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Inclusion compounds of a macrocyclic cavitand cucurbit[8]uril (CB[8]) with cobalt(III) and nickel(II) complexes of 1,3-diaminopropane (tn) and 1,3-diamino-2-propanol (tmOH) { trans-[Co(tn) 2Cl 2]@CB[8]}Cl.14H 2O ( 1), { trans-[Co(tmOH)(tmO)]@CB[8]}Cl 2.22H 2O ( 2), and { trans-[Ni(tmOH) 2]@CB[8]}Cl 2.22H 2O ( 3) were synthesized and characterized by X-ray single crystal analysis, IR spectroscopy, ESI-MS, and by solid-state stripping voltammetry. The encapsulation of trans-[Co(tn) 2Cl 2] (+) within the cavity of CB[8] stabilizes the complex toward ligand substitution reactions in aqueous solution. The electrochemical study demonstrates that CB[8] prefers the oxidized species in trans-[Co(tn) 2Cl 2] (+)/ trans-[Co(tn) 2Cl 2] (0) and trans-[Co(tmO)(tmOH) 2] (2+)/ trans-[Co(tmO)(tmOH) 2] (+) redox couples, but stabilizes the reduced form trans-[Ni(tmOH) 2] (2+) against the oxidized species. The reversibility of voltammogram shapes evidence that for the inclusion compounds 1- 3 electron transfer reactions proceed within the cavity of the host.

The inclusion compound of macrocyclic cavitand cucurbit [8]uril (CB[8]) with the nickel(II) complex containing the tetraazamacrocyclic ligand cyclam, {[Ni(cyclam)]@CB[8]}Cl 2 • •16H 2 O (1), and the inclusion compounds of CB[8] with the copper(II) bis ethylene diamine complex, {trans [Cu(en) 2 (H 2 O) 2 ]@CB[8]}Cl 2 •{CB[8]}•42H 2 O (2a) and {trans [Cu(en) 2 (H 2 O) 2 ]@CB[8]}Cl 2 •17H 2 O (2b), were synthesized and characterized by X ray diffraction analysis, IR and ESR spectroscopy, and electrospray mass spectrometry. Guest-host inclusion compounds can be directly synthesized starting from a metal complex and cucurbit[8]uril, as was exemplified by the preparation of compounds 2a and 2b.Transition metal complexes with polyamines are used as model compounds in studies of metal ion transport in biological systems, 1 for metal regeneration, 2 as NMR con trast agents, 3 for radioactive diagnostics, 4 etc. Metal com plexes with tetraazamacrocyclic ligands are of interest as highly promising materials for use in medicine 5 and as catalysts for various reactions, such as epoxidation or DNA hydrolysis. 6 Inclusion of metal complexes in large organic macro cycles is a rather rare phenomenon. Nevertheless, such compounds, particularly, those with transition metals, are of considerable interest because of a unique environment of the metal ions, which is similar to that observed in metalloenzymes. The first inclusion compounds of macro cycles with metal complexes were synthesized in the late 1980s. 7 In these compounds, alkali metal complexes with crown ethers and cryptands are included in the γ cyclodextrin cavity. For transition metals, an example of inclusion compounds is the zinc pyridylporphyrin com plex included in a macrocycle formed by four other por phyrin complexes. 8 Earlier, inclusion compounds of tran sition metal complexes with polyamines have been syn thesized in the only study, 9 where the inclusion of copper(II) and zinc(II) complexes with the tetraaza macrocyclic ligands cyclam (cyclam is 1,4,8,11 tetraaza cyclotetradecane) and cyclen (cyclen is 1,4,7,10 tetraaza cyclododecane) in the cavity of the organic macrocyclic cavitand cucurbit[8]uril (CB[8]) was described.Cucurbit[n]urils (CB[n]) belong to a family of organic compounds with the composition C 6n H 6n N 4n O 2n . These compounds have a rigid macrocyclic structure consisting of n glycoluril fragments linked via 2n methylene bridges, where n = 5-10. 10,11 Since cucurbiturils have a large intramolecular cavity, they can serve as hosts and form inclusion compounds with guest molecules or ions of ap propriate size (methylpyridinium cations, 12 tetrahydrofu ran molecules, 13 PhP(O) 2 (OH) 14 ). Inclusion of two or more guest molecules in the cavity of large cucurbit[n]urils offers a unique possibility to study new forms of stereo isomerism, bimolecular reactions, and the molecular be havior in the microenvironment. 15, 16 Cucurbit[n]urils differ from other molecular contain ers with cavities of similar size, such as cyclodextrins and calixarenes, in the s...

The unprecedented selective encapsulation of trans-[Co(en)2Cl2]+ from the mixture of trans and cis isomers into the cavity of macrocyclic cavitand cucurbit[8]uril (C48H48N32O16, CB[8]) leads to the inclusion compound {trans-[Co(en)2Cl2]@CB[8]}Cl.17H2O (1). Single-crystal X-ray analysis, 1H NMR, and ESI-MS spectra confirm the formation of host-guest complex 1 in both solid state and solution. The geometry of the complex cation alters significantly upon inclusion, which causes appreciable hypsochromic shifts of the absorption bands of the guest complex. According to TGA data, inclusion of trans-[Co(en)2Cl2]+ dramatically stabilizes the complex toward thermal decomposition. Encapsulation of trans-[Co(en)2Cl2]+ into the CB[8] cavity also increases the stability of the metal complex toward isomerization into the cis form. The supramolecular adduct {cis-[Co(en)2(H2O)2](CB[8])6}Cl3.ca109.5H2O (2) was isolated only after prolonged heating of an aqueous solution of 1 at 120 degrees C in an evacuated tube; it was characterized by X-ray crystallography, IR, and elemental analysis.

Trace amounts of urea derivatives enhance the rate of nitrobenzene N3-sensitized TiO 2 photoreduction by catalyzing the proton transfer. The usually required addition of transition metal co-catalysts becomes dispensable for this visible light photocatalysis, facilitating its application in organic synthesis.