Malcolm S. Tolley

Ein chemisch und elektrochemisch schaltbares [2]Catenan mit Tetrathiafulvalen-Einheit

Ein [2]Catenan als mechanischer Schalter: In dieser Verbindung umschliest ein Cyclobis(paraquat-p-phenylen)-Tetrakation einen makrocyclischen Polyether, der eine redoxaktive Tetrathiafulvalen(TTF)-Einheit und einen 1,5-Dioxynaphthalinring enthalt. Dieser molekulare Schalter last sich chemisch oder elektrochemisch betatigen. Im reduzierten Zustand liegt die neutrale TTF-Einheit „innerhalb”, im oxidierten (TTF+/TTF2+) dagegen „langsseits” des tetrakationischen Cyclophans; der Wechsel zwischen reduziertem und oxidiertem Zustand, I4+ bzw. I5+(I6+), wird von einem deutlichen Farbwechsel begleitet.

Cyclophanes and [2]catenanes as ligands for transition metal complexes: Synthesis, structure, absorption spectra, and excited state and electrochemical properties

Two tetracationic cyclophanes and two [2]catenanes containing paraquat-type units together with one or two transition metal chelating 2,2′-bipyridyl moieties have been synthesized. The metal-binding units have been used to generate novel mono- and binuclear ruthenium(II), rhenium(I), silver(I) (right), and copper(I) complexes.

The Synthesis and Characterization of a New Family of Polyamide Dendrimers

An eight-member family of dendrimers has been built up by both convergent and divergent methodologies from an orthogonally-protected amino-tetraacid. Examination of the series by GPC, 1H NMR and computer modeling suggests that the three-directional fourth-generation dendrimer (right) has a globular, void-containing structure.

A Molecular Chameleon: Chromophoric Sensing by a Self-Complexing Molecular Assembly

A color change from purple to green takes place on addition of tetrathiafulvalene (TTF) to the macrobicyclic receptor 14+ , which is composed of a cyclobis(paraquat-p-phenylene) tetracation that shares one of its paraphenylene rings with a 1,5-naphthoparaphenylene-[36]crown-10 macrocycle. The TTF molecule forces the macrobicycle to turn inside out (see schematic drawing below) and displaces the self-complexed 1,5-dioxynaphthalene ring system from the center of the tetracationic cyclophane.

PROTON SPONGE AS A CARBON NUCLEOPHILE, ADDITION TO A PUTATIVE CARBOCATION LINKED TO A DICARBACOBALTABORANE CAGE

Abstract The proton sponge tetra- N -methyl-1,8-diaminonaphthalene reacts as a carbon nucleophile towards the carbocation centre in [{Co(C 2 B 9 H 10 S) 2 }CH] to produce [4-{Co(C 2 B 9 H 10 S) 2 CH}-C 10 h 5 −1,8-{(NMe 2 ) 2 H}] mixed with the related compound [4-{Co(C 2 B 9 H 10 S) 2 C(OH)}-C 10 H 5 - 1, 8{(NMe 2 )H}]. both being found in the X-ray crystal structure of the reaction product, [4-{Co(C 2 B 9 H 10 S) 2 CH}-C 10 H 5 -1,8-{(NMe 2 )H}-[4-{Co(C 2 B 9 H 10 S) 2 C(OH)}- C 10 H 5 -1,8-{(NMe 2 ) 2 H}] · 2MeCN. In [4-{Co(C 2 B 9 H 10 S) 2 C(OH)}-C 10 H 5 -1,8-{(NMe 2 ) 2 H}], the oxygen forms a hydrogen bond with a {BH} group from one carbaborane cage and is bound to carbon with an unusually long CO bond distance of 1.691(11) A.

Dynamic stereochemistry of imines and derivatives. Part V. Acid catalysis of E–Z imine interconversion

The rate of E–Z isomerization in N-(α-phenyl-4-nitrobenzylidene)methylamine at 35° is shown to be markedly increased by trace amounts of benzoic acid. Dynamic n.m.r. experiments at higher temperature show that the isomerization rate is proportional to the acid concentration and enable activation parameters to be determined. CNDO/2 Calculations performed on the benzylideneammonium ion suggest that the C[graphic omitted] rotational barrier is ca.46 kcal mol–1, and high temperature n.m.r. studies on a related immonium perchlorate also indicate a high rotational barrier. It is suggested that benzoic acid promotes imine isomerization by nucleophilic addition to the C[graphic omitted] bond in the conjugate acid. The relevance of the rate of imine isomerization to the mechanism of the imine–peroxyacid reaction is discussed.

Synthesis, electrochemistry and spectroelectrochemistry of a porphyrin-viologen donor-acceptor diad

A new donor–acceptor (D–A) molecule, 5,10,15,20-[N-benzyl-N′-(4-benzyl-4,4′-bipyridinium-4-pyridyl)]triphenylporphyrin tris(hexafluorophosphate), 4, has been synthesised. The diad, 4, and its precursors, have been fully characterised by 1H and 13C NMR spectroscopy, mass spectrometry, UV/Visible spectroscopy and cyclic voltammetry. In-situ UV/Visible and EPR measurements show that the site of the first electrochemical reduction is the benzylviologen component of the molecule. The second reduction wave from cyclic voltammetry was shown by in-situ EPR to comprise two unresolved one-electron processes, and this was confirmed by chronocoulometry. The first of these two reduction processes rendered the diad diamagnetic, as was shown by the disappearance of the signal due to the benzylviologen radical. The second gave rise to the appearance of a new EPR signal, which was found to correspond to the porphyrin radical. We believe this to be the first reported resolved spectrum of a monoreduced porphyrin radical.

The template-directed synthesis of porphyrin-stoppered [2]rotaxanes

Two [2]rotaxanes, composed of (i) a polyether chain intercepted by (a) one centrally-located and (b) two symmetrically-located π-electron-rich hydroquinol rings and terminated by free-base and metallated (Zn) tetraaryl-porphyrin groups respectively and (ii) a tetracationic cyclophane constructed of two π-electron-deficient bipyridinium units linked by paraphenylenedimethyl residues, have been self-assembled by a clipping procedure.

Dynamic behaviour of a pseudo[n]polyrotaxane containing a bipyridyl-based cyclophane: spectroscopic observations

Abstract We have shown by 1 H n.m.r. spectroscopy that the equilibrium between the cyclophane 5,12,19,26[tetraazoniaheptacyclo[24.2.2.2 2,5 .2 7,10 .2 12,15 .2 16,19 .2 21,24 ]tetraconta2,4,7,9,12,14,16,18,21,23,26,28,29,31,33,35,37, 39-octa-decaene]tetrakis(hexafluorophosphate) ( 1 ) and the polymer [poly(1-(1,4,7-trioxadecenyl)-4-(11-(1-(5-oxynaphthyl)-1,4,7,11-tetroxaundecenyl))benzene)] ( B:N ) n is both rapid and heavily weighted toward the formation of the pseudo[ n ]polyrotaxane at room temperature in both MeCN-d 3 and DMSO-d 6 . At room temperature in DMSO-d 6 there is about one ring upon the polymer for each two repeat units of ( B:N ), at higher temperatures more repeat units are required to support one 1 . At temperatures of ca. 243 K in MeCN-d 3 this system self assembles, by π stacking of the electron-rich polymer aromatics and the electron-poor cyclophane aromatics, into very ordered ‘rods’ that are on average about 10 nm long.

Imines and derivatives. Part 23. Anomalous 1H NMR spectrum of N-[1-(1-naphthyl)ethylidene]-1-phenyl-2-propylamine: conformation in solution, atropisomerism and an X-ray crystal structure

1 H NMR spectra of the title imine in solution indicate the presence of three stereoisomers due to E/Z isomerism about the imino bond and atropisomerism about the 1-naphthyl imino bond in the Z-isomer. The most abundant Z-isomer, which was isolated in crystalline form, exhibits a highly unusual NMR signal at δ 5.9 assigned to a naphthyl proton α to the imino group. The X-ray crystal structure reveals that this hydrogen atom is situated only 2.7 A above the face of the phenyl ring of the N-1-phenyl-2-propyl moiety and hence experiences a large diamagnetic ring current shielding effect. An attractive edge-to-face ring interaction involving this naphthyl proton and the π-electrons of the proximate phenyl group could account for this observation. The marked temperature dependence of this NMR signal is quantitatively analysed in terms of a fast equilibrium in solution between the conformation favoured in the solid state and a second conformation which lacks the ring current effect.