Yu. E. Ovchinnikov

An Unusual sandwich-type nickel oxide-siloxanolate complex {[PhSiO]}6 (μ4-O)2 (μ3-O)4[Ni8(μ3-0)2](μ3-O)4(μ4-O)2 [PhSiO]6}·14n-BuOH·10H2O·2Me2CO. Synthesis and crystal structure

Abstract An X-ray crystal study of the nickel oxide-siloxanolate complex {[PhSiO] 6 (μ 4 -O) 2 (μ 3 -O) 4 [Ni 8 (μ 3 O) 2 ] (μ 3 -O) 4 (μ 4 -O) 2 [PhSiO] 6 }·14n-BuOH·10H 2 O·2MeCO (I or Ia without noncoordinating solvate molecules) having a cage structure has been carried out. The complex studied was prepared by the interaction of NiCl 2 with the product of the reaction of phenylsilsesquioxane (PhSiO 1.5 ) n with NaOH. The polynuclear cage-like centrosymmetric molecule Ia has a sandwich-type structure. The inner two-dimensional nickel oxide fragment Ni 8 o 2 (μ-O) 12 2 = Ni 8 O 8 is structurally identical to a fragment of the NiO crystal layer which is one Ni atom thick and parallel to the (111) plane. All Ni atoms have oxygen atoms in an octahedral coordination (oxide, silanolate, molecules of water, butanol and acetone). The O atoms of the nickel oxide layer have both trigonal pyramidal (μ 3 -O) and distorted tetrahedral (μ 4 -O) coordination. The nickel oxide layer is bonded by NiOSi bridges through silanolate O atoms with two outer 12-membered hexasiloxane (SiO) 6 cycles (sandwich “caps”) with an almost ideal crown conformation. Some of the butanol and H 2 O crystallosolvate molecules do not coordinate the Ni atoms being included in the cavities between Ia molecules. The NiO bond lenghts are 2.006–2.159 A, while the average SiO(Si) and SiO(Ni) bond lengths are 1.637 and 1.618 A, respectively.

Interaction of the (O → Ge)-chelate bis-(lactamo-N-methyl)-cis-dichlorogermanes with trimethyltriflate. Synthesis of bis-(lactamo-N-methyl)-trans-(trifluoromethylsulfonyloxy)chlorogermanes

Abstract Regardless of the ratio of reagents, the interaction of the (O→Ge)-chelate,bis-(lactamo- N -methyl)- cis -dichlorogermanes with trimethylsilyltriflate in acetonitrile, proceeds with substitution of one chlorine atom by the triflate group resulting in products with an inversion of configuration at the germanium atom, viz. (O→Ge)-chelate bis-(lactamo- N -methyl)- trans -(trifluorosulfonyloxy) chlorogermanes. This result as well as conductometric studies allow us to suppose an easy ionization of the final products with formation of a triflate anion and a cation with a pentacoordinated germanium atom. According to X-ray structural studies of the prepared compounds, the Ge atom has an octahedral coordination strongly distorted towards a capped trigonal bipyramid configuration. The GeCl bond (2.13–2.17 A) is the shortest among those observed by us in hypervalent germanium compounds and the GeOTf bond is, on the contrary, the longest (3.02–3.36 A).

Crystal structures of cycloheteropentasilanes (η5-Cp)2Ti(SiPh2)5 and O(SiPh2)5

Abstract An X-ray diffraction study of two heterocyclic polysilanes (η 5 -Cp) 2 Ti(SiPh 2 ) 5 and O(SiPh 2 ) 5 has been carried out. In the titanasilane cycle the relevant bond lengths and angles are as follows: Ti 2.755(7) and 2.765(8) A, SiSi 2.40–2.45(3) A, SiTiSi 99.1(2)°. TiSiSi and SiSiSi 114.4–118.3(3)°; the cycle has a chari conformation and torsion angles of 43–59°. the geometric parameters of the oxasilane cycle are: SiO 1.643 and 1.644(3) A, SiSi 2.369–2.388(2) A, SiOSi 145.7(2)°, OSiSi and SiSiSi 106.5–109.3(1)°; the cycle has a boat conformation.

Synthesis and crystal structure of the salt Na6[(PhSiO1.5)2Co3O6]·7H2O containing a cobaltasiloxane anionic framework

Abstract The interaction of [PhSiO(ONa)] 3 ·3H 2 O with (PhSiO 1.5 ) 8 , NaOH, and CoCl 2 gave a sodium heptahydrate of a new complex, a framework cobaltasiloxane anion whose crystal structure was determined by X-ray crystallography. The cobaltasiloxane framework of the [(PhSiO 1.5 ) 22 Co 3 O 3 O 6 ] 6− polyanion which has approximate C 3 symmetric is formed by three open-edged silsesquioxane cubes each of which one of its Si atoms is replaced by a Co atom, and has tetrahedral 4 x O coordination. Of the Na + cations three are positioned outside, and three are inside the anion framework, and are coordinated with its O atoms and water molecules. The bond lengths are: 1.92–2.01 A for CoO; 1.57 A av. for SiO(Co), and 1.63 A av. for SiAO(Si). The bond angles at the O atoms of the anion are 121–158°, and for the Co-bonded O atoms these angles are consistent with their participation in the O…Na + interactions.

Structural precursors of poly(diphenylsilylene): II. Crystal and molecular structure of HO(SiPh2)4OH and HO(SiPh2)7OH

Abstract An X-ray diffraction study was carried out on HO(SiPh2)4OH (I) and HO(SiPh2)7OH (II), which were prepared from phenylcyclopolysilanes. H bonds, found in both cases, strongly affect the conformation of polysilane chain. The intramolecular H bond in crystal I (O ⋯ O 2.81 A) closes the six-membered pseudocycle OSi4O to give “chair” conformation, with one of the OH groups participating in the intermolecular H bond (O ⋯ O 2.75 A). Two of these bonds link the molecules into the centrosymmetric dimer. In crystal II there are intermolecular H bonds linking the molecules into head-to-tail,type chains (O ⋯ O distance of 2.78 A, SiSiSiSi torsion angles of 149–160°), and in addition there is an OH ⋯ π intramolecular H bond formed by one of the two terminal OH groups with the π-system of the Ph ring (the distances from the O and H atoms to the Ph plane are 3.2 and 2.52 A respectively). The Si-chain conformation of molecule II is intermediate between trans-planar and gauche, the chain is twisted and the degree of twisting increases steadily in both directions from the middle towards each chain end. The SiSi bond lengths in I and II are 2.361–2.412 A, the terminal bonds in the molecule II (av. 2.368 A) are somewhat shorter than the others (av. 2.400 A). In I the SiSiSi bond angles are 108.6 and 113.3°, in II the bond angle at the central Si atom is 118.9°, significantly exceeding other angles (109.6–111.7°).

Crystal and molecular structure of compounds containing a hypervalent O−Si(C3)−O fragment. Parametrization in the description of the coordination environment of the silicon atom

We have carried out an X-ray structural investigation of four pentacoordinated silicon compounds with a hypervalent O−Si(C3)−O fragment. In their molecules, the axial Si−O bond lengths range from 1.711 to 2.785 Å. Analysis of the geometry of such fragments containing other atoms in axial positions shows that the main parameter determining the state of the hypervalent fragment is deviation of the Si atom from the plane of equatorial substituents. Some consequences of this study for structural modeling of nucleophilic substitution reactions are discussed.

PROBLEMS OF SYNTHESIS OF TETRAHEDRAL ORGANOSILSESQUIOXANES. HYDROLYTIC CONDENSATION OF HEXAFUNCTIONAL BRANCHED ORGANOTETRASILOXANES

The hydrolytic condensation of methyltris(methyldichlorosiloxy)silane (1b), methyl(1a), and vinyltris(methyldiethoxysiloxy)silanes (1c) in dilute homogeneous solutions was studied. It was found by X-ray diffraction and1H NMR methods that, irrespective of reaction conditions, only octaorganooctasilsesquioxanes (T8), namely, octamethyloctasilsesquioxane and 1,4-divinylhexamethyloctasilsesquioxane, were obtained instead of the expected tetraorganotetrasilsesquioxanes (T4). These data suggest that the condensation processes involved in the hydrolysis of1a–c are predominantly intermolecular, and the molecules of the starting oligomers do not undergo rearrangements. Probably, the formation ofT4, whose molecules are built of four strained six-membered organosiloxane cycles, is less favorable thermodynamically than the formation of their homologs (T8) built of eightmembered organosiloxane cycles.

Crystal structure of hypervalent silicon compounds. (N → Si)(2-benzothiazolylthiomethyl)trifluorosilane and (N → Si)(2-benzoxazolylthiomethyl)trifluorosilane

Abstract The crystal structures of two hypervalent silicon compounds (N → Si) (2-benzothiazolylthiomethyl)trifluorosilane and (N → Si) (2-benzoxazolylthiomethyl)trifluorosilane have been determined. Both molecules have similar geometrical parameters. The Si atom acquires a distorted trigonal bipyramidal penta-coordination due to five-membered ring closure by a donor-acceptor N → Si bond of lengths of 1.988(3) and 1.967(4) A, respectively. In the second crystal structure, molecules form a stacked packing with the distance between the planar parts of the neighbouring molecules in the stacks equal to 3.45 A.

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.

Influence of a valent environment on the hypervalent bond of a silicon atom

X-ray structural study of two (O-Si)-chelate (lactamo-N-methyl)dichlorosilanes and two (O-Si)-chelate (lactamo-N-methyl)trichlorosilanes with the hypervalent O-Si-Cl bond has been carried out. Introduction of more electronegative substituents into equatorial positions of the trigonal-bipyramidal valent environment of a silicon atom increases the hypervalent bond rigidity. It has been concluded that the influence of nonspecific (including electrostatic) intermolecular interactions on geometric parameters of the hypervalent fragment is insignificant.