Showing papers by "Madeleine Helliwell published in 1997"
TL;DR: The products of the addition of ortholithiated N,N-dialkylnaphthamides to aldehydes are pairs of moderately stable, diastereoisomeric atropisomers, formed with selectivities of up to 90∶10 in favour of the syn-atropisomer as mentioned in this paper.
Abstract: The products of the addition of ortholithiated
N,N-dialkylnaphthamides to aldehydes are pairs of
stable, diastereoisomeric atropisomers, formed with selectivities of up
to 90∶10 in favour of the syn-atropisomer.
61 citations
TL;DR: In this paper, a pro-ligand meso-2,2′-(hydroxyimino)dibutyric acid (R,S-H3hidba) has been synthesised from hydroxylammonium chloride and 2-bromobutyric acids.
Abstract: The new pro-ligand meso-2,2′-(hydroxyimino)dibutyric acid (R,S-H3hidba) has been synthesised from hydroxylammonium chloride and 2-bromobutyric acid. Reaction of H3hidba with [VO(acac)2] (acac = acetylacetonate) yielded the complex [V(R,S-hidba)2]2– 1, which was crystallised in the presence of Ca2+ ions from H2O as blue tabular crystals. X-Ray crystallography confirmed the same distinctive eight-co-ordinate structure of the complex anion as identified for Amavadin, the form in which vanadium(IV) is bound in Amanita muscaria mushrooms. The crystal structure of 1 contains a network of linked Ca and V centres where the asymmetric unit consists of a Ca2V2 box-like configuration. The Ca and V metal ions are bridged to one another via a series of unidentate and bidentate carboxylate groups from H3hidba, extending throughout the lattice framework. The novel interaction between Ca2+ ions and Amavadin-style complexes has been further illustrated in the crystal structure of [Ca(H2O)5][V(hida)2]·H2O (H3hida = N-hydroxyiminodiacetic acid) 2. The unit cell packing arrangement observed for 2 differs from 1, comprising helical chains formed by alternate Ca and V units linked only by unidentate carboxylate groups. Cyclic voltammetric studies of 1 exhibited a reversible VV–VIV redox couple in H2O (E½ = +0.43 V, vs. saturated calomel electrode), this oxidation potential is considerably lower in organic solvents (e.g. Me2SO, E½ = –0.07 V). The chemical oxidation of 1 in aqueous medium by ammonium ceric nitrate produced a dark red solution which was transferred into CH2Cl2 using [PPh4]Br. From this solution [PPh4][V(R,S-hidba)2] 3 was isolated and studied using 1H, 13C and 51V NMR spectroscopy. The cyclic voltammogram of 3 also displays a reversible VV–VIV redox couple in CH2Cl2 (E½ = –0.09 V).
30 citations
TL;DR: The series of mononuclear salts have been synthesized by reaction of============trans-[RuCl(pdma)====== 2============ with 1 equivalent of NaN====== 3============ in acetone at room temperature======Following by reflux with an excess of L−L in butan-2-one.
Abstract: The series of mononuclear salts
trans-[RuCl(pdma)
2
(L–L)]PF
6
[pdma = o-phenylenebis(dimethylarsine);
L–L = 4,4′-bipyridine (4,4′-bipy)
2, fumaronitrile (fmn) 4, di-4-pyridyl disulfide
(dpds) 9 or trans-1,2-bis(4-pyridyl)ethylene (bpe)
11] have been synthesized by reaction of
trans-[RuCl(pdma)
2
(NO)][PF
6
]
2
with 1 equivalent of NaN
3
in acetone at room temperature
followed by reflux with an excess of L–L in butan-2-one. The salt
trans-[RuCl(pdma)
2
(C
5
H
5
NS)]PF
6
6
(C
5
H
5
NS = pyridine-4-thione) was
prepared similarly by using pyridine-4-thiol, and
trans-[RuCl(pdma)
2
(C
5
H
4
NSH)]PF
6
8
(C
5
H
4
NSH = pyridine-4-thiol) was
produced upon prolonged reflux of 9 in butan-2-one. Salts
6 and 8 are readily deprotonated by aqueous NaOH to
give
trans-[RuCl(pdma)
2
(C
5
H
4
NS)]
7 and 10. The dinuclear salts
trans-[{RuCl(pdma)
2
}
2
(µ-L
–L)][PF
6
]
2
[L–L = pyrazine (pyz) 1, 4,4′-bipy
3, fmn 5 or bpe 12] have been synthesized by
reaction of
trans-[RuCl(pdma)
2
(NO)][PF
6
]
2
with 1 equivalent of NaN
3
followed by reflux with 1
equivalent of the monometallic salts
trans-[RuCl(pdma)
2
(pyz)]PF
6
, 2,
4 or 11, respectively, in butan-2-one. The dimer
trans-[{RuCl(pdma)
2
}
2
(µ-dpd
s)][I
3
]
2
13
was prepared by oxidation of 8 with iodine in Me
2
SO
at room temperature. Single-crystal structures of 1,
3, 6 and 13 have been determined, and the
extent of intermetallic electronic coupling in the dimers 1,
3, 5, 12 and 13 is assessed using
cyclic voltammetry.
17 citations
TL;DR: In this paper, the authors used a CCD detector to monitor an area of the diffraction pattern, whilst varying the temperature systematically, and confirmed the transition from primitive to C-centred lattice symmetry with temperature.
Abstract: (1,4,8,11,15,18,22,25-Octahexylphthalocyaninato)nickel is a thermotropic liquid crystal, undergoing a transition to a discotic columnar mesophase at 418 K. Its crystals are weakly diffracting needles. Single-crystal X-ray diffraction studies at 103 K, using intense synchrotron radiation of wavelength 0.504 A at Station F2, CHESS and the `Princeton 1k' CCD area detector, and at 295 K using a Cu Kα rotating anode diffractometer, have respectively shown that the symmetry of the crystals is increased from primitive monoclinic (space group P21/n) to C-centred monoclinic (space group C2/c) when the temperature is raised. Solution of the structure at each temperature shows that the increase in symmetry at 295 K arises from slight movement of the molecules, as well as increased thermal motion of the hexyl groups, and small conformational changes in these groups, indicating the first stage of the transition to the discotic columnar mesophase, when the hexyl groups are thought to become completely mobile. The quality of the refinement of the structure is indicative of what can now be realized by employing multipole wiggler synchrotron radiation and a CCD area detector, as well as cryocooling, for difficult small molecule samples. The temperature of the space group transition was determined at the Daresbury SRS, on Station 7.2, using a CCD detector to monitor an area of the diffraction pattern, whilst varying the temperature systematically. A gradual appearance of spots for h + k = 2n + l occurred between 205 and 195 K. Tests were also made using an image plate system at 195 and 293 K, which confirmed the transition from primitive to C-centred lattice symmetry with temperature. No other changes were apparent on the CCD or IP detectors.
16 citations
TL;DR: In this paper, the stereoselectivity of 2-(1-hydroxy- and 1-alkoxy-alkyl)propenylstannanes with aldehyde was investigated.
Abstract: The 2-(1-hydroxy- and 1-alkoxy-alkyl)propenylstannanes 9 and
11–15, react with aldehydes to form 4-hydroxy- and
4-alkoxy-3-methylidenealkanols 23, 24 and 36–53. The
stereoselectivity of these reactions has been investigated. If the
reactions are carried out by transmetallation of the stannane using a
tin(IV) halide before addition of the aldehyde, modest
stereoselectivity in favour of the 1,4-anti-products 23, 36 and
37 is observed for the hydroxystannane 9, whereas the alkoxystannanes
11–15 give rise preferentially to the
1,4-syn-diastereoisomers 47–53, selectivity
75–85∶25–15. It should be noted that these
stereochemical assignments are the reverse of those reported in the
preliminary communication on this work. The structure of the
1,4-anti-product 36 from the reaction between the
hydroxystannane 9 and p-nitrobenzaldehyde was established by
X-ray diffraction. The stereoselectivity of
BINOL–titanium(IV) catalysed reactions of the
(R)-SEM-stannane (R)-12 with benzaldehyde is
controlled by the configuration of the BINOL and can be used to
synthesize either the 1,4-anti- or 1,4-syn-isomers 40
and 47.
11 citations
TL;DR: An atypical conformation of a tosylamide was found in cis-1-(4-methylphenylsulfonyl)-2,5-bis(1-methylpyrrol-2-yl) pyrrolidine, C21H25N3O2S as discussed by the authors.
Abstract: An atypical conformation of a tosylamide was found in cis-1-(4-methylphenylsulfonyl)-2,5-bis(1-methylpyrrol-2-yl)pyrrolidine, C21H25N3O2S
2 citations