Kinetic resolution of sulfur-stereogenic sulfoximines by Pd(ii)–MPAA catalyzed C–H arylation and olefination

A direct Pd(ii)-catalyzed kinetic resolution of heteroaryl-enabled sulfoximines through an ortho-C–H alkenylation/arylation of arenes has been developed. The coordination of the sulfoximine pyridyl-motif and the chiral amino acid MPAA ligand to the Pd(ii)-catalyst controls the enantio-discriminating C(aryl)–H activation. This method provides access to a wide range of enantiomerically enriched unreacted aryl-pyridyl-sulfoximine precursors and C(aryl)–H alkenylation/arylation products in good yields with high enantioselectivity (up to >99% ee), and selectivity factor up to >200. The coordination preference of the directing group, ligand effect, geometry constraints, and the transient six-membered concerted-metalation–deprotonation species dictate the stereoselectivity; DFT studies validate this hypothesis.

A Pd/MPAA catalysed KR of heteroaryl substituted sulfoximines through C–H alkenylation and arylation (up to >99% ee) is developed. In-depth DFT studies uncover the salient features.     

A quasi particle approach to relaxation phenomena

An evolution equation for the relaxation of a nucleus in a metal is derived, assuming that the electronic thermostat is the vacuum of quasi-particles. The relaxation originates in the successive creations of quasi-boson excitations of the electronic system.The author's interest in this subject was aroused through a collaboration with Prof. I. Berkes. He wishes to thank him. It is pleasure to thank also Prof. R. Coussement and Dr. P. Put for many helpfull discussions and for their hospitality at the I.K.S. Leuven.     

Heme CD as a probe for monitoring local structural changes in hemeproteins: Alkaline transition in hemeproteins

Structural change due to acid-alkaline transition in hemeproteins were monitored by circular dichroism measurements in the Soret region. It was observed that in cytochrome c and horseradish peroxidase, alkaline transition results in a large change in the heme CD due to significant conformational change in the heme cavity region. In metmyoglobin a simple protolytic mechanism associated with alkaline transition involves very small conformational changes.     

Mixed-symmetry states in the neutron-proton interacting boson model

States of mixed proton-neutron symmetry are investigated in different dynamical symmetries of the interacting boson model. We discuss in each of the limits the energy spectrum, the wave functions and the B(M1; 0₁⁺ → 1 _1⁺) values. We also study three classes of transitional nuclei namely the Pd nuclei [U(5) → O(6)], the Sm nuclei [U(5) → SU(3)] and the Pt nuclei [O(6) → SU(3)] with respect to the energy of the lowest non-symmetric J^π = 1⁺, 3⁺ levels as well as the M1 and M3 strengths for exciting these levels from the ground state. For ⁹⁸Pd we compare this calculation with a shell-model calculation. Finally, we adress the problem of the mixing of the non-symmetric J^π = 1⁺ state with nearby hexadecapole (g-boson) configurations.     

Synthesis and spectroscopy of nickel(II) complexes with 5-methyl-3-formylpyrazole N(4)-methyl-N(4)-cyclohexyl thiosemicarbazone (HMPz4MCy): X-ray crystal structure of [Ni(HMPz4MCy)2]Cl2·2.5H2O

The coordination behaviour of a new pyrazolyl thiosemicarbazone, HMPz4MCy, synthesized and characterized (elemental analyses, mass spectrum, i.r. and ¹H-n.m.r) for the first time, is reported via solid state isolation of Ni^II complexes, [Ni(HMPz4MCy)₂]X₂·nH₂O (X = Cl, Br, NO₃, ClO₄ and BF₄; n = 2–3). The complex species were spectroscopically and structurally characterized. I.r. data for the free ligand and its Ni^II complexes indicate that the ligand, HMPz4MCy, exhibits a neutral NNS tridentate function via the pyrazolyl nitrogen (tertiary), azomethine nitrogen and thione sulphur. Electronic spectral data are suggestive of a distorted octahedral environment for the six-coordinate Ni^II species. X-ray crystallography of a representative species, [Ni(HMPz4MCy)₂]Cl₂·2.5H₂O (P2₁/c, monoclinic) has shown unambiguously that the crystallographic asymmetric unit consists of a [Ni(HMPz4MCy)₂]²⁺ cation and two Cl^– anions with the solvent of crystallization consisting of two H₂O molecules with full occupancy and a third H₂O molecule with half occupancy. The two NNS ligands orthogonally coordinate to the central nickel(II) ion with two azomethine nitrogen atoms in trans and the pyrazolyl nitrogen and the thione sulphur atoms in cis-positions. The crystal structure is stabilized by an extensive network of hydrogen bonds and is also additionally stabilized by C—HS contacts restricting free rotation about the N—C single bonds.     

Synthesis, spectroscopy and cyclic voltammetry of new iron(III) complexes with 5-methyl-3-formyl pyrazole 3-hexamethyleneiminyl thiosemicarbazone (HMPz3Hex): X-ray crystallographic identification of [Fe(MPz3Hex)2]ClO4 · 2H2O with an indication for unusual rotation about the azomethine double bond on complexation with iron(III)

New iron(III) complexes of 5-methyl-3-formylpyrazole 3-hexamethyleneiminylthiosemicarbazone (HMPz3Hex), [Fe(MPz3Hex)₂]X · nH₂O (where X = Cl, NO₃or ClO₄ and n = 1–2) have been synthesized and physico-chemically characterized by magnetic data (polycrystalline state), electronic, i.r. and e.p.r. spectral studies. The reported complexes are all cationic electrolytes (1:1) containing two moles of monodeprotonated title ligand and an anionic counterpart. I.r. spectra (4000–200 cm^?1) indicate coordination to the central iron(III) ion via the pyrazolyl (tertiary) ring nitrogen, azomethine nitrogen and thiolato sulphur atoms of the primary ligand molecule. E.p.r. data (r.t. and l.n.t.) show the presence of a low-spin iron(III) cation with d _xz ² d _xz ² d _xz ¹ configuration. Cyclic voltammograms of iron(III) complexes indicate a reversible Fe⁺³/Fe⁺² couple. X-ray data of [Fe(MPz3Hex)₂]ClO₄ · 2H₂O (P₁, triclinic) authenticate a FeN₄S₂ distorted octahedral coordination with the two azomethine nitrogens trans to each other; the pyrazolyl nitrogens and thiolato sulphurs are in cis-positions, indicating an unusual rotation about the azomethine (C=N) double bond of the free HMPz3Hex during complexation with iron(III).     

New insight into the synthesis of a novel azo-based optically active polyamidoamine side chain dendritic polyester architectural photoswitch

[reaction: see text] A novel chiral polyamidoamine side chain dendritic polyester 4 has been synthesized and found to be a photoresponsive system undergoing reversible E/Z photochemical/thermal isomerization of azo units. Thorough characterization (IR,UV-vis, NMR, FAB-MS, elemental analysis, optical rotation, etc.) were performed to ascertain the structures of dendrimers 2, 3, and 4. The intrinsic viscosity of 4 at 36 degrees C in CHCl(3) was found to be 0.48 dl/g.     

Synthesis,characterization and cyclic voltammetric studies of monopicolinate complexes of ruthenium(II)

Summary Two stable monopicolinate complexes of ruthenium(II), [Ru(bipy)₂(pic)]ClO₄ and [Ru(pap)₂(pic)]ClO₄ [bipy = 2,2-bipyridine, pic = picolinate anion, pap = 2-(phenylazo)-pyridine], were prepared and characterized. The complexes are diamagnetic and behave as 1:1 electrolytes in MeCN solution. In the i.r. spectra, they show characteristic vibrations of bipy or pap, pic and ClO _inf4 ^p– . In MeCN solution, both complexes display three intense absorption bands in the visible region, which have been assigned to metal-to-ligand charge-transfer transitions. Each complex shows a reversible ruthenium(II)-ruthenium(III) oxidation in MeCN, the formal potential (E _inf298 ^p0 ) being 0.75 V versus a saturated calomel reference electrode (SCE) for [Ru-(bipy)₂(pic)]⁺ and 1.44 V versus SCE for [Ru(pap)₂(pic)]⁺. Multiple reductions of the coordinated bipy and pap ligands have also been observed.Author to whom all correspondence should be directed.     

Ruthenium complexes with chiral tetradentate imino-sulfoxide ligands

Treatment of 2-(methylsulfinyl)benzaldehyde (1) with ethylenediamine or (1R,2R)-(-)-1,2-diaminocyclohexane afforded N,N'-bis[2-(methylsulfinyl)benzylidene]ethylenediamine (L(1)) or (1R,2R)-N,N'-bis[2-(methylsulfinyl)benzylidene]-1,2-cyclohexanedia mine (L(2)), respectively. Lithiation of 2-bromobenzaldehyde diethylacetal with n-BuLi/TMEDA followed by reaction with (1R,2S,5R)-(-)-menthyl-(S)-p-toluenesulfinate afforded 2-(S)-(p-tolylsulfinyl)benzaldehyde diethyl acetal (2). Deprotection of 2 with pyridinium tosylate followed by condensation with ethylenediamine, (1R,2R)-(-)-diaminocyclohexane, or (S,S)-(+)-diaminocyclohexane afforded N,N'-bis[2-(S)-(p-tolylsulfinyl)benzylidene]ethylenediamine (L(3)), (1R,2R)-N,N'-bis[2-(S)-(p-tolylsulfinyl)benzylidene]-1,2-cyclohexanediamine ((R,R)-L(4)), or (S,S)-N,N'-bis[2-(S)-(p-tolylsulfinyl)benzylidene]-1,2-cyclohexanediamine ((S,S)-L(4)), respectively. Treatment of [Ru(PPh(3))(3)Cl(2)] with L afforded trans-[Ru(L)Cl(2)] [L = L(1) (3), L(2) (4), L(3) (5), (R,R)-L(4) ((R,R)-6), (S,S)-L(4) ((S,S)-6)]. The X-ray structures of (S(S),R(S))-4, (R,R)-6, and (S,S)-6 have been determined. The average Ru-N, Ru-S, and Ru-Cl distances in (S(S),R(S))-4 are 2.063, 2.2301, and 2.4039 A, respectively. The corresponding distances in (R,R)-6 are 2.071, 2.256, and 2.411 A, and those in (S,S)-6, 2.058, 2.2275, and 2.3831 A. Compound 3 exhibited a reversible Ru(III/II) couple at 0.56 V vs Cp(2)Fe(+/0) in CH(2)Cl(2). Treatment of 3 with AgNO(3) in water afforded the aqua compound trans-[Ru(L(1))Cl(H(2)O)][PF(6)] (7), which has been characterized by X-ray crystallography. The Ru-Cl, Ru-O, average Ru-N, and average Ru-S distances in 7 are 2.3733(6), 2.1469(16), 2.071, and 2.2442 A, respectively. Treatment of 3 with AgNO(3) followed by reaction with PPh(3) afforded [Ru(L(1))(PPh(3))(2)][PF(6)](2) (8). Treatment of [Os(PPh(3))(3)Cl(2)] with L(1) resulted in deoxygenation of one sulfoxide group of L(1) and formation of [Os(L(5))Cl(2)(PPh(3))] (9) (L(5) = N-[2-(methylsulfinyl)benzylidene]-N'-[2-(methylthio)benzylididene]ethylenediamine), which has been characterized by X-ray crystallography. The average Os-S(O), Os-N(trans to P), Os-N(trans to S), Os-P, and Os-Cl distances are 2.1931, 2.085, 2.175, 2.3641, and 2.4266 A, respectively.     

The quadrupole moments of195–197Aum(11/2) and the low temperature thermal relaxation of gold in cadmium

^195,197mHg has been oriented at low temperature in a cadmium single crystal. From the orientation pattern of the 388 keV gamma ray V_ZZ (HgCd) =+1.82(25).10¹⁸ V/cm² has been deduced. Using the dipole-relaxation mechanism on the gold isomeric state, the relaxation constant C_K=0.044(5)Ks, the quadrupole interaction frequencies _Q (195m-AuCd)=+395(18) MHz, _Q (197m-AuCd)=+380(58) MHz and (E2/M1; 261 keV) < 0 are obtained from the orientation pattern of the 261 and 279 keV gamma rays. Using literature electric field gradient of gold in cadmium, Q(195m-Au,11/2)=(+) 1.41(1.0)b and Q(197m-Au,11/2)=(+)1.35(22)b can be deduced.