Hexacoordinate Silicon Complexes Research Articles

The Hexacoordinate Si Complex SiCl4(4-Azidopyridine)2—Crystallographic Characterization of Two Conformers and Probing the Influence of SiCl4-Complexation on a Click Reaction with Phenylacetylene

4-Azidopyridine (1) and SiCl4 react with the formation of the hexacoordinate silicon complex SiCl4(4-azidopyridine)2 (2). Upon dissolving in warm chloroform, the complex dissociates into the constituents 1 and SiCl4 and forms back upon cooling. Depending on the cooling, two different crystalline modifications of 2 were obtained, which feature two different trans-conformers. Slow cooling to room temperature afforded conformer 2′, which features coplanar pyridine rings. Rapid cooling to −39 °C afforded crystals of conformer 2″, in which the planes of the pyridine ligands are nearly orthogonal to one another. Whereas 2′ resembles the molecular arrangement of various other known SiX4(pyridine)2 (X = halide) complexes, 2″ represents the first crystallographically confirmed example of a SiX4(pyridine)2 complex in this conformation. Conformers 2′ and 2″ were studied with 13C and 29Si solid state NMR spectroscopy. Their differences in 29Si chemical shift anisotropy, as well as energetic differences, were further investigated with computational analyses. In spite of the similar stabilities of the two conformers as isolated molecules, the crystal packing of 2″ is less stable, and its crystallization is interpreted as a kinetically controlled effect of seed formation. (3+2)-cycloaddition of 1 and phenylacetylene in toluene at 110 °C yields a mixture of 1-(4-pyridyl)-4-phenyl-1,2,3-triazole (1,4-3) and 1-(4-pyridyl)-5-phenyl-1,2,3-triazole (1,5-3) in approximate 1:2 molar ratio. The crystal structures of the two isomers were determined via X-ray diffraction. In chloroform (at 60 °C), this reaction is slow (less than 2% conversion within 4 h), but the presence of SiCl4 enhanced the rate of the reaction slightly, and it shifted the triazole isomer ratio to ca. 1:6 in favor of 1,5-3.

Pd–Si complexes of the type ClPd(μ2-pyO)4SiR (R = Me, Ph, Bn, Allyl, κO-(pyO)PdCl(η3-allyl); pyO = pyridine-2-olate): The influence of substituent R on the Pd–Si bond

The reactions of organosiliconpyridine-2-olates (pyridyl-2-oxysilanes) RSi(pyO)3 (pyO = pyridine-2-olate, R = Me (1a), Ph (1b), Bn (1c) and Allyl (1d)) and [PdCl2(NCMe)2] in chloroform afforded the hexacoordinate silicon complexes RSi(μ2-pyO)4PdCl (R = Me (2a), Ph (2b), Bn (2c) and Allyl (2d), respectively), which feature a Pd–Si bond, in which the Pd atom is the formal lone pair donor toward Si. The new compounds 2b, 2c, 2d were characterized with multi-nuclear NMR spectroscopy and elemental analysis. The effect of the Si-bound substituent R on the trans-disposed Pd–Si bond was studied by single-crystal X-ray diffraction and computational analyses (e.g., Natural Localized Molecular Orbitals, NLMO; topological analyses of the electron density at the bond critical point with Quantum Theory of Atoms-In-Molecules, QTAIM). A structurally related byproduct, (η3-allyl)ClPd(pyO)Si(μ2-pyO)4PdCl 2d’, which formed along with target product 2d and features an Si–O bond trans to Pd–Si, was included in this systematic study. Another byproduct from the synthesis of 2d, the pentanuclear complex ClPd(μ2-pyO)2Si(μ2-pyO)2Pd(μ2-pyO)2Si(μ2-pyO)2PdCl (compound 3) was characterized crystallographically. This compound features pentacoordinate Si atoms within trigonal–bipyramidal Si(O4Pd) coordination spheres with equatorial Pd–Si bonds to the terminal Pd atoms. The Pd–Si bond situation in this compound was elucidated with the aid of computational analyses. QTAIM analyses of 3 in conjunction with a model compound PdSi4, which features two silyl groups and two silylene ligands, indicate topological properties of the electron density at the Pd–Si bond critical point which are similar to Pd–Si bonds of silyl and silylene compounds. The latter exhibit greater similarity, which indicates features of a Pd←Si bond. In contrast, NLMO analyses of 3 identify a polar covalent Pd–Si bond with predominant Pd contribution (formal Pd→Si donation).

A comparative study of DFT functionals and basis sets for describing the luminescent spectra of hexacoordinated silicon complexes

This article presents a comparative study of DFT functionals - B3LYP, BHandHLYP and CAM-B3LYP in combination with basis sets – 6-311++g(d,p), cc-pVDZ and cc-pVTZ to describe the luminescence spectra of optimized structures of neutral hexacoordinated silicon complexes. The calculation accuracy of an obtained theoretical data of an electronic absorption spectra of the structures was compared with the known experimental data. To perform comparative calculations with the experimental values, a neutral optimized structure of hexacoordinated Si(bzimpy)2 complex containing 2,6-bis(benzimidazol-2'-yl)pyridine ligand was considered. A comparison of the absorption spectra of the Si(bzimpy)2 structure showed that the use of the 6-311++g(d,p) basis set in combination with the B3LYP functional gives the best agreement with the experimental data. Based on the obtained results of the study, a comparison was made of the absorption spectra of other silicon compounds - Si(bzimpyMeO)2, Si(bzimpyMe2)2 and Si(bzimpyMeOMe2)2. Comparative graphs of the structures showed the proximity of the location of intense peaks for all four structures. Thus, we can say that the B3LYP functional gives the best agreement with the experimental data for neutral hexacoordinated silicon complexes. Also this shows that in a more detailed study of the absorption spectra, it can be noted that the use of the 6-311++g(d,p) basis set in combination with the B3LYP functional gives the most accurate values.

A straightforward synthesis of neutral hexacoordinated silicon(IV) complexes with SiN6 skeleton

Three neutral hexacoordinate silicon(IV) complexes with SiN6 skeleton were obtained via one-pot synthesis by using tetra(thiocyanato-N)silane, Si(NCS)4 with an equimolar amount of 2,2′-bipyridyl (bipy), 4,4′-dimethyl-2,2′-dipyridyl (dmp) and 1,10-phenanthroline (phen) respectively. The complexes obtained; (bipy)Si(NCS)4 (1), (dmp)Si(NCS)4 (2), and (phen)Si(NCS)4 (3) belong to a family of neutral hexacoordinate silicon(IV) with SiN6 coordinating framework, which has been less studied both by single-crystal X-ray diffraction and 29Si NMR spectroscopies. All the complexes were characterized by single-crystal X-ray diffraction, solution 1H, 13C{H}, 29Si, solid-state 29Si CP/MAS NMR spectroscopies, and elemental analysis was used to confirm the structures. Comparison of the 29Si chemical shieldings of the complexes 1–3 in the solution and solid-state indicated that all complexes maintain the hexacoordination at silicon atom in DMSO-D6 solution. This works demonstrated the synthetic potential of Si(NCS)4 for the synthesis of new neutral hexacoordinate silicon complexes with SiN6 skeleton via one-pot synthesis.

Studies on stability and structural aspects of hydrazide-based hypercoordinate silicon(IV) complexes

The concept of hypercoordination has been extensively used and debated in the literature specifically in case of silicon complexes from the last three decades which has neither been proved nor disproved. In fact, all these silicon complexes reported in the literature consist of various bonding features i.e. covalent (C–Si, N–Si or X–Si), dative (N→Si or O→Si) and/or ionic (X-{Si+}, X = halogen). The present work compares the structural features of selected hypercoordinate silicon(IV) complexes derived from the hydrazide ligands and describes the relative stability aspects of penta- and hexa-coordinate hydrazide-based silicon dichelates with respect to the charge on central silicon atoms. Some selected examples of penta- and hexa-coordinate silicon complexes without having Si-halogen covalent bond reported in the literature were selected for the comparison of structural properties through DFT calculations. The results indicate that the electrophilicity on silicon atom in penta-coordinate silicon complexes are significantly higher, thus, indicating their better reactivity compared to their hexa-coordinate analogues.

Synthesis and structural characterization of neutral hexacoordinate silicon(IV) complexes containing salophen and thiocyanato-N ligands

Abstract The reaction of the H2salophen ligand, 2,2′-((1E,1′E)-(1,2-phenylenebis(azanylylidene))bis (methanylylidene))diphenol, with one molar equivalent of Si(NCS)4, MeSi(NCS)3 (13), or HMeSi(NCS)2 afforded neutral hexacoordinate silicon complexes, which have an-NCS bi-functionality (complex 1) and mono-functionality (complex 14). The reaction of Si(NCS)4 with the H2salophen-type ligand1,1′-((1E,1′E)-(1,2-phenylenebis(azanylylidene))bis(methanylylidene)) bis(naphthalen-2-ol) (H2Noph), afforded the hexacoordinate silicon complex 15, which has an-NCS bi-functionality. Single-crystal X-ray structural and elemental analyses were used to characterize and confirm the structure of the starting material 13 and complexes 1, 14, and 15. The complexes were characterized in solution by 1H, 13C, and silicon-29 nuclear magnetic resonance (29Si NMR) and in the solid state by 29Si cross-polarization/magic angle spinning (CP/MAS) NMR. Because of the poor solubility of complex 1, it was only possible to characterize it in the solid state by 13C and 29Si CP/MAS NMR and in solution by 1H NMR.

Si(bzimpy)2 - a hexacoordinate silicon pincer complex for electron transport and electroluminescence.

A neutral hexacoordinate silicon complex containing two 2,6-bis(benzimidazol-2'-yl)pyridine (bzimpy) ligands has been synthesized and explored as a potential electron transport layer and electroluminescent layer in organic electronic devices. The air and water stable complex is fluorescent in solution with a λmax = 510 nm and a QY = 57%. Thin films grown via thermal evaporation also fluoresce and possess an average electron mobility of 6.3 × 10-5 cm2 V-1 s-1. An ITO/Si(bzimpy)2/Al device exhibits electroluminescence with λmax = 560 nm.

Progress in the Synthesis and Bioactivity of Hexacoordinate Silicon(IV) Complexes

(Arenediolato)bis(polypyridyl)silicon(IV) complexes contain hexacoordinate silicon and are surprisingly stable against hydrolysis in water. In an ongoing research program, we are aiming to exploit them as new structural templates for the design of bioactive compounds. As a follow‐up to previous work, here we present our progress in the synthesis of hexacoordinate silicon complexes by selective ortho‐double nitration of the electron‐rich catecholato ligand, followed by reduction to diamines and condensation either with 1,2‐diketones or with aldehydes. Binding epitopes of some representative complexes to G‐quadruplex DNA as determined by NMR spectroscopic titration are presented.

Synthesis, stereoisomerism and crystal structures of neutral hexacoordinate silicon(IV) complexes with Salen-O,N,N,O and thiocyanato-N ligands

The reaction of methyldi(thiocyanato-N)silane (HMeSi(NCS)2) with the Salen-type ligands 2,2′-{ethane-1,2-diylbis[nitrile(E)methylylidene]}diphenol (H2Salen) and 2,2′-{ethane-1,2-diylbis[nitrile(1E)eth-1-yl-1-ylidene]}diphenol (H2MeSalen) leads to the formation of the neutral hexacoordinate silicon(IV) complexes (Salen)SiMe(NCS) (4) and (MeSalen)SiMe(NCS) (5) with one –NCS functional group and a SiO2N3C coordination framework. The reaction of Si(NCS)4 with the H2MeSalen ligand leads to the formation of (MeSalen)Si(NCS)2 (6), a neutral silicon(IV) complex bi-functionalized with –NCS. 29Si NMR solution studies confirmed that silicon complexes 4–6 are hexacoordinated and that complex 6 exists as a mixture of the three possible stereoisomers trans-6, all-cis-6 and cis-6 in approximately a 2.25/1.75/1.00 ratio, respectively. The assignments of the stereoisomers of 6 in dmso-d6 solution were achieved by quantitative 29Si NMR analysis and their relative energies (ΔH0298 values) obtained from density functional theory (DFT) calculations. All of the complexes were characterized by FT-IR spectroscopy, solid-state 29Si CP/MAS and solution 1H, 13C and 29Si NMR. Single-crystal X-ray diffraction and elemental analysis were used to confirm the structures and compositions of all of the complexes.

Tp*Cu(I)-CN-SiL2-NC-Cu(I)Tp*--a hexacoordinate Si-complex as connector for redox active metals via π-conjugated ligands.

Hexacoordinate silicon complexes L2SiX2 (L = a 2-benzoylpyrrol-1-yl derivative, X = CN, NCS) were synthesized from L2SiCl2 by ligand exchange with trimethylsilyl reagents Me3SiX. In the presence of [Tp*CuNCMe] and Me3SiCN the silicon complex L2Si(NC(CuTp*))2 was obtained, which contains a linear Cu-CN-Si-NC-Cu unit (Tp* = hydrotris(3,5-dimethylpyrazolyl)borato).

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.

Donor-stabilized hypercoordinated silicon(IV) chelates with cyclohexylideneimino-N ligand group: Role of substituents on ionization

N-Cyclohexylideneimino-O-(trimethylsilyl)acylimidates react smoothly with XSiCl3 (X=Me, Ph, vinyl and Cl) in a transsilylation reaction producing ionic pentacoordinate bischelates and neutral hexacoordinated complexes depending on the electronic and steric behavior of the ligands. These hypercoordinated silicon complexes are characterized by UV–Vis, FT-IR and NMR spectroscopic techniques. A neutral hexacoordinate silicon complex with dichloro ligands was characterized by single crystal X-ray analysis. The UV–Vis absorption data showed a significant bathochromic shift of λmax in hypercoordinated silicon complexes on comparison with their corresponding hydrazide ligands. The 29Si NMR chemical shifts strongly depend on nature of X group directly attached to the central silicon atom toward ionization.

Synthesis and Functionalization of Hexacoordinate (Arenediolato)bis(polypyridyl)silicon(IV) Complexes

AbstractHexacoordinate (arenediolato)silicon(IV) complexes that contain two additional 2,2′‐bipyridine or 1,10‐phenanthroline ligands are surprisingly stable against aqueous hydrolysis and therefore constitute attractive and novel templates for the design of bioactive compounds. In this article, we report the synthesis of (arenediolato)bis(polypyridyl)silicon(IV) complexes, including a case of diastereoselective synthesis of a nonracemic hexacoordinate (binaphtholato)silicon(IV) complex, and methods for their post‐coordinative functionalization with halides, nitro, and carbonyl groups. Several X‐ray crystal structures are provided and demonstrate the octahedral coordination of silicon in these complexes.

Neutral Hexacoordinate Silicon(IV) Complexes with a Tridentate Dianionic O,N,X Ligand (X = O, N, S), Bidentate Monoanionic X,N Ligand (X = O, S), and Phenyl Ligand: Compounds with a SiO3N2C, SiSO2N2C, SiO2N3C, SiSON3C, or SiS2ON2C Skeleton

AbstractA series of neutral hexacoordinate silicon(IV) complexes (4a, 4b, 5a, 5b, 6a, and 6b) with a SiO3N2C, SiSO2N2C, SiO2N3C, SiSON3C, or SiS2ON2C skeleton have been synthesized and structurally characterized by solid‐state and solution NMR spectroscopy and single‐crystal X‐ray diffraction. These studies were performed with a special emphasis on comparing the respective O/NMe/S analogues 4a/5a/6a and 4b/5b/6b and the O/S pairs 4a/4b, 5a/5b, and 6a/6b with respect to their structures and NMR spectroscopic parameters.

Neutral Hexacoordinate Silicon(IV) Complexes with a SiO4NC or SiO3N2C Skeleton and Neutral Pentacoordinate Silicon(IV) Complexes Containing a Trianionic Tetradentate O,N,O,O Ligand

AbstractA series of neutral hexacoordinate silicon(IV) complexes with a SiO4NC or SiO3N2C skeleton was synthesized. Additionally, two neutral pentacoordinate silicon(IV) complexes with a SiO3NC skeleton were synthesized. All compounds studied were structurally characterized by multinuclear NMR spectroscopy in the solid state and in solution and by single‐crystal X‐ray diffraction. The hexacoordinate compounds studied contain a tridentate dianionic O,N,O or N,N,O ligand, a phenyl ligand, and a symmetrically substituted derivative of an acetylacetonato ligand of the formula type RC(O)–CH=C(OSiMe3)R (R = Me, Ph, CF3). The two pentacoordinate complexes contain a tetradentate trianionic O,N,O,O ligand and a phenyl ligand.

Pentacoordinate mono(β-diketonato)- and hexacoordinate bis-(β-diketonato)-silicon(IV) complexes obtained from (thiocyanato-N)hydridosilanes

Three novel neutral hypercoordinate silicon(IV) complexes containing the O,O′-donor deprotonated β-diketone ligands 1,3-diphenylpropane-1,3-dione (HL1) and 1-phenylbutane-1,3-dione (HL2) were synthesized starting from the hitherto unknown diphenyl(thiocyanato-N)silane [HPh2Si(NCS)] and methyldi(thiocyanato-N)silane [HMeSi(NCS)2], a class of silicon source with Si–NCS and Si–H reactive functionalities. The reaction of HL1 with the new starting material HPh2Si(NCS) only afforded a neutral pentacoordinate silicon complex containing one β-diketonato ligand coordinated in a bidentate fashion (complex 16). The reaction of HL1 and HL2 with HMeSi(NCS)2 yielded bis-β-diketonato neutral hexacoordinate silicon complexes (17 and 18, respectively). The three compounds 16–18 were characterized using solution 1H, 13C and 29Si INEPT NMR and FT-IR spectroscopies, and compounds 17 and 18 were also studied using solid-state 29Si CP/MAS NMR. Elemental analysis and single-crystal X-ray diffraction were used to establish the composition and the structure of all of the new complexes. The 29Si INEPT NMR solution studies confirmed that compounds 16–18 maintain the same hypercoordination in solution that they have in the solid state. Compound 16 has a SiO2NC2 coordinating framework and represents the first example of a pentacoordinate silicon β-diketonato whose X-ray single crystal structure has been elucidated, and compounds 17 and 18 are the first neutral, non-zwitterionic, hexacoordinate silicon complexes with a SiO4NC coordinating framework bearing only one –NCS functionality. The usefulness of the (thiocyanato-N)hydridosilanes HPh2Si(NCS) and HMeSi(NCS)2 as starting materials for the preparation of hypercoordinate organosilicon complexes is confirmed.

Synthesis and Characterization of Dianionic Hexacoordinate Silicon(IV) Complexes of Substituted Catechols, Flavones, and Fluorone: X-Ray Crystal Structures of [(n-C3H7)2NH2]2[(Cl4C6O2)3Si] · 3 CH3CN and [(n-C3H7)2NH2]2[(Br4C6O2)3Si] · 2 (CH3)2SO

Reaction of tetraethoxysilane (TEOS) with substituted catechols (I-X), 7,8-dihydroxyflavone (XI), 3,3′,4′-trihydroxyflavone (XII), 3′,4′,5,7-tetrahydroxyflavone (XIII), and 9-phenyl-2,3,7-trihydroxy-6-fluorone (XIV) in the presence of an amine (molar ratio 1:3:2) in acetonitrile affords the corresponding dianionic hexacoordinate silicon(IV) complexes 1-15 having a “SiO6” structural fragment. The dianionic silicates were isolated as di-n-propylammonium/triethylammonium/di-n-butylammonium salts and were characterized by elemental analysis and various spectroscopic data (IR, 1H, 13C, and 29Si NMR). The solid state structures of compounds [(n-C3H7)2NH2]2[{Cl4C6O2}3Si] (1) and [(n-C3H7)2NH2]2[{Br4C6O2}3Si] (2) were determined by single crystal X-ray diffraction. Both 1 and 2 crystallize in the monoclinic space group C2/c and reveal (i) bidentate mode of ligation, (ii) octahedral coordination around silicon, and (iii) hydrogen bonding features. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.

Hexa-Coordinated Silicon Complexes Derived from Regioisomeric Aminotriphenylethanols and Their use as Dopants for Liquid Crystals

Tridentate imine ligands that are obtained from the chiral, regioisomeric amino alcohols 2-amino-1,1,2-triphenyethanol and 2-amino-1,2,2-triphenylethanol serve for the formation of bis-chelated silicon complexes. Whereas the complex based on the former amino alcohol is obtained as a diastereomeric mixture, the complex that is derived from 2-amino-1,2,2-triphenylethanol forms in a completely diastereoselective manner, and its configuration is determined as (A,R,R), according to a crystal structure analysis. The new silicon complexes are found to be efficient dopants for the conversion of nematic liquid crystals into cholesteric phases. GRAPHICAL ABSTRACT

Hexacoordinate Silacyclobutane Dichelate Complexes: Structure, Properties, and Ligand Crossover

Hexacoordinate dichelate silacyclobutane complexes have been synthesized from dichlorosilacyclobutane and O-trimethylsilylated hydrazides by transsilylation. Like previously reported hexacoordinate silicon complexes, they readily and quantitatively undergo ligand exchange with other silicon compounds (XSiCl3 and differently substituted O-trimethylsilylated hydrazides), evidence that ionic dissociation does not play a significant role in the exchange mechanism. Germanium tetrachloride causes central-element exchange and formation of analogous hexacoordinate germanium complexes. Likewise, silicon tetrachloride replaces germanium from its hexacoordinate complexes, obeying certain selectivity constraints. When silicon complexes have strongly electron-withdrawing chelate-ring substituents (CF3 or CH2CN), GeCl4 causes, in addition to central-element exchange, also oxidative opening of the four-membered ring and addition of two chlorine atoms. Both chelate exchange and central-element exchange are shown to be dominated by monodentate ligand priorities.

Novel neutral hexacoordinate benzamidinatosilicon(iv) complexes with SiN3OF2, SiN3OCl2, SiN3OBr2, SiN5O and SiN3O3 skeletons

The neutral pentacoordinate monoamidinatosilicon(IV) complex 1 (SiN(2)Cl(3) skeleton) and the neutral hexacoordinate monoamidinatosilicon(IV) complexes 2-9 (SiN(3)OF(2), SiN(3)OCl(2), SiN(3)OBr(2), SiN(5)O and SiN(3)O(3) skeletons) were synthesised and characterised by elemental analyses, single-crystal X-ray diffraction (except for 1) and NMR spectroscopy in the solid state and in solution. Compounds 2-9 contain one bidentate monoanionic N,N'-diisopropylbenzamidinato ligand, one bidentate monoanionic ligand derived from 8-hydroxyquinoline and (i) two identical monoanionic ligands (F, Cl, Br, N(3), NCO, NCS, OSO(2)CF(3)) or (ii) one bidentate dianionic benzene-1,2-diolato ligand. The dynamic behavior of 2-4 (SiN(3)OX(2) skeleton; X = F, Cl, Br) and 9 (SiN(3)O(3)) in solution was studied by multinuclear variable-temperature NMR experiments. Compound 1 was synthesised by reaction of SiCl(4) with the corresponding lithium amidinate, and compound 2 was obtained by reaction of 1 with 8-hydroxyquinoline and triethylamine. Compound 2 served as the starting material in the syntheses of 3-9, in which the two chloro ligands of 2 were substituted by two identical (pseudo)halogeno ligands, two trifluoromethanesulfonato ligands or one benzene-1,2-diolato ligand. Compounds 3 and 4 contain the novel SiN(3)OBr(2) and SiN(3)OF(2) skeletons, while compounds 5-7 are the first neutral hexacoordinate silicon(IV) complexes with an SiN(5)O skeleton.