New synthetic route to polyphosphine ligands bearing 1,2,4,5-tetrakis(phosphino)benzene framework: structural characterizations of 1,4-(PPh2)2-2,5-(PR2)2-C6F2 (R = Ph, Pr, Et)

Reactions of 1,4-dibromo-2,5-difluorobenzene with two equivalents of lithium diisopropylamide at low temperature (T < −90 °C) followed by a quench with a slight excess of ClPPh₂ afford 1,4-dibromo-2,5-bis(diphenylphosphino)-3,6-difluorobenzene (1) in good yields. Reacting 1 with two equivalents of BuLi followed by a quench with a slight excess of ClPR₂ yield novel 1,2,4,5-tetrakis(phosphino)-3,6-difluorobenzenes 1,4-(PPh₂)₂-2,5-(PR₂)₂-C₆F₂ (R = Ph (2a); R = ⁱPr (2b); R = Et (2c)) in moderate yields. Compounds 1 and 2a-c were characterized by multinuclear NMR spectroscopy and elemental analyses. In addition, molecular structures of 2a-c have been determined by single crystal X-ray crystallography. Phosphorus atoms of PPh₂/PR₂ substituents in 2a-c are displaced from the plane of the central phenyl ring due to steric interactions with neighboring groups.     

Dimeric and trimeric diorganosilicon chalcogenides (PhRSiE)2,3 (E = S, Se, Te; R = Ph, Me)

Ph₂SiCl₂ and PhMeSiCl₂ react with Li₂E (E = S, Se, Te) under formation of trimeric diorganosilicon chalcogenides (PhRSiE)₃ (R = Ph: 1a-3a, R = Me: cis/trans-4a (E = S), cis/trans-5a (E = Se)). In case of E = S, Se dimeric four-membered ring compounds (PhRSiE)₂ (R = Ph: 1b-2b, R = Me: cis/trans-4b (E = S), cis/trans-5b (E = Se)) have been observed as by-products. 1a-5b have been characterized by multinuclear NMR spectroscopy (¹H, ¹³C, ²⁹Si, ⁷⁷Se, ¹²⁵Te). Four- and six-membered ring compounds differ significantly in ²⁹Si and ⁷⁷Se chemical shifts as well as in the value of ¹J_SiSe.The molecular structures of 2a, 3a and trans-5a reported in this paper are the first examples of compounds with unfused six-membered rings Si₃E₃ (E = Se, Te). The Si₃E₃ rings adopt twisted boat conformations. The crystal structure of 3a reveals an intermolecular Te-Te contact of 3.858 Å which yields a dimerization in the solid state.     

Substituted lithiumtrimethylsiloxysilanides LiSiRR′(OSiMe3) - Investigations of their synthesis, stability and reactivity

The reactions of the trimethylsiloxychlorosilanes (Me₃SiO)RR′SiCl (1a-h: R′ = Ph, 1a: R = H, 1b: R = Me, 1c: R = Et, 1d: R = ⁱPr, 1e: R = ^tBu, 1f: R = Ph, 1g: R = 2,4,6-Me₃C₆H₂ (Mes), 1h: R = 2,4,6-(Me₂CH)₃C₆H₂ (Tip); 1i: R = R′ = Mes) with lithium metal in tetrahydrofuran (THF) at −78 °C and in a mixture of THF/diethyl ether/n-pentane in a volume ratio 4:1:1 at −110 °C lead to mixtures of numerous compounds. Dependent on the substituents silyllithium derivatives (Me₃SiO)RR′SiLi (2b-i), Me₃SiO(RR′Si)₂Li (3a-g), Me₃SiRR′SiLi (4a-h), (LiO)RR′SiLi (12e, 12g-i), trisiloxanes (Me₃SiO)₂SiRR′ (5a-i) and trimethylsiloxydisilanes (6f^∗, 6h^∗, 6i^∗) are formed. All silyllithium compounds were trapped with Me₃SiCl or HMe₂SiCl resulting in the following products: (Me₃SiO)RR′SiSiMe₂R″ (6b-i: R″ = Me, 7c-i: R″ = H), Me₃SiO(RR′Si)₂SiMe₂R″ (8a-g: R″ = Me, 9a-g: R″ = H), Me₃SiRR′SiSiMe₂R″ (10a-h: R″ = Me, 11a-h: R″ = H) and (HMe₂SiO)RR′SiSiMe₂H (13e, 13g-i). The stability of trimethylsiloxysilyllithiums 2 depends on the substituents and on the temperature. (Me₃SiO)Mes₂SiLi (2i) is the most stable compound due to the high steric shielding of the silicon centre. The trimethylsiloxysilyllithiums 2a-g undergo partially self-condensation to afford the corresponding trimethylsiloxydisilanyllithiums Me₃SiO(RR′Si)₂Li (3a-g). (Me₃)Si-O bond cleavage was observed for 2e and 2g-i. The relatively stable trimethylsiloxysilyllithiums 2f, 2g and 2i react with n-butyllithium under nucleophilic butylation to give the n-butyl-substituted silyllithiums ⁿBuRR′SiLi (15g, 15f, 15i), which were trapped with Me₃SiCl. By reaction of 2g and 2i with 2,3-dimethylbuta-1,3-diene the corresponding 1,1-diarylsilacyclopentenes 17g and 17i are obtained.X-ray studies of 17g revealed a folded silacyclopentene ring with the silicon atom located 0.5 Å above the mean plane formed by the four carbon ring atoms.     

Chemically modified oximato complexes of titanium(IV) isopropoxide as new precursors for the sol-gel preparation of nano-sized titania: Crystal and molecular structure of [Ti{ONC10H16}4·2CH2Cl2]

Reactions of [Ti(OPrⁱ)₄] with various oximes, in anhydrous refluxing benzene yielded complexes of the type [Ti{OPrⁱ}_4−n{L}_n], where, n = 1-4 and LH = (CH₃)₂CNOH (1-4), C₉H₁₆CNOH (5-8) and C₉H₁₈CNOH (9-12). The compounds were characterized by elemental analyses, molecular weight measurements, FAB-mass, FT-IR and NMR (¹H, ¹³C{¹H}) spectral studies. The FAB-mass spectra of mono- (1), and di- (2), (6), (10) substituted products indicate their dimeric nature and that of tri- (3) and tetra- (4), (8) substituted derivatives suggest their monomeric nature. Crystal and molecular structure of [Ti{ONC₁₀H₁₆}₄·2CH₂Cl₂] (8A) suggests that the oximato ligands bind the metal in a dihapto η²-(N, O) manner, leading to the formation of an eight coordinated species. Thermogravimetric curves of (3), (6) and (10) exhibit multi-step decomposition with the formation of TiO₂ as the final product in each case, at 900 °C. Low temperature (∼600 °C) sol-gel transformations of (2), (3), (4), (6), (7) and (8) yielded nano-sized titania (a), (b), (c), (d), (e) and (f), respectively. Formation of anatase phase in all the titania samples was confirmed by powder XRD patterns, FT-IR and Raman spectroscopy. SEM images of (a), (b), (c), (d), (e) and (f) exhibit formation of nano-grains with agglomer like surface morphologies. Compositions of all the titania samples were investigated by EDX analyses. The absorption spectra of the two representative samples, (a) and (f) indicate an energy band gap of 3.17 eV and 3.75 eV, respectively.     

Quantum chemistry studies on the Ru-M interactions and the P NMR in [Ru(CO)3(Ph2Ppy)2(MCl2)] (M = Zn, Cd, Hg)

To study the Ru-M interactions and their effects on ³¹P NMR, complexes [Ru(CO)₃(Ph₂Ppy)₂] (py = pyridine) (1) and [Ru(CO)₃(Ph₂Ppy)₂MCl₂] (M = Zn, 2; Cd, 3; Hg, 4) were calculated by density functional theory (DFT) PBE0 method. Moreover, the PBE0-GIAO method was employed to calculate the ³¹P chemical shifts in complexes. The calculated ³¹P chemical shifts in 1-3 follow 2 > 3 > 1 which are consistent to experimental results, proving that PBE0-GIAO method adopted in this study is reasonable. This method is employed to predict the ³¹P chemical shift in designed complex 4. Compared with 1, the ³¹P chemical shifts in 2-4 vary resulting from adjacent Ru-M interactions. The Ru → M or Ru ← M charge-transfer interactions in 2-4 are revealed by second-order perturbation theory. The strength order of Ru → M interactions is the same as that of the P-Ru → M delocalization with Zn > Cd > Hg, which coincides with the order of ³¹P NMR chemical shifts. The interaction of Ru → M, corresponding to the delocalization from 4d orbital of Ru to s valence orbital of M²⁺, results in the delocalization of P-Ru → M, which decreases the electron density of P nucleus and causes the downfield ³¹P chemical shifts. Except 2, the back-donation effect of Ru ← M, arising from the delocalization from s valence orbital of M²⁺ to the valence orbital of Ru, is against the P-Ru → M delocalization and results in the upfield ³¹P chemical shifts in 4. Meanwhile, the binding energies indicate that complex 4 is stable and can be synthesized experimentally. However, as complex [Ru(CO)₃(Ph₂Ppy)₂HgCl]⁺5 is more stable than 4, the reaction of 1 with HgCl₂ only gave 5 experimentally.     

Reactions of trimethylsiloxychlorosilanes with lithium metal - On the mechanism of the formation of trimethylsiloxysilyllithium compounds LiSiRR’(OSiMe3)

The reaction pathway for the formation of the trimethylsiloxysilyllithium compounds (Me₃SiO)RR′SiLi (2a: R = Et, 2b: R = ⁱPr, 2c: R = 2,4,6-Me₃C₆H₂ (Mes); 2a-c: R′ = Ph; 2d: R = R′ = Mes) starting from the conversion of the corresponding trimethylsiloxychlorosilanes (Me₃SiO)RR′SiCl (1a-d) in the presence of excess lithium in a mixture of THF/diethyl ether/n-pentane at −110 °C was investigated.The trimethylsiloxychlorosilanes (Me₃SiO)RPhSiCl (1a: R = Et, 1b: R = ⁱPr, 1c: R = Mes) react with lithium to give initially the trimethylsiloxysilyllithium compounds (Me₃SiO)RPhSiLi (2a-c). These siloxysilyllithiums 2 couple partially with more trimethylsiloxychlorosilanes 1 to produce the siloxydisilanes (Me₃SiO)RPhSi-SiPhR(OSiMe₃) (Ia-c), and they undergo bimolecular self-condensation affording the trimethylsiloxydisilanyllithium compounds (Me₃SiO)RPhSi-RPhSiLi (3a-c). The siloxydisilanes I are cleaved by excess of lithium to give the trimethylsiloxysilyllithiums (Me₃SiO)RPhSiLi (2). In the case of the two trimethylsiloxydisilanyllithiums (Me₃SiO)RPhSi-RPhSiLi (3a: R = Et, 3b: R = ⁱPr) a reaction with more trimethylsiloxychlorosilanes (Me₃SiO)RPhSiCl (1a, 1b) takes place under formation of siloxytrisilanes (Me₃SiO)RPhSi-RPhSi-SiPhR(OSiMe₃) (IIa: R = Et, IIb: R = ⁱPr) which are cleaved by lithium to yield the trimethylsiloxysilyllithiums (Me₃SiO)RPhSiLi (2a, 2b) and the trimethylsiloxydisilanyllithiums (Me₃SiO)RPhSi-RPhSiLi (3a, 3b). The dimesityl-trimethylsiloxy-silyllithium (Me₃SiO)Mes₂SiLi (2d) was obtained directly by reaction of the trimethylsiloxychlorosilane (Me₃SiO)Mes₂SiCl (1d) and lithium without formation of the siloxydisilane intermediate. Both silyllithium compounds 2 and 3 were trapped with HMe₂SiCl giving the products (Me₃SiO)RR′Si-SiMe₂H and (Me₃SiO)RPhSi-RPhSi-SiMe₂H.     

Aqueous syntheses of [(Cp-R)M(CO)3] type complexes (Cp = cyclopentadienyl, M = Mn, Tc, Re) with bioactive functionalities

We describe reactions of [^99mTc(H₂O)₃(CO)₃)]⁺ (1) with Diels-Alder products of cyclopentadiene such as “Thiele’s acid” (HCp-COOH)₂ (2) and derivatives thereof in which the corresponding [(Cp-COOH)^99mTc(CO)₃)] (3) complex did form in water. We propose a metal mediated Diels-Alder reaction mechanism. To show that this reaction was not limited to carboxylate groups, we synthesized conjugates of 2 (HCp-CONHR)₂ (4a-c) (4a, R = benzyl amine; 4b, R = N_α-Boc-l-2,3-diaminopropionic acid and 4c, R = glycine). The corresponding ^99mTc complexes [(4a)^99mTc(CO)₃)] 6a, [(4b)^99mTc(CO)₃)] 6b and [(4c)^99mTc(CO)₃)] 6c have been prepared along the same route as for Thiele’s acid in aqueous media demonstrating the general applicability of this synthetic strategy. The authenticity of the ^99mTc complexes on the no carrier added level have been confirmed by chromatographic comparison with the structurally characterized manganese or rhenium complexes.Studies of the reaction of 1 with Thiele’s acid bound to a solid phase resin demonstrated the formation of [(Cp-COOH)^99mTc(CO)₃)] 3 in a heterogeneous reaction. This is the first evidence for the formation of no carrier added ^99mTc radiopharmaceuticals containing cyclopentadienyl ligands via solid phase syntheses. Macroscopically, the manganese analogue 5a and the rhenium complexes 5b-c have been prepared and characterized by IR, NMR, ESI-MS and X-ray crystallography for 5a (monoclinic, P2₁/c, a = 9.8696(2) Å, b = 25.8533(4) Å, c = 11.8414(2) Å, β = 98.7322(17)°) in order to unambiguously assign the authenticity of the corresponding ^99mTc complexes.     

Syntheses and X-ray crystallographic studies of {[Ni(en)2(pot)2]0.5CHCl3} and [Ni(en)2](3-pytol)2

Two novel Ni(II) complexes {[Ni(en)₂(pot)₂]0.5CHCl₃} (3) {pot = 5-phenyl-1,3,4-oxadiazole-2-thione} (1) and [Ni(en)₂](3-pytol)₂ (4) {3-pytol = 5-(3-pyridyl)-1,3,4-oxadiazole-2-thiol} (2) have been synthesized using en as coligand. The metal complexes have been characterized by physical and analytical techniques and also by single crystal X-ray studies. The complexes 3 and 4 crystallize in monoclinic system with space group P21/a and P121/c, respectively. The complex 3 has a slightly distorted octahedral geometry with trans (pot)⁻ ligands while 4 has a square planar geometry around the centrosymmetric Ni(II) center with ionically linked trans (3-pytol)⁻ ligands. The π?π (face to face) interaction plays an important role along with hydrogen bondings to form supramolecular architecture in both complexes.     

Synthesis and characterization of palladium(II) complexes with chiral aminophosphine ligands: Catalytic behaviour in asymmetric hydrovinylation. Crystal structure of cis-[PdCl2(PPh((R)-NHCHCH3Ph)2)2]

Optically active ligands of type Ph₂PNHR (R = (R)-CHCH₃Ph, (a); (R)-CHCH₃Cy, (b); (R)-CHCH₃Naph, (c)) and PhP(NHR)₂ (R = (R)-CHCH₃Ph, (d); (R)-CHCH₃Cy, (e)) with a stereogenic carbon atom in the R substituent were synthesized. Reaction with [PdCl₂(COD)₂] produced [PdCl₂P₂] (1) (P = PhP(NHCHCH₃Ph)₂), whose molecular structure determined by X-ray diffraction showed cis disposition for the ligands. All nitrogen atoms of amino groups adopted S configuration. The new ligands reacted with allylic dimeric palladium compound [Pd(η³-2-methylallyl)Cl]₂ to gave neutral aminophosphine complexes [Pd(η³-2-methylallyl)ClP] (2a-2e) or cationic aminophosphine complexes [Pd(η³-2-methylallyl)P₂]BF₄ (3a-3e) in the presence of the stoichiometric amount of AgBF₄. Cationic complexes [Pd(η⁴3-2-methylallyl)(NCCH₃)P]BF₄ (4a-4e) were prepared in solution to be used as precursors in the catalytic hydrovinylation of styrene. ³¹P NMR spectroscopy showed the existence of an equilibrium between the expected cationic mixed complexes 4, the symmetrical cationic complexes [Pd(η³-2-methylallyl)P₂]BF₄ (3) and [Pd(η³-2-methylallyl)(NCCH₃)₂]BF₄ (5) coming from the symmetrization reaction. The extension of the process was studied with the aminophosphines (a-e) as well as with nonchiral monodentate phosphines (PCy₃ (f), PBn₃ (g), PPh₃ (h), PMe₂Ph (i)) showing a good match between the extension of the symmetrization and the size of the phosphine ligand. We studied the influence of such equilibria in the hydrovinylation of styrene because the behaviour of catalytic precursors can be modified substantially when prepared ‘in situ’. While compounds 3 and bisacetonitrile complex 5 were not active as catalysts, the [Pd(η³-2-methylallyl)(η²-styrene)₂]⁺ species formed in the absence of acetonitrile showed some activity in the formation of codimers and dimers. Hydrovinylation reaction between styrene and ethylene was tested using catalytic precursors solutions of [Pd(η³-2-methylallyl)LP]BF₄ ionic species (L = CH₃CN or styrene) showing moderate activity and good selectivity. Better activities but lower selectivities were found when L = styrene. Only in the case of the precursor containing Ph₂PNHCHCH₃Ph (a) ligand was some enantiodiscrimination (10%) found.     

Synthesis and properties of novel 5-(cyclohepta-2′,4′,6′-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-triones: methodology for synthesizing cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates

Novel condensation reaction of tropone with N-substituted and N,N′-disubstitued barbituric acids in Ac₂O afforded 5-(cyclohepta-2′,4′,6′-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (8a-f) in moderate to good yields. The ¹³C NMR spectral study of 8a-f revealed that the contribution of zwitterionic resonance structures is less important as compared with that of 8,8-dicyanoheptafulvene. The rotational barriers (ΔG^‡) around the exocyclic double bond of mono-substituted derivatives 8a-c were obtained to be 14.51-15.03 kcal mol⁻¹ by the variable temperature ¹H NMR measurements. The electrochemical properties of 8a-f were also studied by CV measurement. Upon treatment with DDQ, 8a-c underwent oxidative cyclization to give two products, 7 and 9-substituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates (11a-c·BF₄⁻ and 12a-c·BF₄⁻) in various ratios, while that of disubstituted derivatives 8d-f afforded 7,9-disubstituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborate (11d-f·BF₄⁻) in good yields. Similarly, preparation of known 5-(1′-oxocycloheptatrien-2′-yl)-pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (14a-d) and novel derivatives 14e,f was carried out. Treatment of 14a-c with aq. HBF₄/Ac₂O afforded two kinds of novel products 11a-c·BF₄⁻ and 12a,c·BF₄⁻ in various ratios, respectively, while that of 14d-f afforded 11d-f. The product ratios of 11a-c·BF₄⁻ and 12a-c·BF₄⁻ observed in two kinds of cyclization reactions were rationalized on the basis of MO calculations of model compounds 20a and 21a. The spectroscopic and electrochemical properties of 11a-f·BF₄⁻ and 12a-c·BF₄⁻ were studied, and structural characterization of 11c·BF₄⁻ based on the X-ray crystal analysis and MO calculation was also performed.     

U(IV)/Ln(III) unexpected mixed site in polymetallic oxalato complexes. Part I. Substitution of Ln(III) for U(IV) from the new oxalate (NH4)2U2(C2O4)5·0.7H2O

A new ammonium uranium (IV) oxalate (NH₄)₂U₂(C₂O₄)₅·0.7H₂O (1) and three mixed uranium (IV)-lanthanide (III) oxalates, (N₂H₅)_2.6U_1.4M_0.6(C₂O₄)₅·xH₂O (M=Nd (2) and M=Sm (3)), Na_2.56U_1.44Nd_0.56(C₂O₄)₅·7.6H₂O (4) and Na₃UCe(C₂O₄)₅·10.4H₂O (5), have been prepared. The crystal structures of compounds 1, 4 and 5 have been determined by single-crystal X-ray diffraction. The crystal structures were solved by the direct methods and Fourier difference techniques, and refined by a least square method on the basis of F² for all unique reflections. Compounds 2 and 3 are isotypic with 1. Crystallographic data: 1, hexagonal, space group P6₃/mmc, a=19.177(3), c=12.728(4) Å, Z=6, R₁=0.0575 for 52 parameters with 1360 reflections with I?2σ(I); 2, hexagonal, space group P6₃/mmc, a=19.243(4), c=12.760(5) Å, Z=6; 3, hexagonal, space group P6₃/mmc, a=19.211(3), c=12.274(4) Å, Z=6; 4, orthorhombic, space group Pbcn, a=18.79(3), b=11.46(1), c=12.77(2) Å, Z=4, R₁=0.0511 for 183 parameters with 3026 reflections with I?2σ(I); 5, monoclinic, space group C2/c, a=18.878(6), b=11.684(4), c=12.932(4) Å, β=95.97(1)°, Z=4, R₁=0.0416 for 213 parameters with 4060 reflections with I?2σ(I). The honeycomb-like structure of the five compounds is built from the same three-dimensional arrangement of metallic and oxalate ions. Similar hexagonal rings of alternating metallic and oxalate ions form layers parallel to the (001) plane that are pillared by another oxalate ion. Indeed, some torsions or rotations of the bridging oxalate ligands led to modifications of the network symmetry. The monovalent cations and the water molecules occupy the hexagonal tunnels running down the [001] direction. Starting from the uranium (IV) compound A₂U₂(C₂O₄)₅·0.7H₂O with A=NH₄⁺ (1), the mixed U(IV)/Ln(III) oxalates are obtained by partial substitution of U(IV) by Ln(III) in a ten-coordinated site, the charge deficit being compensated by intercalation of supplementary monovalent ions within the tunnels. The distortion of the arrangement in the [001] direction for the Na-containing compounds allows the accommodation of a greater number of water molecules that insure an octahedral coordination of the Na atoms.     

Reactions of Mo(II)-tetraphosphine complex [MoCl2{meso-o-C6H4(PPhCH2CH2PPh2)2}] with a series of small molecules

Reactions of Mo(II)-tetraphosphine complex [MoCl₂(κ⁴-P4)] (2; P4 = meso-o-C₆H₄(PPhCH₂CH₂PPh₂)₂) with a series of small molecules have been investigated. Thus, treatment of 2 with alkynes RCCR′ (R = Ph, R′ = H; R = p-tolyl, R′ = H; R = Me, R′ = Ph) in benzene or toluene gave neutral mono(alkyne) complexes [MoCl₂(RCCR′)(κ³-P4)] containing tridentate P4 ligand, which were converted to cationic complexes [MoCl(RCCR′)(κ⁴-P4)]Cl having tetradentate P4 ligand upon dissolution into CDCl₃ or CD₂Cl₂. The latter complexes were available directly from the reactions of 2 with the alkynes in CH₂Cl₂. On the other hand, treatment of 2 with 1 equiv. of XyNC (Xy = 2,6-Me₂C₆H₃) afforded a seven-coordinate mono(isocyanide) complex [MoCl₂(XyNC)(κ⁴-P4)] (7), which reacted further with XyNC to give a cationic bis(isocyanide) complex [MoCl(XyNC)₂(κ⁴-P4)]Cl (8). From the reaction of 2 with CO, a mono(carbonyl) complex [MoCl₂(CO)(κ⁴-P4)] (9) was obtained as a sole isolable product. Reaction of 9 with XyNC afforded [MoCl(CO)(XyNC)(κ⁴-P4)]Cl (10a) having a pentagonal-bipyramidal geometry with axial CO and XyNC ligands, whereas that of 7 with CO resulted in the formation of a mixture of 10a and its isomer 10b containing axial CO and Cl ligands. Structures of 7 and 9 as well as [MoCl(XyNC)₂(κ⁴-P4)][PF₆](8′) and [MoCl(CO)(XyNC)(κ⁴-P4)][PF₆] (10a′) derived by the anion metathesis from 8 and 10a, respectively, were determined in detail by the X-ray crystallography.     

Synthesis, structure and dynamic stereochemistry of (O → Si)-chelate N-(trifluorosilylmethyl)-[N-(S)-(1-phenylethyl)]acetamide and 1-(trifluorosilylmethyl)-2-oxoperhydroazepine: Retention of the O → Si coordination in the adduct with KF and 18-crown-6

The novel compounds, N-(trifluorosilylmethyl)-[N-(S)-(1-phenylethyl)]-acetamide (1a) and 1-(trifluorosilylmethyl)-2-oxoperhydroazepine (1b) have been prepared from the corresponding NH-compounds using ClCH₂SiCl₃/Et₃N or ClCH₂SiCl₃/(Me₃Si)₂NH followed by methanolysis or hydrolysis of the reaction mixture in the presence of Lewis bases, and then BF₃ etherate. Potassium-(18-crown-6)-(2-oxoperhydroazepinomethyl)tetrafluorosilicate (2) was synthesized by reaction of the trifluoride (1b) with KF in the presence of 18-crown-6. Using ¹⁹F, ²⁹Si NMR and X-ray diffraction techniques it was established that the silicon atom is pentacoordinate in the trifluorides (1a, b) and hexacoordinate in the adduct 2. Thus the internal coordination of the O → Si bond present in the trifluoride (1b) is retained in the adduct 2.The stereochemical non-rigidity of the trifluorides (1a, b) and the N-(trifluorosilylmethyl)-N-methylacetamide (1c) was investigated using dynamic ¹⁹F NMR spectroscopy. The activation barriers for permutational isomerization are in the range 9.5-10 kcal mol⁻¹. Lower values of ΔG^# for permutation of trifluorides (1a-c) compared to the monofluorides with the coordination core OSiC₃F together with small negative values for the activation entropy implies a non-dissociative mechanism. Quantum-chemical analysis suggests a mechanism involving a turnstile rotation.     

Synthesis and characterization of organophosphine/phosphite stabilized silver(I) methanesulfonates: Crystal structures of [Ph3PAgO3SCH3] and [(Ph3P)2AgO3SCH3]

Six organophosphine/phosphite stabilized silver(I) methanesulfonates of type [L_nAgO₃SCH₃] (L = Ph₃P, n = 1, 2a; n = 2, 2b; n = 3, 2c; L = (EtO)₃P; n = 1, 2d; n = 2, 2e; n = 3, 2f) were synthesized by the reaction of silver methanesulfonates with triphenylphosphine or triethylphosphite in dichloromethane under nitrogen atmosphere. These complexes were obtained in high yields and characterized by elemental analysis, ¹H-, ¹³C{H} NMR, IR spectroscopy and thermogravimetric analysis (TGA), respectively. X-ray single crystal analysis reveals that complex 2a is a tetramer [Ph₃PAgO₃SCH₃]₄ and complex 2b is a monomer. The thermal stability of 2a has been studied by applying thermogravimetric analysis. It starts to decompose between 50 and 440 °C in a three-step process. The final residue (Ag) is about 20.50%.     

Synthesis, crystal structure, infrared and Raman spectra of Sr4Cu3(AsO4)2(AsO3OH)4·3H2O and Ba2Cu4(AsO4)2(AsO3OH)3

The two new compounds, Sr₄Cu₃(AsO₄)₂(AsO₃OH)₄·3H₂O (1) and Ba₂Cu₄(AsO₄)₂(AsO₃OH)₃(2), were synthesized under hydrothermal conditions. They represent previously unknown structure types and are the first compounds synthesized in the systems SrO/BaO-CuO-As₂O₅-H₂O. Their crystal structures were determined by single-crystal X-ray diffraction [space group C2/c, a=18.536(4) Å, b=5.179(1) Å, c=24.898(5) Å, β=93.67(3)°, V=2344.0(8) Å³, Z=4 for 1; space group P4₂/n, a=7.775(1) Å, c=13.698(3) Å, V=828.1(2) Å³, Z=2 for 2]. The crystal structure of 1 is related to a group of compounds formed by Cu²⁺-(XO₄)³⁻ layers (X=P⁵⁺, As⁵⁺) linked by M cations (M=alkali, alkaline earth, Pb²⁺, or Ag⁺) and partly by hydrogen bonds. In 1, worth mentioning is the very short hydrogen bond length, D···A=2.477(3) Å. It is one of the examples of extremely short hydrogen bonds, where the donor and acceptor are crystallographically different. Compound 2 represents a layered structure consisting of Cu₂O₈ centrosymmetric dimers crosslinked by As1φ₄ tetrahedra, where φ is O or OH, which are interconnected by Ba, As2 and hydrogen bonds to form a three-dimensional network. The layers are formed by Cu₂O₈ centrosymmetric dimers of CuO₅ edge-sharing polyhedra, crosslinked by As1O₄ tetrahedra. Vibrational spectra (FTIR and Raman) of both compounds are described. The spectroscopic manifestation of the very short hydrogen bond in 1, and ABC-like spectra in 2 were discussed.     

Synthesis and characterization of anionic lanthanide complexes {[o-(Me3SiN)2C6H4]Ln(MeC5H4)2}{Li(DME)3} (Ln = Yb, Sm, Nd) and their catalytic activity for the polymerization of methyl methacrylate

The syntheses and structures of a series of new lanthanide complexes supported by a chelating diamide ligand N,N′-bis(trimethylsilyl)-o-phenylenediamine are described. Anhydrous LnCl₃ reacts with Li₂[o-(Me₃SiN)₂C₆H₄], followed by treatment of NaC₅H₄Me in 1:1:2 molar ratio to afford the corresponding anionic complexes: {[o-(Me₃SiN)₂C₆H₄]Ln(MeC₅H₄)₂}{Li(DME)₃} [Ln = Yb (1), Sm (2), Nd(3)] in high yield. These complexes were characterized by elemental analysis, IR and ¹H NMR. The molecular structures of 1 and 2 were further determined by X-ray diffraction techniques to be an ion-pair complex composed by an anion [o-(Me₃SiN)₂C₆H₄]Ln(MeC₅H₄)₂] and a cation [Li(DME)₃]. Complexes 1-3 showed high catalytic activity for the polymerization of methyl methacrylate (MMA) at r.t., giving the syndiotactic-rich polymers with relatively narrow molecular weight distributions (M_w/M_n = 1.64-1.82).     

Syntheses, crystal structures and DFT studies of [Me3EM(CO)5] (E = Sb, Bi; M = Cr, W), cis-[(Me3Sb)2Mo(CO)4], and [Bu3BiFe(CO)4]

Syntheses of [Me₃SbM(CO)₅] [M = Cr (1), W (2)], [Me₃BiM(CO)₅] [M = Cr (3), W (4)], cis-[(Me₃Sb)₂Mo(CO)₄] (5), [^tBu₃BiFe(CO)₄] (6), crystal structures of 1-6 and DFT studies of 1-4 are reported.     

A DFT/TDDFT study on the structures, trend in DNA-binding and spectral properties of molecular “light switch” complexes [Ru(phen)2(L)](L = dppz, taptp, phehat)

Theoretical studies on a series of molecular “light switch” complexes [Ru(phen)₂L]²⁺ (phen = 1,10-phenanthroline; L: dppz = dipyrido [3,2-a:2′,3′-c]phenazine; taptp = 4,5,9,18-tetraazaphenanthreno-[9,10-b]triphenylene; phehat = 1,10-phenanthrolino[5,6-b]1,4,5,8,9,12-hexaazatriphenylene) 1-3 have been carried out applying DFT/TDDFT (density functional theory and time-dependent DFT) methods. The geometric and electric structure-characteristics of these complexes have been revealed, and the trend in their DNA-binding constants (K_b), i.e., K_b (2) < K_b (3) < K_b (1), which closely relates to the luminescence properties of the complexes in DNA, has been reasonably explained. The results show that simply increasing the planar area of intercalative ligand may be ineffective on improvement of DNA-binding of resulting complex because of going with the increase in the LUMO (and LUMO + x) energy, but introducing some heteroatoms (e.g., N atom) with stronger electronegativity into the ring skeleton of intercalative ligand should be effective because of the decrease in the LUMO (and LUMO + x) energy to a certain extent. In addition, the spectra of this series of complexes in vacuo are also computed, simulated, and minutely discussed by the DFT/TDDFT methods, and it is interesting to find that the symmetries of the excited and accepting orbitals of the transition with the largest f value are the same.     

The (phosphino)tetraphenylborate ligand in ruthenium-arene chemistry

The synthesis of a series of anionic half-sandwich ruthenium-arene complexes [E][RuCl₂(η⁶-p-cymene){PR₂(p-Ph₃BC₆H₄)}] (E = Bu₄N⁺: R = Ph, 1a, ⁱPr, 1b or Cy, 1c; E = bis(triphenylphosphine)iminium or PNP⁺: R = Ph, 1a′, ⁱPr, 1b′ or Cy, 1c′) are reported. X-ray crystallographic studies of 1a′ and 1b′ confirmed the three-legged piano-stool coordination geometry. In solution, complexes 1a-c and 1a′-c′ are proposed to form monomer-dimer equilibria as a result of chloride ligand dissociation. Complexes 1a-c and 1a′-c′ also form the formally neutral zwitterionic complexes [RuCl(L)(η⁶-p-cymene){PR₂(p-Ph₃BC₆H₄)}] (L = pyridine: R = Ph, 2a, ⁱPr, 2b or Cy, 2c; L = MeCN: R = Ph, 3a, ⁱPr, 3b or Cy, 3c) via chloride ligand abstraction using AgNO₃ or MeOTf.