Higher-Coordinated Molecular Silicon Compounds

{N-[1-(2-Oxidophen-yl)ethyl-idene]-dl-alaninato}(pentane-1,5-di-yl)silicon(IV)

The title SiIV complex, C16H21NO3Si, is built up by a tridentate dinegative Schiff base ligand bound to a sila-cyclo-hexane unit. The coordination geometry of the penta-coordinated SiIV atom is a distorted trigonal bipyramid. The presence of the sila-cyclo-hexane ring in the complex leads to an unusual coordination geometry of the SiIV atom with the N atom from the Schiff base ligand and an alkyl-C atom in apical positions of the trigonal bipyramid. There is a disorder of the methyl group at the imine bond with two orientations resolved for the H atoms [major orientation = 0.55 (3)]. In the crystal, C-H⋯O inter-actions are found within corrugated layers of mol-ecules parallel to the ab plane.

Molecular Structures of the Silicon Pyridine-2-(thi)olates Me3Si(pyX), Me2Si(pyX)2 and Ph2Si(pyX)2 (py = 2-Pyridyl, X = O, S), and Their Intra- and Intermolecular Ligand Exchange in Solution

A series of pyridine-2-olates (pyO) and pyridine-2-thiolates (pyS) of silicon was studied in solid state and in solution. The crystal structures of Me3Si(pyO) (1a), Me3Si(pyS) (1b), Me2Si(pyO)2 (2a), Me2Si(pyS)2 (2b), Ph2Si(pyO)2 (3a) and Ph2Si(pyS)2 (3b) were determined by X-ray diffraction. For that purpose, crystals of the (at room temperature) liquid compounds 1a and 1b were grown in a capillary on the diffractometer. Compounds 1a, 1b, 2a, 2b and 3a feature tetracoordinate silicon atoms in the solid state, whereas 3b gave rise to a series of four crystal structures in which the Si atoms of this compound are hexacoordinate. Two isomers (3b1 with all-cis arrangement of the C2N2S2 donor atoms in P, and 3b2 with trans S-Si-S axis in P21/n) formed individual crystal batches, which allowed for their individual 29Si NMR spectroscopic study in the solid state (the determination of their chemical shift anisotropy tensors). Furthermore, the structures of a less stable modification of 3b2 (in C2/c) as well as a toluene solvate 3b2×(toluene) (in P) were determined. In CDCl3, the equimolar solutions of the corresponding pairs of pyO and pyS compounds (2a/2b and 3a/3b) showed substituent scrambling with the formation of the products Me2Si(pyO)(pyS) (2c) and Ph2Si(pyO)(pyS) (3c), respectively, as minor components in the respective substituent exchange equilibrium.

Si⋯O proximity in imidosilanes – absence of orbital interactions

New N-silylated phthalimides, succinimides, and 1,8-napthalimides were synthesised by reactions of the alkali imides with chlorosilanes in THF. Six different mono-, di-, tri- and tetra-iminosilanes of the type (CH3)4–n Si(imide) n were obtained and the products analysed with 1H, 13C, 29Si NMR, and Raman spectroscopy. The molecular structures of four imidosilanes have been determined by single-crystal X-ray diffraction. A characteristic structural feature of the compounds is the fact that all intramolecular Si⋯O distances are significantly below the sum of the van-der-Waals radii of silicon and oxygen of 3.62 Å. Experimentally found values for Si⋯O distances range from 2.813 to 3.030 Å. However, there are no significant orbital interactions between silicon and oxygen atoms, as shown by quantum chemical analysis with AIM and NBO methods. The short Si⋯O distances in these molecules are caused by the geometry of the rigid imide group bound to the silicon atom, and there is no evidence for an increase of the coordination number of the Si atoms.

The synthesis, characterization, and theoretical analysis of novel Si-substituted silylethyl derivatives of 2-mercaptobenzoxazole and 2-mercaptobenzothiazole

Trifluorosilylethyl derivatives of 2-mercaptobenzoxazole and 2-mercaptobenzothiazole C₆H₄NYCS(CH₂)₂SiF₃ (Y = O, S) have been synthesized in order to study the intramolecular N → Si interaction in compounds with the SiCCSCN fragment.

The challenge of separating and determining biologically active electrostatically stabilized silanates using the high-performance liquid chromatography technique

We present the results of research on the optimal conditions for the separation and determination of newly obtained hypercoordinated compounds, which belong to the group of electrostatically stabilized silanates. The research involved five stationary and four mobile phases. The best selectivity was obtained using the graphite phase and the mobile phase consisting of acetonitrile/water (80/20). The maximum selectivity of the determined electrostatically stabilized silanates was 1.13 and 1.06 for (1), (2), (3); 1.10 and 1.15 for (4), (5), (6); and 1.12 and 1.15 for (7), (8), (9). The octadecyl phase (which is recommended as standard) did not yield satisfactory results.

Carbene-Stabilized Disilicon as a Silicon-Transfer Agent: Synthesis of a Dianionic Silicon Tris(dithiolene) Complex

Reaction of carbene-stabilized disilicon (1) with the lithium-based dithiolene radical (2^. ) affords the first dianionic silicon tris(dithiolene) complex (3). Notably, the formation of 3 represents the unprecedented utilization of carbene-stabilized disilicon (1) as a silicon-transfer agent. The nature of 3 was probed by multinuclear NMR spectroscopy, single-crystal X-ray diffraction, and DFT computations.

Semi-bridging σ-silyls as Z-type ligands

The reactions of SiHPh(NCH₂PPh₂)₂C₆H₄-1,2 with zerovalent group 10 reagents afford the homoleptic bimetallic complexes [M₂{μ-κ³-Si,P,P′-SiPh(CH₂PPh₂)₂C₆H₄}₂] (M = Ni, Pd, Pt) in which the M–M bond is unsymmetrically bridged by two σ-silyl groups.

Synthesis and Characterization of the {Si(NHCH2CH2NH)3[Mo(CO)3]2}2- Complex Comprising the Si(NHCH2CH2NH)32- Octahedron

Reactions of K₁₂Si₁₇ with the low-valent transition-metal complex Mo(CO)₃(C₇H₈) in ethylenediamine/toluene solutions in the presence of 2,2,2-cryptand yield the {Si(NHCH₂CH₂NH)₃[Mo(CO)₃]₂}^2- dianion, which contains an octahedral Si(NHCH₂CH₂NH)₃^2- subunit. The SiN₆ core comprises a rare example of a doubly deprotonated ethylenediame ligand in a coordination complex and is also the first structurally characterized example of a homoleptic Si(N∩N)₃ trischelate. Its structure and spectroscopic properties are described.

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

Proceeding our initial studies of compounds with formally dative TM→Si bonds (TM = Ni, Pd, Pt), which feature a paddlewheel arrangement of four (N,S) or (N,N) bridging ligands around the TM–Si axis, the current study shows that the (N,O)-bidentate ligand 2-pyridyloxy (pyO) is also capable of bridging systems with TM→Si bonds (shown for TM = Pd, Cu). Reactions of MeSi(pyO)3 with [PdCl2(NCMe)2] and CuCl afforded the compounds MeSi(µ-pyO)4PdCl (1) and MeSi(µ-pyO)3CuCl (2), respectively. In the latter case, some crystals of the Cu(II) compound MeSi(µ-pyO)4CuCl (3) were obtained as a byproduct. Analogous reactions of Si(pyO)4, in the presence of HpyO, with [PdCl2(NCMe)2] and CuCl2, afforded the compounds [(HpyO)Si(µ-pyO)4PdCl]Cl (4), (HpyO)2Si[(µ-pyO)2PdCl2]2 (5), and (HpyO)2Si[(µ-pyO)2CuCl2]2 (6), respectively. Compounds 1–6 and the starting silanes MeSi(pyO)3 and Si(pyO)4 were characterized by single-crystal X-ray diffraction analyses and, with exception of the paramagnetic compounds 3 and 6, with NMR spectroscopy. Compound 2 features a pentacoordinate Si atom, the Si atoms of the other complexes are hexacoordinate. Whereas compounds 1–4 feature a TM→Si bond each, the Si atoms of compounds 5 and 6 are situated in an O6 coordination sphere, while the TMCl2 groups are coordinated to pyridine moieties in the periphery of the molecule. The TM–Si interatomic distances in compounds 1–4 are close to the sum of the covalent radii (1 and 4) or at least significantly shorter than the sum of the van-der-Waals radii (2 and 3). The latter indicates a noticeably weaker interaction for TM = Cu. For the series 1, 2, and 3, all of which feature the Me–Si motif trans-disposed to the TM→Si bond, the dependence of the TM→Si interaction on the nature of TM (Pd(II), Cu(I), and Cu(II)) was analyzed using quantum chemical calculations, that is, the natural localized molecular orbitals (NLMO) analyses, the non-covalent interaction (NCI) descriptor, Wiberg bond order (WBO), and topological characteristics of the bond critical points using the atoms in molecules (AIM) approach.

A closer look into close packing: pentacoordinated silicon in a high-pressure polymorph of danburite

Due to their high technological and geological relevance, silicates are one of the most studied classes of inorganic compounds. Under ambient conditions, the silicon in silicates is almost exclusively coordinated by four oxygen atoms, while high-pressure treatment normally results in an increase in the coordination from four- to sixfold. Reported here is a high-pressure single-crystal X-ray diffraction study of danburite, CaB2Si2O8, the first compound showing a step-wise transition of Si coordination from tetrahedral to octahedral through a trigonal bipyramid. Along the compression, the Si2O7 groups of danburite first transform into chains of vertice-sharing SiO5 trigonal bipyramids (danburite-II) and later into chains of edge-sharing SiO6 octahedra (danburite-III). It is suggested that the unusual formation of an SiO5 configuration is a consequence of filling up the pentacoordinated voids in the distorted hexagonal close packing of danburite-II.

Neutral six-coordinate bis(dithiocarbamato)silicon(iv) complexes with an SiCl2S4 skeleton

Treatment of SiCl₄ with lithium dithiocarbamates of the formula type Li[R₂NCS₂] (R = Ph, iPr) in a molar ratio of 1 : 2 afforded the respective six-coordinate silicon(iv) complexes [Ph₂NCS₂]₂SiCl₂ (3) and [iPr₂NCS₂]₂SiCl₂ (4), which were isolated as the solvates 3·MeCN and 4·MeCN. Compounds 3·MeCN and 4·MeCN were structurally characterised by single-crystal X-ray diffraction and multinuclear NMR spectroscopic studies in the solid state and in solution. In this study, dithiocarbamato ligands were implemented in silicon coordination chemistry for the first time. Compounds 3 and 4 represent the first six-coordinate silicon(iv) complexes with an SiCl₂S₄ skeleton.