Daniela Gerlach

Octahedral HSiCl3 and HSiCl2Me adducts with pyridines.

Stable solid adducts of substituted pyridines (Rpy) with HSiCl(3) and HSiCl(2)Me were prepared in high yields under aprotic and anaerobic conditions at room temperature. The octahedral complexes of HSiCl(3) underwent dismutation reactions in polar solvents. In contrast, the HSiCl(2)Me(Rpy)(2) adducts were not susceptible to dismutation under comparable conditions, but they tended to dissociate more easily because of the reduced Lewis acidity of HSiCl(2)Me relative to HSiCl(3). The bonding between silicon and its surrounding ligands is highly ionic, as can be seen from QTAIM and charge distribution analyses. (29)Si CP/MAS spectra in combination with quantum-chemical calculations show that the lowest shielding is along the Cl-Si-Cl axis. The other two components of the shielding tensor are oriented along the N-Si-N and H-Si-Cl/Me axes. It is known that many reactions of (hydrido)chlorosilanes are catalyzed by pyridine bases. Therefore, the results presented here provide a basis for better control of these reactions, especially chlorine substitution and hydrosilylation.

New Insights into Hexacoordinated Silicon Complexes with 8- Oxyquinolinato Ligands: 1,3-Shift of Si-Bound Hydrocarbyl Substituents and the Influence of Si-Bound Halides on the 8-Oxyquinolinate Coordination Features

Abstract The transsilylation reaction between allyltrichlorosilane and 8-trimethylsiloxyquinoline in the molar ratio 1 : 3 yields the hexacoordinated silicon tris-chelate (oxinate)2Si(adho) (“oxinate” = 8- oxyquinolinate, “adho” = di-anion of 2-allyl-1,2-dihydro-8-oxyquinoline) comprising an SiO3N3 skeleton. The identity of this complex was established by single-crystal X-ray diffraction analysis and 29Si CP=MAS NMR spectroscopy of its chloroform solvate. Benzyltrichlorosilane and dibenzyldichlorosilane, comprising benzyl (Bn) as an “aromatically stabilized allyl moiety” did not undergo such rearrangement. Instead, the complexes (oxinate)2SiBnCl and (oxinate)2SiBn2 were obtained even upon using three molar equivalents of 8-trimethylsiloxyquinoline. We determined the crystal structure of a non-disordered bis-chelate (oxinate)2SiBnCl with Sibound hydrocarbyl and halogen substituents (the previously published (oxinate)2SiMeCl was disordered with alternative Me=Cl site occupancies). (Oxinate)2SiBnCl exhibits surprisingly poor response of the N-Si bonds to the different trans-disposed Si-X (X=Bn, Cl) bonds. For comparison and deeper insights into the coordination chemistry of oxinato silicon complexes with halide substituents, we determined the crystal structures of (oxinate)2SiPhCl·CHCl3, (oxinate)2SiCl2, (oxinate)2SiF2·1.5(CHCl3), and (8-oxyquinaldinate)2SiF2. Furthermore, the crystal structures of BnSiCl3 and Bn2SiCl2 (and its dibromo analog) are reported. The influence of the Si-C-C-C torsion angles of the benzyl group on the 29Si NMR shift of benzylsilanes (which is noticeably upfield with respect to analogous methyl silanes) was analyzed by quantum-chemical calculations.

Surprising Insights in the Various Molecular Structures of Hypercoordinate Bis(oxinato)silicon Complexes

The syntheses of two cyclic diorganosilicon enamines =CH2) [R = Ph (2a), Me (2b)] are described. These compounds react with 8-oxyquinoline leading to bis(oxinato)silicon complexes RPhSi(oxinate)2 [R = Ph (5a), Me (5b)]. Their X-ray structures reveal hexacoordination of the Si atom with the monodentate substituents in cis-positions and N atoms as well as O atoms in trans-positions. In crystalline dimethylbis(oxinato)silicon, Me2Si(oxinate)2 (7), the silicon atom is only bicapped tetrahedrally coordinated, while for dichlorobis(oxinato)silicon, Cl2Si(oxinate)2 (8), there is an octahedral coordination of the Si atom with chlorine atoms in trans-positions. This conclusion is based on the results of spectroscopic analysis (IR, 29Si CP/MAS NMR) as well as quantum chemical calculations. The first example of a silicon-bis-oxinate with the N→Si dative bonds in a trans-arrangement has been detected in the hexacoordinate silicon tris-chelate (oxinate)2Si(PhN-CH2CH2-NPh) (11). Its configuration was proven by X-ray structure analysis. Thus, for hexacoordinate bis(oxinato)silicon compounds three new architectures were found which complement the previously established building pattern of the N,N’-cis-O,O’-trans-bis(oxinato)silicon complexes. The mer-tris(oxinato)siliconium cation (9+) (its configuration being proven by 1H and 13C NMR spectroscopy) features at least three coordination patterns with (O,O;N,N)-cis,cis-, -cis,trans- as well as -trans,cis-arrangements of two oxinate ligands.