Donald H. Berry

Reactivity of molybdenum and tungsten disilene complexes

Abstract The reactions of the η2 -disilene complexes Cp2M(η 2-Me2SiSiMe2) (M = Mo, 1a; W, 1b) with a variety of inorganic and organic substrates are reported. Compound 1a reacts with methanol to yield Cp2Mo(SiMe 2H)(SiMe2OMe) (2,> 80%) and Cp2Mo(H)(Si Me2SiMe2OMe) (3,

Transfer dehydrogenative coupling of triethylsilane catalysed by ruthenium and rhodium complexes. A new Si–C bond forming process

Four-legged piano stool complexes (η6-arene)Ru(H)2(SiEt3)2 and (η5-C5Me5)Rh(H)2(SiEt3)2 catalyse the transfer dehydrogenative coupling of Et3SiH in the presence of a hydrogen acceptor such as tert-butylethylene to yield the carbosilane dimer, HSiEt2CHMeSiEt3, and 2,2-dimethylbutane by a mechanism involving an intermediate η2-silene complex, LnM(Et2SiCHMe), generated by β-hydrogen elimination from a silyl group.

Structure and reactivity of Cp2Zr(η2-Me2SiNtBu)(CO): An unusual silanimine carbonyl complex with extensive σ-π∗ back-bonding

The carbonyl silanimine complex Cp2Zr(η2-Me2SiNtBu)(CO) (2) has been prepared by ligand substitution on the phosphine derivative, Cp2Zr(η2-Me2SiNtBu) (PMe3) (1) and by generation of the alkyl derivative Cp2Zr(CH2SiMe3) (NtBuSiMe2H) under a carbon monoxide atmosphere. Most aspects of the spectroscopic properties and structural parameters are consistent with the formulation of 2 as a zirconium (IV) metallacycle, containing a ZrSiN three-membered ring and a linear, terminal carbonyl ligand. However, the carbonyl stretching frequency for 2 is observed at 1797 cm−1 in the infrared, much lower than expected for a zirconium (IV) complex, and indeed, lower than any other zirconocene carbonyl. ZINDO molecular orbital calculations indicate that the origin of this anomalously low stretching band is donation of electron density into the CO π∗ orbital directly from an orbital on the adjacent silicon center, i.e. σ-π∗ back-bonding. Consistent with this picture, the formally non-bonding Si/3.C distance in 2 (2.347(7) A) is much longer than a typical single bond (ca 1.87 A), but in the range observed for delocalized organic π-ligands bonded to silicon. Although the bond between the silicon and carbonyl ligand is not fully formed in the ground state of 2, thermolysis in the presence of PMe3 yields the five-membered metallacycle cyclo-Cp2Zr[OC(PMe3)SiMe2NtBu] (3), resulting from CO insertion into the ZrSi bond and formation of a cyclic silaacyl, followed by attack of phosphine at the electrophilic acyl carbon.

SPIN-ON-GLASS THIN FILMS PREPARED FROM A NOVEL POLYSILSESQUIOXANE BY THERMAL AND ULTRAVIOLET-IRRADIATION METHODS

New dielectric films are prepared by both pyrolytic and photolytic conversion of β-chloroethyl-silsesquioxane (BCESSQ). Film thickness, refractive index, composition, density and morphology are characterized using a palette of techniques including ellipsometry, Rutherford backscattering and forward recoil spectrometry, X-ray reflectivity, and atomic force and electron microscopies. After annealing at 350°C, BCESSQ films, initially 200 nm thick reach about 55% of their original thickness after 20 min. For films heated in air for 4 h, the atom fractions of carbon and hydrogen monotonically decrease to 10 and 30%, respectively, as annealing temperature increases from 225 to 450°C. The BCESSQ reactivity is reflected in the loss of chlorine at 400°C. At 450°C, the film density is 1.88 g/cm3, or 84% of thermally-grown silicon oxide. Upon exposure to ultraviolet ozone radiation, films ranging from ca. 200 to 700 nm are found to convert to ormosil films within 30 min. Surprisingly, the chlorine concentration is found to decrease more quickly than the hydrogen and carbon concentrations, suggesting that the ormosil film evolves HCl leaving a vinyl group of SiCHCH2. This reaction pathway differs from the thermal case. For films prepared by pyrolytic and photolytic methods, atomic force and electron microscopy studies show that the surface is smooth and featureless, the bulk is void free when view at a magnification of 50 000×, and the ormosil/substrate interface is continuous.

Staged Development of Modified Silicon Dioxide Films

The hydrolytic generation of SiO2 films from chlorosilanes or alkoxysilanes is interrupted by incorporating labile organic groups which stop SiO2 formation at a processable prepolymer stage. The monomers for the prepolymer have electron withdrawing substituents in the β-position. The organic groups are removed from the prepolymer at low temperature, extruding ethylene. The formation of SiO2 proceeds by intramolecular condensation of the electronegative substituents which are now in a hydrolytically unstable bond with silicon and hydroxyl groups or ambient moisture. Films of the prepolymer spun onto silicon wafers are converted into uniform SiO2-rich films at temperatures between 150–400°C.

Synthesis of ferroelectric thin films via metallo- organic decomposition

Abstract Barium titanate (BaTiO 3 films have been deposited on platinum and silicon substrates via spin casting metallo-organic compounds and annealing in a conventional oven to 600°C. This method, called metallo-organic deposition, produces BaTiO 3 films with the tetragonal structure and provides for excellent control of film stoichiometry as determined by X-ray and Auger analysis. Variable thicknesses (0.1–5 μm) were achieved by spin casting multiple layers of the films. The films on both platinum and silicon were uniform and showed no cracks by scanning electron microscopy. The films show ferroelectric behavior as evidenced by a polarization vs. electric field hyeteresis and a peak in the dielectric permittivity around 120°C.

Ultraviolet laser-induced formation of thin silicon oxide film from the precursor β-chloroethyl silsesquioxane

Formation of silicon oxide thin films from spin-coated β-chloroethyl silsesquioxane (β-cesq) on silicon, NaCl, and quartz was induced by 193 nm laser pulses. The silicon oxide deposition is characterized by ir, uv, ellipsometry, and Rutherford backscattering spectrometry. The silicon oxide films obtained by uv irradiation were found to have much less carbon and chlorine as impurities and have a higher refractive index as compared to those obtained by annealing. The photoinduced oxide films were found to be smooth, without laser-induced microrough or periodic structures.

β-Acetoxyethyl Silsesquioxanes: Chloride-Free Precursors for SiO2 Films Via Staged Hydrolysis

Silsesquioxanes containing β-acetoxyethyl (BAE) groups are processible resins that can be employed as spin-on-glass precursors to dielectric silica films. Thermal treatment >250 °C results in extrusion of ethylene from the CH 2 CH 2 OCOCH 3 moiety with formation of Si- OCOCH 3 groups, which undergo facile hydrolysis to a silica network. A minor pathway involving extrusion of acetic acid leaves some silicon vinyl groups, leading to residual organic carbon in the material. However, addition of a fluoride ion catalyst greatly accelerates the major reaction, resulting in lower conversion temperatures (

Electrochemistry of Ruthenium Bis(imino)pyridine Compounds: Evidence for an ECE Mechanism and Isolation of Mono and Dicationic Complexes

The electrochemical properties of a series of ruthenium complexes bearing the redox noninnocent bis(imino)pyridine ligand were investigated with cyclic voltammetry. An unexpected electrochemical feature in one of the complexes indicated a possible electrochemical-chemical-electrochemical (ECE) process. Further investigation into the oxidation mechanism included the synthesis and isolation of cationic and dicationic analogues of the complex. Density functional theory calculations suggested that a solvent interaction facilitated the ECE mechanism, so a solvent adduct was also synthesized and isolated. Calculations of this series of compounds were used to investigate the stabilizing role of the ligands over various oxidation states. As the overall charge of the complex was varied from anion to dication, a relatively constant Ru metal center oxidation state was found over all four states probed. This result suggests the strong involvement of the coligands in the redox behavior of the complexes investigated.