Phosphasila-, phosphagerma-, and phosphaarsaallenes --P=C=E (E = Si,Ge, As) and arsa- and diarsaallenes --As=C=E" (E" = C,As)

The paper reviews the contribution from our group to the studies of heteroallenes. The transient 1,3-phosphasilaallene ArP=C=Si(Ph)Tip (Ar = 2,4,6-tri-tert-butylphenyl, Tip = 2,4,6-triisopropylphenyl) and 1,3-phosphagermaallene ArP=C=GeMes₂ (Mes = 2,4,6-trimethylphenyl) were characterized below –40 °C by NMR spectroscopy and chemical trapping. These compounds dimerize above –40 °C through two routes. With increased steric hindrance on germanium, the phosphagermaallene ArP=C=Ge(Bu^t)Tip was stabilized as monomer at room temperature. 3-Chloro-2-lithio-1,3-phosphasilapropene ArP=C(Li)Si(Cl)CMeR₂ (CMeR₂ = 9-methylfluorenyl) behaves, at least in some cases, as a synthetic equivalent of the functionalizable allene ArP=C=Si(Cl)CMeR₂. Arsaallene ArAs=C=CR₂, phosphaarsaallenes ArP=C=AsAr and ArP=C=AsDmt (Dmt = 2,6-dimesityl-4-methylphenyl), and diarsaallene ArAs=C=AsAr exhibit a higher thermal, air, and moisture stability than the above phosphasilaallenes and phosphagermaallenes. The physicochemical data for the arsaallenes and diarsaallenes, particularly, their X-ray structural parameters, display a bonding system close to allenes. On going down the Periodic table, the stabilization becomes more difficult. For this reason, tin allenic derivatives are very rare and antimony allenic compounds have not yet been isolated.     

Low-Valent Group 14 NHC-Stabilized Phosphinidenide ate Complexes and NHC-Stabilized K/P-Clusters

The N-heterocyclic carbene (NHC)-stabilized phosphinidenide, SIMesPK [SIMes=1,3-bis(2,4,6-trimethylphenyl)imidazolidine-2-ylidene], was used as an (NHC)P-transfer reagent for the synthesis of the low-valent Group 14 ate complexes K[(SIMesP)₃E] (E=Ge: 2 , Sn: 3 , Pb: 4 ), which were characterized by ¹H NMR, ³¹P NMR, IR spectroscopy as well as elemental and X-ray analysis. Furthermore, SIMesPK was used in reactions with potassium amides and alkoxides to form the molecular phosphorus–potassium clusters [K₄(SIMesP)₂(hmds)₂] [ 5 , hmds=N(SiMe₃)₂] and [K₆(SIMesP)₂(OtBu)₄] ( 6 ). Finally, the reaction of SIMesPK with Li[Al(OC₄F₉)₄] led to the potassium-rich ionic compound [(SIMesP)₄K₅][Al(OC₄F₉)₄] ( 7 ).     

Neighboring Group Participation in Glycosylation Reactions by 2,6-Disubstituted 2-O-Benzoyl groups: A Mechanistic Investigation

Variable yields and glycosylation stereoselectivity were obtained for NIS/TfOH-medi- ated reaction of 4-methoxyphenyl 2,4,6-tetra-O-acetyl-β-D-galactopyranoside and thiogalactosides bearing acetyl, benzoyl, 2,6-dimethoxylbenzoyl, 2,4,6-trimethylbenzoyl, or 2,6-dichlorobenzoyl groups at the 2-positions and acetyl at the remainder. X-ray structures of 4-methylphenyl 2,3,4,6-tetra-O-(2,4,6-trimethylbenzoyl)-1-thio-β-D-galactopyr anoside and 4-methylphenyl 3,4-O-isopropylidene-2,6-di-O-(2,4,6-trimethylbenzoyl)-1-thio-β-D-galactopyranoside revealed slightly distorted ⁴ C ₁ chair conformations. Variable temperature NMR revealed that activation of 4-methylphenyl 2,3,4,6-tetra-O-(2,4,6-trimethylbenzoyl)-1-thio-β-D-galactopyranoside afforded only dioxolenium ion, whereas 4-methylphenyl 3,4,6-tri-O-acetyl-2-O-(2,4,6-trimethylbenzoyl)-1-thio-β-D-galactopyranoside gave a 1:1 mixture of dioxolenium ion and glycosyl triflate. However, the reaction intermediates formed from these deactivated donors do not influence the glycosylation stereoselectivity; instead, it is influenced by steric and electronic interactions at the transition states.     

Phenyllead(IV) diorganophosphinodithioates,PhnPb(S2PR2)4−n. Synthesis,spectroscopic characterization,and NMR study of the redistribution/decomposition of diphenyllead(IV) derivatives

Tri- and diphenyllead(IV) diorganophosphinodithioates, Ph_nPb(S₂PR₂)_4−n (n = 2 and 3; R = Me, Et, Ph) were prepared by reacting the corresponding organolead(IV) chloride with the sodium or ammonium salt of the phosphinodithioic acid. The title compounds were investigated by infrared, ¹H and ³¹P NMR, and mass spectroscopy, and possible structures were proposed. The diphenyllead(IV) phosphinodithioates, Ph₂Pb(S₂PR₂)₂, undergo decomposition on standing or on moderate heating, the least stable being the ethyl derivative. The process was monitored by using ¹H and ³¹P NMR spectroscopy, and a reaction pathway leading to Ph₃PbS₂PR₂, Pb(S₂PR₂)₂, and R₂P(S)SPh was established.     

Experimental and theoretical study on the reaction of bicyclo[2.2.1]hept-5-en-endo-2-ylmethanamine with glycidyl ethers

Reactions of bicyclo[2.2.1]hept-5-en-endo-2-ylmethanamine with phenyl, 4-methylphenyl, 3-methylphenyl, 2-methylphenyl, 4-methoxyphenyl, cyclohexyl, and cyclohexenyl 2,3-epoxypropyl ethers gave the corresponding N-mono- and N,N-bis(3-R-oxy-2-hydroxypropyl) derivatives. The structure of the newly synthesized amino alcohols and regioselectivity of oxirane ring opening were determined by IR spectroscopy, ¹H and ¹³C NMR, and mass spectrometry. The reaction mechanism was studied by quantum chemistry at the PCM/B3LYP/6-31G(d) level of theory.     

Proton nuclear magnetic resonance and infra-red studies of the outer-sphere hydration of pentane-2,4-dionato metal complexes in benzene solution

Studies of hydrogen bonding between water and bis(pentane-2,4-dionato)-beryllium(II) (Be(acac)₂), bis(3-methylpentane-2,4-dionato)-beryllium(II) (Be(Meacac)₂), and tris(pentane-2,4-dionato)cobalt(III) (Co(acac)₃) have been undertaken in [²H]₆-benzene solution using¹H NMR and infra-red spectroscopy. Equilibrium constants for 1:1 water-metal complex hydrates, and approximate enthalpies and entropies of reaction, have been measured from the¹H NMR data. The equilibrium constants are larger for Co(acac)₃ than for the Be(II) complexes, in line with previous data for the partition of these chelates between water and aliphatic hydrocarbon solvents.     

Synthesis, crystal structures, electrochemical and spectroscopic properties of ruthenium(II) complexes containing diamino-1,3,5-triazine derivatives

Three Ru(II) complexes [Ru(bpy)₂(1-IQTNH)](ClO₄)₂ (1), [Ru(bpy)₂(2-QTNH)](ClO₄)₂ (2) and [Ru(bpy)₂(3-IQTNH)](ClO₄)₂ (3) (bpy = 2,2′-bipyridine, 1-IQTNH = 6-(isoquinolin-1-yl)-1,3,5-triazine- 2,4-diamine, 2-QTNH = 6-(quinolin-2-yl)-1,3,5-triazine- 2,4-diamine, 3-IQTNH = 6-(isoquinolin-3-yl)-1,3,5-triazine-2,4-diamine) have been synthesized and characterized by elemental analysis, ¹H NMR spectroscopy, electrospray ionization mass spectrometry and X-ray crystallography. The electrochemical and spectroscopic properties of the complexes differ from those of [Ru(bpy)₃]²⁺ owing to the structural differences between the ligands and their complexes.     

Synthesis,crystal structure,and NMR spectroscopy of a 1,3,2λ5,4λ5-oxathiadiphosphetane

From the crude product of the synthesis of the dithiadiphosphetane [RP(S)S]₂ (with R = 2,4,6-iPr₃C₆H₂), the trans-oxathiadiphosphetane has been isolated, C₃₀H₄₀OP₂S₃. X-ray structure analysis and mass spectroscopic investigations give unequivocal evidence for this structure: monoclinic, C2/c (no. 15), a = 13.066(8), b = 21.726(8), c = 12.070(6) Å, β = 103.54(10)°, V = 3331 ų, Z = 4, and D_c = 1.158 g/cm³. The asymmetric unit consists of half the formula unit. Solid-state ³¹P NMR spectra give information about the chemical shift anisotropy. Results of IGLO calculations of the ³¹P nuclear magnetic shielding tensor agree satisfactorily with the experimental data. Monitoring the reaction of several dithiadiphosphetanes with benzophenone in solution by ³¹P NMR spectroscopy indicates that additional oxathiadiphosphetanes as well as thiotrimetaphosphonates are present. © 1996 John Wiley & Sons, Inc.     

Primary Studies on Variation in Position of Trifluoromethyl Groups in Several Aromatic Group‐14 Derivatives by 19F‐NMR Spectroscopy

Variation in the position of CF₃ groups in several aromatic Group‐14 compounds was studied by ¹⁹F‐NMR spectroscopy. In these compounds R_nECl_4?n (n=1 or 2; E=Si, Ge, or Sn; R=2,4,6‐(CF₃)₃C₆H₂ (=Ar), 2,6‐(CF₃)₂C₆H₃ (=Ar′), or 2,4‐(CF₃)₂C₆H₃ (=Ar″)), Ar, Ar′, and Ar″ are all bulky, strongly electron‐withdrawing ligands. The ¹⁹F‐NMR studies of the variation in position of the CF₃ substituents in these compounds as revealed by chemical shifts could be correlated with the electronegativities of the central elements E, and with intramolecular E–F interactions derived from single‐crystal X‐ray diffraction data. These interactions are considered to play an important role in the stabilization of these compounds.     

Synthesis and phosphorus 31 n.m.r studies of neutral and cationic compounds with platinum-mercury bonds

Summary The preparation and properties of the following neutral and cationic compounds containing Pt-Hg bonds is described: [(PPh₃)₂ClPt-HgR] (R=2,4,6-C₆H₂Cl₃; 2,3,4,6- and 2,3,5,6-C₆HCl₄ and C₆Cl₅), and [(PPh₃)₂LPt-Hg(C₆Cl₅)]ClO₄ (L=pyridine, , and -picoline; 2,4-lutidine and -colidine). All the compounds have been characterized by³¹P n.m.r. spectroscopy. The dependence of P, J(³¹P-¹⁹⁵Pt) and²J(³¹P-¹⁹⁹Hg) on the slight changes of the electronic properties of the ligands L and R has been studied.     

Bisphosphinodihalogensilane-vorstufen zum 1,3-diphospha-2-silaallen

The syntheses and NMR spectra of the phosphinosilanes (ArHP)₂SiCl₂, (ArHP)₂SiBr₂ and ArHPSiCl₃ are described (Ar = 2,4,6-t-Bu₃C₆H₂). Treatment of (ArHP)₂SiCl₂ with t-BuLi results in the formation of a 1,3-diphospha-2-silaallyl anion, which has been identified by ³¹P and ²⁹Si NMR spectroscopy.     

Rare-Earth-Metal Pentadienyl Half-Sandwich and Sandwich Tetramethylaluminates–Synthesis,Structure, Reactivity,and Performance in Isoprene Polymerization

Targeting the synthesis of rare-earth-metal pentadienyl half-sandwich tetramethylaluminate complexes, homoleptic [Ln(AlMe₄)₃] (Ln=Y, La, Ce, Pr, Nd, Lu) were treated with equimolar amounts of the potassium salts K(2,4-dmp) (2,4-dmp=2,4-dimethylpentadienyl), K(2,4-dipp) (2,4-dipp=2,4-diisopropylpentadienyl), and K(2,4-dtbp) (2,4-dtbp=2,4-di-tert-butylpentadienyl). The reactions involving the larger rare-earth-metal centers lanthanum, cerium, praseodymium, and neodymium gave selectively the desired half-sandwich complexes [(2,4-dmp)La(AlMe₄)₂], [(2,4-dipp)La(AlMe₄)₂], and [(2,4-dtbp)Ln(AlMe₄)₂] (Ln=La, Ce, Pr, Nd) in high crystalline yields. Smaller rare-earth-metal centers yielded preferentially the sandwich complexes [(2,4-dmp)₂Ln(AlMe₄)] (Ln=Y, Lu) and [(2,4-dipp)₂Y(AlMe₄)]. Activation with fluorinated borate/borane co-catalysts gave highly active catalyst systems for the fabrication of polyisoprene, displaying molecular weight distributions as low as M_w/M_n=1.09 and a maximum cis-1,4 selectivity of 90.4 %. The equimolar reaction of half-sandwich complex [(2,4-dtbp)La(AlMe₄)₂] with B(C₆F₅)₃ led to the isolation and full characterization of the single-component catalyst {{(2,4-dtbp)La[(μ-Me)₂AlMe(C₆F₅)]}[Me₂Al(C₆F₅)₂]}₂. The reaction of the latter complex with 10 equivalents of isoprene could be monitored by ¹H NMR spectroscopy. Also, a donor-induced aluminato/gallato exchange was achieved with [(2,4-dtbp)La(AlMe₄)₂] and GaMe₃(OEt₂) leading to [(2,4-dtbp)La(GaMe₄)₂].     

Adsorption of phenols from contaminated water through titania-silica mixed imidazolium based ionic liquid: Equilibrium,kinetic and thermodynamic modeling studies

The present study describes the synthesis and characterization of titania-silica mixed imidazolium based ionic liquid (Ti-Si-IL) as well as evaluation of its adsorption behavior towards the 2,4-dinitrophenol (2,4-DNP) and 2,4,6-trichlorophenol (2,4,6-TCP). Synthesized Ti-Si-IL adsorbent was characterized by Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), BET surface area Brunauer-Emmett-Teller (BET), thermogravimetric analysis (TGA) and elemental analysis (CHN). The adsorption of 2,4-DNP and 2,4,6-TCP on Ti-Si-IL was investigated systematically by evaluating the effects of adsorbent dosage, initial pH, contact time and temperature. Satisfactory adsorption 95% and 65% for 2,4-DNP and 2,4,6-TCP was observed at pH 4 and 6, respectively. The kinetic results for 2,4-DNP and 2,4,6-TCP on Ti-Si-IL indicated that the kinetic data follows pseudo-second-order model (R² = 0.9985 and 0.9750, respectively). Adsorption isotherms were fitted well by the Langmuir model for 2,4-DNP (q_m = 44.64 mg g^?1 at 318 K) and Freundlich model for 2,4,6-TCP (K_F = 0.63 mg g^?1 at 318 K). The +ΔH° and -ΔG° values demonstrated that the adsorption of 2,4-DNP was endothermic and spontaneous in nature. While the -ΔH° and +ΔG° values for 2,4,6-TCP adsorption demonstrated exothermic and comparatively nonspontaneous. During the removal process, the role of different functional groups, cyclic structure was monitored and found that the ionic property as well as π-π interactions of host molecules played important role in the extent of adsorption.     

Synthesis and Characterization of β‐Diketiminate Zinc Complexes

The monomeric β‐diketiminate zinc complex (Mes)NacNacZnMe 1 (MesNacNac = {[2,6‐(2,4,6‐Me₃‐C₆H₂)N(Me)C)]₂CH}) was obtained in almost quantitative yield from the reaction of ZnMe₂ with (Mes)NacNacH. Reaction of 1 with either Me₃NHCl or a solution of HCl in Et₂O yielded (Mes)NacNacZnCl 2 , whereas (Mes)NacNacZnI 3 was obtained from the reaction of 1 with I₂. 1 – 3 were characterized by elemental analyses, mass and multinuclear (¹H, ¹³C{¹H}) NMR spectroscopy, 3·THF also by single crystal X‐ray analysis.     

Synthesis of Enantiomerically Pure 1,5,5‐Trideuterated cis‐ and trans‐2,4‐Dioxa‐3‐phosphadecalins. 31P‐NMR Evidence of Covalent‐Bond Formation and the Stereochemical Implications in the Course of the Inhibition of δ‐Chymotrypsin

The irreversible inhibition of δ‐chymotrypsin with the enantiomerically pure, P(3)‐axially and P(3)‐equatorially X‐substituted cis‐ and trans‐configurated 2,4‐dioxa‐3‐phospha(1,5,5‐²H₃)bicyclo[4.4.0]decane 3‐oxides (X=F, 2,4‐dinitrophenoxy) was monitored by ³¹P‐NMR spectroscopy. ¹H‐Correlated ³¹P{²H}‐NMR spectra enabled the direct observation of the vicinal coupling (³J) between the P‐atom of the inhibitor and the CH₂O moiety of Ser¹⁹⁵ (=‘Ser¹⁹⁵’(CH₂O)), thus establishing the covalent nature of the ‘Ser¹⁹⁵’(CH₂O? P) bond in the inhibited enzyme. The stereochemical course of the phosphorylation is dependent on the structure of the inhibitor, and neat inversion, both inversion and retention, as well as neat retention of the configuration at the P‐atom was found.     

Synthesis and thermal decomposition of a novel hyperbranched polyphosphate ester used for flame retardant systems

A novel hyperbranched polyphosphate ester (HPPE) was synthesized via the polycondensation of bisphenol-A as an A₂ monomer and phosphoryl trichloride as a B₃ monomer at 100 °C, without gelation. The initial molar ratio of A₂ to B₃ was set to be 1.5:1. The final product was precipitated from methanol. ³¹P NMR spectroscopy was used to monitor the reaction. The formed HPPE was characterized by FTIR and ¹H NMR to confirm its end groups. Differential scanning calorimetry data revealed that the cured bisphenol-A epoxy resin with HPPE as a curing agent possessed improved glass transition temperature. Dynamic mechanical thermal analysis also showed the increase in the glass transition temperature. The thermal degradation properties and flame retardancy were investigated by thermogravimetric analysis and limiting oxygen index (LOI). The results showed that the incorporation of HPPE into bisphenol-A epoxy resin increased its thermal stability and char yield during the decomposition by raising the second stage decomposition temperature. The LOI value increased from 23 to 31 when HPPE, instead of bisphenol-A, was used as a curing agent.     

Synthese,Struktur und Reaktivität von Tris‐, Bis‐ und Mono(2,4‐dimethylpentadienyl)‐Komplexen des Neodyms,Lanthans und des Yttriums

The tris(2,4‐dimethylpentadienyl) complexes [Ln(η⁵‐Me₂C₅H₅)₃] (Ln = Nd, La, Y) are obtained analytically pure by reaction of the tribromides LnBr₃·nTHF with the potassium compound K(Me₂C₅H₅)(thf)_n in THF in good yields. The structural characterization is carried out by X‐ray crystal structure analysis and NMR‐spectroscopically. The tris complexes can be transformed into the dimeric bis(2,4‐dimethylpentadienyl) complexes [Ln₂(η⁵‐Me₂C₅H₅)₄X₂] (Ln, X: Nd, Cl, Br, I; La, Br, I; Y, Br) by reaction with the trihalides THF solvates in the molar ratio 2:1 in toluene. Structure and bonding conditions are determined for selected compounds by X‐ray crystal structure analysis and NMR‐spectroscopically in general. The dimer‐monomer equilibrium existing in solution was investigated NMR‐spectroscopically in dependence of the donor strength of the solvent and could be established also by preparation of the corresponding monomer neutral ligand complexes [Ln(η⁵‐Me₂C₅H₅)₂X(L)] (Ln, X, L: Nd, Br, py; La, Cl, thf; Br, py; Y, Br, thf). Finally the possibilities for preparation of mono(2,4‐dimethylpentadienyl)lanthanoid(III)‐dibromid complexes are shown and the hexameric structure of the lanthanum complex [La₆(η⁵‐Me₂C₅H₅)₆Br₁₂(thf)₄] is proved by X‐ray crystal structure analysis.     

Diselenadiphosphetandiselenide und Triselenadiphospholandiselenide – Synthese und Charakterisierung mittels 31P‐ und 77Se‐Festkörper‐NMRSpektroskopie

Diselenadiphosphetane Diselenides and Triselenadiphospholane Diselenides – Synthesis and Characterization by ³¹P and ⁷⁷Se Solid‐State NMR Spectroscopy 1,3‐Diselena‐2,4‐diphosphetane‐2,4‐diselenides (RPSe₂)₂ with R = Me, Et, t‐Bu, Ph, 4‐Me₂NC₆H₄, 4‐MeOC₆H₄ have been synthesized by different methods. The insoluble compounds were investigated by ³¹P and ⁷⁷Se solid‐state NMR and the purity of the compounds has been checked by their CP MAS sideband NMR spectra. The structure of the investigated compounds has been confirmed by the isotropic and anisotropic values of the chemical shifts and the ¹J_P–Se coupling constants. In addition, two new 1,2,4‐triselena‐3,5‐diphospholane‐3,5‐diselenides, (RPSe₂)₂Se (R = Me, Et), formed under similar synthesis conditions, were investigated. Their structure was derived from the ⁷⁷Se satellites of ³¹P solution spectra and from solid‐state spectra. For (t‐BuPSe₂)₂ the experimentally obtained principal values of phosphorus and selenium shielding tensors are compared with values from IGLO calculations (HF und SOS DFPT). The calculated orientations of the principal axes are discussed.     

Experimental and Theoretical Studies of Bromination of Diethyl 2,4,6‐Trimethyl‐1,4‐dihydropyridine‐3,5‐dicarboxylate

A reaction of diethyl 2,4,6‐trimethyl‐1,4‐dihydropyridine‐3,5‐dicarboxylate with 1, 2, and more equivalents of N‐bromosuccinimide (NBS) in methanol was investigated by NMR spectroscopy at a temperature interval ranging from 25 to 40°C. The reaction was found to proceed through several steps. The structures of the intermediates diethyl 3‐bromo‐2,4,6‐trimethyl‐3,4‐dihydropyridine‐3,5‐dicarboxylate, diethyl 3‐bromo‐2‐methoxy‐2,4,6‐trimethyl‐1,2,3,4‐tetrahydropyridine‐3,5‐dicarboxylate, and diethyl 3,5‐dibromo‐2‐methoxy‐2,4,6‐trimethyl‐2,3,4,5‐tetrahydropyridine‐3,5‐dicarboxylate were identified by multinuclear (¹H, ¹³C, and ¹⁵N) NMR spectral data. The optimal structures of all species participating in the reaction as well as changes in their relative energies along with the proposed pathway of the reaction were analyzed by quantum‐chemical calculations. The mechanism of bromination of diethyl 2,4,6‐trimethyl‐1,4‐dihydropyridine‐3,5‐dicarboxylate with NBS in methanol was found to favor the bromination in the 2,6‐methyl side chains as the only products in full agreement with experimental observations.     

Synthesis,characterization, crystal structure,and antibacterial evaluation of Ni (II) complex with new dithiophosphorus compound

The reaction of 2,4-bis (4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane-2,4-disulfide (Lawesson^’s reagent) with phenylethylamine produced [H₃NCH₂CH₂C₆H₅]⁺ [(C₆H₅CH₂CH₂NH)(p C₆H₄OMe)PS₂]^? (1). Furthermore, reaction of 1 with NiCl₂ in dry methanol led to the novel complex 2. The compounds were characterized by ¹H and ³¹P NMR, IR spectroscopy, and elemental analysis. A single crystal X-ray structure of complex 2 showed that the nickel complex is square planar. The complex formed a supramolecular structure via intermolecular S1…H7B and O1…H2N2 hydrogen bonds. The X-ray crystallography of complex showed [R²₂](18) and R⁴₄(18) motifs in the monomers were connected to each other via S1…H7B, O1…H2N2 hydrogen bonds with donor–acceptor distance of 2.89 and 2.51 Å, respectively. The new compounds were additionally tested in view of their antibacterial properties.