Synthesis, molecular and crystal structure, and features of the electronic structure of bis(O’i)-chelated bis(2,2-dimethylbenzo-[2H]-4-oxo-1,3-oxazino-3-methyl)difluorosilane

A method has been developed for the synthesis of a bis(O→Si)-chelated bis(2,2-dimethylbenzo[2H]-4-oxo-1,3-oxazino-3-methyl)difluorosilane from 2,2-dimethyl-3-trimethylsilylbenzo[2H]-1,3-oxazin-4-one and bis(chloromethyl)dichlorosilane via the intermediate formation of the corresponding unstable bis-chelated dichloride, subsequent hydrolysis with NaHCO₃ and, without separation, treatment of the hydrolysis product with boron trifluoride etherate. Analysis of the electron density distribution showed the presence of dative bonding in both O→Si-F fragments. Dedicated to Prof. Edmunds Lukevics on the occasion of his 70th birthday __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1866–1879, December, 2006.     

Synthesis and molecular and crystal structures of mono-and bis-chelate hypercoordinate silicon compounds containing the C,O-chelating 2,2-dimethyl-4-oxo-2,3-dihydro-1,3-oxazin-3-ylmethyl ligand

New mono-and bis-chelate hypercoordinate silicon complexes containing the monoanionic C,O-chelating 2,2-dimethyl-2,3-dihydrobenzo-1,3-oxazin-3-ylmethyl (BonCH₂) ligand were synthesized starting from 2,2-dimethyl-2,3-dihydrobenzo-1,3-oxazin-4-one (1) through its TMS derivative 2. The reactions of compound 2 with the chlorosilylmethylating agents ClCH₂SiMe₂Cl, ClCH₂SiMeCl₂, and (ClCH₂)₂SiCl₂ followed by the transformations of the initially formed chlorosilanes BonCH₂SiMe₂Cl (3), BonCH₂SiMeCl₂ (6), and [(BonCH₂)₂Si(Cl)]⁺Cl⁻ (8), respectively, into the target products afforded neutral monochelates, viz., monofluoride BonCH₂SiMe₂F (5) and difluoride BonCH₂SiMeF₂ (7), and the bis-chelate disiloxane cation-anion complexes {[(BonCH₂)₂Si]₂O}²⁺·Cl⁻·ClHCl⁻ (9) and {[(BonCH₂)₂Si]₂O}²⁺·2TfO⁻ (10). The reaction of ditriflate 10 with boron trifluoride etherate produced fluoride triflate (BonCH₂)₂Si(F)OTf (11). The X-ray diffraction study of compounds 5, 7, 9, 10, and 11, as well as of NH-heterocycle 1 and disiloxane (BonCH₂SiMe₂)₂O (4) studied earlier, demonstrated that the Si atoms in complexes 5, 7, 9, and 10 are pentacoordinate through the formation of an intramolecular O→Si bond. The coordination of silicon in fluoride triflate 11 can be described as 5+1. In disiloxane 4, one of two Si atoms is pentacoordinate. Dinuclear cation-anion complexes 9 and 10 contain the diastereomeric bis-silylium ions {[(BonCH₂)₂Si]₂O}²⁺, which differ in the configuration of the chiral bis-chelate fragments (BonCH₂)₂Si. In complex 9, these fragments have opposite configurations (ΛΔ); in ditriflate 10, the same configurations (ΛΛ). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 446–458, March, 2007.     

(Amidomethyl)dimethylsilanol hydrohalides: Synthesis, NMR and IR studies. Characteristic features of the electronic structure from high-resolution X-ray study and quantum chemical calculation

(C,O)-chelate silanol hydrohalides RC(O)NHCH₂SiMe₂OH · HHal (2a,b and 5b), and their precursors, (C,O)-chelate chlorosilanes RC(O)NHCH₂SiMe₂Cl (6a,b) and disiloxanes [RC(O)NHCH₂SiMe₂]₂O (8a,b) (R = Me (a), Ph (b); Hal = Cl (2), Br (5)), were obtained by several routes. The original scheme of hydrolysis of the above chlorides was discussed in detail. X-ray analysis has shown that the silanol hydrohalogenides PhC(O)NHCH₂SiMe₂OH · HX (2b and 5b) in the crystal exist in the form of cation-anion pairs [PhC(O)NHCH₂SiMe₂(OH₂)]⁺ · X⁻ (14b · Cl⁻ and 14b · Br⁻) assembled by H-bonds in a 3D framework. The Si atom in the cation has a trigonal bipyramidal configuration with the oxygen atom of the carbonyl group and protonated hydroxyl exo-substituent in axial positions. The endocyclic Si-O bonds are equal with an average of 1.905 Å while the exocyclic Si-O bonds are 1.979 and 2.009 Å, for Hal = Cl and Br, respectively.Quantum chemical calculations have shown that the cation [PhC(O)NHCH₂SiMe₂(OH₂)]⁺ (14b) is stable only in the crystal. Based on a high-resolution X-ray study and a quantum chemical calculation, it was found that the chemical bonding pattern in the OSiO axial fragment of the cation 14b corresponds to a three-centred four electron interaction. The cation 14b should be considered as a silylium cation stabilized by coordinated H₂O molecules rather than a silyloxonium ion.     

Synthesis and crystal and molecular structures of cation-anionic complexes of five-coordinate silicon-containing disiloxane dications with lactamomethyl andN-methylacetamidomethyl C,O-chelating ligands

The reactions of bis(chloromethyl)dichlorosilane withN-trimethylsilyl lactams andN-trimethylsilyl-N-methylacetamide taken in a ratio of 1∶2 followed either by treatment with HgCl₂ in the presence of atmospheric moisture or by hydrolysis under a wet atmosphere afforded cation-anionic complexes, which contain disiloxane dications of the general formula [L₂SiOSiL₂]²⁺ (L is the lactamomethyl orN-methylacetamidomethyl bidentate ligand) and hexachlorodimercurate, tetrachloromercurate, and hydroxonium trichloride counter-ions, respectively. X-ray diffraction analysis demonstrated that the disiloxane dications in these complexes contain two five-coordinate Si atoms and occur as silicenium ions stabilized through two O→Si coordination bonds. In the case of lactamomethyl ligands, the disiloxane dications exist as diastereomers whose bischelate ligands adopt opposite configurations, whereas whenN-methylacetamidomethyl ligands are present, the bischelate ligands adopt identical configurations. The first example of the presence of a hydroxonium trichloride ion as a counter-ion in the crystal has been found. It consists of the hydroxonium cation, which holds three Cl⁻ anions through strong hydrogen bonds. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 997–1007, May, 1998     

Synthesis and crystal and molecular structures of six-coordinate tin dibromides and diiodides containing lactamomethyl C,O-chelating ligands

New (O−Sn)-bischelate bis(lactamomethyl)dibromo- and-diiodostannanes [L⁽ⁿ⁾]₂SnX₂ (L is the bidentate lactamomethyl C,O-chelating ligand;n is the size of the lactam ring, 5–7; X=Br or I) were prepared both by the direct method from metallic tin and the correspondingN-(halomethyl)lactams and by the reactions of dichlorides [L⁽ⁿ )]₂SnCl₂ with lithium halides. According to the data of X-ray diffraction analysis, the tin atom in [L⁽ⁿ⁾]₂SnBr₂ (n=5–7) and [L⁽ⁿ⁾]₂SnI₂ (n=5 or 6) adopts an octahedral configuration with the carbon atoms intrans positions and the coordinating oxygen and halogen atoms incis-positions with respect to each other. A comparison with the structures of analogous lactamomethyl halide derivatives of five-and six-coordinate Si, Ge, and Sn demonstrates that the spatial structures of the hypervalent fragments containing six-coordinate atoms are less sensitive to the replacement of the halide ligands and the central atom. The covalence of the M−Hal bond increases and the covalence of the M−O bond decreases in the series M=Si, Ge, and Sn. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1988–1998, October, 1999.     

Silicon—nitrogen bond cleavage in N-(dimethylimidosilylmethyl)imides and dimethyl(lactamomethyl)aminosilanes with BF3 etherate as an alternative route to N-(dimethylf luorosilylmethyl)imides and related compounds

N-(Dimethylfluorosilylmethyl)succinimide (2a) and N-(dimethylfluorosilylmethyl)phthalimide (2b) were synthesized by the Si—N bond cleavage in readily accessible N-(dimethylimidosilylmethyl)imides with BF₃ etherate. Analogously, (O→Si)-chelated 1-(dimethylfluorosilylmethyl)-2-pyrrolidone was prepared from 1-(dimethylmorpholinosilylmethyl)-2-pyrrolidone. X-ray diffraction study demonstrated that the silicon atom in the crystals of 2b is pentacoordinated. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 558–561, March, 2006.     

Chemical bonding in isolated molecules and crystals of zwitterionic pentacoordinate silicon chelates

The electronic structures of a number of zwitterionic pentacoordinate silicon chelates were investigated using the results of X-ray diffraction studies and quantum-chemical calculatoins by the MPW1PW91/6-311G(d) method. The topological analysis of the electron density distribution function and the study in the framework of the natural bond orbital partitioning scheme showed that the character of chemical bonding in the axial fragments of the molecules under consideration changes from dative to three-center, four-electron as the silicon atom assumes a trigonal-bipyramidal coordination.     

Synthesis,crystal structure and stereochemical non-rigidity of (O-Sn)-bischelated bis(lactamomethyl)dichlorostannanes

Previously unknown (0-Sn)-bischelated bis(lactamomethyl)dichlorostannanes have been synthesized by a direct method from metallic tin and N-chloromethyllactams. According to X-ray structural analysis data, in the solid state in these compounds the tin atom is hexacoordinated and has an octahedral configuration with the two carbon atoms in the transposition, and both coordinating oxygen atoms and the two halogen atoms in thecis-position. A comparison to Ge-analogs indicates that the replacement of the central atom of the coordination unit MCl₂O₂C₂ has inconsistent effects on the parameters of the latter. According to¹H and¹¹⁹1 Sn NMR data, the hexacoordination of tin and the geometry of the coordination unit are also retained in solution at low temperatures. At higher temperatures a dynamic process takes place resulting in isochronisms of the protons signals of the NCH₂Sn groups. Quantum-chemical calculations of isomeric bis(lactamomethyl)dichlorostannanes by MNDO and MNDO/PM3 methods have been discussed.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11, pp 2768–2779, November, 1996.     

Crystal and molecular structures of six-coordinate germanium difluorides and dibromides containing lactamomethyl C,O-chelating ligands

The structures of (O−Ge)-bischelate bis(lactamomethyl)difluoro- and-dibromogermanes [L⁽ⁿ⁾]₂GeX₂, where L is the bidentate lactamomethyl C,O-chelating ligand,n=5–7 (the size of the lactam ring), and X=F or Br, were studied by X-ray diffraction analysis. The six-coordinate Ge atom in these compounds is involved in two hypervalent X−Ge−O bonds whose parameters are compared with the corresponding values in analogous dichlorides and five-coordinate Ge derivatives. On going from difluorides to dichlorides and then to dibromides, the coordination environment about the Ge atom approaches the ideal octahedron. An analogous effect is observed as the size of the lactam ring increases. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1799–1805, October, 2000.     

X-ray diffraction and quantum-chemical study of 3-(1,3-dioxolan-2-yl)-4,6-dinitrobenzo[d]isoxazole

X-ray diffraction study of the molecular structure of 3-(1,3-dioxolan-2-yl)-4,6-dinitrobenzo[d]isoxazole in the crystal, and quantum-chemical calculations of the isolated molecule demonstrated that the differences in the reactivity of the nitro groups at positions 4 and 6 are not associated with the electronic structure of the molecule but are, apparently, attributed to the properties of the corresponding ipso- complexes.     

Synthesis and structures of tris(pentafluorophenyl)silylamines

Tris(pentafluorophenyl)silylamines were synthesized by silylation of amines and imines with (C₆F₅)₃SiCl or (C₆F₅)₃SiOTf in the presence of triethylamine. The crystal structures of the (C₆F₅)₃SiN(H)CH₂Ph and (C₆F₅)₃SiN(CH=CMe₂)CH₂Ph compounds were studied by X-ray diffraction. The crystal packings were analyzed by quantum chemical calculations in terms of the density functional theory (PBE exchange-correlation functional). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1345–1352, July, 2007.     

Transition metal complexes with heterocyclic analogs of fluorene. 1. Synthesis, structures, and haptotropic rearrangements of tricarbonylchromium complexes of dibenzothiophene

The complex formation of dibenzothiophene with chromium carbonyl complexes of the general formula L₃Cr(CO)₃ (L = Py, NH₃, or CO) afforded ⁶-C₁₂H₈SCr(CO)₃ (1). In the presence of tetramethylethylenediamine, complex 1 was selectively metallated with BuLi at position 4 of the coordinated ring to form ⁶-4-LiC₁₂H₈SCr(CO)₃ (2). In decane, the tricarbonylchromium group is reversibly and intramolecularly migrates from the unsubstituted to substituted ring due to the inter-ring haptotropic rearrangement (IRHR) at 130 °C for 100 h. In decane, the rate constant of IRHR was estimated experimentally by ¹H NMR spectroscopy and theoretically by the density functional theory (DFT).     

Synthesis and crystal structure of dimeric 2,4,6-triphenylphenylbismuthdichloride

Reaction of BiCl₃ with one equivalent of 2,4,6-triphenylphenyllithium in toluene results in the formation of crystalline 2,4,6-triphenyl-phenylbismuthdichloride toluene disolvate (1). The crystal structure of 1 has been determined by X-ray diffraction. In spite of the extremely bulky substituents at the bismuth atom, complex 1 is dimeric in the solid state with intramolecular Bi-Cl bond lengths of 2.530(1) Å and bridging Bi-Cl of 3.074(1) Å.     

On the electronic structures of the 1,3-diboracyclobutane-1,3-diyls and their valence isomers with a B2E2 skeleton (E=N,P, As)

The concept of through-space versus through-bond interactions on the stabilization of biradical structures with a singlet or triplet ground state is evaluated for the 1,3-diboracyclobutane-1,3-diyls and related congeners. Singlet biradicals are favored when the intermediate units E feature singlet character (PH(2) (+), AsH(2) (+)), while E fragments with triplet character (NH(2) (+)) induce small energy separations between the lowest singlet and triplet states. These considerations are supported by quantum chemical calculations with energy optimization at 1) MCSCF level plus MR-MP2 correction, 2) MR-MP2 level, and 3) two different types of density functional levels for the planar (D(2h)) geometries. The singlet-triplet energy separations in the planar compounds increase with increasing singlet stability of the corresponding E fragments. In addition to this newly developed principal features for singlet stabilization, which primarily occurs in bonded structures with higher main-group elements, the corresponding valence isomers with bicyclobutane, cyclobutene and cis-butadiene structures are investigated.     

The synthesis,molecular, crystal,and electronic structures of [ReBr2(O)(OCH3)(PPh3)2]

[ReBr₂(O)(OCH₃)(PPh₃)₂] has been obtained in the reaction of [ReBr₃O(PPh₃)₂] or [ReBr₂(η²-N₂COPh-N′,O)(PPh₃)₂] with an excess of methanol. [ReBr₂O(OMe)(PPh₃)₂] crystallizes in the triclinic space group P-1. The complex was characterized by infrared, UV-Vis, and ¹H NMR spectra. The electronic structure of the obtained compound has been calculated using the DFT/TD–DFT method.     

Synthesis, crystal and electronic structures, and magnetic properties of LiLn9Mo16O35 (Ln = La, Ce, Pr, and Nd) compounds containing the original cluster Mo16O36

The new compounds LiLn(9)Mo(16)O(35) (Ln=La, Ce, Pr, and Nd) were synthesized from stoichiometric mixtures of Li(2)MoO(4), Ln(2)O(3), Pr(6)O(11) or CeO(2), MoO(3), and Mo heated at 1600 °C for 48 h in a molybdenum crucible sealed under a low argon pressure. The crystal structure, determined from a single crystal of the Nd member, showed that the main building block is the Mo(16)O(36) unit, the Mo(16) core of which is totally new and results from the fusion of two bioctahedral Mo(10) clusters. It can also be viewed as a fragment of an infinite twin chain of edge-sharing Mo(6) octahedra. The Mo(16)O(36) cluster units share some oxygen atoms to form infinite chains running parallel to the b axis, which are separated by the rare-earth and lithium cations. (7)Li-NMR experiments, carried out at high field on the nonmagnetic LiLa(9)Mo(16)O(35), provided insights into the local environment of the lithium ions. Magnetic susceptibility measurements confirmed the trivalent oxidation state of the magnetic rare-earth cations and indicated the absence of localized moments on the Mo(16) clusters. The electronic structure of the LiLn(9)Mo(16)O(35) compounds was analyzed using molecular and periodic quantum calculations. The study of the molecular orbital diagrams of isolated Mo(16)O(36) models allowed the understanding of this unique metallic architecture. Periodic density functional theory calculations demonstrated that few interactions occur between the Mo(16) clusters, and predicted semiconducting properties for LiLn(9)Mo(16)O(35) as a band gap of 0.57 eV was computed for the lanthanum phase.     

Synthesis, crystal, molecular and electronic structures of ruthenium complexes with a benzoxazole derivative ligand

[RuCl₂(HBO)(PPh₃)₂] and [RuCl(CO)(HBO)(PPh₃)₂] complexes with the 2-(2-hydroxyphenyl)benzoxazole (C₁₃H₉NO₂) ligand were synthesized and characterized by infra red, proton and phosphorus nuclear magnetic resonances, electronic absorption and emission spectroscopies and X-ray crystallography. The experimental studies were completed by theoretical calculations. The calculations show that the donor properties of the carbonyl group predominates the π-acceptor ability in the ruthenium(II) complex. The small transfer of electron density to the acceptor π^∗ carbonyl orbitals is compensated by the presence of the chloride acceptor ligand. The electronic structures of these complexes, presented in particular by density of states diagrams, have been correlated with their ability to fluorescence and have been used to analyze the UV-Vis spectra.     

Synthesis and crystal structure of new titanyl phosphate Sr2TiO(PO4)2

New strontium titanyl phosphate Sr₂TiO(PO₄)₂ (1) was synthesized and characterized by X-ray powder diffraction, electron diffraction, high-resolution electron microscopy, and band structure calculations. Titanyl phosphate 1 is isostructural with vanadyl phosphate Sr₂VO(PO₄)₂ and has a layered structure. The titanium atoms are shifted from the centers of the TiO₆ octahedra and form short (1.74 Å) titanyl bonds. The structure of 1 is an unusual example of the disordered orientation of the chains formed by TiO₆ octahedra in complex titanium phosphates.     

Synthesis and structures of boron complexes of acyl hydroxy coumarins

New boron chelates were synthesized by the reactions of 3-acetyl-4-hydroxycoumarin and 8-acyl-7-hydroxy-4-methylcoumarins with boron trifluoride etherate and hydroxybenzodioxaborole. The structure of 3-acetyl-4-difluoroboryloxycoumarin containing an intramolecular C=O...B coordination bond was established by X-ray diffraction. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2012–2015, November, 2006.