The synthesis of hypervalent tris(catecholato)silicate ion, [(C6H4)2)3Si]2− with six different counter cations: (i) diethylammonium (I), (ii) triethylammonium (II), (iii) diisopropylam-monium (III), (iv) morpholinium (IV), (v) piperazinium (V) and (vi) N-methylpiperazinium (VI) has been achieved (yield: ca.95%) by the reaction of catechol and tetraethoxysilane in presence of the corresponding amine. Single crystal X-ray structure of compound (III) has been determined. It crystallizes in orthorhombic system [space group P212121; a = 11.735(2), b = 13.708(3), c = 23.283(5) Å; α = 90°, β = 90°, γ = 90°; Volume = 3745.4(11) Å3; Density = 1.165 gem-3; Z = 4; R = 0.0585; wR2(I) = 0.1610 and 3677 reflections] and the structure shows slightly distorted octahedral geometry around silicon. Results of TG, DT and EG analysis of compounds (I) - (VI) reveal the influence of the counter cation on thermal stability. Bench scale pyrolysis of (I) and (II) convert them to [C6H4O2)2Si], by the quantitative expulsion of ammonium catecholate salt, (M+)2[(C6H4O2)]2−. CP-MAS 29Si -nmr spectral data suggests that [(C6H4O2)2Si]1, is a simple mixture. © 1999 OPA (Overseas Publishers Association) N.V.

Jesudoss V. Kingston

Babu Vargheese

Madhugiri N. Sudheendra Rao

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Synthesis and Characterization of Tris(catecholato)Silicates, [(C6H4O2)3Si]2− with Different Counter Cations – First Pyrolysis Study and X-ray Structure of [{(CH3)2CH}2NH2]2[(C6H4O2)3Si] · 2CH3CN · H2O

Main Group Chemistry

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 "SiO 6" 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-C 3H 7) 2NH 2] 2[{Cl 4C 6O 2} 3Si] (1) and [(n-C 3H 7) 2NH 2] 2[{Br 4C 6O 2} 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. © 2012 Copyright Taylor and Francis Group, LLC.

Phosphorus, Sulfur and Silicon and the Related Elements

Synthesis and characterization of dianionic hexacoordinate silicon(iv) complexes of substituted catechols, flavones, and fluorone: X-ray crystal structures of [(n -C3H7) 2NH2] 2[(Cl 4C 6O 2) 3Si] · 3 CH 3CN and [(n-C 3H 7) 2NH 2] 2[(Br4C6O2) 3Si] · 2 (CH3)2SO

A new series of transition metal complexes [M = Cr(III) (1), Mn(II) (2), Co(III) (3), Ni(II) (4a-d), and Cu(II) (5a-b)] with the dianionic hypervalent, tris(catecholato)silicate, [Si(C6H4O2) 3]2-, have been synthesized by an ion exchange method under both aqueous and non-aqueous conditions using bis(triethylammonium) tris(catecholato)silicate and a cationic transition metal complex, [ML n]X [L = ethylenediamine (en), diethylenetriamine (dien), ammonia or water and X = Cl-, SO42-]. Different ammonium tris(catecholato)silicates [viz. morpholinium, diisopropylammonium and diethylammonium] also serve as appropriate for the ion exchange reaction. Ligands like H2O and NH3 afford less stable complexes compared to the ligands en and dien. The powdered form of Ni(II) complexes, [NiL6][Si(C6H4O2)3] (L = H2O, NH3), readily convert to [Ni(en)3] [Si(C6H4O2)3] quantitatively when treated with en. The new derivatives have been characterized on the basis of analytical, spectroscopic (IR, UV-Vis, solid state NMR, EPR and MS) and magnetic data. The results of TG and EG analysis of the complexes 1-5 reveal (i) different decomposition behaviour compared to ammonium catecholatosilicates and (ii) the influence of the bulky tris(catecholato)silicate anion on the thermal stability of these complexes. The bulk pyrolysis study of the above complexes provides a stoichiometric mixture of the corresponding metal oxide and silica except in case of Co(III) which gave the orthosilicate, Co 2SiO4. Variable temperature magnetic susceptibility measurements indicate a weak antiferromagnetic interaction in case of [Ni(en)3][Si(C6H4O2)3] and [Cu(en)2][Si(C6H4O2) 3]. © 2003 Elsevier Ltd. All rights reserved.

Polyhedron

Dianionic silicate derivatives of transition metals: Synthesis by a facile ion exchange route, characterization and thermolysis studies

Synthesis of the hypervalent tris(catecholato)silicate ion, [(C 6H4O2)3-Si]2- having five different primary ammonium cations viz. n-propylammonium (1), isopropylammonium (2) n-butylammonium (3), cyclohexylammonium (4), benzylammonium (5), and a bulky secondary ammonium cation, namely diisobutylammonium (6), have been achieved by the reaction of catechol and tetraethoxysilane (TEOS) in presence of the corresponding amine. Elemental analysis, IR, NMR (1H, 13C, and 29Si), and mass spectral data have been used for their characterization. Single crystal x-ray structures of 1 and 6 indicate nearly same distortion of the "SiO6" octahedron but interesting differences in the hydrogen bonding interactions arising from the catecholato oxygens and the N-H bonds of the ammonium cations. While compound 1 exhibits hydrogen bonding more discretely and by revealing strong interaction between the n-propylammonium ions, compound 6 shows an extended intermolecular hydrogen bonding aided by a water molecule present in the lattice to lead to infinite one dimensional chain arrangement. TG and EG analyses of compounds, 1-5 indicate 1) the formation of the previously observed spirosilane intermediate, [Si(C6H 4O2)2] and 2) their less thermal stability compared to those having secondary or tertiary ammonium cations.

Six coordinate tris(catecholato)silicates of primary amine residues - Synthesis, characterization, and thermolysis studies

Room-temperature reactions of asymmetric phosphines, (Ph)(DCA)(R)P (R = Et2N-, Bu2nN-) with S4N4 in acetonitrile afforded phosphiniminocyclotrithiazenes, (Ph)(DCA)(R)P=N-S3N3 (R = Et2N-, I ; Bu2nN-, II) in modest yields (ca 50%). The heterocycles have been characterized by spectroscopic [IR, UV-vis, NMR (1H and 31P) and mass] and single crystal X-ray diffraction methods. Strikingly, the angle at P-N(4)-S(1) is 135° in I, the largest observed so far and is 119.3° in II. This is also accompanied by the shortest exocyclic S(1)-N(4) bond length of 1.537 Å observed in the case of I. In the unit cell of II, two types of molecules with slightly differing degree of deviation of the tricoordinate sulfur (0.664 and 0.673 Å from the mean plane [N(1)-S(2)-N(2)-S(3)-N(3)] are observed. Copyright © 1997 Elsevier Science Ltd.

Cyclic S-N compounds and phosphorus reagents-XV [1]. Synthesis, spectral and X-ray structural characterization of (Ph)(DCA)(R)P=N-S3N3 [R=(C2H5)2N-; (n-C4H9)2N-]

Room temperature reactions of both tris(catecholato)silicate, M2[Si(o-C6H4O2)3] {M=Na, Et3NH} and glycolato silicate, K2[Si2(O2C2H4)5] with PCl3, POCl3, SOCl2 and SO2Cl2 proceed exothermally and afford easy isolation of the corresponding cyclic derivatives of catechol/glycol (1-8) in high yield, exemplifying the merit of hypervalent silicon centres in synthesis. (Et3NH)2[Si(o-C6H4O2)3] afford near quantitative conversions.

Tetrahedron Letters

High yield synthesis of cyclic phosphites, phosphates, sulphites and sulphates of catechol and glycol mediated by hypervalent silicon centres

Inorganic Chemistry

Catecholate Complexes of Silicon: Synthesis and Molecular and Crystal Structures of [Si(cat)2].cntdot.2THF and Li2[Si(cat)3].cntdot.3.5dme (cat = Catecholate Dianion)

Science

5-Coordinate Si Compounds as Intermediates in the Synthesis of Silicates in Nonaqueous Media

Chemical Reviews

Reactivity of penta- and hexacoordinate silicon compounds and their role as reaction intermediates

Synthesis and characterization of tris(catecholato) silicates, [(C6H4O2)3Si]2− with different counter cations - first pyrolysis study and X-ray structure of [((CH3)2CH)2NH2]2[(C6H4O2)3Si] · 2CH3CN · H2O

Journal	Main Group Chemistry
ISSN	10241221
Open Access	No