A straightforward synthesis of the zwitterionic benzoquinonemonoimine 8 is reported. This molecule is a rare example of a zwitterion being more stable than its canonical forms. It is shown that 8 is best described as constituted of two chemically connected but electronically not conjugated 6 pi electron subunits. Its reactivity with electrophiles such as H(+), CH(3)(+), and metal salts leads to the synthesis of new 12 pi electron molecules 12 (H(+)), 14 (CH(3)(+)), and 20 (Pd(2+)), respectively, in which one or both 6 pi electron subsystems localize into an alternation of single and double bonds, as established by X-ray diffraction. The acidity of the N[bond]H protons of 8 can be modulated by an external reagent. Dependent on the electrophile used, the control of the pi system delocalization becomes possible. When the electrophile simply adds to the zwitterion as in 12, 14, or 15, there is no more negative charge to be delocalized and only the positive charge remains delocalized between the nitrogen atoms. Furthermore, when a reaction with the electrophilic reagent results in deprotonation, as in 17-21, there remains no charge in the system to be delocalized. DFT calculations were performed on models of 8, 12, 14, 20, and on other related zwitterions 9 and 10 in order to examine the influence of the fused cycles on the charge separation and on the singlet-triplet energy gap. An effect of the nitrogen substituents in 8 is to significantly stabilize the singlet state. The dipole moment of 8 was measured to be 9.7 D in dichloromethane, in agreement with calculated values. The new ligands and complexes described in this article constitute new classes of compounds relevant to many areas of chemistry.

Photodynamic therapy (PDT) is a relatively new cytotoxic treatment, predominantly used in anticancer approaches, that depends on the retention of photosensitizers in tumor and their activation after light exposure. This technology is based on the light excitation of a photosensitizer which induces very localized oxidative damages within the cells by formation of highly reactive oxygen species, the most important being singlet oxygen. Many photo-activable molecules have been synthesized such as porphyrins, chlorins and more recently phthalocyanines which present a strong light absorption at wavelengths around 670 nm and are therefore well-adapted to the optical window required for PDT application. However, the lack of selective accumulation of these photo-activable molecules within tumor tissue is a major problem in PDT, and one research area of importance is developing targeted photosensitizers. Indeed, targeted photodynamic therapy offers the advantage to enhance photodynamic efficiency by directly targeting diseased cells or tissues. Many attempts have been made to either increase the uptake of the dye by the target cells and tissues or to improve subcellular localization so as to deliver the dye to photosensitive sites within the cells. The aim of this review is to present the actual state of the development of phthalocyanines covalently conjugated with biomolecules that possess a marked selectivity towards cancer cells; for some of them their photophysical properties and photodynamic activity will be presented.

Transition-metal-catalyzed asymmetric allylic substitutions are widely employed. Steric course and regioselectivity of these reactions vary considerably, depending on the metal ion, ligands, the nucleophile, and the leaving group. Today, Pd catalysts [1] are usually employed for 1,3-disubstituted allylic substrates, while Ir catalysts [2] serve well for a broad range of monosubstituted allylic substrates.The currently best Ir catalysts are prepared from [{Ir-(cod)Cl} 2 ] (cod = cycloocta-1,5-diene) and a chiral phosphoramidite by C À H activation with base (Scheme 1). Although enantioselectivity is high, this catalyst system suffers from several deficiencies: 1) It is sensitive towards oxygen.2) Long-term stability is low. 3) High selectivities are obtained only with solvents of low polarity, preferably THF. The catalyst system is stable against water and alcohols; however, enantioselectivity in these solvents is lower than in THF. 4) Regioselectivity can be as low as 3:1 (2/3), for example, with substrates 1 b-e.[3]We have now developed a modified catalyst derived from dibenzo[a,e]cyclooctatetraene (dbcot) and L2, which allows substitutions to be run without inert gas for the first time. In addition, regioselectivities with the new catalyst are considerably improved over those with presently used catalysts. Furthermore, we have observed that catalyst preparation by CÀH activation is reversible for complexes of L2 under the standard reaction conditions.The ligand cod can be removed from iridium or altered by a number of reactions. For improvement, dbcot appeared promising because its bonding to Ir is stronger than that of cod, its Ir complexes do not undergo intramolecular CÀH activation at the dbcot moiety, and it is a better electron acceptor than cod. [4] Preparations of dbcot [5] and [{Ir(dbcot)Cl} 2 ][4] were straightforward. The latter was subjected to C À H activation under argon by treatment with 1,5,7-triazabicyclo-[4.4.0]dec-5-ene (TBD) [6] or n-propylamine (Scheme 3). [7] Substitution reactions were investigated with ligands L1-L3 (Scheme 1); the best results were obtained with L2.

Dinuclear, divalent acetylacetonato (acac) complexes of the type [M(acac){mu-C6H2(--NR)4}M(acac)] (M = Ni, Pd) have been prepared by the reaction of the corresponding bis(acac) metal precursor with 2,5-diamino-1,4-benzoquinonediimines C6H2(NHR)2(=NR)2 (4a, R = CH2-t-Bu; 4b, R = CH2Ph; 4c, R = Ph), which are metalated and become bridging ligands, also like in the complex [(C8H11)Pt{mu-C6H2(--NCH2-t-Bu)4}Pt(C8H11)] (6) obtained by the reaction of 4a with [PtCl2(COD)]. The complexes were fully characterized, including by X-ray diffraction for [Ni(acac){mu-C6H2(--NCH2Ph)4}Ni(acac)] (9b) and [Pd(acac){mu-C6H2(--NCH2-t-Bu)4}Pd(acac)] (10a). The coordination geometry around the metal ions is square-planar, and a complete electronic delocalization of the quinonoid pi system occurs between the metal centers over the two N--C--C--C--N halves of the ligand. The nature of the N substituent explains the differences between the supramolecular stacking arrangements found for [Ni(acac){mu-C6H2(--NR)4}Ni(acac)] (9a; R = CH2-t-Bu; 9b, R = CH2Ph). The Ni complexes were evaluated as catalyst precursors for ethylene oligomerization in the presence of AlEtCl(2) or MAO as the cocatalyst, in particular in order to study possible cooperative effects resulting from electronic communication between the metal centers and to examine the influence of the N substituent on the activity and selectivity. These catalysts afforded mostly ethylene dimers and trimers.