A novel cyclic titanasiloxane derived from [Ph2Si(OH)]2O: synthesis and crystal structure of [Cp*Ti(Cl)(OSiPh2OSiPh2OSiPh2O)]

Synthesis and Reactivity of the First Isolated Hydrogen-Bridged Silanol-Silanolate Anions

We report on the first examples of isolated silanol–silanolate anions, obtained by utilizing weakly coordinating phosphazenium counterions. The silanolate anions were synthesized from the recently published phosphazenium hydroxide hydrate salt with siloxanes. The silanol–silanolate anions are postulated intermediates in the hydroxide‐mediated polymerization of aryl and alkyl siloxanes. The silanolate anions are strong nucleophiles because of the weakly coordinating character of the phosphazenium cation, which is perceptible in their activity in polysiloxane depolymerization.

Thermolabile Organotitanium Monoalkyl Phosphates: Synthesis, Structures, and Utility as Epoxidation Catalysts and Single-Source Precursors for TiP2O7

The reaction of [Cp*TiCl₃] (Cp* = C₅Me₅) with monoalkyl phosphates (RO)PO₃H₂ (R = Me, Et, and ⁱPr) in tetrahydrofuran (THF) at 25 °C leads to the formation of binuclear complexes [Cp*₂Ti₂(μ-O₂P(OH)OR)₂(μ-O₂P(O)OR)₂] [R = Me (1), Et (2), and ⁱPr (3)]. On the other hand, the reaction of ( ^tBuO)₂PO₂K with [Cp*TiCl₃] in acetonitrile or THF results in isolation of either the dinuclear [Cp*₂Ti₂(μ-O₂P(OH)O ^tBu)₂(μ-O₂P(O)O ^tBu)₂] (4) or the trinuclear titanophosphate [Cp*₃Ti₃(μ-O₃PO ^tBu)₂(μ-O)₂(μ-O₂P(O ^tBu)₂)] (5), respectively. The formation of compounds 4 and 5 is facilitated by partial hydrolysis of the tert-butoxy groups of ( ^tBuO)₂PO₂K. New titanophosphates 1-5 have been characterized by spectroscopic and analytical methods, and the molecular structures have further been confirmed by single-crystal X-ray diffraction studies. Thermal decomposition studies of 1-5 reveal the initial loss of thermally labile alkyl substituents of the organophosphate ligands, followed by the loss of C₅Me₅ groups to form an organic-free amorphous titanophosphate in the temperature range 300-500 °C. This material transforms to highly crystalline titanium pyrophosphate TiP₂O₇ at 800 °C. Compounds 1-5 and the TiP₂O₇ materials obtained at 300, 500, and 800 °C through the thermal decomposition of 3 have been employed as efficient homogeneous catalysts for the alkene epoxidation reaction. Using hydrogen peroxide as the oxidant in an acetonitrile medium, these catalysts exhibit >90% alkene conversion with >90% epoxide selectivity in 4 h at temperatures below 100 °C.

In situ generated polysiloxanes stabilizing μ3-oxo bridged Sb3 triangles

The reaction of RSbO3H2 with t-butylsilanetriol has led to the isolation of organoantimony(v) based molecular triangles stabilized by siloxane frameworks. Depending on the reaction conditions employed or the substituents present on the antimony atom, either a combination of a disiloxane and a tetrasiloxane framework or a trisiloxane framework was generated in situ leading to the stabilization of the Sb3 triangle.

Synthesis and characterization of complexes containing Ti–O–Si moieties. Catalytic activity in olefin epoxidation

Reaction of [Cp*TiMe3] with O(SiPh2OH)2 yields the titanium siloxide derivative [Cp*TiMe{(OSiPh2)2O}]. Complex reacts with H2O to yield the corresponding oxo-titanium derivative [(Cp*Ti{(OSiPh2)2O})2(micro-O)]. The molecular structure of complex has been established by X-ray diffraction. Complex reacts with triphenylsilanol to give the asymmetric titanium siloxide [Cp*Ti(OSiPh3){(OSiPh2)2O}]. Treatment of the dinuclear titanium compound [(Cp*TiCl2)2(micro-O)] with an equimolar amount of O(SiPh2OH)2 yields complex [(Cp*TiCl)2{micro-(OSiPh2)2O}(micro-O)] in which the disiloxide moiety is bridging two titanium atoms. The structure of has been determined by X-ray diffraction. Reaction of [Cp*TiMe3] with HOSiPh3 yields the titanium triphenylsiloxide [Cp*TiMe2(OSiPh3)]. Complex reacts with water to yield [{Cp*TiMe(OSiPh3)}2(micro-O)]. The triflate compound [Cp*Ti(OSiPh3)2(OTf)] can be prepared by reaction of with HOTf and triphenylsilanol. We have tested the catalytic activity of some of the complexes in the epoxidation of cyclohexene.

Trisilane-1,3-diolato Complexes of Ti and Zr: Syntheses and X-ray Crystal Structures

The syntheses and structures of zirconium and titanium complexes containing the novel chelating trisilane-1,3-diolate ligand [Me2Si(R2SiO)2]2- (R = SiMe3) (5)-H2 are reported. The chloride complexes [Me2Si(R2SiO)2]TiCl2 (7a) and [Me2Si(R2SiO)2]ZrCl2 x 2 THF (7b) were prepared by the reaction of MCl4 (M = Ti, Zr) with [Me2Si(R2SiO)2]2Ti (6a) and [Me2Si(R2SiO)2]2Zr (6b), which are derived from the reaction of 5 with M(NEt2)4, respectively. In the presence of TiCl4, complexes 6a and 7a undergo a ring-opening reaction to produce the dinuclear complex [Me2Si(R2SiO)2][TiCl3]2 (9). [Me2Si(R2SiO)2]TiMe2 (10) and [Me2Si(R2SiO)2]TiBnz2 (11) were prepared in moderate yields from reactions of 7a with 2 equiv of MeMgBr and BnzMgCl, respectively. According to NMR spectroscopic investigations, the reaction of the dimethyltitanium complex 10 with B(C6F5)3 led to full exchange of both methyl groups by C6F5 groups under quantitative formation of [Me2Si(R2SiO)2]Ti(C6F5)2 (12) and a mixture of B(C6F5)(3-n)Me(n), where n = 1-3. The structure of 12 is further evidenced by the preparation of an identical sample from the reaction of 7a with 2 equiv of C6F5MgBr. Refluxing an ether solution of 12 surprisingly gave [Me2Si(R2SiO)2]2TiC6F5]2O (13) as a result of ether cleavage. The structures of the complexes 7a, 7b, 9, 10, and 13 were determined by X-ray crystallography, and structural discussion of the bond parameters will be given.

Polyhedral Cobalt(II) and Iron(II) Siloxanes: Synthesis and X-ray Crystal Structure of [(RSi(OH)O2)Co(OPMe3)]4 and [(RSiO3)2(RSi(OH)O2)4(μ3-OH)2Fe8(THF)4] (R = (2,6-iPr2C6H3)N(SiMe3))

The cobalt(II) and iron(II) siloxane compounds were prepared by the reaction of lipophilic N-bonded silanetriol 1 with metal silylamides M[N(SiMe3)2]2 (M = Co (2), Fe (3)) in a 1:1 and 3:4 molar ratio, respectively. A plot of 1/chi versus temperature in the range of 2-300 K indicates the paramagnetic behavior of 2 and 3. The composition and molecular structures of 2 and 3 were fully determined by IR, elemental analysis, and X-ray crystal structural analyses. Compound 2 possesses a pseudo-4-fold (S4) symmetry, whereas 3 reveals an inversion center. Compound 2 represents a tetracobalt(II) drum while 3 exhibits an octairon(II) cage containing siloxane ligands.

Monomeric, Tetrameric, and Polymeric Copper Di-tert-butyl Phosphate Complexes Containing Pyridine Ancillary Ligands,

The reaction of di-tert-butyl phosphate (((t)BuO)(2)P(O)(OH), dtbp-H) with copper acetate in the presence of pyridine (py) and 2,4,6-trimethylpyridine (collidine) has been investigated. Copper acetate reacts with dtbp-H in a reaction medium containing pyridine, DMSO, THF, and CH(3)OH to yield a one-dimensional polymeric complex [Cu(dtbp)(2)(py)(2)(mu-OH(2))](n) (1) as blue hollow crystalline tubes. The copper atoms in 1 are octahedral and are surrounded by two terminal phosphate ligands, two pyridine molecules, and two bridging water molecules. The mu-OH(2) ligands that are present along the elongated Jahn-Teller axis are responsible for the formation of the one-dimensional polymeric structure. Recrystallization of 1 in a DMSO/THF/CH(3)OH mixture results in the reorganization of the polymer and its conversion to a more stable tetranuclear copper cluster [Cu(4)(mu(3)-OH)(2)(dtbp)(6)(py)(2)] (2) in about 60% yield. The molecular structure of 2 is made up of a tetranuclear core [Cu(4)(mu(3)-OH)(2)] which is surrounded by six bidentate bridging dtbp ligands. While two of the copper atoms are pentacoordinate with a tbp geometry, the other two copper atoms exhibit a pseudooctahedral geometry with five normal Cu-O bonds and an elongated Cu-O linkage. The pentacoordinate copper centers bear an axial pyridine ligand. The short Cu.Cu nonbonded distances in the tetranuclear core of 2 lead to magnetic ordering at low temperature with an antiferromagnetic coupling at approximately 20 K (J(P) = -44 cm(-1), J(c) = -66 cm(-1), g = 2.25, and rho = 0.8%). When the reaction between di-tert-butyl phosphate (dtbp-H) and copper acetate was carried out in the presence of collidine, large dark-blue crystals of monomeric copper complex [Cu(dtbp)(2)(collidine)(2)] (3) formed as the only product. A single-crystal X-ray diffraction study of 3 reveals a slightly distorted square-planar geometry around the copper atom. Thermogravimetric analysis of 1-3 revealed a facile decomposition of the coordinated ligands and dtbp to produce a copper phosphate material around 500 degrees C. An independent solid-state thermolysis of all the three complexes in bulk at 500-510 degrees C for 2 days produced copper pyrophosphate Cu(2)P(2)O(7) along with small quantities of Cu(PO(3))(2) as revealed by DR-UV spectroscopic and PXRD studies.

Reactivity studies, structural characterization, and thermolysis of cubic titanosiloxanes: precursors to titanosilicate materials which catalyze olefin epoxidation

The cubic titanosiloxane [RSiO(3)Ti(OPr(i))](4) (R = 2,6-Pr(2)(i)C(6)H(3)NSiMe(3)) (1) is found to be relatively inert in its attempted reactions with alcohols and other acidic hydrogen containing compounds. The reaction of 1 with silanol (Bu(t)O)(3)SiOH however proceeds over a period of approximately 3 months to result in the hydrolysis of (Bu(t)O)(3)SiOH and yield the transesterification product [RSiO(3)Ti(OBu(t))](4) (2) rather than the expected [RSiO(3)Ti(OSi(OBu(t))(3))](4). Products 1 and 2 have been characterized by elemental analysis, thermal analysis, and spectroscopic techniques (IR, EI-MS, and NMR). The solid-state structures of both 1 and 2 have been determined by single-crystal X-ray diffraction studies. Compounds 1 and 2 are isomorphous and crystallize in a cubic space group with a central cubic Ti(4)Si(4)O(12) core. Solid state thermolysis of 1 was carried at 450, 600, 800, 900, 1000, and 1200 degrees C in air, and the resulting titanosilicate materials 1a-f were characterized by spectroscopic (IR and DR UV), powder XRD, and electron microscopic methods. While, the presence of Ti-O-Si linkages appears to be dominant in the samples prepared at lower temperatures (450-800 degrees C), phase separation of anatase and rutile forms of TiO(2) occurs at temperatures above 900 degrees C as revealed by IR spectral and PXRD studies. The presence of octahedral titanium centers was observed by DR UV spectroscopy for the samples heated at higher temperatures. The use of new titanosilicate materials as catalysts for olefin epoxidation has been investigated. The titanosilicate materials produced at temperatures below 800 degrees C with a large number of Ti-O-Si linkages (or tetrahedral titanium centers) were found to be more active catalysts compared to the materials produced above 900 degrees C. The observed conversion in the epoxidation reactions was found to be somewhat low although the selectivity of the epoxide formation over the other possible oxidized products was found to be very good.

O–H Bond elongation in co-ordinated water through intramolecular PO⋯H–O bonding. ‘Snap-shots’ in phosphate ester hydrolysis

Molecular structure of [Cu(dtbp)2(phen)(OH2)] (dtbp-H = di-tert-butylphosphate, phen = 1,10-phenanthroline), determined at 293, 203 and 93 K, provides useful snap-shots of O-H bond activation of a metal-bound water, which is aided by an intramolecular P=O...H-O hydrogen bonding interaction.

Di-tert-butyl phosphate as synthon for metal phosphate materials via single-source coordination polymers [M(dtbp)(2)](n) (M = Mn, Cu) and [Cd(dtbp)(2)(H2O)](n) (dtbp-H = (tBuO)(2)P(O)OH)

Reaction of M(OAc)(2).xH(2)O (M = Mn, Cu, or Cd) with di-tert-butyl phosphate (dtbp-H) in a 1:2 molar ratio in methanol followed by slow crystallization of the resultant solid in MeOH/THF medium results in the formation of three new polymeric metal phosphates [M(dtbp)(2)](n)() [M = Mn, 1 (beige); M = Cu, 2 (blue)] and [Cd(dtbp)(2)(H(2)O)](n)(), 3 (colorless)] in good yields. The formation of [Mn(dtbp)(2)](n) (1) proceeds via tetrameric manganese phosphate [Mn(4)(O)(dtbp)(6)] (4), which has been isolated in an analytically pure form. Perfectly air- and moisture-stable compounds 1-4 were characterized with the aid of analytical, thermoanalytical, and spectroscopic techniques. The molecular structures of 1-3 were further established by single-crystal X-ray diffraction studies. Crystal data for 1: C(32)H(72)Mn(2)O(16)P(4), monoclinic, P2(1)/c, a = 19.957(4) A, b = 13.419(1) A, c = 18.083(2) A, beta = 91.25(2) degrees, Z = 4. Crystal data for 2: C(16)H(36)CuO(8)P(2), orthorhombic, Pccn, a = 23.777(2) A, b = 10.074(1) A, c = 10.090(1) A, Z = 4. Crystal data for 3: C(48)H(114)Cd(3)O(27)P(6), triclinic, P1, a = 12.689(3) A, b = 14.364(3) A, c = 22.491(5) A, alpha = 84.54(3) degrees, beta = 79.43(3) degrees, gamma = 70.03(3) degrees, Z = 2. The diffraction studies reveal three different structural forms for the three compounds investigated, each possessing a one-dimensional coordination polymeric structure. While alternating triple and single dtbp bridges are found between the adjacent Mn(2+) ions in 1, uniform double dtbp bridges across the adjacent Cu(2+) ions are present in 2. The cadmium ions in the structure of 3 are pentacoordinated. Thermal analysis (TGA and DSC) indicates that compounds 1-3 convert to the corresponding crystalline metaphosphate materials M(PO(3))(2), in each case at temperatures below 500 degrees C. Similarly, the thermal decomposition of 4 results in the formation of Mn(PO(3))(3) and Mn(2)P(2)O(7). The final materials obtained by independent thermal decomposition of bulk samples have been characterized using IR spectroscopic, powder diffraction, and N(2) adsorption studies.