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.

Recent advances in hexacoordinate silicon with pyridine-containing ligands: Chemistry and emerging applications

“…Remarkably, compound 12 was crystallized separately in both the hexacoordinate state and the tetracoordinate state (monocapped tetrahedral). In the hexacoordinate state, 12 exhibited an average Si-N bond length of 2.11 Å and an average O-Si-O bond angle of 162 o , while in the tetracoordinate state, 12 exhibited Si-N bond lengths of 2.76 Å and 3.99 Å and an O-Si-O = 99.2 o .The majority of the oxyquinolate complexes have been synthesized through reaction with the deprotonated oxyquinolate with the appropriate chlorosilane or through trans-silylation with 8trimethylsiloxyquinoline (Scheme 3) [28]. The reaction with 8-trimethylsiloxyquinoline is sufficient for the more Lewis acidic silanes, while the less acidic silanes are usually combined with the deprotonated oxyquinolate reagent.…”

Towards Visible‐Light Photocatalytic Reduction of Hypercoordinated Silicon Species

“…We started to investigate the reactivity of hexacoordinated silicon compounds with bidentate N,O ligands such as 8‐oxyquinolinato ligands. We first prepared compound 1a from phenyltrichlorosilane and 8‐hydroxyquinoline using the procedure developed by Wägler in 2014 ( Scheme ) . We tried to evaluate the reduction potential of 1a by cyclic voltammetry (CV) but, due to the insolubility of this organosilicon in acetonitrile and THF, it could not be determined.…”

(2-Pyridyloxy)silanes as Ligands in Transition Metal Coordination Chemistry

“…The Si-C bond (1.853(4) Å) is only marginally longer than in the starting silane MeSi(pyO) 3 (1.837(2) Å), thus hinting at only a weak Pd→Si lone pair donor action. At hexacoordinate silicon with trans-disposed stronger donor (e.g., another hydrocarbyl group [42,43], 2-pyridinethiolato N atom [28] or 8-oxyquinolinyl N atom [44,45]), one would expect a Si-C bond lengthening beyond 1.90 Å. The Pd-Cl bond (2.891(1) Å), however, is unexpectedly long, thus hinting at ionic dissociation.…”