The molecular and electronic structure features of silatranes, germatranes, and their carbon analogs

Molecular geometries of fifty-six metallatranes N(CH₂CH₂Y)₃M-X and fifty-six carbon analogs HC(CH₂CH₂Y)₃M-X (M = Si, Ge; X = H, Me, OH, F; Y = CH₂, O, NH, NMe, NSiMe₃, PH, S) were optimized by the DFT method. Correlations between changes in the bond orbital populations, electron density ρ(r), electron density laplacian ∇²ρ(r), |λ₁|/λ₃ ratio, electronic energy density E(r), bond lengths, and displacement of the central atom from the plane of three equatorial substituents and the nature of substituents X and Y were studied. As the number of electronegative substituents at the central atom increases, the M←N, M-X, and M-Y bond lengths decrease, while the M←N bond strength and the electron density at critical points of the M←N, M-X, and M-Y bonds increase. An increase in electronegativity of a substituent (X or Y) is accompanied by a decrease in the ionicities of the other bonds (M-X, M-Y, and M←N) formed by the central atom (Si, Ge). A new molecular orbital diagram for bond formation is proposed, which takes into account the interaction of all five substituents at the central atom (M = Si, Ge) in atrane molecules. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 448–460, March, 2006.     

Modeling of self-organization of silicate systems: Precursor nanoclusters and self-assembly of Na<Subscript>3</Subscript>MSi<Subscript>3</Subscript>O<Subscript>9</Subscript> (M = Y,Eu-Lu; oP256) crystal structures producing two interpenetrating diamond-type frameworks

In the M-T-O model system (M is a polyvalent metal with CN ≥ 4; T is Si), cyclic clusters have been deduced as graphs in the T/M range from one to three. The case is considered when monocyclic cluster M₂T₂ is modified by T-tetrahedra that form diortho groups T₂. The M sites of the cluster have either topologically different local MT structures (four types) or identical local MT structures (two types). The cluster types for T/M = 3 obtained by modeling were used in analysis of one of the most complicated types of silicate crystal structures Na₃MSi₃O₉ (M = Y; Eu-Lu; T/M = 3) with the Pearson index oP256 and 64 independent atoms. The TOPOS program package was used to carry out the complete 3D reconstruction of the self-assembly of the crystal structure: suprapolyhedral precursor nanocluster → primary chain → microlayer → microframework (supraprecursor) → ... three-dimensional framework. The calculation of the coordination sequences of site atoms in the 3D network of the MT framework MT₃O₉ revealed topological symmetry related to a three-dimensional separation of the framework into two interpenetrating frameworks. Each framework structure is generated by topologically equivalent cyclic precursor clusters Na₂M₂T₆ consisting of two YO₆ octahedra comprising three diortho groups Si₂O₇ and two Na atoms located above and below the ring center. The 3D graphs characterizing the connectivity of the centers of crystallographically equivalent clusters in the frameworks correspond to diamond-type networks.     

Structure of (O→Si)-(acetoxymethyl)trifluorosilane in three phase states and in solutions

According to the IR spectroscopy data, the molecules of (O→Si)-(acetoxymethyl)trifluorosilane having in the liquid state and in polar media the intramolecular bond C=O→Si, exist in the gas phase in the temperature range 438–538 K in the equilibrium with the molecules with tetracoordinate silicon atom. This allowed to determine experimentally the enthalpy of formation of the intramolecular bond C=O→Si for the gas phase to be ΔH = 2.2±0.1 kcal mol⁻¹. In the solid state at 110 K and in the CS₂ solution, along with molecule with the C=O→Si bond, the dimers exist, which include both tetra- and pentacoordinate silicon atom. The data of quantum-chemical calculations (B3LYP/6-311G**) show that the shortest intermolecular bond Si-F→Si is realized in the associate formed by the molecules in the ap,sp- and sp,sp-forms, and the longest one, when both components are in the sp,sp-forms.     

Palladium(II) complexes with 1-allyl-3-(2-pyridyl)thiourea: Synthesis and spectroscopic characterization

New Pd(II) complexes with 1-allyl-3-(2-pyridyl)thiourea (APTU) of the formulas [Pd(C₉H₁₁N₃S)Cl₂] (I) and [Pd(C₉H₁₁N₃S)₂]Cl₂ (II) were obtained and examined by UV-Vis, IR, and 1H NMR spectroscopy. The conditions for the complexation reactions were optimized. The instability constants and molar absorption coefficients of these complexes were calculated. Comparison of the characteristic bands in the UV-Vis and IR spectra of the complexes and free APTU revealed that the ligand in both complexes is coordinated to the metal atom in the thione form in the bidentate chelating mode through the S atom of the thiourea group and the pyridine N atom. In the UV-Vis spectra of the complexes, the charge transfer bands (π → π* Py) and n → π* (C=N_Py), (C=S) experience hypsochromic shifts by 450–470 cm⁻¹ caused by the coordination of APTU to the metal ion, which gives rise to ligand-metal charge-transfer bands (C=N_Py → Pd, n → π* (C=S)) and (SPd). The protons in the 6-, 4-, and 3-positions of the pyridine ring and the thiourea NH proton in the chelate ring are most sensitive to the complexation.     

Ab initio study on the mechanism of cycloaddition reaction between H<Subscript>2</Subscript>Si=Si: and formaldehyde

The mechanism of the cycloaddition reaction between singlet H₂Si=Si: and formaldehyde has been investigated with the CCSD(T)//MP2/6-31G* method. From the potential energy profile, it could be predicted that the reaction has three competitive dominant reaction pathways. The reaction rules presented is that the 3p unoccupied orbital of the Si: atom in H₂Si=Si: inserts the π orbital of formaldehyde from the oxygen side, resulting in the formation of an intermediate. Isomerization of the intermediate further generates a four-membered ring silylene (the H₂Si–O in the opposite position). In addition, the [2+2] cycloaddition reaction of the two π-bonds in H₂Si=Si: and formaldehyde also generates another four-membered ring silylene (the H₂Si–O in the syn-position). Because of the unsaturated property of the Si: atom in the two four-membered ring silylenes, the two four-membered ring silylenes could further react with formaldehyde, generating two silicic bis-heterocyclic compounds. Simultaneously, the ring strain of the four-membered ring silylene (the H₂Si–O in the syn-position) makes it isomerize to a twisted four-membered ring product.     

Reaction of methyl iodide with organylethynyl silatranylmethyl chalcogenides

The reactivity of organylethynyl silatranylmethyl chalcogenides RC=CYCH₂Si(OCH₂CH₂)₃N (R=Ph, Me₃Si; Y=S, Se, Te) in the reaction with methyl iodide depending on the nature of the chalcogen Y, the substituent R at the triple bond, and the reaction conditions was studied. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2550–2551, December, 1998.     

IR-spektroskopische Untersuchungen an Halogenmethyl-, Benzyl- und α-Halogenbenzyl-Substituierten Alkoxysilanen,Phenoxysilanen und Disiloxanen

I.R.-spectroscopic Investigation on Halogenomethyl-, Benzyl-, and α-Halogenobenzyl-substituted Alkoxysilanes, Phenoxysilanes, and Disiloxanes Frequencies of Si? O-characteristic vibrations and the relative basicity of oxygen have been measured for Si? O compounds of the type X(CH₃)₂Si? OY (X = halogenomethyl, benzyl, α-halogenobenzyl; Y = alkyl, phenyl, Si(CH₃)₂X). With exception of the less Si? O-characteristic C? O? (Si)-stretching vibration of alkoxysilanes the observed data show a significant dependence from the inductive effect of substituents at Si. There are no informations on conjugative interactions between Si and β-standing halogeno or phenyl groups.     

Umsetzung von 2-Dimethylamino-(1,3,2)-diox-, oxathi- und dithi-arsolanen mit Alkoholen und Thiolen

Reaction of 2-Dimethylamino-(1,3,2)-diox-, oxathi-, and dithi-arsolanes with Alcohols or Thiols The reactions of 2-dimethylamino-(l, 3,2)-diox-, oxathi- and dithi-arsolanes (CH₂)₂XYAs? N(CH₃)₂ (X = Y = O or S; X = S, Y = O) with alcohols and thiols yield by cleavage of the As? N bond in the formation of alkoxy and alkylmercaptoarsolanes (CH₂)₂XYAs? ZR (X = Y = Z = O or S; X = Y: O, Z = S; X = Y = S, Z = O; X = S, Y = O, Z = O or S), respectively. Some of these arsolanes are not stable but rearrange under formation of 1,2-Bis-(arsolanyl)ethane and arsinous acid esters.     

Quantum-chemical study of the stereoelectronic structure of 1-fluorosilatrane, 1,1-difluoroquasisilatrane, 1,1,1-trifluorohyposilatrane,and cations formed thereof

Quantum-chemical study of the electronic structure and the equilibrium geometry of the molecules X_4−n M(OCH₂CH₂) _n NH_3−n and cations X_3−n [M(OCH₂CH₂) _n NH_3−n ]⁺ (M = Si, Ge; X = F, H; n = 1–3) is performed by the B3LYP method using the cc-PVDZ basis set. It is shown that for X = F the strength of the coordination bond N→M increases with the number of the cycles (n), while for X = H, on the contrary, decreases, that is, the strength of the N→M bond increases with the total electronegativity of the substituents surrounding atom M. Effect of the number of the coordination cycles on the strength of the N→M bond in the cations is negligible. The obtained results agree with the experimental data on the structure and spectral properties of the studied compounds.     

Theoretical study on the mechanism of extraction reaction between silylene carbene and its derivatives and thiirane

The mechanism of the sulfur extraction reaction between singlet silylene carbine and its derivatives and thiirane has been investigated with density functional theory (DFT), including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated by B3LYP/6-311G(d, p) method. From the potential energy profile, it can be predicted that the reaction pathway of this kind consists in two steps: (1) the two reactants firstly form an intermediate through a barrier-free exothermic reaction; (2) the intermediate then isomerizes to a product via a transition state. This kind of reactions has similar mechanism: when the silylene carbene and its derivatives [X₂Si=C: (X = H, F, Cl, CH₃)] and thiirane approach each other, the shift of 3p lone electron pair of S in thiirane to the 2p unoccupied orbital of C in X₂Si=C: gives a p → p donor-acceptor bond, thereby leading to the formation of intermediate (INT). As the p → p donor-acceptor bond continues to strengthen (that is the C-S bond continues to shorten), the intermediate (INT) generates product (P + C₂H₄) via transition state (TS). It is the substituent electronegativity that mainly affect the extraction reactions. When the substituent electronegativity is greater, the energy barrier is lower, and the reaction rate is greater.     

Quantum chemical study of silicon pentacoordination in (Aroyloxymethyl)trifluorosilanes and their analogs

Pentacoordinated silicon compounds of the series 4-XC₆H₄C(O)O(CH₂)_mSi(CH₃)_3-nF_n (m = 1, 2; n= 1,2,3) with an intramolecular 0→Si bond are studied by ab initia and semiempirical (AMI) quantum chemical methods. The results are compared with published experimental data. The C₆H₅C(O)OCH₂SiF₃ molecule is calculated in an RHF approximation using the 6–31G*basis set. The total energy of the molecule for its geometry optimization is calculated by the MP2 method including electron correlation. This leads to considerably improved agreement between the calculated coordination energy (25.3 kJ/mole) and the experimental value (28.5 kJ/mole). The geometry and the dipole moment calculated by both ab initio (HF/6-31G*//HF/6-31G*, MP2/6-31G*//MP2/6-31G*) methods and by the AMI method are in satisfactory agreement with the experimental data.     

Ab initio study of mechanism of forming a silicic <Emphasis Type="Italic">bis</Emphasis>-heterocyclic compound between (CH<Subscript>3</Subscript>)<Subscript>2</Subscript>Si=Si: and ethane

The mechanism of the cycloaddition reaction of forming a silicic bis-heterocyclic compound between singlet state (CH₃)₂Si=Si: and ethene has been investigated with the CCSD(T)//MP2/6-31G* method. From the potential energy profile, it can be predicted that the reaction has one dominant reaction pathway. The presented rule of this dominant reaction pathway that the 3p unoccupied orbital of Si: in (CH₃)₂Si=Si: and the π orbital of ethane forming a π → p donor-acceptor bond, resulting in the formation of a three-membered ring intermediate (INT1); Then, INT1 isomerizes to a four-membered ring silylene (P1), which driven by ring-enlargement effect; Due to sp ³ hybridization of Si: atom in the four-membered ring silylene (P1), P1 further combines with ethene to form a silicic bis-heterocyclic compound (P2).     

Hydrosilylation of non-1-ene with phenylsilane in the presence of yttrium and lutetium bisguanidinate hydride complexes

Some regularities of hydrosilylation of non-1-ene with phenylsilane catalyzed by yttrium and lutetium bisguanidinate hydride complexes {[(Me₃Si)₂NC(NR)₂]₂Ln(μ-H)}₂ (Ln = Y, Lu; R = Prⁱ, Cy (Cy is cyclohexyl)) have been studied. The addition of PhSiH₃ to the double bond of non-1-ene in the presence of a {[(Me₃Si)₂NC(NPrⁱ)₂]₂Y(μ-H)}₂ complex has the first order in olefin and zero order in phenylsilane. This indicates that the insertion of non-1-ene into the Ln-H bond is a rate determining stage of the process, whereas the metathesis of the Ln-C σ-bond upon the action of phenylsilane proceeds rapidly. The first example of successive double alkylation of phenylsilane with an olefin catalyzed by a rare-earth metal complex with the formation of tertiary silane has been discovered.     

Polymorphism for a novel phosphoramidate; NMR and X-ray crystallography

Abstract  

New phosphoramidates with formula 3-NC₅H₄C(O)NHP(O)XY (X=Y=Cl (1), X=Y=NH–C(CH₃)₃ (2a,2b), X=Y=N(C₄H₉)₂ (3), X=Cl, Y=N(C₂H₅)₂ (4) were synthesized and characterized by IR, ¹H-, ¹³C-, ³¹P-NMR spectroscopy and CHN elemental analysis. Surprisingly, the reaction of compound 2a with LaCl₃, 7H₂O in 3:1 M ratio leads to a polymorph of this compound (2b). NMR spectra indicate that ² J(PNH_amide) in 2b (7.0 Hz) is very much greater than in 2a (4.1 Hz), while δ(³¹P) values are identical for both of them. In IR spectra, υ(P=O) is weaker but υ(C=O) is stronger in 2a than in 2b. The structures of 2a, 2b were determined by X-ray crystallography. These compounds form centrosymmetric dimers via two intermolecular P=O……H–N hydrogen bonds. Strong intermolecular N–H…N, N–H…O and weak C–H…O hydrogen bonds lead to a three-dimensional polymeric cluster in the 2a while intermolecular strong N–H……N and weak C–H……O hydrogen bonds form a two-dimensional polymeric chain in 2b.     

1H and13C NMR study of tin-containing sulfoxide, sulfimide, and sulfoximide

Sulfoxide RS(O)R′ (1), sulfimide RS(=NSO₂Ar)R′ (2), and sulfoximide RS(O)(=NSO₂Ar)R′ (3) (R=Me₃Sn(CH₂)₃, R′=n-C₅H₁₁, Ar=4-C₆H₄Cl) were investigated by¹H and¹³C NMR spectroscopy. Unlike 3, compounds 1 and 2 have a cyclic structure due to the intramolecular donor-acceptor S→Sn interaction. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1966–1969, November, 1997.     

Mono- and bi-metallic complexes based on redox-active tris(3,5-dimethylpyrazolyl)borato-molybdenum nitrosyls,part III.(1) Complexes containing meta-substituted benzene- and naphthalenediols or -diamines

Summary The complexes [MoL^*(NO)Cl(YC₆H₄YH-m)] (Y = O or NH), [MoL^*(NO)Cl(YC₁₀H₆YH-1,5)], (Y = O or NH), [MoL^*(NO)Cl(OC₁₀H₆OH-2,7)], [{MoL^*(NO)Cl}₂(XC₆H₄Y-m)] (X=Y=O, NH or S; X=O, Y=NH), [{MoL^*(NO)-C1}₂(YC₁₀H₆Y-1,5)] (Y=O or NH) and [{MoL^*(NO)Cl₂-(OC₁₀H₆-2,7)] have been prepared and studied by cyclic voltammetry. The monometallic species undergo a reversible oneelectron reduction, whereas the bimetallics undergo two oneelectron reductions. A comparison of E_1/2 (E_1/2(1)-E_1/2(2)) values for those new species with those obtained frompara- substituted analogues and bimetallics containing extended bridges YC₆H₄ZC₆H₄Y (e.g. Z = S or CH₂CH₂) established that the interaction between the redox centres in these new species is intermediate (YC₆H₄Y-m; NHC₁₀H₆NH-1,5) or weak (OC₁₀H₆O).In earlier papers^1,2 we have described the synthesis and electrochemical properties of a series of mono- and bi-metallic complexes of the type [MoL^*(NO)X(YC₆H₄YH)], [MoL^*(NO)X}₂(YC₆H₄Y)] and [{MoL^*(NO)X}₂(YC₆H₄-ZC₆H₄Y)] [L^*=tris(3,5-dimethylpyrazolyl)borate, HB(Me₂C₃HN₂)₃] where the arene ring ispara-substituted (X=Cl or I while Y=O, S or NH and Z = nothing, CH₂, CH₂CH₂, S, SO₂ or O). We have shown that the E_1/2-values of these species are dependent on X and Y, and that the bimetallic species undergo two one-electron reduction processes.We have established that there is strong interaction between the redox centres in bimetallics bridged byp-YC₆H₄Y, but that weak-to-negligible interaction occurs in those species containing YC₆H₄ZC₆H₄Y bridges. In this paper we describe our investigations ofmete-substituted bridging systems,m-YC₆H₄Y, and comparable systems containing naphthalene bridges,e.g. 1,5- or 2,7-YC₁₀H₂Y. From these studies we hoped to establish the extent of interaction between the two redox centres and how this compared to thepara-substituted arene counterparts.     

Vergleichende Untersuchungen an Silyloxy- und Disilanyloxy-Verbindungen

Comparative Investigations on Silyloxy and Disilanyloxy Compounds The frequencies of Si? O? Y characteristic IR bands and relative basicities or acidities of Me₃SiOY and Me₅Si₂OY have been compared with analog data of compounds of the common type XMe₂SiOY (X = halogenomethyl, benzyl, α-halogenobenzyl; Y = H, alkyl, phenyl, SiMe₂X). There are good linear correlations between these data and Taft σ*-constants with exception of the values for disilanyl-compounds (X = Me₃Si). These deviations are explained by a specific acceptor of the Si? Si bond.     

In search of 1,3-disila/germa/stannabicyclo[1.1.1]pentanes with short bridgehead-bridgehead distances and low ring strain energies

The strain energies and through-space distances between the two bridgehead E atoms of a selection of 1,3-dimethyl-1,3-ditetrelbicyclo[1.1.1]pentanes (tetrel E = Si, Ge or Sn) were examined by quantum chemical calculations at MP2 and B3LYP levels. The aim is to identify which bridges lead to short through-space E,E distances, and simultaneously, to as low strain as possible. A short E,E distance should improve through-space interaction, and a low strain should promote the thermal stability and possibly also facilitate their synthesis. The bridges examined included CH₂, CMe₂, CtBu₂, C(CH₂)n (n = 2–4), O, NMe, S, PMe, SiMe₂, GeMe₂, and SnMe₂. The calculations indicate that the phospha bridge is a good compromise providing reasonably low strain as well as E,E through-space distances which are only longer than normal E–E single bonds by factors of 1.06–1.10. This paper is dedicated to Professor Mitsuo Kira in recognition of his stimulating Si chemistry and his 2005 Wacker Award.