Synthesis and characterization of mono and polymeric cyclopalladated compounds: Crystal and molecular structure of [{Pd(dmba)(ONO(2))}(2)(mu-pz)] center dot H(2)O (pz = pyrazine)

In the treatment of cyclometallated dimer [Pd(dmba)(mu-Cl)](2) (dmba = N,N-dimethylbenzylamine) with AgNO(3) and acetonitrile the result was the monomeric cationic precursor [Pd(dmba)(NCMe)(2)](NO(3)) (NCMe=acetonitrile) (1). Compound 1 reacted with m-nitroaniline (m-NAN) and pirazine (pz), originating [Pd(dmba)(ONO(2))(m-NAN)] (2) and [{Pd(dmba)(ONO(2))}(2)(mu-pz)] center dot H(2)O (3), respectively. These compounds were characterized by elemental analysis, IR and NMR spectroscopy. The IR spectra of (2-3) display typical bands of monodentade O-bonded nitrate groups, whereas the NMR data of 3 are consistent with the presence of bridging pyrazine ligands. The structure of compound 3 was determined by Xray diffraction analysis. This packing consists of a supramolecular chain formed by hydrogen bonding between the water molecule and nitrato ligands of two consecutive [Pd(2)(dmba)(2)(ONO(2))2(mu-pz)] units. (c) 2008 Elsevier Ltd. All rights reserved.

A novel route for the preparation of dimeric tetraorganodistannoxanes

The reaction of polymeric diorganotin oxides, (R₂SnO)_n (R=Me, Et, n-Bu, n-Oct, c-Hex, i-Pr, Ph), with saturated aqueous NH₄X (X=F, Cl, Br, I, OAc) in refluxing 1,4-dioxane afforded in high yields dimeric tetraorganodistannoxanes, [R₂(X)SnOSn(X)R₂]₂, and in a few cases diorganotin dihalides or diacetates, R₂SnX₂. The reported method appears suitable for the synthesis of fluorinated tetraorganodistannoxanes. Identification of [R₂(OH)SnOSn(X)R₂]₂ (R=n-Bu; X=Cl, Br) and [R₂(OH)SnOSn(X)R₂] [R₂(X)SnOSn(X)R₂] suggest a serial substitution mechanism starting from [R₂(OH)SnOSn(OH)R₂]₂. X-ray crystal structure determinations are reported for [Me₂(AcO)SnOSn(OAc)Me₂]₂ (29a), [i-Pr₂(Br)SnOSn(Br)i-Pr₂]₂ (20a), [c-Hex2(F)SnOSn(F)c-Hex₂]₂ (5a) and [c-Hex₂(F)SnOSn(Cl)c-Hex₂]₂ (36), respectively. These show the presence of a central (R₂Sn)₂O₂ core that is connected, via the oxygen atoms, to R₂Sn entities. Acetate (29a) or halides (5a, 20a, 36) complete the coordination about the tin centres.

Synthesis and reactivity towards DIBAL-H of Cyclo-Siloxanes cyclo-[R2SiOSi(Ot-Bu)2O]2, cyclo-(t-BuO)2Si(OSiR2)2O, and cyclo-R2Si[Osi(Ot-Bu)2]2O (R=Me, Ph)

The six-, eight- and twelve-membered cyclo-siloxanes, cyclo-[R₂SiOSi(Ot-Bu)₂O]₂ (R = Me (1), Ph (2)), cyclo-(t-BuO)₂Si(OSiR₂)₂O (R = Me (3), Ph (4)), cyclo-R₂Si[OSi(Ot-Bu)₂]₂O (R = Me (5), Ph (6)) and cyclo-[(t-BuO)₂Si(OSiMe₂)₂O]₂ (3a) were synthesized in high yields by the reaction of (t-BuO)₂Si(OH)₂ and [(t-BuO)₂SiOH]₂O with R₂SiCl₂ and (R₂SiCl)₂O (R = Me, Ph). Compounds 1 - 6 were characterized by solution and solid-state ²⁹Si NMR spectroscopy, electrospray mass spectrometry and osmometric molecular weight determination. The molecular structure of 4 has been determined by single crystal X-ray diffraction and features a six-membered cyclo-siloxane ring that is essentially planar. The reduction of 1 - 6 with i-Bu₂AlH (DIBAL-H) led to the formation of the metastable aluminosiloxane (t-BuO)₂Si(OAli-Bu₂)₂ (7) along with Me₂SiH₂ and Ph₂SiH₂.

Synthesis, molecular structure, and isomerisation in solution of (Me3SbS)2Me2SnCl2. Concomitant hypercoordination of tin and antimony

The reaction of Me₃SbCl₂ and (Me₂SnS)₃ afforded the complex (Me₃SbS)₂Me₂SnCl₂ in high yields, whose molecular structure features both hypercoordinated tin and antimony atoms. In solution, (Me₃SbS)₂Me₂SnCl₂ undergoes a reversible dissociation and ligand interchange reaction to give Me₃SbS, Me₃SbCl₂ and (Me₂SnS)₃.

Diorganotin dications stabilized by neutral ligands in the solid state: [R2Sn(H2O)2(OPPh3)2](O3SCF3)2 (R = Me, Bu)

The synthesis of [R₂Sn(H₂O)₂(OPPh₃)₂](O₃SCF₃)₂ (R = Me (1), Bu (2)) by the consecutive reaction of R₂SnO (R = Me, Bu) with triflic acid and Ph₃PO is described. Compounds 1 and 2 feature dialkyltin(IV) dications [R₂Sn(H₂O)₂(OPPh₃)₂]^₂+ apparently stabilized by the neutral ligands in the solid state. Compounds 1 and 2 readily dehydrate upon heating at 105 and 86 °C, respectively. The preparative dehydration of 1 afforded [Me₂Sn(OPPh₃)₂(O₃SCF₃)](O₃SCF₃) (1a), which features both bidentate and non-coordinating triflate anions. In compounds 1 and 2 the ligands Ph₃PO and H₂O are kinetically labile in solution and undergo reversible ligand exchange reactions. Compounds 1, 1a and 2 were characterized by multinuclear solution and solid-state NMR spectroscopy, IR spectroscopy, electrospray mass spectrometry, conductivity measurements, thermogravimetry and X-ray crystallography.

Synthesis and structure of new oligomethylene-bridged double ladders. How far can the layers be separated?

The synthesis of the α,ω-bis[dichloro(trimethylsilylmethyl)stannyl]alkanes, (Me₃SiCH₂)C1₂Sn(CH₂)_nSnCl₂(CH₂SiMe₃) (13, n=5; 14, n=6; 15, n=7; 16, n=8; 17, n=10; 18, n=12) and the corresponding oligomethylene-bridged diorganotin oxides [(Me₃SiCH₂)(O)Sn(CH₂)_nSn(O)(CH₂SiMe₃)]_m (19, n=5; 20, n=6; 21, n=7; 22, n=8; 23, n=10; 24; n=12) is reported. The reaction of the diorganodichlorostannanes 13–18 with the corresponding diorganotin oxides 19–24 provided the spacer-bridged tetraorganodistannoxanes {[(Me₃SiCH₂)ClSn(CH₂)_nSnCl(CH₂SiMe₃)]O}₄ (25, n=5; 26, n=6; 27, n=7; 28, n=8; 29, n=10; 30, n=12). Compounds 13–30 have been identified by elemental analyses and multinuclear NMR spectroscopy. Compounds 25, 27, 29 and 30 have also been characterised by single crystal X-ray diffraction analysis and electrospray mass spectrometry. For the latter the essential double ladder motif is maintained for all n in the solid state, but subtle changes in alignment of the ladder planes occur. Separation between the two layers of the double ladder ranges from approx. 8.7  Å (for 25, n=5) to approx. 15 Å (for 30, n=12). In solution there is some dissociation of the double ladders into the corresponding dimers. The degree of dissociation is favoured by increasing oligomethylene chain length n.

Oligomethylene-bridged dinuclear triorganotin triflates and diphenylphosphinates. Ion pairing in the solid state and electrolytic dissociation in solution of [Ph2Sn(CH2)nSnPh2X](O3SCF3) (X = OH, O2PPh2; n = 1-3)

The condensation of [Ph₂(OH)Sn(CH₂)_nSn(OH)Ph₂] (1-3; n = 1-3) with HO₃SCF₃ and HO₂PPh₂ provided [Ph₂Sn(CH₂)_nSnPh₂(OH)](O₃SCF₃) (4-6; n = 1-3) and [Ph₂(O₂PPh₂)Sn(CH₂)_nSn(O₂PPh₂)Ph₂] (10-12; n = 1-3), respectively. The reaction of [Ph₂Sn(CH₂)_nSnPh₂(OH)](O₃SCF₃) (4-6; n = 1-3) with HO₂PPh₂ and NaO₂PPh₂ gave rise to the formation of [Ph₂Sn(CH₂)_nSnPh₂(O₂PPh₂)](O₃SCF₃) (7-9; n = 1-3) and [Ph₂(OH)Sn(CH₂)_nSn(O₂PPh₂)Ph₂] (13-15; _n = 1-3), respectively. In the solid state, compounds 4-9 comprise ion pairs of cationic cyclo-[Ph₂SnCH₂SnPh₂(OH)]₂²⁺, cyclo-[Ph₂Sn(CH₂)_nSnPh₂(OH)]⁺ (n = 2, 3), and cyclo-[Ph₂Sn(CH₂)_nSnPh₂(O₂PPh₂)]⁺ (n = 1-3) and triflate anions. In MeCN, the eight-membered-ring system cyclo-[Ph₂SnCH₂SnPh₂(OH)]₂²⁺ appears to be in equilibrium with the four-membered-ring system cyclo-[Ph₂SnCH₂SnPh₂(OH)]⁺. In contrast, compounds 10-15 show no ionic character. Compounds 1-15 were characterized by multinuclear NMR spectroscopy in solution and in the solid state, IR spectroscopy, conductivity measurements, electrospray mass spectrometry, osmometric molecular weight determinations, and X-ray crystallography (4, 5, 7, and 12).

Anion recognition and anion-mediated self-assembly with thiourea-functionalised fused [3]polynorbornyl frameworks

Three conformationally preorganised host molecules based on the [3]polynorbornyl framework and incorporating di-urea receptors were synthesised and their interaction with a series of anions investigated by 1H NMR spectroscopy. A high affinity of each host molecule for dihydrogenphosphate (H2PO4–) and dihydrogenpyrophosphate (H2P2O72–) was identified. In addition to binding to the urea receptors of the host molecules, evidence for an interaction involving the non-polar C–H groups within the binding cavity of the framework and guest anions was also discovered. Furthermore, an unusual 2 : 1 host-to-anion stoichiometry was indicated when binding H2P2O72–, and a model for the anion-mediated self-assembly of this complex species is proposed.

New insights in asymmetric tetraorganodistannoxane ladder formation. A NMR-spectroscopic and crystallographic study

The syntheses of the asymmetrically substituted tetraorganodistannoxanes [t-Bu₂(X)SnOSn(Y)(CH₂SiMe₃)₂1₂ (1, X = Y = OH; 2, X = Cl, Y = OH; 3, X = Y = Cl) are reported and their structures in solution and in the solid state are characterized by multinuclear NMR spectroscopy and single crystal X-ray analyses. In toluene, the tetrahydroxy-substituted derivative 1 is in equilibrium with the organotin oxides cyclo-[t-Bu₂Sn{OSn(CH₂SiMe₃)₂}₂O] (4), cyclo[(Me₃SiCH₂)₂Sn(OSnt-Bu₂)₂O] (5), and cyclo-(t-Bu₂SnO)₃, and some additional, undefined species containing pentacoordinated tin atoms. In contrast, the dihydroxydichloro-substituted derivative 2 is inert in solution.

Creatine transporters: a reappraisal

Creatine (Cr) plays a key role in cellular energy metabolism and is found at high concentrations in metabolically active cells such as skeletal muscle and neurons. These, and a variety of other cells, take up Cr from the extra cellular fluid by a high affinity Na⁺/Cl^--dependent creatine transporter (CrT). Mutations in the crt gene, found in several patients, lead to severe retardation of speech and mental development, accompanied by the absence of Cr in the brain.
In order to characterize CrT protein(s) on a biochemical level, antibodies were raised against synthetic peptides derived from the N- and C-terminal cDNA sequences of the putative CrT-1 protein. In total homogenates of various tissues, both antibodies, directed against these different epitopes, recognize the same two major polypetides on Western blots with apparent Mr of 70 and 55 kDa. The C-terminal CrT antibody (α-CrTCOOH) immunologically reacts with proteins located at the inner membrane of mitochondria as determined by immuno-electron microscopy, as well as by subfractionation of mitochondria. Cr-uptake experiments with isolated mitochondria showed these organelles were able to transport Cr via a sulfhydryl-reagent-sensitive transporter that could be blocked by anti-CrT antibodies when the outer mitochondrial membrane was permeabilized. We concluded that mitochondria are able to specifically take-up Cr from the cytosol, via a low-affinity CrT, and that the above polypeptides would likely represent mitochondrial CrT(s). However, by mass spectrometry techniques, the immunologically reactive proteins, detected by our anti-CrT antibodies, were identified as E2 components of the agr-keto acid dehydrogenase multi enzyme complexes, namely pyruvate dehydrogenase (PDH), branched chain keto acid dehydrogenase (BC-KADH) and α-ketoglutarate dehydrogenase (α-KGDH). The E2 components of PDH are membrane associated, whilst it would be expected that a mitochondrial CrT would be a transmembrane protein. Results of phase partitioning by Triton X-114, as well as washing of mitochondrial membranes at basic pH, support that these immunologically cross-reactive proteins are, as expected for E2 components, membrane associated rather than transmembrane. On the other hand, the fact that mitochondrial Cr uptake into intact mitoplast could be blocked by our α-CrTCOOH antibodies, indicate that our antisera contain antibodies reactive to proteins involved in mitochondrial transport of Cr. The presence of specific antibodies against CrT is also supported by results from plasma membrane vesicles isolated from human and rat skeletal muscle, where both 55 and 70 kDa polypeptides disappeared and a single polypeptide with an apparent electrophoretic mobility of ~ 60 kDa was enriched This latter is most likely representing the genuine plasma membrane CrT.
Due to the fact that all anti-CrT antibodies that were independently prepared by several laboratories seem to cross-react with non-CrT polypeptides, specifically with E2 components of mitochondrial dehydrogenases, further research is required to characterise on a biochemical/biophysical level the CrT polypeptides, e.g. to determine whether the ~ 60 kDa polypeptide is indeed a bona-fide CrT and to identify the mitochondrial transporter that is able to facilitate Cr-uptake into these organelles. Therefore, the anti-CrT antibodies available so far should only be used with these precautions in mind. This holds especially true for quantitation of CrT polypeptides by Western blots, e.g. when trying to answer whether CrT's are up- or down-regulated by certain experimental interventions or under pathological conditions.
In conclusion, we still hold to the scheme that besides the high-affinity and high-efficiency plasmalemma CrT there exists an additional low affinity high Km Cr uptake mechanism in mitochondria. However, the exact biochemical nature of this mitochondrial creatine transport, still remains elusive. Finally, similar to the creatine kinase (CK) isoenzymes, which are specifically located at different cellular compartments, also the substrates of CK are compartmentalized in cytosolic and mitochondrial pools. This is in line with ¹⁴C-Cr-isotope tracer studies and a number of [³¹P]-NMR magnetization transfer studies, as well as with recent [¹H]-NMR spectroscopy data.

Inorganic-organic hybrids of the p,p'-diphenylmethylenediphosphinate ligand with bivalent metals: a new 2D-layered phenylphosphinate zinc(II) complex

By reaction of Zn(CH₃COO)₂ with p,p′-diphenylmethylenediphosphinic acid in water a new inorganic–organic polymeric hybrid of formula [Zn(CH₂(P(Ph)O₂)₂)] has been synthesized and completely characterized. The X-ray analysis established that the structure consists of 2D-layered polymeric array, the 2D-sheets being built up through strong covalent linkages between the zinc metal and the oxygen donors of the phenylphosphinate ligand. The 2D-layers, which are featuring a mesh-net fashion, present voids of various dimensionality, up to 24-membered rings. The organic parts of the hybrid ligand, namely the phenyl rings, are shielding the inorganic skeleton of the layers, preventing the propagation of the polymer in the third dimension. No water molecules are present in the lattice, both of coordination and crystallization. Crystal data are: monoclinic, P2₁Ic, a=11.840(2), b=9.646(9), c=12.516(5) Å, β=95.03(2), V=1423.9(15) ų, Z=4. The solid material has been characterized by ³¹P MAS NMR spectroscopy and thermogravimetric analysis.

The first dimeric trioganotin fluoride : stabilization by unsymmetrically oriented menthyl substituents

In the solid state, (-)-tris([1R,2S,5R]-menthyl)tin fluoride, Men₃SnF (6), exhibits a dimeric structure in which one tin atom is four-coordinate and the other five-coordinate. This novel dimeric association mode is attributed to the orientation of the unsymmetrical menthyl groups, which are arranged to allow a minimum Sn···Sn separation of 4.84 Å within the dimer. The exocyclic isopropyl groups of the menthyl groups point in opposite directions on each tin atom of the dimer, thus preventing further association (Sn···Sn separation outside the dimer 10.49 Å). ¹¹⁹Sn and ¹⁹F MAS NMR spectroscopy were utilized to probe the diverse coordination numbers found by X-ray crystallography for the geometries of the two tin and fluorine sites. In solution, 6 is a monomer at both room temperature and -100 °C. However, upon addition of Bu₄NF, 6 is in equilibrium with [(Men₃SnF)₂F]- (6a), [Men₃SnF₂]^- (6b), and noncoordinating fluoride anions.

The interplay of secondary Te···N, Te···O, Te···I and I···I interactions, Te···π contacts and π-stacking in the supramolecular structures of [{2-(4-nitrobenzylideneamino)-5-methyl}phenyl](4-methoxyphenyl)tellurium dihalides

The unsymmetrical1y substituted diorganotellurium dihalides [2-(4,4'-N0₂C₆H₄CHNC₆H₃Me]RTeX₂ (R = 4-MeOC₆H₄, X = Cl,
1a; Br, 1b; I, 1c; R =4-MeC₆H₄ ; X = Cl, 2; R =C₆H₅, X = Cl, 3) were prepared in good yields and characterized by solution and solid-state ¹²⁵Te NMR spectroscopy, IR spectroscopy and X-ray crystallography. In the solid-state, molecular structures of 1a and 1c possess scarcely observed 1,4-type intramolecular Te···N secondary interaction. Crystal packing of these compounds show an unusually rich diversity of intermolecular secondary, Te·· ·0, Te· .. \ and 1···1 interactions, Te·· ·π contacts as well as extensive
π-stacking of the organic substituents.

Generalised 2D-correlation NMR analysis of a wine fermentation

A wine fermentation has been monitored on a daily basis by 1H NMR spectroscopy. Following data pre-processing that includes synthesis of the spectra to ensure all peaks are of constant half-width, the series of spectra were examined using generalised two-dimensional correlation techniques. Synchronous and asynchronous data maps have been generated and employed to interpret the changes in the fermentation process as a function of time. The results illustrate the potential of high resolution NMR with multivariate data analysis as a tool for process monitoring and the manner in which two-dimensional correlation mapping can aid in data interpretation.

The reactivity of diorganotellurium oxides towards phenol and o-nitrophenol. Hypervalent and secondary bonding of four different product classes

The reaction of the diorganotellurium oxides R2TeO (R = Ph, p-MeOC6H4, p-Me2NC6H4) with phenol and o-nitrophenol produces diorganotellurium hydroxy phenolates, R2Te(OH)OPh (1, R = Ph; 2, R = p-MeOC6H4; 3, R = p-Me2NC6H4), diorganotellurium bis(phenolates) R2Te(OPh)2 (4, R = Ph; 5, R = p-MeOC6H4; 6, R = p-Me2NC6H4), tetraorganoditelluroxane bis(o-nitrophenolates), (R′O)R2TeOTeR2(OR′) (7, R = p-MeOC6H4; 8, R = p-Me2NC6H4; R′ = o-NO2C6H4), and a hexaphenyltritelluroxane bis(o-nitrophenolate) (R′O)Ph2TeOTePh2OTePh2(OR′) (9, R′ = o-NO2C6H4), respectively. The redistribution reactions of R2Te(OPh)2 (4, R = Ph; 5, R = p-MeOC6H4; 6, R = p-Me2NC6H4) with the corresponding diorganotellurium oxides R2TeO and diorganotellurium dichlorides R2TeCl2 (R = Ph, p-MeOC6H4, p-Me2NC6H4) give rise to the formation of moisture sensitive tetraorganoditelluroxane bis(phenolates) (PhO)R2TeOTeR2(OPh) (10, R = Ph; 11, R = p-MeOC6H4; 12, R = p-Me2NC6H4) and diorganotellurium chloro phenolates, R2Te(Cl)OPh (13, R = Ph; 14, R = p-MeOC6H4; 15, R = p-Me2NC6H4), respectively. The reaction of the diorganotellurium oxides R2TeO with the corresponding diorganotellurium dichlorides R2TeCl2 (R = Ph, p-MeOC6H4, p-Me2NC6H4) affords tetraorganoditelluroxane dichlorides ClR2TeOTeR2Cl (16, R = Ph; 17, R = p-MeOC6H4; 18, R = p-Me2NC6H4) as air-stable solid materials. The reactivity of 1–18 can be rationalized by the kinetic lability of the Te–O and Te–Cl bonds. Compounds 1–18 have been characterized by solution and solid-state 125Te NMR spectroscopy and 2, 4, 6, 7, 9, 17, and 18 have also been analyzed by X-ray crystallography.