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The stability of the 4,4′-bis(dimethylamino)diphenylmethane carbocation is significantly enhanced in aqueous solution by its inclusion in the cucurbit[7]uril host cavity. The formation of the host–guest complex (KCB[7] = 2.0 × 104 M−1) shifts the carbinol–carbocation equilibrium, maximizing the formation of the intensely blue carbocation to 90% at pH 5.2.

The protonated forms of the chiral molecules ( S )- and ( R )- N -benzyl-1-(1-naphthyl)ethylamine (BNEAH + ) form very stable 1:1 guest–host complexes with cucurbit[7]uril in aqueous solution. The stoichiometry and stability constants for the guest–host complexes were determined by 1 H NMR, UV–visible and circular dichroism spectroscopy and electrospray mass spectrometry. The molecular optical rotations of the guests increase in magnitude by about 5-fold upon formation of the {BNEAH·CB[7]} + species. Energy minimized structures of the guests and guest–host complexes indicate changes in the dihedral angles about the stereogenic centre upon ion-dipole and H-bonding interactions between the ammonium hydrogens of the guest and the carbonyl groups of the cucurbituril portals. The increases in the optical rotations are discussed in terms of restricted rotations of the naphthyl groups and in preferential solvation of benzylamine in the cucurbit[7]uril cavity.

The effects of β-cyclodextrin on the kinetics of the oxidation of three novel bisferrocenyl cationic complexes; [(η 5 -C 5 H 5 )Fe(η 5 -C 5 H 4 CH 2 N(CH 3 ) 2 CH 2 ( p -C 6 H 4 )CH 2 N(CH 3 ) 2 CH 2 η 5 -C 5 H 4 )Fe(η 5 -C 5 H 5 )] 2+ ( 1 ), [(η 5 -C 5 H 5 )Fe(η 5 -C 5 H 4 CH 2 N(CH 3 ) 2 (CH 2 ) 12 N(CH 3 ) 2 CH 2 η 5 -C 5 H 4 )Fe(η 5 -C 5 H 5 )] 2+ ( 2 ), and [(η 5 -C 5 H 5 )Fe(η 5 -C 5 H 4 CH 2 N(CH 3 ) 2 CH 2 η 5 -C 5 H 4 )Fe(η 5 -C 5 H 5 )] + ( 3 ), by bis(pyridine-2,6-dicarboxylato)cobaltate(III) have been investigated in aqueous media. 1 H NMR and electrospray ionization mass spectroscopy revealed that these compounds form 1:1 and 2:1 host–guest complexes with β-cyclodextrin. The respective stability constants, K CD and K 2CD , of 3700±400 and 1500±200 M −1 for 1 , 6800±800 and 1600±200 M −1 for 2 , and 4000±500 and 1500±200 M −1 for 3 , were determined from fits of the kinetic data. The electron transfer rate constants were observed to decrease significantly upon the formation of a 1:1 host–guest complex with β-CD (890±30 to 260±40 M −1 s −1 for 1 , 870±50 to 300±65 M −1 s −1 for 2 , and 520±40 to 350±50 M −1 s −1 for 3 at 25.0°C). The 2:1 host–guest complexes were found to be unreactive to oxidation (0±50 M −1 s −1 ). The decreased reactivities of the inclusion complexes are attributed to decreased thermodynamic driving forces and steric hindrances to the approach of the oxidant. The molecular structure of compound 3 was determined by X-ray structure analysis.

This report describes the synthesis and characterization of Pt(II)-bis(guanosine)(R-phen) complexes (where R=H (phen) or 2,9-dimethyl (dmphen)), as a model for bifunctional covalent adduct formation between antitumor (dichloro)Pt(II)amine complexes and DNA bases. The 1 H and 13 C NMR spectra (in D 2 O) of the isolated product in the reaction of the corresponding [(dichloro)(R-phen)Pt(II)] complex, with 2 mole equivalents of guanosine, reveal formation of a cis -bis(guanosine)(phen)Pt(II) ( 1 ) and a trans -bis(guanosine)-(dmphen)(Cl)Pt(II) ( 2 ). The 1 H NMR spectrum of 1 reveals a mixture of head-to-tail ( htt ) and head-to-head ( hth ) rotamers that do not interconvert on the NMR time scale (200 and 400 MHz, 298–343 K). For complex 2 the formation of a trans -bis(guo) complex with monocoordinated dmphen ligand is in accord with recent findings in analogous reactions of [Pt(dmphen)Cl 2 ] with alkenes, alkynes and aryl phosphine ligands. It is noteworthy that the room-temperature 1 H NMR spectrum of 2 in D 2 O showed no intramolecular process due to ‘flipping’ of the mono-coordinated dmphen ligand; this is in contrast to observations with trans -bis(PPh 3 ) complex (in CD 2 Cl 2 ,RT) previously reported. The NMR spectral data of the two complexes have been re-examined and the different behavior is discussed.

The stability constants for the inclusions of the [FeCp(CpCH2N(CH3)3]+ cation in α- (150±10 M−1), β- (4810±600 M−1), dmβ- (5010±800 M−1) and γ-cyclodextrins (500±50 M−1) have been determined at 25 °C by means of 1H NMR chemical shift titrations. The effects of cyclodextrin inclusion of the substituted ferrocene couple on the kinetics of its electron-transfer reactions have been investigated in aqueous solution at 25.0 °C. The inclusions of [FeCp(CpCH2N(CH3)3]+ by cyclodextrins decrease the rate constant for its oxidation by bis(pyridine-2,6-dicarboxylato)cobaltate(III) (from 930 to 20 M−1 s−1 upon β-CD inclusion). The rate constants for the oxidations of ascorbic acid by [FeCp(CpCH2N(CH3)3]2+ increase (from 640 to 2600 M−1 s−1 for β-CD) upon inclusion of the oxidant by α- (KCD=10±5 M−1), β- (150±15 M−1) and dmβ-cyclodextrin (140±30 M−1) inclusions of the oxidant. The γ-cyclodextrin has a negligible effect on the electron-transfer rate constant. The effects of cyclodextrin inclusion on the kinetics of these electron-transfer reactions are discussed in terms of changes in the thermodynamic driving force of the reaction and shielding of the reactants.

The kinetics of the outer-sphere oxidation of L-ascorbic acid (H2A) by tris(2,2′-bypyridine) and tris-(4,4′-dimethyl-2,2′-bipyridine) complexes of osmium(III), ruthenium(III), and nickel(III) have been investigated in acidic aqueous media at 9–25 °C. The observed inverse acid dependence, -d[ML3+3]/dt = 2(k1 + k2K1/[H+])(ML3+3][H2A], suggest a mechanism involving H2A and HA− pathways, for which the specific rate and activation parameters have been determined. These and previously reported rate constants for cross-reactions involving ascorbate species are correlated in terms of the Marcus relationships. Estimates of the self-exchange parameters for the one-electron couples: H2A/H2A+·, k11 = 2 × 103 M− s−1; HA−/HA·, k11 = 1 × 105 M− s−1; A2−/A−·, k11 = 2 × 105 M− s−1], based on ascorbate radical reduction potentials calculated from proton and redox equilibrium constant, are presented.

The kinetics of the outer-sphere reduction of the hexakis(urea)manganese(III) ion by a series of nickel(II) macrocycles and metal(II) tris(polypyridine) complexes have been investigated in acetonitrile at 25 °C. The electron self-exchange rate constant for the Mn(urea) 6 2+/3+ . couple has been derived from the cross-reaction kinetic data using the Marcus relationship and calculated using a semi-classical model. The rate constant derived from the cross-reactions with the nickel macrocycle complexes is in reasonable agreement with the value calculated from the semi- classical model, at 10 −1 M −1 s −1 . A range of much lower self-exchange rate constants, 10 −5 –10 −2 M −1 s −1 , results from the cross-reactions of Mn(urea) 6 3+ with the metal(II) tris(polypyridine) complexes. The discrepancies in the rate constants are discussed in terms of the degree of nonadiabaticity in the cross- reactions, and its relationship to the nature of the substituents on the polypyridine complexes. The self-exchange rate constant for Mn(urea) 6 2+/3+ is compared with those of other Mn(lI)/Mn(IlI) couples and related to the reorganization barriers to electron exchange.

A kinetic study shows that carbon monoxide substitution reactions of the seventeen-electron complex {(η) 5 -C 5 H 5 )Cr(CO) 3 } proceed via an associative process.