Janet Braddock-Wilking

Synthesis and characterization of sterically hindered diarylsilanes containing 2,4,6-trimethylphenyl and 2,4,6-tris(trifluoromethyl)phenyl substituents. X-ray crystal structure of bis[2,4,6-tris(trifluoromethylphenyl)]fluorosilane☆

Abstract Sterically hindered diarylsilanes have been prepared by two synthetic routes. Dimesitylsilane, Mes2SiH2 (1), (Mes = 2,4,6-trimethylphenyl) was synthesized by reaction of mesityl magnesium bromide with HSiCl3 followed by reduction with LiAlH4, or by reaction of mesityl magnesium bromide with (TfO)2SiH2. The mixed diaryl system, MesPhSiH2 (2), was prepared by reaction of (TfO)PhSiH2, with one equivalent of MesMgBr. Diarylsilanes containing the 2,4,6-tris(trifluoromethyl)phenyl substituent, RF, were prepared by reaction of HSiCl3 with 2 equivalents of RFLi to give (RF)2SiHF (3) through a Cl/F halogen exchange. Reduction of 3 with LiAlH4 afforded (RF)2SiH2 (4) which can also be prepared from RFLi and (TfO)2SiH2. All compounds have been characterized by multinuclear NMR, IR, mass spectrometry and chemical analyses. An X-ray crystallographic study of 3 shows that the immediate geometry about silicon is approximately tetrahedral with a CSiC angle of 115.8(1)°. There are unusual intramolecular interactions in 3 with four short Si…F contacts with the ortho-CF3 substituents on the aromatic ring which results in an overall tetracapped tetrahedral geometry about silicon. Crystal data for 3 are as follows: monoclinic, P21/c, with a = 9.827(2) A , b = 15.938(3) A , c = 13.239(3) A , V = 2072.6(8) A 3 , Z = 4, and R = 0.0492 (Rw = 0.0535). The short intramolecular Si…F contacts are observed in solution for both 3 and 4 by 29Si NMR spectroscopy.

13C NMR spectroscopy of amorphous hydrogenated carbon nitride

Abstract The 13 C NMR spectra of chemical vapor deposited amorphous hydrogenated carbon nitride thin films were measured and a number of sharp lines superimposed on top of a broad peak were observed. These sharp lines have been interpreted as arising from nanocrystals of nitrogen-containing aromatic rings terminated by amino groups. The concentration of these nanocrystals increases with increasing nitrogen concentration and decreases with thermal annealing. These nanocrystals are responsible for the increased structural order in these films. Similar nanocrystals are probably present in sputtered carbon nitride thin films. There is no 13 C NMR evidence of any phase of crystalline carbon nitride in either the chemical vapor deposited or sputtered films.

Reactivity of {(Ph3P)Pt[μ-η2-HSiH(Ar)]}2 (Ar=2-isopropyl-6-methylphenyl) with phosphines. X-ray crystal structure of trans-{(dppe)Pt[μ-SiH(Ar)]}2

Abstract The dinuclear PtSi complex {(Ph 3 P)Pt{μ-η 2 -HSiH(IMP)]} 2 ( trans - 1a – cis - 1b =3:1; IMP=2-isopropyl-6-methylphenyl) reacted with basic phosphines such as 1,2-bis(diphenylphosphino)ethane (dppe) and dimethylphenylphosphine (PMe 2 Ph) to afford different dinuclear PtSi complexes with loss of H 2 , {(P) 2 Pt[μ-SiH(IMP)]} 2 [P=dppe, trans - 2a (major), cis -2b (trace); PMe 2 Ph, 3 ( trans only)]. Complexes 2 and 3 were characterized by multinuclear NMR spectroscopy and X-ray crystallography ( 2a ). In contrast, the reaction of 1a , b with the sterically demanding tricyclohexylphosphine (PCy 3 ) afforded {(Cy 3 P)Pt{μ-η 2 -HSiH(IMP)]} 2 ( trans - 4a – cis - 4b 2:1) analogous to 1a , b where the central Pt 2 Si 2 (μ-H) 2 core remains intact but the PPh 3 ligands have been replaced by PCy 3 . Complexes 4a and 4b was characterized by multinuclear NMR and IR spectroscopies.

Synthesis and characterization of sterically hindered arylsilanes containing the 2,4,6-trimethoxyphenyl ligand (TMP): X-ray structures of (TMP)SiH3, (TMP)2SiH2, and (TMP)3SiH

Abstract The homologous series of primary, secondary and tertiary silanes containing the sterically demanding 2,4,6-trimethoxyphenyl (TMP) group have been prepared in yields ranging from 22 to 45%. The arylsilanes were characterized by multinuclear NMR, IR, GC–MS, elemental analyses, and X-ray crystallography. Relatively short intramolecular distances are observed between Si and the O atoms in the ortho-methoxy groups of the aryl ligand and are shorter than the sum of the van der Waal’s radii in the solid state for all three arylsilanes.

Evidence for and role of boron carbide icosahedra in the hardness of amorphous hydrogenated boron carbide

We report both infrared absorption and 11B nuclear magnetic resonance measurements that provide evidence for the presence of boron carbide icosahedra in amorphous hydrogenated boron carbide (a‐B:C:H) thin films. The infrared absorption spectra are dominated by a broad line at 1280 cm-1 with a FWHM of 320 cm-1, and the 11B nuclear magnetic resonance spectra are dominated by a line with a chemical shift of 4 ppm and FWHM of 35 ppm; similar features have been previously reported in polycrystalline boron carbide, where boron carbide icosahedra make up the unit cell. We also suggest that it is these icosahedra that increase the hardness of these films over those films without boron, by playing the role of nanocrystals in a nanocrystal/amorphous matrix composite system.

13C NMR spectroscopy of amorphous hydrogenated carbon — further evidence of inhomogeneity

Abstract We report the 13C NMR spectra of amorphous hydrogenated carbon grown at various substrate temperatures and deconvolute these spectra into a contribution from hydrogen-bonded carbon and one from non-hydrogen bonded carbon. We interpret this deconvolution as evidence that this material is inhomogeneous and consists of hydrogen-rich and hydrogen-poor regions. As the substrate temperature is increased, the films have fewer hydrogen-rich regions, but the composition and structure of the hydrogen-rich regions do not change. Our results are in agreement with inhomogeneity model of Jager, Gottwald, Spiess and Newport.

Synthesis and characterization of μ,μ′-M(B5H8)2 (M=Cd, Hg and Zn): a reassignment of the NMR spectra for 2,3-μ-metalloderivatives of pentaborane(9)

Abstract The series of compounds μ,μ′-M(B 5 H 8 ) 2 , where M=Cd ( I ), Zn ( II ), or Hg ( III ), has been prepared from the reaction between K(B 5 H 8 ) and the metal chloride in THF at low temperatures. The species were characterized by multinuclear NMR spectroscopy, elemental analysis and mass spectrometry. The NMR spectral assignments were confirmed using 11 B{ 1 H} selective decoupling experiments and heteronuclear 11 B– 1 H chemical shift correlation spectroscopy. The results appeared to be in conflict with the earlier assignment of the 11 B-NMR spectra for 2,3-μ-metalloderivatives of pentaborane(9) which appear in the literature. For systems with an electrophilic group replacing a bridging H atom in B 5 H 9 , the B atoms most shifted in the 11 B-NMR spectrum, which appear at the lower field, were assigned to the ones closest to the metal group. Our results for I – III suggested that the assignment was reversed, that is the higher field resonance is the one closest to the metal group. Thus, we reexamined the spectra of a series of related compounds including 2,3-μ-SnPPh 3 (B 5 H 8 ), μ,μ′-SnPh 2 (B 5 H 8 ), μ,1′-SnPh 2 (B 5 H 8 ), other Sn species and 2,3-μ-Cu(dppe)B 5 H 8 . In all cases our assignments were in accord with those for I – III and we suggest that this is general for all such B 5 H 9 derivatives.

The regiochemistry of reduction of mono-ethyl fumarate and maleate using a ruthenium BINAP catalyst

Abstract The regiochemistry of the reduction of mono-ethyl fumarate using bis (carboxylato){2,2′- bis (diphenylphosphino)-[R]-1,1-binapthyl}-ruthenium(II) (Ru[BINAP]) in H 2 /CH 3 OD is reported and occurs opposite to the regiochemistry observed in the reduction of tiglic acid. Reduction of mono-ethyl maleate with D 2 /CH 3 OD is very sluggish but produces meso -dideuteriosuccinic acid with high stereoselectivity. Reduction of mono-ethyl maleate with Ru[BINAP](O 2 CR) 2 and H 2 /CH 3 OD results in mono-ethyl succinate-d 1 with nearly complete loss of regiochemistry.

13 C NMR Spectroscopy of Amorphous Hydrogenated Carbon and Amorphous Hydrogenated Boron Carbide

We report the 13 C NMR spectra of amorphous hydrogenated carbon and boron carbide. The amorphous hydrogenated carbon spectra consist primarily of a sp 2 carbon peak at 40 ppm and a sp 3 carbon peak at 140 ppm and are in reasonable agreement with recent theoretical calculations of Mauri, Pfrommer, and Louie, but there are some noteable discrepancies. The amorphous hydrogenated boron carbide spectra are very different from that of amorphous hydrogenated carbon, showing two sharp lines at 135 and 170 ppm at low boron concentrations and an intense, broader line at 15 ppm at high boron concentrations. We suggest the two sharp lines at 135 and 170 ppm could be due to carbon atoms in boron-containing aromatic rings, and the broader line at 15 ppm as due to carbon atoms in boron carbide icosahedra. These lines provide evidence of nanocrystalline structure imbedded in an amorphous hydrogenated boron carbide matrix.