A series of dicationic bis-chelated palladium(II) complexes [Pd(N-N)2][X]2 (N-N = 2,2‘-bipyridine (bipy), 1,10-phenanthroline (phen), and their substituted derivatives; X = PF6 -, BF4 -, OTf-, OTs-) has been synthesized and completely characterized both in the solid state and in solution. The synthetic procedure involves a simple one-pot reaction between Pd(MeCOO)2 and [(N-N)H][X]. These compounds are very active precatalysts for the CO/styrene copolymerization yielding perfectly alternating polyketones. The crystal structures of some complexes of the series provide evidence that a distorsion from the ideal square planar geometry toward a twist conformation occurs. In DMSO solution, one of the two nitrogen-donor ligands is involved in a dissociative equilibrium yielding a monochelated complex with two cis coordination sites available for the copolymerization catalytic process. The catalytically active species is very stable in 2,2,2-trifluoroethanol, where its activity was found unaltered for at least 48 h of reaction without apparent decomposition to palladium metal. The addition of 1,4-benzoquinone (BQ) to the catalytic system has a strong influence on the yield and, above all, on the molecular weight of polyketones. The zerovalent palladium complexes [Pd(N-N)(BQ)], which might be formed during the copolymerization process, have been synthesized and characterized. The crystal structure of [Pd(bipy)(BQ)] shows that benzoquinone acts as a mono-olefinic ligand to Pd. In the presence of protons, the Pd(0) complexes are readily oxidized to Pd(II) with the reduction of benzoquinone to hydroquinone. When [(N-N)H][X] is used as the source of protons, the resulting Pd(II) species is the precatalyst and can immediately re-enter the catalytic cycle.

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protect' the axial Co-C bond. The axial R ligand, coordinated to the upper or psite of the corrin ring, is 5'-deoxyadenosyl in B12 coenzyme (Ado-Cbl), CN in vitamin B1 (CN-Cbl), and an alkyl group in alkylcobalamins (alkyl-Cbl). The benzimidazole residue is coordinated to cobalt in the lower or a-site. A second organocobalamin, Me-Cbl, is also an important cofactor for many enzymic processes. CN-Cbl serves as a metabolic precursor for both coenzymes. Their

Reaction of a ditopic urea "strut" (L1) with cis-(tmen)Pd(NO3)2 yielded a [3+3] self-assembled molecular triangle (T) [L1 = 1,4-di(4-pyridylureido)benzene; tmen = N,N,N',N'-tetramethylethane-1,2-diamine]. Replacing cis-(tmen)Pd(NO3)2 in the above reaction with an equimolar mixture of Pd(NO3)2 and a clip-type donor (L2) yielded a template-free multicomponent 3D trigonal prism (P) decorated with multiple urea moieties [L2 = 3,3'-(1H-1,2,4-triazole-3,5-diyl)dipyridine]. This prism (P) was characterized by NMR spectroscopy, and the structure was confirmed by X-ray crystallography. The P was employed as an effective hydrogen-bond-donor catalyst for Michael reactions of a series of water-insoluble nitro-olefins in an aqueous medium. The P showed better catalytic activity compared to the urea-based ligand L1 and the triangle T. Moreover, the confined nanospace of P in addition to large product outlet windows makes this 3D architecture a perfect molecular vessel to catalyze Diels-Alder reactions of 9-hydroxymethylanthracene with N-substituted maleimide in the aqueous medium. The present results demonstrate new observations on catalytic aqueous Diels-Alder and Michael reactions in heterogeneous fashion employing a discrete 3D architecture of Pd(II). The prism was recycled by simple filtration and reused several times without significant loss of activity.

(9) [PTA = 1,3,5-triaza-7-phosphaadamantane; enac = 1,2-bis-(isopropyleneimino)ethane; OTf = CF 3 SO 3 -] were prepared from Ru-[9]aneS 3 -dmso precursors and structurally characterized, both in solution and in the solid state by X-ray crystallography. Some of them are analogs of known cytotoxic organometallic Ru II -(η 6 -arene) and Ru II -(η 5 -cyclopentadienyl) compounds, in which the aromatic fragment is replaced by the sulfur macrocycle 1,4,7-trithiacyclononane, while the rest of the coordination sphere is left unchanged. Similarly to the aromatic analogs for which data are available, in aqueous solution the Ru-[9]aneS 3 complexes (with the exception of 5) hydrolyze a chloride (or a dmso in the

Self-assembly of a cis-blocked Pd(II) 90° ditopic acceptor [ cis-(tmeda)Pd(NO)] (M) with a tetradentate donor L [benzene-1,4-di(4-terpyridine)] in 2:1 molar ratio yielded two isometric molecular barrels MB1 and MB3 in DMSO [tmeda = N, N, N' N'-tetramethylethane-1,2-diamine]. Exclusive formation of the symmetrical tetrafacial barrel (MB1) was achieved when the self-assembly was performed in aqueous medium. The presence of a large confined cavity makes MB1 a potential molecular container. Spiropyran (SP) compounds exist in stable closed spiro form in visible light and convert to transient open merocyanine (MC) form upon irradiation with UV-light or upon strong heating. The transient MC form readily converts to the stable closed SP form in visible light. MB1 has been employed as a safe container to store the planar and unstable merocyanine isomers (MC1/2) of different spiropyran molecules (SP1/2) [SP1/2 = 6-bromo-spiropyran and 6-nitrospiropyran] for several days. The transient MC forms (MC1 and MC2) were found to be stable inside the molecular container MB1 under visible light and even in the presence of different stimuli such as heat and UV light for a long time. Such stabilization of MC forms inside the confined cavity of MB1 is noteworthy. This phenomenon was generalized by utilizing a carbazole-based molecular barrel (MB2) as a host, which also showed a similar stabilization of transient MC form in visible light at room temperature. Moreover, reverse thermochromism was observed as a result of heating of the MC1 ⊂ MB2 complex, which de-encapsulates the guest in the form of SP1 to give a colorless solution. Moreover, both the host molecules (MB1, MB2) were capable of stabilizing transient MC2 even in the solid state. Such stabilization of transient MC forms in the solid state and transformation of SP forms to MC forms in the solid state in the presence of molecular barrel are remarkable, and these properties have been employed in developing a magic ink.

A new nonsymmetric bis(aryl‐imino)acenaphthene (Ar‐BIAN) ligand, featured by a subtle steric and electronic unbalance of the N‐donor atoms, is reported. With the new ligand and the corresponding symmetrically substituted derivatives, both neutral and monocationic PdCH3 compounds have been synthesized and characterized. The series of the monocationic complexes [Pd(CH3)(L)(Ar‐BIAN)][PF6] (L=CH3CN, dmso) has been extended to dimethyl sulfoxide derivatives. The monocationic complexes are tested as precatalysts for the ethylene/methyl acrylate cooligomerization under mild reaction conditions of temperature and ethylene pressure. The catalytic product is a mixture of ethylene/acrylate cooligomers and higher alkenes. The catalysts containing the new nonsymmetric ligand are found to be more productive than those with the symmetric Ar‐BIANs. The Pd–dmso catalysts are more productive and show a longer lifetime than their Pd–NCCH3 counterparts.

The photophysical properties of two supramolecular building blocks oc and oc2 consisting of a perylene bisimide chromophore substituted with either one or two calix [4]arene units in the N-imide position as well as those of the reference compound oref without calix[4]arene substituents were investigated. A complete picture of the processes taking place after photoexcitation in toluene, CH 2 Cl 2 , and benzonitrile was obtained by means of UV/vis absorption, steady state and time-resolved emission, and femtosecond transient absorption spectroscopy. It has been found that the fluorescence emission of compounds oc (Φ fl ) 0.03 in CH 2 Cl 2 ) and oc2 (Φ fl < 0.01 in CH 2 Cl 2 ) is almost completely quenched compared with the highly emissive reference compound oref (Φ fl ) 0.99 in CH 2 Cl 2 ) because of fast electron-transfer processes from the calix[4]arene moieties to the perylene bisimide chromophore. This predominantly takes place with rate constants of k CS ) 3 × 10 10 s -1 (τ CS ) 32 ps) for compound oc and k CS ) 9 × 10 10 s -1 (τ CS ) 11 ps) for compound oc2 (in CH 2 Cl 2 ) leading to a short-lived charge-separated state consisting of the reduced perylene bisimide unit and the oxidized calix[4]arene moiety.