CH₂)₂P(O)PhR′ (R = Me, t-Bu; Rt? = OEt, t-Bu; X = Cl, Br) have been synthesized by halogen cleavage of the corresponding tetraorganotin compounds R₂R²Sn(CH₂)₂P(O)PhR′ (R² = Me or Ph), I–IV. The solid state structure of Me₂Sn (Br) (CH₂)₂P(O)PhBu-t (IX), determined by X-ray diffraction, shows a distorted trigonal-bipyramidal structure at the tin atom, with intramolecular coordination of the PO group. Spectroscopic data are in agreement with such a structure in solution for compounds V–IX. Upon varying the temperature, concentration or solvent in solutions of compounds V–IX a stereoisomerization is observed. On the basis of NMR ¹H, ¹³C, ³¹P, ¹¹⁹Sn), IR and conductivity studies, it is suggested that this stereoisomerization involves a hexacoordinated transition state at the tin atom.