The global phase behavior of the two-component systems with intracomponent association: Flory approach

Within the Flory approach we study the phase diagrams of two-component fluids, the molecules of each component A(f(A)), B(f(B)) bearing f(A) (f(B)) functional groups capable of forming thermoreversible A-A and B-B bonds. We develop a general procedure to classify these diagrams depending on the values of four governing parameters -- entropies and normalized energies of A-A and B-B bonds, and give full topological classification of phase diagrams with f(A,B)> or =3. We show that these phase diagrams can have immiscibility loops and up to four critical points.     

Cyclic polycarbene ligands with crown ether structure

The cyclization reaction of coordinated β‐functional phenyl isocyanides was used to generate coordinated anellated N‐heterocyclic carbenes. Coordinated 2‐trimethylsiloxyphenyl isocyanide reacts, after Si O bond cleavage, to yield a complex with a coordinated benzoxazol‐2‐ylidene ligand. The cyclization reaction of coordinated 2‐aminophenyl isocyanide, obtained in situ from 2‐azidophenyl isocyanide, yields the coordinated benzimidazol‐2‐ylidene. Both ylidenes can be alkylated at the nitrogen atoms. Attempts to generate four benzimidazol‐2‐ylidenes at Pt^II and to bridge them by N‐alkylation leading to a crown ether‐like ligand with carbene donors are presented here. Free N‐heterocyclic carbenes derived from benzimidazole with large N‐substituents exist as monomers while they dimerize to dibenzotetraazafulvalenes when substituted with sterically less‐demanding substituents at the ring nitrogen atoms. A chemical equilibrium between the monomeric carbene and its dimerized enetetraamine exists for the N,N′‐isopropyl substituted derivative. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:540–549, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10099     

Adduct formation of [(η7-C7H7)Hf(η5-C5H5)] with isocyanides,phosphines and N-heterocyclic carbenes: An experimental and theoretical study

The reactions of [(η⁷-C₇H₇)Hf(η⁵-C₅H₅)] (1b) with the two-electron donor ligands tert-butyl isocyanide (tBuNC), 2,6-dimethylphenyl isocyanide (XyNC), 1,3,4,5-tetramethylimidazolin-2-ylidene (IMe) and trimethylphosphine (PMe₃) are reported. The 1:1 complexes [(η⁷-C₇H₇)Hf(η⁵-C₅H₅)L] (2b, L = tBuNC; 3b, L = XyNC; 4b, L = IMe, 5b, L = PMe₃) have been isolated in crystalline form, and their molecular structures have been determined by X-ray diffraction analyses. The stabilities of these hafnium complexes were probed via spectroscopic and theoretical methods, and the results were compared to those previously reported for the corresponding zirconium complexes derived from [(η⁷-C₇H₇)Zr(η⁵-C₅H₅)] (1a). The X-ray crystal structure of the PMe₃ adduct [(η⁷-C₇H₇)Zr(η⁵-C₅H₅)(PMe₃)] (5a) was also established.     

Reactivity of a Frustrated Lewis Pair and Small‐Molecule Activation by an Isolable Arduengo Carbene?B{3,5‐(CF3)2C6H3}3 Complex

Tris[3,5‐bis(trifluoromethyl)phenyl]borane reacts with the sterically demanding Arduengo carbenes 1,3‐di‐tert‐butylimidazolin‐2‐ylidene and 1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene to form isolable normal adducts. In the case of 1,3‐di‐tert‐butylimidazolin‐2‐ylidene, the adduct exhibits dynamic behaviour in solution and frustrated‐Lewis‐pair (FLP) reactivity. Fast cleavage of dihydrogen and THF, the C? H activation of phenylacetylene, and carbon dioxide fixation were achieved by using solutions of this adduct in benzene. This adduct is stable at room temperature in the absence of suitable substrates; however, thermal rearrangement into an abnormal carbene–borane adduct can be observed. In contrast, the 1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene adduct exhibits no evidence of FLP reactivity or of dissociation in solution. DFT calculations confirmed the experimental behaviour and stability of these carbene–borane adducts.     

From a cycloheptatrienylzirconium allyl complex to a cycloheptatrienylzirconium imidazolin-2-iminato "pogo stick" complex with imido-type reactivity

The reaction of the cycloheptatrienylzirconium half-sandwich complex [(η(7)-C(7)H(7))ZrCl(tmeda)] (1) (tmeda = N,N,N',N'-tetramethylethylenediamine) with Li(Im(Dipp)N), generated from bis(2,6-diisopropylphenyl)imidazolin-2-imine (Im(Dipp)NH) with methyllithium, yields the imidazolin-2-iminato complex [(η(7)-C(7)H(7))Zr(Im(Dipp)N)(tmeda)] (2). The corresponding tmeda-free complex [(η(7)-C(7)H(7))Zr(Im(Dipp)N)] (5) can be synthesized via the 1,3-bis(trimethylsilyl)allyl complex [(η(7)-C(7)H(7))Zr{η(3)-C(3)H(3)(TMS)(2)}(THF)] (3; TMS = SiMe(3)), which undergoes an acid-base reaction with Im(Dipp)NH to form 5 and 1,3-bis(trimethylsilyl)propene. 5 exhibits an unusual one-legged piano stool ("pogo stick") geometry with a particularly short Zr-N bond of 1.997(2) ?. Addition of 2,6-dimethylphenyl or tert-butyl isocyanide affords the complexes [(η(7)-C(7)H(7))Zr(Im(Dipp)N)(CNR)] (R = o-Xy, 6; R = t-Bu, 7), while the reaction with 2,6-dimethylphenyl isocyanate results in a [2 + 2] cycloaddition to form the ureato(1-) complex [(η(7)-C(7)H(7))Zr{Im(Dipp)N(C═O)N-o-Xy}] (8). 5 can also act as an initiator for the ring-opening polymerization of ε-caprolactone. These reactivity patterns together with density functional theory calculations reveal a marked similarity of the bonding in imidazolin-2-iminato and conventional imido transition-metal complexes.     

Temperature dependence of hydrogen overvoltage on nickel and iron in acid solution

The temperature dependence of hydrogen overvoltage on mechanically and chemically polished nickel electrodes, on iron armco, and iron of high purity in 0.25 M H₂SO₄ are studied in the interval of temperatures 298–278 K. It is established that the influence of temperature on the slope of Tafel line depends essentially on the type of electrodes. The apparent energy of activationE and pre-exponential factorB are determined. The results show an important role of the electrode surface treatment and purity of the metal in the determination of energetic parameters of the hydrogen evolution reaction. The most striking result is that in the case of nickel electrodes with mechanically polished surfaceE increases andB decreases with the increase of overvoltage. Some aspects of nonclassical behavior of electrodes studied are discussed. Dedicated to the ninetieth anniversary of Ya.M. Kolotyrkin’s birth.     

Stereoselective Hydrolysis of Substituted Cyclopropanedicarboxylates with Pig Liver Esterase

The hydrolysis of the meso-cyclopropane-1,2-dicarboxylates 1a - 3a , 4 , 5a , 6a , and 9 , containing various substituents at C(3), and of the rac-3-phenylcyclopropane-1,2-dicarboxylates 7a , 8a , and 10 with pig liver esterase (PLE) is described. The stereoselectivtty and absolute configurations of the products were determined. An interpretation of results was attempted on the basis of a recent active-site model for PLE.     

Nucleoside und Nucleotide. Teil 16. Verhalten von 1-(2′-Desoxy-β-D-ribofuranosyl)-2(1 H)-pyrimidinon-5′-triphosphat, 1-(2′-Desoxy-β-D-ribofuranosyl)-2(1 H)pyridinon-5′-triphosphat und 4-Amino-1-(2′-Desoxy-β-D-ribofuranosyl)-2(1 H)-pyridinon-5′-triphosphat gegenüber DNA-Polymerase

Nucleosides and Nucleotides. Part 16. The Behaviour of 1-(2′-Deoxy-β-D -ribofuranosyl)-2(1H)-pyrimidinone-5′-triphosphate, 1-(2′-Deoxy-β-D -ribofuranosyl-2(1H))-pyridinone-5′-triphosphate and 4-Amino-1-(2′-desoxy-β-D -ribofuranosyl)-2(1H)-pyridinone-5′-triphosphate towards DNA Polymerase The behaviour of nucleotide base analogs in the DNA synthesis in vitro was studied. The investigated nucleoside-5′-triphosphates 1-(2′-deoxy-β-D -ribofuranosyl)-2(1 H)-pyrimidinone-5′-triphosphate (pppM_d), 1-(2′-deoxy-β-D -ribofuranosyl)-2(1 H)-pyridinone-5′-triphosphate (pppII_d) and 4-amino-1-(2′-deoxy-β-D -ribofuranosyl)-2(1 H)-pyridinone-5′-triphosphate (pppZ_d) can be considered to be analogs of 2′-deoxy-cytidine-5′-triphosphate. However, their ability to undergo base pairing to the complementary guanine is decreased. When pppM_d, pppII_d or pppZ_d are substituted for pppC_d in the enzymatic synthesis of DNA by DNA polymerase no incorporation of these analogs is observed. They exhibit only a weak inhibition of the DNA synthesis. The mode of the inhibition is uncompetitive which shows that these nucleotide analogs cannot serve as substrates for the DNA polymerase.     

Nucleosides and Nucleotides. Part 13. Synthesis and spectral properties of 1- (3′-O-Phosphoryl-2′-deoxy-β -D-ribofuranosyl)-2(1H)-pyridone-(3′-5′)-1-(2′-deoxy-β-D-ribofuranosyl)-2 (1H)-pyridone

The dinucleoside phosphate Π_dpΠ_d ( 4 ) was synthesized from the monomers 1-(5′-O-monomethoxytrityl - 2′ - deoxy - β - D - ribofuranosyl) - 2 (1 H) - pyridone ((MeOTr) Π_d, 2 ) and 1-(5′-O-phosphoryl-3′-O-acetyl-2′-deoxy-β-D -ribofuranosyl)-(1H)-pyridone (pΠ_d(Ac), 3 ). Its 6.4% hyperchromicity and an analysis of the ¹H-NMR. spectra indicate that the conformation and the base-base interactions in 4 are similar to those in natural pyrimidine dinucleoside phosphates.