Chelation and Stereodynamic Equilibria in Neutral Hypercoordinate Organosilicon Complexes of 1-Hydroxy-2-pyridinone

Synthesis and crystal structures of bis-[1-oxopyridin-2-olato(1-)]bis-(penta-fluoro-phen-yl)silicon(IV)-tetra-hydro-furan-pentane (2/1/1), bis-[1-oxopyridin-2-olato(1-)]bis-(p-tol-yl)silicon(IV), and dimesitylbis[1-oxopyridin-2-olato(1-)]silicon(IV)

The neutral organosilicon(IV) complex, (C6F5)2Si(OPO)2 (OPO = 1-oxopyridin-2-one, C5H4NO2), was synthesized from (C6F5)2Si(OCH3)2 and 2 equiv. of 1-hy-droxy-pyridin-2-one in tetra-hydro-furan (THF). Single crystals grown from the diffusion of n-pentane into a THF solution were identified as a THF hemisolvate and an n-pentane hemisolvate, (C6F5)2Si(OPO)2·0.5THF·0.5C5H12 (1). p-Tol-yl2Si(OPO)2 (2) and mesit-yl2Si(OPO)2 (3) crystallized directly from reaction mixtures of 2 equiv. of Me3Si(OPO) with p-tol-yl2SiCl2 and mesit-yl2SiCl2, respectively, in aceto-nitrile. The oxygen-bonded carbon and nitro-gen atoms of the OPO ligands in 1, 2, and 3 were modeled as disordered indicating co-crystallization of up to three possible diastereomers in each. Solution NMR studies support the presence of exclusively the all-cis isomer in 1 and multiple isomers in 2. Poor solubility of 3 limited its characterization in solution.

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.

A 3,2-Hydroxypyridinone-based Decorporation Agent that Removes Uranium from Bones In Vivo

Searching for actinide decorporation agents with advantages of high decorporation efficiency, minimal biological toxicity, and high oral efficiency is crucial for nuclear safety and the sustainable development of nuclear energy. Removing actinides deposited in bones after intake is one of the most significant challenges remaining in this field because of the instantaneous formation of highly stable actinide phosphate complexes upon contact with hydroxyapatite. Here we report a hydroxypyridinone-based ligand (5LIO-1-Cm-3,2-HOPO) exhibiting stronger affinity for U(VI) compared with the reported tetradentate hydroxypyridinone ligands. This is further revealed by the first principles calculation analysis on bonding between the ligand and uranium. Both in vitro uranium removal assay and in vivo decorporation experiments with mice show that 5LIO-1-Cm-3,2-HOPO can remove uranium from kidneys and bones with high efficiencies, while the decorporation efficiency is nearly independent of the treatment time. Moreover, this ligand shows a high oral decorporation efficiency, making it attractive for practical applications.

(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.

Molecular structures of various alkyldichlorosilanes in the solid state

A series of organodichlorosilanes RR'SiCl₂ (R,R' = (CH₂)₃; (CH₂)₄; (CH₂)₅; Me,Me; Me,H; Me,Cl) was studied by single-crystal X-ray diffraction analyses. At ambient temperature liquid chlorosilanes (melting points in the range of 180-220 K) were transferred into glass capillaries and crystallized in situ on a diffractometer. In the solid state structure these chlorosilanes are monomeric, even in the case of the sterically less demanding 1,1-dichlorosilacyclobutane (CH₂)₃SiCl₂. Interestingly, regardless the steric demand of the alkyl substituents, the dialkyldichlorosilanes exhibit essentially the same Cl-Si-Cl angle (for (CH₂)₃SiCl₂, (CH₂)₄SiCl₂, (CH₂)₅SiCl₂, Me₂SiCl₂: 106.08(3)°, 106.07(4)°/105.86(4)°, 106.91(2)° and 105.59(6)°, respectively). Replacement of one alkyl group by hydrogen has only a marginal influence on the Cl-Si-Cl angle (MeHSiCl₂ 106.31(3)°), whereas in MeSiCl₃ slightly wider Cl-Si-Cl angles are found (ranging between 107.04(11)° and 107.86(11)°), in accordance with VSEPR. Computational analyses, i.e., potential energy surface scans of the Cl-Si-Cl angle variation, of (CH₂)₃SiCl₂, Me₂SiCl₂, MeHSiCl₂ and H₂SiCl₂ reveal essentially identical energy profiles for the Cl-Si-Cl deformation in these four dichlorosilanes with basically superimposed curves for (CH₂)₃SiCl₂ and Me₂SiCl₂, whereas with increasing H-substitution the energetic minimum is shifted to a slightly wider Cl-Si-Cl angle. In the crystal packing only MeHSiCl₂ exhibits weak intermolecular SiCl van der Waals contacts, whereas the Si-Cl moieties of the other five chlorosilanes engage in intermolecular ClH and (for (CH₂)₃SiCl₂, (CH₂)₄SiCl₂ and MeSiCl₃) ClCl contacts.

Crystal structures of tris-[1-oxo-pyridine-2-olato(1-)]silicon(IV) chloride chloro-form-d 1 disolvate, tris-[1-oxo-pyridine-2-olato(1-)]silicon(IV) chloride aceto-nitrile unqu-anti-fied solvate, and fac-tris-[1-oxo-pyridine-2-thiol-ato(1-)]silicon(IV) chloride chloro-form-d 1 disolvate

The cations in the title salts, [Si(OPO)3]Cl·2CDCl3, (I), [Si(OPO)3]Cl·xCH3CN, (II), and fac-[Si(OPTO)3]Cl·2CDCl3, (III) (OPO = 1-oxo-2-pyridin-one, C5H4NO2, and OPTO = 1-oxo-2-pyridine-thione, C5H4NOS), have distorted octa-hedral coordination spheres. The first two structures contain the same cation and anion, but different solvents of crystallization led to different solvates and packing arrangements. In structures (I) and (III), the silicon complex cations and chloride anions are well separated, while in (II), there are two C-H⋯Cl distances that fall just within the sum of the van der Waals radii of the C and Cl atoms. The pyridine portions of the OPO ligands in (I) and (II) are modeled as disordered with the planar flips of themselves [(I): 0.574 (15):0.426 (15), 0.696 (15):0.304 (15), and 0.621 (15):0.379 (15); (II): 0.555 (13):0.445 (13), 0.604 (14):0.396 (14) and 0.611 (13):0.389 (13)], demonstrating that both fac and mer isomers are co-crystallized. In (II), highly disordered solvent, located in two independent channels along [100], was unable to be modeled. Reflection contributions from this solvent were fixed and added to the calculated structure factors using the SQUEEZE [Spek (2015 ▸). Acta Cryst. C71, 9-18] function of program PLATON, which determined there to be 54 electrons in 225 Å(3) accounted for per unit cell (25 electrons in 109 Å(3) in one channel, and 29 electrons in 115 Å(3) in the other). In (I) and (II), all species lie on general positions. In (III), all species are located along crystallographic threefold axes.

Analysis of the hypersensitivity of the (29)Si NMR chemical shift of the pentacoordinate silicon compounds to the temperature effect. N-(Silylmethyl)acetamides

Theoretical investigation of the phenomenon of hypersensitivity of the (29)Si NMR chemical shift, δ, in the pentacoordinate silicon compounds to the temperature effect has been performed by the example of N-(silylmethyl)acetamides MeC(O)NMeCH2SiX3 (X = Me, 1; OMe, 2; F, 3) and MeC(O)NMeCH2SiMe2F (4) with the use of experimental dynamic NMR (DNMR) (29)Si data. It is based on the following: (i) the analysis of the potential energy surface of molecules 1-4 in polar solvents and the energetics of interconversion between their possible isomeric forms; (ii) the calculations of δ at different temperatures taking into account the dependence of the dielectric constant (ε) of the medium on T, and (iii) the isolation of dynamic, geometrical, and polar contributions to the temperature drift of δ. The results obtained allowed us to give a consistent explanation of the DNMR (29)Si spectra of acetamides 1-4 and to elucidate the nature of an unusual effect of T on δ.

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).

Synthesis, characterization of silicon(iv) compounds containing 2-alkyl-aminopyridine ligands and evaluation of them as CVD precursors

A family of silicon(iv) compounds, where the Si centers of trimethylsilyl (–SiMe₃) are linked with 2-alkyl-aminopyridine ligands, has been synthesized by reaction of the corresponding lithium salt of these ligands and SiMe₃Cl in a general procedure.

Synthesis, characterization, thermal properties of silicon(iv) compounds containing guanidinato ligands and their potential as CVD precursors

The title compounds of the type (Me₃Si)₂N–C(N′R)(–N′′RSiMe₃) (with R = iPr or Cy) as potential CVD precursors have been synthesized and characterized by X-ray diffraction, ¹H NMR, ¹³C NMR, ²⁹Si NMR and elemental analysis where necessary.

2-Acylpyrroles as mono-anionic O,N-chelating ligands in silicon coordination chemistry

Kryptopyrrole (2,4-dimethyl-3-ethylpyrrole) was acylated with, for example, benzoyl chloride to afford 2-benzoyl-3,5-dimethyl-4-ethylpyrrole (L(1)H). With SiCl4 this ligand reacts under liberation of HCl and formation of the complex L(1)2SiCl2. In related reactions with HSiCl3 or H2SiCl2, the same chlorosilicon complex is formed under liberation of HCl and H2 or liberation of H2, respectively. The chlorine atoms of L(1)2SiCl2 can be replaced by fluoride and triflate using ZnF2 and Me3Si-OTf, respectively. The use of a supporting base (triethylamine) is required for the complexation of phenyltrichlorosilane and diphenyldichlorosilane. The complexes L(1)2SiCl2, L(1)2SiF2, L(1)2Si(OTf)2, L(1)2SiPhCl, and L(1)2SiPh2 exhibit various configurations of the octahedral silicon coordination spheres (i.e. cis or trans configuration of the monodentate substituents, different orientations of the bidentate chelating ligands relative to each other). Furthermore, cationic silicon complexes L(1)3Si(+) and L(1) SiPh(+) were synthesized by chloride abstraction with GaCl3. In contrast, reaction of L(1)2SiCl2 with a third equivalent of L(1)H in the presence of excess triethylamine produced a charge-neutral hexacoordinate Si complex with a new tetradentate chelating ligand which formed by Si-templated C-C coupling of two ligands L(1).