Rodney J. Geue

Novel cationic surfactants derived from metal ion cage complexes: potential anthelmintic agents

The synthesis of stable highly charged cationic detergents derived from metal ion cage complexes is described along with some of their properties and effects on helminth membranes.

Circular dichroism of cobalt(III) complexes: dependence on the outer sphere configuration

Abstract The single crystal axial CD of three Co(III) completes has been measured between 295 and 9 K. For Λ-Co (sepulchrate) (NO3)3 the rotational strength R(1T1(E) ← 1A1) decreases from ≈11 × 10−40 c.g.s. units at 295 K to ≈0 at 80 K. The main features of the single crystal CD spectra can be explained by a static coupling model of optical activity.

A new template encapsulation strategy for larger cavity metal ion cages

Stereospecific sequential condensation of paraformaldehyde and propionaldehyde with a tripodal bis(triamine)cobalt(III) template rapidly encapsulates the metal, and a subsequent facile reduction of imine functions gives an expanded cavity hexaazabicyclic cage system with unusual structural and chromophore electron properties, complemented by an exceptional stability and relatively fast CoII/III electron exchange rates.

Specificity in template syntheses of hexaaza-macrobicyclic cages: [Pt(Me5-tricosatrieneN6)]4+ and [Pt(Me5-tricosaneN6)]4+

The racemic C3 hexadentate cage complex, [Pt(Me5-tricosatrieneN6)]Cl4 (1,5,9,13,20-pentamethyl-3,7,11,15,18,22-hexaazabicyclo[7.7.7]tricosa- 3,14,18-triene)platinum(IV) tetrachloride), was synthesised stereospecifically and regiospecifically from a reaction of the bis-triamine template [Pt(tamc)2]Cl4 (bis[1,1,1-tris(aminomethyl)ethane]- platinum(IV) tetrachloride) with formaldehyde and then propanal, in acetonitrile under basic conditions. Largely, one racemic diastereoisomer was obtained in a surprisingly high yield (approximately 50%), even though the molecule has seven chiral centres. The origins of the stereoselective synthesis are addressed. The crystal structure of [Pt(Me5-tricosatrieneN6)]-(ZnCl4)1.5Cl.2H2O showed that all three imines were attached to one tame fragment with a chiral amine site ([symbol: see text] SSS, delta RRR) and a chiral methine carbon site ([symbol: see text] RRR, delta SSS) on each ligand strand. The PtN6(4+) moiety had a slightly distorted octahedral configuration with the two types of Pt-N bonds related to the imine and the amine donors, 2.050(7) and 2.072(6) A, respectively. Treatment with sodium borohydride (15 s, 20 degrees C) at pH approximately 12.5 reduced the imine groups, but not the Pt(IV) ion, producing a C3 saturated ligand complex [Pt(Me5-tricosaneN6)]Cl4 ((1,5,9,13,20- pentamethyl-3,7,11,15,18,22- hexaazabicyclo[7.7.7]tricosane)platinum(IV)tetrachloride). X-ray crystallographic analysis showed that the average Pt-N bond distance in the cation increased upon imine reduction to 2.10 (av) A. The cyclic voltammograms of the two cage complexes displayed irreversible two-electron reduction waves in aqueous media and a approximately 0.3 V shift to more positive potentials compared to that of the smaller cavity sar (3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane) analogue. After reduction, net dissociation of one strand of the cage was also evident, to give unstable square planar Pt(II) macrocyclic products.

An electrospray mass spectrometry study of some metal-ion cage complexes

A series of cationic metal complexes of the bicyclic hexaamine cage compound fac-1,5,9,13,20-pentamethyl-3,7,11,15,18,22-hexaazabicyclo[7.7.7]tricosane have been examined by electrospray ionisation (ESI) mass spectrometry, along with metal complexes of related smaller and larger hexaamine cages. The ESI mass spectra are considerably simpler than the corresponding fast atom bombardment (FAB) mass spectra. The most abundant ion in the ESI mass spectra of divalent metal-ion cage complexes is the doubly charged molecular ion [M(cage)]2+. For trivalent metal-ion complexes spectra obtained using a low-resolution quadrupole mass spectrometer suggested that the most abundant ion is of the type [M(cage)3+– H+]2+. However, when the spectra of several of these cage complexes were obtained using a high-resolution sector instrument it can be shown that the most intense peaks are due to mixtures of these and other ions, [M(cage)]2+, formed by reduction of the metal ion in the ion source. The ESI mass spectra of both di- and tri-valent metal-ion complexes also show the presence of ion pairs [M(cage)x++ anion–](x–1)+. In general ions arising from the free cage are not observed which makes the ESI technique suited for characterising the complex cations. However, varying the cone and skimmer potentials can alter the relative abundances of ions, and the degree to which reduction of the central ion occurs, so these parameters must be carefully controlled. The ESI mass spectra of analogous cobalt(III) complexes containing ammonia or ethane-1,2-diamine displayed more extensive fragmentation compared to those of the cobalt(III) cage complexes. This study demonstrates the potential of ESI mass spectrometry for the characterisation of metal cage complexes as a powerful adjunct to NMR spectroscopy and microanalysis.

Phospha-capped cobalt(III) cage molecules: synthesis, properties, and structure

Base-induced condensation of [Co(sen)]3+[sen = 4,4′,4″-ethylidynetris(3-azabutan-1-amine)] with paraformaldehyde and phosphine leads to the phospha-capped bicyclic cage complexes [Co(Mephosphasar)]3+(Mephosphasar = 8-methyl-3,6,10,13,16,19,1-hexa-azaphosphabicyclo[6.6.6]icosane) and its phosphine oxide derivative [Co(Me, Ophosphasar)]3+; the complexes have surprisingly different spectral and electrochemical properties which are attributed to their different conformations and the X-ray crystal structure of [Co(Me, Ophosphasar)][ZnCl4]Cl has been determined.

Stabilization of an unusual conformation of an encapsulated metal ion cobalt(methylarsasarcophagine): synthesis and structure

Base-catalysed condensation of [Co(sen)]3+(1)[sen = 4,4′,4″-ethylidyne-tris(3-azabutan-1-amine)] with formaldehyde yields the stable tri-imine [Co(sim)]3+(2)[sim = 6,6′,6″-ethylidyne-tris(2,5-diazahex-1-ene)] that is converted into the arsenic capped cage molecule [Co(Mearsasar)]3+(3)(Mearsasar = 8-methyl-1,3,6,10,13,16,19-arsahexa-azabicyclo[6.6.6]icosane) by reaction with AsH3; an X-ray crystallographic analysis of (3) reveals an unusual oblique conformation of the encapsulating ligand, which affects the properties of the complex in a marked manner.

The influence of cavity size on the properties of encapsulated rhodium(III) lons: long-lived metal-centred emission in a symmetric expanded cavity rhodium cage system

Efficient and rapid metal template reactions of rhodium(III) hexaamine complexes with paraformaldehyde and nitromethane under non-aqueous conditions lead to both optimal and expanded cavity cage complexes with widely differing X-ray structures and electronic properties; the larger cavity homologues feature a strongly enhanced metal-centred phosphorescence in water at 77 K.

A new strategy for the metal template synthesis of organic metal ion cages

High yield template syntheses of hexa-azabicycloeicosanes and related imines are described arising from non-aqueous condensations of mixed aldehydes with the 4,4′,4″-ethylidyne-tris(3-azabutan-1-amine)cobalt(III) ion in basic media.

Configurational and conformational effects on electron transfer rates

Electron transfer rate constants of the cage complexes Λ, Δ, fac, mer-[Co{(NH3)2, Me3sar}]5+/4+[where {(NH3)2, Me3sar}=(4R,12R,17R) or (4R,11R,17R)-trimethyl-3,6,10,13,16,19 -hexa-azabicyclo[6.6.6]icosane-1,8-diamine or the catoptric (S) forms] show >103-fold differences for these very similar diastereoisomeric ions which are ascribed primarily to lel–ob conformational changes and their effect on the redox potentials of the couples as well as on the electron transfer rates.