Mariam G. Ezernitskaya

Cryostructuring of polymer systems. Wide pore poly(vinyl alcohol) cryogels prepared using a combination of liquid–liquid phase separation and cryotropic gel-formation processes

Novel, previously unknown, wide pore poly(vinyl alcohol) cryogels (PVACGs) have been prepared through a cryotropic gelation approach when water–PVA–gum arabic (GuAr) ternary liquid systems were used as feeds. The following set of conditions necessary for obtaining wide-porous, permeable for a water flow, and, simultaneously, mechanically strong enough PVACGs was established: the total concentration of gelling component—PVA (MW of 86 kDa) and non-gelling polymer—GuAr (MW of ∼650 kDa) should exceed ∼14 wt%, the GuAr : PVA ratio should be near 1 : 1 (w/w), and the feed pH should be within the range of ∼5 to 11. The phase diagrams for the water–PVA–GuAr ternary liquid systems at pH 5.3 and 10.0 have demonstrated that such “optimum” compositions are in the vicinity of the rectilinear diameters of the respective diagrams, and that the limit of GuAr solubility in the PVA-rich phase is small. In such cases this GuAr fraction strongly binds with PVA, especially under alkaline conditions, within the gel forming phase of heterophase PVACG. Light microscopy studies revealed the presence of at least three distinct kinds of pores in these cryogels. First, there are interconnected channel-like gross pores with a cross-section of 100–200 μm and larger which are the replicas of continuous GuAr-rich phase in the two-phase polymeric systems appearing due to the liquid–liquid phase separation in the ternary water–PVA–GuAr system. The second type are isolated roundish large pores ca. 10–70 μm in diameter being the replicas of the GuAr-rich phase dispersed as liquid droplets in the PVA-rich phase. In the third, there are smaller rounded pores ∼1 to 5 μm in diameter being the replicas of ice polycrystals. Such a sophisticated “poly-porous” morphology of the studied PVA cryogels is their unique feature distinguishing them from other known PVA cryogels.

Vibrational spectra of tris(cyclopentadienyl)zirconium and -hafnium hydrides and deuterides, Cp3MX (M Zr, Hf; X H, D)

The synthesis has been performed of tris(cyclopentadienyl)hafnium hydride and deuteride from Cp4Hf treated with LiAlH4 and LiAlD4, respectively. The IR spectra (4000—100 cm-1) and Raman spectra of tris(cyclopentadienyl)zirconium and -hafnium hydrides and deuterides have been studied. The compounds are shown to have the structure (η5-C5H5)3MX (M  Zr, Hf; X  H, D) with three identically bonded cyclopentadienyl ligands. The spectral characteristics obtained are consistent with metal—ring coordination of the central type. An increase is noted in the strength of the M—H and M—Cp bonds when passing from zirconium to hafnium.

Synthesis of ferrocenylacetylide derivatives of gold-ruthenium and gold-osmium clusters. Crystal structures of M3(AuPPh3)(C≡CFc)(CO)9 (M=Ru or Os; Fc is ferrocenyl)

The synthesis and crystal structures of the clusters M3(AuPPh3)(C≡CFc)(CO)9 (M=Ru,3a; or M=Os,3b) are described. Compound3a was synthesized by deprotonation of Ru3H(C≡CFc)(CO)9 under the action of KOH/EtOH followed by treatment of the anionic complex [Ru3(C≡CFc)(CO)9]− with chloro(triphenylphosphine)gold. Compound3b was prepared by the reaction of Os3(CO)10(NCMe)2 with FcC≡CAuPPh3, which was synthesized by the reaction of FcC≡CNa with ClAuPPh3. The pentanuclear cluster Ru4(AuPPh3)(C≡CFc)(CO)12 (4a), which was prepared by the reaction of3a with Ru3(CO)12, was characterized by spectral methods.

Structures, dynamic behaviour in solution and cross-coupling reactions of the α-palladiated (η6-alkylarene)tricarbonylchromium complexes containing a palladium-chromium bond

Abstract Structures of the complexes ( η 3 -C 3 H 5 )Pd( μ - η 6:1 -CH 2 Ph Cr ( CO ) 3 and ( η 3 -C 3 H 5 )Pd[ μ - η 6:1 -CH(Ph)Ph]Cr(CO) 3 in solution were evaluated by NMR ( 1 H and 13 C) and IR spectroscopy. The dynamic behaviour of the complexes was investigated. Quick rotation (on the NMR time scale) of the tricarbonylchromium groups around the axis passing through the centre of the η 6 -coordinated phenyl ring and the chromium atom takes place at room temperature and becomes slow on cooling. The η 3 -allylic ligand was proved to undergo no dynamic changes in solution. Unlike the solid state, the semi-bridging carbonyl groups between chromium and palladium atoms are absent or very weak in solution. Cross-coupling reactions of the complexes with organohalides are described.

IR study of rotational isomerism in dirhenium and diruthenium complexes of the ferrole type

Abstract A novel type of rotational isomerism was found in binuclear dirhenium complex of ferrole type Re2(CO)7(C8H7Ph2Fc2) (II) by Fourier transform IR spectroscopy in a wide temperature range (165–293 K) in pentane and liquid xenon solutions. The conformers result from internal rotation of a metal carbonyl moiety about the multicentred bond involving another metal carbonyl fragment. According to IR and Raman spectroscopy, the diruthenium complex Ru2(CO)6{C4Fc2(CCFc)2} (III) exists in the solid state and in solution as two different conformers. In the solid state the ‘non-sawhorse’ conformation with the semibridging carbonyl group was found, which transforms in solution to the conformation containing only terminal carbonyl groups.

Reactions of H2Os3(CO)10 with triallylboranes: formation of novel triosmium boron-containing olefin clusters

H2Os3(CO)10 (1) reacts with triallylborane B(CH2CHCH2)3 at 25 °C to form the cluster [Os3(CO)10(μ-η2:η2-trans-MeHCCH)2BC3H7] (2). Reaction of 1 with a mixture of triallylborane–trimethallylborane (1 : 3) gives a mixture of clusters 2, [Os3(CO)10(μ-η2:η2-Me2CCH)2BC3H7] (3) and {Os3(CO)10[μ-η2:η2-(trans-MeCHCH)(Me2CCH)]BC3H7} (4). The reaction results in the B–C bond cleavage and the isomerization of two allyl fragments into substituted vinyl groups coordinated to the osmium atoms in an η2-fashion, and reduction of the third fragment to a propyl group. The mechanism of the reaction is discussed based on isotope labelling and influence of the boron substituent ligand on the reaction path and product identity. Clusters 2, 3, 4 are characterized by spectroscopic means as well as by X-ray studies.

Synthesis and the crystal structure of the triosmium cluster with the μ-dehydrobenzene ligand, Os3(μ-H)2(CO)7(μ-C6H4){μ3-Ph2PCH2P(C6H4)Ph}

The Os3(μ-H)2(CO)7(μ-C6H4){μ3-Ph2PCH2P(C6H4)Ph} complex, which was isolated from the products of thermolysis of Os3(CO)10(μ-dppm) (dppm is Ph2PCH2PPh2) in toluene, was characterized by X-ray diffraction analysis. Protonation of the resulting complex with trifluoroacetic acid afforded the cationic complex [Os3(μ-H)3(CO)7(μ-C6H4){μ3-Ph2PCH2P(C6H4)Ph}]+.

Reactions of the Ru3(CO)10(μ-Ph2PCH2PPh2) cluster with enynes RCH=CHC≡CR (R is phenyl or ferrocenyl). Formation of indenone derivatives of triruthenium clusters

The thermal reaction of Ru3(CO)10(μ-Ph2PCH2PPh2) (1) with enyne PhCH=CHC≡CPh afforded the trinuclear ruthenium clusters Ru3(CO)6{μ3-P(Ph)CH2PPh2}{μ3-C(Ph)=CHCC(Ph)(1,2-C6H4)C(=0)} (2), Ru3(μ-H)(CO)5{μ3-P(Ph)CH2PPh2}{μ3-C(Ph)=CHCC(Ph)(1,2-C6H4)C(—0)} (3), and Ru3(CO)6(μ-CO){μ3-P(Ph)CH2PPh2}{μ3-C(C=CPh2)CH=C(H)Ph} (4) and also two isomers of Ru3(CO)5(μ-CO)(μ-Ph2PCH2PPh2){μ3-C4Ph2(CH=CHPh)2} (5a and 5b). Clusters 2, 3, and 4 were characterized by IR spectroscopy, 1H and 31P NMR spectroscopy, and X-ray diffraction analysis. The reaction of complex 1 with enyne FcCH=CHC≡CFc gave rise to the Ru3(CO)6{μ3-P(Ph)CH2PPh2}{μ3-C(Fc)=CHCC(Fc)(1,2-C6H4)C(=0)} (6) and Ru3(μ-H)(CO)5{μ3-P(Ph)CH2PPh2}{μ3-C(Fc)=CHCC(Fc)(1,2-C6H4)C(—0)} (7) clusters. According to the spectral data, the latter compounds are isostructural to complexes 2 and 3, respectively.

Synthesis of the gold-dirhenium ferrocenylacetylide cluster. The crystal structure of Re2(μ-C≡CFc){Au(PPh3)}(CO)8

The thermal reaction of Re2(CO)8(NCMe)2 with Au(C≡CFc)PPh3 afforded the cluster Re2(μ-C≡CFc){Au(PPh3)}(CO)8, which was characterized by X-ray diffraction analysis.

A mechanistic study of the Lewis acid–Brønsted base–Brønsted acid catalysed asymmetric Michael addition of diethyl malonate to cyclohexenone

The Michael addition of diethyl malonate (Michael Donor, MD) to cyclohexenone (Michael Acceptor, MA) catalysed by the mono-lithium salt of (S)- or (R)-BIMBOL in dichloromethane is shown to exhibit biomimetic behavior. A combination of kinetics, spectroscopic studies, synthesis of catalyst analogues, inhibition studies and DFT calculations are used to show that the catalyst activates both components of the reaction and uses a chain of proton transfers to facilitate the deprotonation of diethyl malonate. The initial reaction rate was first order relative to both MA and MD and 0.5 order relative to the catalyst, indicating that an equilibrium exists between monomeric and dimeric forms of the catalyst, with the dimer predominating, but only the monomeric form being catalytically active. This was supported by DOSY 1H NMR experiments. The importance of the Lewis acidic lithium cation in the catalytic step was established by complete inhibition of the reaction by lithium complexing agents. The importance of the number of OH-groups and their relative intramolecular orientation and acidities in the polyol catalyst was shown by studying the relative catalytic activities of catalyst analogues. DFT calculations allowed the relative energies and structures of the likely intermediates on the reaction coordinate to be calculated and indicated that the ionisation of MD was facilitated due to the Lewis acidity of the lithium cation and hydrogen bond formation between deprotonated MD (MD−1) and the OH groups of the BIMBOL moiety.