Long-chain alkanes with an internal H2SiSiH2 linkage

Synthesis, characterisation and electronic properties of naphthalene bridged disilanes

Synthesis of naphthalene bridged disilanes 2_R (R = Me, Ph) was performed via catalytic dehydrocoupling. Using RhCl(PPh₃)₃ as a catalyst, an intramolecular Si-Si bond was readily formed from the corresponding disilyl precursors 1_R (R = Me, Ph). For catalytic reactions using (C₆F₅)₃B(OH₂), bridged siloxanes (3_Ph and 3_Me) were observed. Attempts to install the 1,8-naphthalene bridge directly onto a disilane resulted in an unusual product (4), containing two silicon centres bridged through one naphthyl group, and another naphthyl group attached to a single Si centre. In order for this product to form, both a Si to Si hydrogen shift rearrangement as well as Si-Si bond cleavage occurred. The effects of phenyl and methyl substitutions on the structure and electronic properties of the synthesised compounds was investigated by single crystal X-ray diffraction, as well as IR and multinuclear NMR spectroscopic analysis. In addition, theoretical UV-Vis absorption maxima were evaluated using density functional theory (TD-SCF) on a B3LYP/6-31(++)G** level of theory and compared with experimental UV-Vis spectroscopic data.

Synthesis of Butane-Like SiGe Hydrides: Enabling Precursors for CVD of Ge-Rich Semiconductors

The synthesis of butane-like (GeH(3))(2)(SiH(2))(2) (1), (GeH(3))(2)SiH(SiH(3)) (2), and (GeH(3))(2)(SiH(2)GeH(2)) (3) Si-Ge hydrides with applications in low-temperature synthesis of Ge-rich Si(1-x)Ge(x) optoelectronic alloys has been demonstrated. The compositional, vibrational, structural, and thermochemical properties of these compounds were studied by FTIR, multinuclear NMR, mass spectrometry, Rutherford backscattering, and density functional theory (DFT) simulations. The analyses indicate that the linear (GeH(3))(2)(SiH(2))(2) (1) and (GeH(3))(2)(SiH(2)GeH(2)) (3) compounds exist as a mixture of the classic normal (n) and gauche (g) conformational isomers which do not seem to interconvert at 22 degrees C. The conformational proportions in the samples were determined using a new fitting procedure, which combines calculated molecular spectra to reproduce those observed by varying the global intensity, frequency scale, and admixture coefficients of the individual conformers. The (GeH(3))(2)(SiH(2))(2) (1) species was then utilized to fabricate Si(0.50)Ge(0.50) semiconductor alloys reflecting exactly the Si/Ge content of the precursor. Device quality layers were grown via gas source MBE directly on Si(100) at unprecedented low temperatures 350-450 degrees C and display homogeneous compositional and strain profiles, low threading dislocation densities, and atomically planar surfaces. Low energy electron microscopy (LEEM) analysis has demonstrated that the precursor is highly reactive on Si(100) surfaces, with H(2) desorption kinetics comparable to those of Ge(2)H(6), despite the presence of strong Si-H bonds in the molecular structure.

Binary Si/N-[4.4]-Spirocycles with Two SiH(2)SiH(2) Loops

Tetra(alkylamino)silanes Si(NHR)(4) with R = Me, n-Pr, n-Bu, and i-Pr (1a-d) have been prepared via improved methods and characterized by complementary analytical and spectroscopic data. The reaction of 1a-c with 2 equiv of Tf-SiH(2)SiH(2)-Tf (Tf = trifluoromethylsulfonyloxy, "triflate") and triethylamine in toluene gives good yields of the spirocyclic compounds [(SiH(2)NR)(2)](2)Si (2a-c). 2a is obtained as a crystalline, but highly volatile, product (mp 35 degrees C, bp(0.05) 46-47 degrees C), the crystal and molecular structure of which has been determined by single-crystal X-ray diffraction methods (monoclinic, space group P2(1)/n, Z = 8). The lattice contains two independent molecules in the asymmetric unit, which have very similar dimensions. The two five-membered rings are almost planar and close to perpendicular to each other. Owing to sterical hindrance, the analogous reaction of 1d gives only low yields of the corresponding spirocycle {[SiH(2)N(i-Pr)](2)}(2)Si, 2d. A silylammonium salt {[SiH(2)N(i-Pr)](2)Si-[NH(i-Pr)]-[NH(2)(i-Pr)]}(+)Tf(-) (3) is produced as a major product. Compound 3 is one of the very few silylammonium salts as confirmed by a full structural analysis (monoclinic, space group P2(1)/c, Z = 4). In the crystal, 2 equiv are grouped together as a centrosymmetrical cluster of two cations and two anions with hydrogen bonds between the amino/ammonio and the sulfonate groups. Equimolar quantities of 1d and the 1,2-disilanediylbis(triflate) in the presence of NEt(3) give good yields of the monocyclic compound [SiH(2)N(i-Pr)](2)Si[NH(i-Pr)](2), 4. Compounds 1a-d and 2a-c are hydrogen- and silicon-rich precursor molecules for the production of silicon nitride in pyrolytic, plasma- or laser-induced (thermal) decomposition and for the preparation of silazane networks and gels by controlled aminolysis or by metathesis of the Si-Si bonds.

1,2-Disilanediyl Bis(triflate), F(3)CSO(3)-SiH(2)SiH(2)-O(3)SCF(3), as the Key Intermediate for a Facile Preparation of Open-Chain and Cyclic 1,1- and 1,2-Diaminodisilanes

Convenient high-yield syntheses for several open-chain and cyclic diaminodisilanes with fully hydrogenated Si-Si linkages are reported. The key intermediate for the preparation of the title compounds, 1,2-bis(((trifluoromethyl)sulfonyl)oxy)disilane (1), reacts with 2 equiv of diethylamine to afford a mixture of the isomers Et(2)NSiH(2)SiH(2)NEt(2) (2a) and (Et(2)N)(2)SiHSiH(3) (2a'). Isopropylamine and 1 give (i)Pr(2)NSiH(2)SiH(2)N(i)Pr(2) (2b) exclusively. Treatment of 1 with 1 equiv of a primary alkylamine affords 2,3,5,6-tetrasilapiperazines [RNSiH(2)SiH(2)RNSiH(2)SiH(2); R = (i)Pr (3a), (t)Bu (3b), Bzl (3c)] comprising two SiH(2)-SiH(2) linkages. 1,3-Bifunctional bis(isopropylamino)silanes [((i)PrNH)(2)SiR(2); R = Me, Ph] were found to react with 1 to give trisilaimidazolidines [((i)PrN)SiR(2)((i)PrN)SiH(2)SiH(2); R = Me (4a), Ph (4b)] again comprising the N-SiH(2)-SiH(2)-N unit. The crystal structures of N,N'-diisopropyl-2,2-diphenyl-2,4,5-trisilaimidazolidine (4b) and N,N'-di-tert-butyl-2,3,5,6-tetrasilapiperazine (3b) were determined in X-ray diffraction studies; the five-membered ring of 4b is nearly planar with all nitrogen atoms in a planar configuration. The six-membered ring of 3b has a twist conformation, but again with the two nitrogen atoms in a planar configuration. Surprisingly, the treatment of 1 with 1,4-bifunctional N,N'-dialkylethylenediamines [(RNHCH(2)-)(2); R = (i)Pr, (t)Bu] does not give the analogous six-membered-ring compounds but leads selectively to the isomeric five-membered heterocycles [(CH(2)NR)(2)SiHSiH(3); R = (i)Pr (5a), (t)Bu (5b)], which are the products of a Si --> Si hydrogen shift rearrangement.