Toluene-d8 Solution Research Articles

Direct Extraction of Sodium Hydroxide by Calix[4]pyrrole-Based Ion-Pair Receptors.

Described in this work are calix[4]pyrrole-based ion-pair receptors, cis/trans-1 and cis/trans-2, designed for the extraction of sodium hydroxide. An X-ray diffraction analysis of a single crystal of the cis-1·NaOH isomer isolated from a mixture of cis/trans-1 revealed a unique dimeric supramolecular structure. An average dimer in toluene-d8 solution was inferred on the basis of diffusion-ordered spectroscopy (DOSY). Support for the proposed stoichiometry came from density functional theory (DFT) calculations. The structural stability of the dimeric cis-1·NaOH complex in toluene solution was further confirmed by ab initio molecular dynamics (AIMD) simulation with explicit representation of solvent. Under conditions of liquid-liquid extraction (LLE), purified receptors cis- and trans-2 were both found to remove NaOH from a pH 11.01 aqueous source phase into toluene with extraction efficiencies (E%) of 50-60% when used equimolar to NaOH. However, in all cases, precipitation was observed. Complexities associated with precipitation could be avoided by immobilization of the receptors onto a chemically inert poly(styrene) resin by means of solvent impregnation. The use of solvent-impregnated resins (SIRs) eliminated precipitation in solution while retaining the extraction efficiency toward NaOH. This allowed both the pH and salinity of the alkaline source phase to be lowered.

Cooperative Binding in a Phosphine Oxide-Based Halogen Bonded Dimer Drives Supramolecular Oligomerization.

Triphenylphosphine oxide forms halogen-bonded (XB) complexes with pentafluoroiodobenzene and a 1,4-diaryl-5-iodotriazole. The stability of these complexes is assessed computationally and by 31P NMR spectroscopy in toluene-d8 solution, where both complexes are weakly associated. This knowledge is applied to the design and synthesis of two self-complementary phosphine oxide-iodotriazole hybrids that incorporate a phosphine oxide XB acceptor and a 1,4-diphenyl-5-iodotriazole XB donor within the same molecule. The self-complementary design of these modules facilitates their assembly in both toluene-d8 and, surprisingly, DCM-d2 into dimers, with significant stabilities, through the formation of halogen-bonded diads. The stability of these assemblies is a result of significant levels of cooperative binding that is present in both solvents. The connection of two of these hybrid units together, using a flexible spacer, facilitates the aggregation of these modules in DCM-d2 solution, through halogen bonding, forming oligomeric assemblies.

Synthesis of (Adamantylimido)vanadium(V) Dimethyl Complex Containing (2-Anilidomethyl)pyridine Ligand and Selected Reactions: Exploring the Oxidation State of the Catalytically Active Species in Ethylene Dimerization

V(NAd)Me2(L) [2a, L = 2-ArNCH2(C5H4N), Ar = 2,6-Me2C6H3], prepared from V(NAd)Cl2(L) (1) by reaction with LiMe (2.0 equiv), exhibited remarkable catalytic activities for ethylene dimerization in the presence of MAO affording 1-butene with high selectivity [TOF = 1 120 000–1 530 000 h–1 (311–425 s–1), C4′ = 97.1–98.4%], and the catalyst performances (activity, selectivity) were similar to those by the dichloride analogue (1) under the same conditions. The dimethyl complex (2a) reacted with 1.0 equiv of R′OH to yield the mono alkoxide complexes, V(NAd)Me(OR′)(L) [R′ = OC(CF3)3 (3a), OC(CH3)(CF3)2 (3b), OC(CH3)3 (3c)], and structures of these complexes (3a–c) and 2a were determined by X-ray crystallography. Reactions of 2a with [Ph3C][B(C6F5)4] in Et2O and 3c with B(C6F5)3 in THF afforded the corresponding cationic complexes confirmed by NMR spectra. Both NMR and V K-edge XANES analysis of the toluene or toluene-d8 solution of 1 and 2a did not show any significant changes in the oxidation state upon addition...

TMPZnN(SiMe3)2, [TMPZn(μ-OiPr)]2 and TMPZn[OCMe2C(O)OEt]. Their role in the ring-opening of rac-lactide and ε-caprolactone where TMP = 1,5,9-trimesityldipyrromethene

From the reaction between Zn[N(SiMe3)2]2 and TMP-H (1 equiv.) in toluene at room temperature TMPZn[N(SiMe3)2] was prepared and subsequently reacted with PriOH (1 equiv.) and HOCMe2C(O)OEt (1 equiv.) to give [TMPZn(μ-OPri)]2 and TMPZn[OCMe2C(O)OEt], respectively. The three compounds were each crystallized and characterized by single crystal X-ray diffraction. The compound TMPZn[N(SiMe3)2] was a three coordinated N3Zn compound with an anagostic N(SiMe3)2 ligand where one SiMe3 was annexed to the Zn2+ ion. The compound [TMPZn(μ-OPri)]2 has a molecular C2 axis and is dimeric in toluene-d8 solution having a N2ZnO2 core for each Zn2+ ion. In TMPZn[OCMe2C(O)OEt] compound the Zn2 + ion is four-coordinated. This too is present in solution (IR) and also present in toluene-d8 and THF where there is evidence of fluxionality with Tc ∼15 °C and −85 °C, respectively. The compound [TMPZn(μ-OPri)]2 polymerizes both ε-caprolactone (ε-CL) and rac-lactide (rac-LA) to give polycaprolactone (PCL) and polylactic acid (PLA), respectively. The rate of the reactions are ε-CL > LA and are influenced by the nature of solvent, THF > CD2Cl2/CH2Cl2. The nature of PLA derived from rac-LA is heterotactic: Pr = 0.96 in THF and Pr = 0.75 in CD2Cl2/CH2Cl2. In the copolymerization of rac-LA: ε-CL by both [TMPZn(μ-OPri)]2 and TMPZn[OCMe2C(O)OEt] only PLA is produced, PCL is not formed.

Steric Effects in Reactions of Decamethyltitanocene Hydride with Internal Alkynes, Conjugated Diynes, and Conjugated Dienes

Titanocene hydride [Cp*2TiH] (Cp* = η5-C5Me5) (1) readily inserts simple internal alkynes R1C≡CR2 into its Ti–H bond, yielding titanocene alkenyl Ti(III) compounds of two structural types. The less sterically congested products [Cp*2Ti(R1C═CHR2)] (2a–e) contain a σ1-bonded alkenyl group, whereas the products bearing at least one trimethylsilyl substituent and other bulky substituents (R1 = SiMe3; R2 = SiMe3, 4a; CMe3, 4b; and Ph, 4c) possess a remarkable Ti–H agostic bond of the σ1-bonded alkenyl group. This feature is consistent with solution EPR spectra of 4a–4c showing a doublet due to coupling of the hydrogen nucleus with the Ti(III) d1 electron. Compound 1 reacts with one molar equivalent of conjugated buta-1,3-diynes (RC≡C)2 to give η3-butenyne complexes (R = SiMe3, 5a; CMe3, 5b). The Ti(III) complexes 2a–2e and 5a and 5b were oxidatively chlorinated with PbCl2 to give Ti(IV) chloro-alkenyl complexes [Cp*2TiCl(R1C═CHR2)] 3a–3e and chloro-alkenynes 6a and 6b, respectively. 1H and 13C NMR spectra of 3a–3e and 6a and 6b revealed that these compounds form equilibria of two atropisomers differing by the anti- and syn-position of the chlorine and the alkenyl hydrogen atoms. Such atropisomers are denoted by appended (a) and (b), respectively. Compound 1 reacted with 1,3-butadiene to give a thermally stable π-bonded 1-methylallyl complex (7) and with penta-1,3-diene to give a thermally labile 1,3-dimethylallyl complex (8). In toluene-d8 solutions 7 dissociated at 80 °C and 8 at room temperature to give [Cp*Ti(C5Me4CH2)] and corresponding alkenes. Other methyl-substituted dienes, isoprene, 4-methylpenta-1,3-diene, and 2,3-dimethylbuta-1,3-diene, did not yield observable π-bonded allyl products; the dienes were, however, hydrogenated to olefins with concomitant formation of [Cp*Ti(C5Me4CH2)]. Compound 1 was shown to catalyze the hydrogenation of the alkynes and dienes to olefins and ultimately to alkanes under lower than atmospheric hydrogen pressure at room temperature. Single-crystal structures were determined for 3d(a), 3e(a), 4a–4c, 5a, 6b, and 7.

A Nuclear Magnetic Resonance Study of the Binding of Trimethylphosphine Selenide to Cadmium Oleate

We report an NMR study on the binding of trimethylphosphine selenide (Se═PMe3) to cadmium oleate (Cd(OA)2) in CDCl3 and toluene-d8. At room temperature in CDCl3, Se═PMe3 binds to Cd(OA) 2 in 1:1 ratio with a binding constant of 20 ± 3 as determined by NMR titration. The Cd-bound and free Se═PMe3 are in fast exchange on the NMR time scale at room temperature and gives only one (31)P NMR peak. At ca. 190 K, three (31)P NMR peaks were observed for a toluene-d8 solution of 1:1 mixture of Cd(OA)2 and Se═PMe3. These three peaks were tentatively assigned to free Se═PMe3 (9.0 ppm), 1:1 (19.5 ppm), and 2:1 complex between Se═PMe3 and Cd(OA)2 (18.8 ppm).

Mixed Aggregates of an Alkyl Lithium Reagent and a Chiral Lithium Amide Derived from N-Ethyl-O-triisopropylsilyl Valinol

The crystal structure of a mixed aggregate containing lithiated (S)-N-ethyl-3-methyl-1-(triisopropylsilyloxy)butan-2-amine derived from (S)-valinol and cyclopentyllithium is determined by X-ray diffraction. The mixed aggregate adopts a ladder structure in the solid state. The ladder-type mixed aggregate is also the major species in a toluene-d8 solution containing an approximately 1:1 molar ratio of the lithiated chiral amide to cyclopentyllithium. A variety of NMR experiments including diffusion-ordered NMR spectroscopy (DOSY) with diffusion coefficient-formula (D-FW) weight correlation analyses and other one- and two-dimensional NMR techniques allowed us to characterize the complex in solution. Solution state structures of the mixed aggregates of n-butyl, sec-butyllithium, isopropyllithium with lithiated (S)-N-ethyl-3-methyl-1-(triisopropylsilyloxy)butan-2-amine are also reported. Identical dimeric, ladder-type, mixed aggregates are the major species at a stoichiometric ratio of 1:1 lithium chiral amide to alkyllithium in toluene-d8 solution for all of the different alkyllithium reagents.

Carbazole-bis(oxazolines) as Monoanionic, Tridentate Chelates in Lanthanide Chemistry: Synthesis and Structural Studies of Thermally Robust and Kinetically Stable Dialkyl and Dichloride Complexes.

The carbazole-bis(oxazoline) ligand 1,8-bis(4′,4′-dimethyloxazolin-2′-yl)-3,6-di-tert-butylcarbazole (H-Czx, 14) was prepared and reacted with Ln(CH2SiMe3)3(THF)2 to afford the five-coordinate dialkyl complexes (Czx)Ln(CH2SiMe3)2 (Ln = Y, 15; Er, 16; Yb, 17) in high yield. Deprotonation of 14 with NaN(SiMe3)2, followed by reaction with LnCl3(THF)x, affords the six-coordinate dichloride complexes cis,mer-(Czx)Ln(Cl)2(THF) (Ln = Y, 18; Er, 19; Yb, 20). Dialkyl complexes 15–17 were also prepared by reaction of the dichloride complexes 18–20, respectively, with 2 equiv of LiCH2SiMe3. Complexes 16–20 were characterized by X-ray crystallography. The dialkyl complexes 16 and 17 display a five-coordinate trigonal-bipyramidal geometry with the Czx ligand spanning both axial and one equatorial site with the CH2SiMe3 rotated such that the SiMe3 groups sit over the carbazole ring system. The solution structure for 15–20 was found to be consistent with that in the solid state by NMR spectroscopy. However, paramagnetic dichloride 20 was shown by variable-temperature 1H NMR studies to undergo rapid THF exchange by a dissociative process in toluene-d8 solution (ΔH‡ = 98 ± 10 kJ mol–1, ΔS‡ = +185 ± 25 J mol–1 K–1). Treatment of dialkyl 18 with [Ph3C]+[B(C6F5)4]− cleanly produces the alkyl cation [(Czx)Y(CH2SiMe3)]+[B(C6F5)4]− (21) by 1H NMR spectroscopy, but this species does not insert 2,3-dimethylbutadiene.

Kinetics and Thermodynamics of the Monomer−Dimer Equilibria of Dialkoxydibutylstannanes

Enthalpies and entropies of dimerization have been determined as functions of concentration for dibutyltin dipropoxide, dibutyltin dibutoxide, and dibutyltin diisopropoxide in toluene-d8 and cyclohexane-d12 solutions from the variation in 119Sn NMR chemical shifts with temperature. The values of ΔH and ΔS obtained in toluene-d8 for dibutyltin dibutoxide were −69.5 ± 3.0 kJ mol−1 and −197 ± 10 J mol−1 K−1, respectively, and for dibutyltin diisopropoxide −67.1 ± 1.4 kJ mol−1 and −244 ± 9 J mol−1 K−1, respectively. Enthalpies and entropies of activation for this process for dibutyltin diisopropoxide have been derived by simulation of the temperature-dependent broadening of the 119Sn NMR spectra. The free energy of activation for dimerization was 33 kJ mol−1. The same thermodynamic parameters for a greater range of dibutyltin dialkoxides were derived theoretically by using MP2 single-point calculations on B3LYP-optimized geometries using the LANL2DZdp basis set with diffuse and polarization functions and its effective core potential for tin and 6-311G(2d,p)//6-31G(d,p) for other atoms. Quite good agreement with the experimental results was achieved with this level of theory. The present study confirms that steric effects dictate the degree of dimerization for dibutyltin dialkoxides, with monomers becoming favored at room temperature when the alkoxide groups are changed from primary to secondary.

ChemInform Abstract: Atropisomerism in Doubly peri-Substituted 9-(2-Methylbenzyl)triptycene Derivatives, 8-Chloro- and 8-Bromo-1,4-dimethyl-9-(2-methylbenzyl) triptycenes.

The 13C dynamic NMR study revealed that 9-(2-methylbenzyl)triptycene has an energy barrier to gear rotation of 11.8 kcal mol−1 (1 cal = 4.184 J). Introduction of substituents at two of the peri-positions was expected to raise the barrier enough for atropisomerism to be realized in this system. Actually, two stable rotational isomers, ap and sc*(9S*), were separately isolated for 8-chloro- (7) and 8-bromo-1,4-dimethyl-9-(2-methylbenzyl)triptycene (8). Classical kinetic studies in toluene-d8 solutions revealed that the isomerization barriers (ΔG≠ at 350 K) are 26.4 and 27.2 kcal mol−1 for 7 and 8, respectively. Isomerization pathways were investigated by molecular mechanics calculations, which suggested that gear rotational pathway was favored. In either compound, the sc* (9S*) rotamer was found to thermally isomerize to the ap rotamer in the solid state. X-Ray crystallographic analysis of the rotameric crystals showed that the rotamers had different crystal structures and thus the crystal would be destroye...

Bis(pyridyl)siloxane Oligomeric Ligands for Palladium(II) Acetate: Synthesis and Binding Properties

The complexation of a series of new bis(meta-pyridyl)methylsiloxane ligands with palladium(II) acetate in dilute toluene-d8 solution was studied by 1H NMR at 233−363 K, measuring the binding affinity and ring−chain distribution as a function of ligand structure, temperature, and concentration. Significant differences in the ring distribution and Pd binding affinity were observed as a function of siloxane chain length, with hexa- and heptasiloxane spacers binding Pd most effectively. The 1H NMR resonance of the singlet ortho aromatic proton was shifted unusually far downfield for the bidentate complex; the effect was strongest for the shortest chains and disappeared for chains with 10 or more siloxane units. Fitting the experimental data to a modified Jacobson−Stockmayer model demonstrated that the bidentate bis(pyridyl)siloxane complexes function as chelates in the concentration range 1−10 mM. Variable-temperature studies showed that all of the observed cyclic coordination oligomers are strainless. Theref...

Reversible Neutral Dissociation of the N−Si Dative Bond in Hexacoordinate Hydrido Complexes of Silicon

Hexacoordinate silicon dichelates with hydrido and methyl monodentate ligands were prepared by transsilylation. The temperature-dependent 29Si NMR spectra of toluene-d8 or CDCl3 solutions provide evidence for a reversible, neutral dissociation of the dative N−Si bond, accompanied by a shift of the 29Si resonance from high field (hexacoordinate) to lower field (pentacoordinate) with increasing temperature. When a phenyl group is attached directly to silicon (replacing methyl), the N−Si dissociation is prevented, presumably due to electron withdrawal by the phenyl. Two of the silicon complexes were characterized by crystallographic analysis. Quantum chemical calculations at the RB3LYP/6-31G(d) level confirm the stability of an N−Si dissociated species (1.03 kcal mol−1 lower in energy than the hexacoordinate dichelate) and rule out the alternative possibility of an O−Si zwitterionic dissociation, thus supporting the mechanism suggested by the experimental results.

Metal Fluorides Form Strong Hydrogen Bonds and Halogen Bonds: Measuring Interaction Enthalpies and Entropies in Solution

The organometallic compound trans-(tetrafluoropyrid-2-yl)bis(triethylphosphine)-fluoronickel(II) (NiF) is shown to serve as a strong hydrogen bond and halogen bond acceptor in solution via intermolecular interactions with the fluoride ligand. The nature of the interactions has been confirmed by multinuclear NMR spectroscopy. Experimental binding constants, enthalpies, and entropies of interaction with hydrogen-bond-donor indole and halogen-bond-donor iodopentafluorobenzene have been determined by 19F NMR titration. In toluene-d8 solution indole forms a 1:1 and 2:1 complex with NiF (K1 = 57.9(3), K2 = 0.58(4)). Interaction enthalpies and entropies are -23.4(2) kJ mol-1 and -44.5(8) J mol-1 K-1, respectively, for the 1:1 complex; -14.8(8) kJ mol-1 and -53(3) J mol-1 K-1, respectively, for the 2:1 complex. In toluene-d8 solution iodopentafluorobenzene forms only a 1:1 complex (K1 = 3.41(9)) with enthalpy and entropy of interaction of -16(1) kJ mol-1 and -42(4) J mol-1 K-1, respectively. A marked solvent effect was observed for the halogen bond interaction. NMR titrations in heptane solution indicated formation of both 1:1 and 2:1 complexes of iodopentafluorobenzene with NiF (K1 = 21.8(2), K2 = 0.22(4)). Interaction enthalpies and entropies are -26(1) kJ mol-1 and -63(4) J mol-1 K-1, respectively, for the 1:1 complex; -21(1) kJ mol-1 and -83(5) J mol-1 K-1, respectively, for the 2:1 complex. There is a paucity of such experimental energetic data particularly for halogen bonds despite substantial structural data. These measurements demonstrate that halogen bonds are competitive with hydrogen bonds as intermolecular interactions and provide a suitable benchmark for theoretical calculations and quantitative input into design efforts in supramolecular chemistry and crystal engineering.

Study of Molecular Structures and Properties of Europium(III) Complexes with Phosphine Oxides by NMR Analysis

The 31P-NMR spectra of europium complexes with β-diketones and phosphine oxides in CDCl3, DMSO-d6, toluene-d8 with dissolved fluorinated polymers, and fluorinated solvent were investigated as well as the temperature dependence of these spectra. When a mixture of europium complex 1 and 1.0 molar equivalent of trioctylphosphine oxide and triphenylphosphine oxide was dissolved in a fluorinated solvent, europium complex 2 with two types of phosphine oxides was formed at room temperature. In CDCl3 and toluene-d8 solutions, however, this complex was identified only at low temperatures. This difference is thought to be due to the differences in the speed of ligand exchanges. In DMSO-d6 solution, no signal corresponding to the europium complex with phosphine oxides was observed. This implies that the major portion of phosphine oxides is not coordinated with europium ions in DMSO-d6 solution. The fluorescence intensity of each europium complex in a solvent was correlated to the solvent and the 31P-NMR spectrum. It was found that the fluorescence intensity was the highest in the fluorinated solvent.

Discrete bridging and terminal copper carbenes in copper-catalyzed cyclopropanation.

The Cu(I) beta-diketiminate [Me2NN]Cu(eta2-ethylene) (2) catalyzes the cyclopropanation of styrene with N2CPh2 to give 1,1,2-triphenylcyclopropane in 67% yield. Addition of N2CPh2 to 2 equiv of 2 allows for the isolation of the dicopper carbene [[Me2NN]Cu]2(mu-CPh2) (3) in which the diphenylcarbene moiety is symmetrically bound between two [Me2NN]Cu fragments (Cu-C = 1.922(4) and 1.930(4) A) with a Cu-Cu separation of 2.4635(7) A. In toluene-d8 solution, 3 reversibly dissociates a [Me2NN]Cu fragment to give [Me2NN]Cu(toluene) and the terminal carbene [Me2NN]Cu=CPh2. Dicopper carbene 3 reacts with 3 equiv of styrene to give 1,1,2-triphenylcyclopropane and 2 equiv of [Me2NN]Cu(eta2-styrene) within minutes. DFT studies with simplified ligands indicate a stronger Cu-C pi-back-bonding interaction from two Cu(I) centers to the carbene acceptor orbital in a dicopper carbene than that present in a monocopper carbene. Nonetheless, the terminal carbene [Me3NN]Cu=CPh2 (8) that possesses a p-methyl group on each beta-diketiminato N-aryl ring may be isolated and exhibits a shortened Cu-C distance of 1.834(3) A. The stoichiometric cyclopropanation of styrene by 8 in 1,4-dioxane is first-order in both copper carbene 8 and styrene with activation parameters DeltaH = 10.4(3) kcal/mol and DeltaS = -32.3(9) cal/mol.K. In 1,4-dioxane, 8 decomposes to Ph2C=CPh2 via first-order kinetics with activation parameters DeltaH = 21(1) kcal/mol and DeltaS = -8(3) cal/mol.K. Arene solutions of thermally sensitive terminal carbene 8 decompose to [Me3NN]Cu(arene), which reacts with 8 still present in solution to give the more thermally stable [[Me3NN]Cu]2(mu-CPh2).

Activation of C(sp2)−H and Reduction of CE (E = CH, N) Bonds with an Osmium-Hexahydride Complex: Influence of E on the Behavior of RCHE-py Substrates

The hexahydride complex OsH6(PiPr3)2 (1) reacts with 2-vinylpyridine to give the trihydride derivative (2). The β- and γ-positions of the pyridine ring are quantitatively and selectively deuterated by addition of 1 (5%) to toluene-d8 and benzene-d6 solutions of 2. Under hydrogen atmosphere, 2 reacts with HBF4·OEt2 to afford [HNC5H4-o-Et]BF4 and regenerate 1. Under argon atmosphere, the addition of HBF4·OEt2 to dichloromethane solutions of 2 leads to the hydride-dihydrogen (3), which catalyzes the hydrogenation of 2-vinylpyridine to 2-ethylpyridine. In dichloromethane 3 evolves into the neutral chloro-dihydrogen compound (4). Complex 1 also reacts with N-methylene-2-pyridinamine and (E)-N-(phenylmethylene)-2-pyridinamine. The reaction with the first pyridinamine leads to a 3:1 mixture of the trihydride complexes (5) and (6), while the reaction with the second one selectively affords (7). Similarly to 2, the addition of 1 (5%) to toluene-d8 and benzene-d6 solutions of 6 produces the quantitative and selective deuteration of the β- and γ-positions of the pyridine ring. The addition of HBF4·OEt2 to diethyl ether solutions of 5 leads to (8). Isotope labeling experiments suggest that the reduction of the CC double bond of 2-vinylpyridine takes place by concerted addition of a dihydrogen ligand, while the reduction of the CN double bond of N-methylene-2-pyridinamine occurs by sequential addition of H- and H+. In solution the hydride ligands of these compounds undergo two different site exchange processes. Their activation parameters have been calculated by 1H NMR spectroscopy. Complexes 2, 3, and 5 have been characterized by X-ray diffraction analyses.

Synthesis, Structure, and Unusual Reactivity of the First Norbornene Carbonyl Complexes of Tungsten

Two new norbornene complexes of tungsten(0), W(CO)5(η2-C7H10) (1) and trans-W(CO)4(η2-C7H10)2 (2), have been obtained and characterized by IR and NMR spectroscopy, and initial studies of their reactivity are reported here. The molecular structure of compound 1, relatively unstable in solution, was established by single-crystal X-ray diffraction studies. Complex 1 can, depending on reaction conditions, give rise to different types of reactions: in a pure polychloromethane solution, it transforms to a species initiating the ring-opening metathesis polymerization of norbornene (ROMP), whereas in the presence of alcohol (ca. 1%), it leads to catalytic C−C bond formation with selective addition of polychloromethane to the olefinic bond of norbornene. The two-electron chemical oxidation of stable trans-W(CO)4(η2-C7H10)2 (2) by SnCl4 gives a very labile norbornene complex of tungsten(II) (3). The latter compound decomposes in CDCl3 solution to give chloronorbornane, whereas in benzene-d6 or toluene-d8 solution ...

New Tris(tert-butoxy)siloxy Complexes of Aluminum and Their Transformation to Homogeneous Aluminosilicate Materials via Low-Temperature Thermolytic Pathways

The new tris(tert-butoxy)siloxy complexes of aluminum, Al[OSi(OtBu)3]3(THF) (1), Al[OSi(OtBu)3]3(HOiPr)·0.5[Al(OiPr)3]4 (2), and [(iPrO)2AlOSi(OtBu)3]2 (3), were synthesized. Compounds 2 and 3 were structurally characterized by single-crystal X-ray crystallography. Thermolysis of a toluene-d8 solution containing 1 and 0.5 equiv of [Al(OiPr)3]4 resulted in the formation of 3 and free THF (by 1H NMR spectroscopy). The low-temperature decompositions of 1, 2, and 3 allowed for their use as single-source precursors to high surface area aluminosilicate xerogels via solution (toluene) thermolyses. The DSC traces of the xerogels derived from the 1:1 Al/Si precursors (2 and 3) exhibited sharp exothermic transitions at ≈1000 °C, attributed to the crystallization of mullite, with that for the xerogel from 3 having a larger associated heat flow. The DSC trace of the xerogel derived from 1 exhibited a weak exothermic transition at a slightly higher temperature. Although these xerogels have similar 27Al MAS NMR spectra, their microstructures appear to be quite different, as indicated by the substantially more efficient transformation to mullite (by PXRD) of the xerogel from 2. All of the xerogels are homogeneous; however, the microstructure of the xerogel from 2 appears to more closely resemble that of mullite, given the enhanced formation of mullite (by PXRD) and the reduced free energy difference associated with mullite formation (by DSC). Acidity measurements characterized the Lewis/Brønsted site ratios as 1.2, 1.6, and 1.0 for the xerogels from 1, 2, and 3, respectively.

Structure and molecular lability of N-(thio)phosphoryl(thio)amides: XL. Interpretation of the N-benzoyl(acetyl)amidothiophosphate→ N-thiobenzoyl(acetyl)amidophosphate rearrangement by means of 1H, 13C, and 31P NMR spectroscopy

The N-benzoyl(acetyl)amidothiophosphate→N-thiobenzoyl(acetyl)amidophosphate in CCl4 and toluene-d8 solutions was studied by means of 1H, 13C, and 31P NMR spectroscopy. The transformation of one amide form to the other is accompanied by intramolecular migrations of the amide proton and (thio)phosphoryl group and is a complex equilibrium of two dynamic systems.

1H and 19F NMR Investigation of the Reaction of B(C6F5)3 with Water in Toluene Solution

Titrations of B(C6F5)3 (1) with water, in toluene-d8 solution, monitored by 19F and 1H NMR at 196 K, showed first the formation of the adduct [(C6F5)3B(OH2)] (2) and then its stepwise transformation into the two aqua species [(C6F5)3B(OH2)]·H2O (3) and [(C6F5)3B(OH2)]·2H2O (4) containing, respectively, one or two water molecules hydrogen-bonded to the protons of the B-bound water molecule. The NMR data show that in each titration step only two species were present in significant concentration: 1 and 2 up to 1 equiv, 2 and 3 between 1 and 2 equiv, 3 and 4 between 2 and 3 equiv. Above 3 equiv the solutions rapidly attained saturation and phase separation occurred (although there was evidence of interaction of 4 with more water molecules). Titrations at room temperature indicated an analogous stepwise course. Variable-temperature experiments demonstrated water exchange between the different aqua species and between the different water sites in the adducts 3 and 4 (“internal” or B-bound and “external” or H-bound). The rate of these processes increased with the amount of water bonded to B(C6F5)3. The exchange of B-bound water among the different B(C6F5)3 molecules (resulting in the 1 ⇔ 2 interconversion) caused the averaging of the 19F resonances of 1 and 2, above 273 K. Band shape analysis in the temperature range 235−312 K provided the kinetic constants, whose dependence on the concentration revealed a dissociative mechanism (ΔH⧧ 67(2) kJ mol-1, ΔS⧧ 58(7) J mol-1 K-1). For the adduct [(C6F5)3B(OH2)]·H2O (3), four different dynamic processes have been recognized: (i) the exchange of H-bound water among different [(C6F5)3B(OH2)] adducts (the 2 ⇔ 3 exchange) or (ii) among different [(C6F5)3B(OH2)].H2O adducts (the 3 ⇔ 4 exchange), (iii) the exchange between H-bound and B-bound water, (iv) the hopping of H-bound water between the two protons of B-bound water. This process was so fast that an averaged signal for the protons of internal water was observed even at 187 K. The rate of the process (i) increased with the concentration of 2, so that separate 19F and 1H signals for 2 and 3 were observed only in very dilute solutions at the lowest temperatures. Linear plots of the kinetic constants (estimated from 1H NMR spectra in the near fast exchange region, temperature range 188−214 K) vs the concentration of 2 allowed the estimation of the constant for the dissociative pathway (4 orders of magnitude faster than for the exchange of B-bound water) and for the bimolecular pathway [ΔH⧧ 30(2) kJ mol-1, ΔS⧧ 3(10) J mol-1 K-1]. Process (ii) was too fast on the NMR time scale to allow any kinetic investigation. Process (iii) caused the parallel broadening of both the 1H signals of 3 at T > 225 K, with a rate quite close to that of the dissociative exchange of water among different B(C6F5)3 molecules. The activation parameters (ΔH⧧ 55(2) kJ mol-1, ΔS⧧ 7(3) J mol-1 K-1, temperature range 233−273 K) allowed no discrimination between the exchange of an entire water molecule and the mere exchange of protons. Even small amounts of 4 accelerated process (iii), due to the occurrence of two much faster processes: the 3 ⇔ 4 exchange and the exchange between the protons of internal and external water in 4. The study of any kind of water mobility concerning the trihydrate 4 was prevented by the occurrence of proton exchange processes (so fast as to broaden the signals of internal and external water even at 188 K), possibly favored by the acidic dissociation of the protons of the B-bonded water molecule of 4.