pH-Driven Cu2+ Translocation in Ferrocene-Containing Ligands

Controlled translocation of palladium(II) within a 22 ring atom macrocyclic ligand

Double aza-Michael addition of n-butylamine to the two acrylamide groups of acyclic N(2),N(6)-bis(6-acrylamidopyridin-2-yl)pyridine-2,6-dicarboxamide gives the corresponding macrocycle, H₄L. H₄L has potential coordination pockets associated with the 2,6-dicarboxamide (head) and the butylamine (tail) regions of the macrocycle. Depending on the conditions employed, macrocyclic complexes with palladium(II) coordinated to either the tail or the head of the macrocycle can be isolated. Thus, treatment of H₄L with [PdCl2(NCPh)2] and sodium acetate, or [Pd(OAc)2] gives the closely related "tail-coordinated" complexes [PdCl(H3L)] (3a) or [Pd(OAc)(H3L)] (3b), respectively. However, employment of the bases 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) or pyridine during the treatment of H₄L with [Pd(OAc)2] results in the "head-coordinated" complexes [Pd(NH2R)(H2L)] (NH2R = N-(3-aminopropyl)caprolactam, which is formed by hydrolysis of DBU) (5) or [Pd(OH2)(H2L)] (6), respectively. Translocation of the palladium ion from the macrocycle tail in 3b to the head occurs on treatment with either DBU or N-(3-aminopropyl)caprolactam. In both cases the product 5 is formed. The aqua ligand in 6 is labile and easily displaced by the N-donor ligands n-butylamine, N-(3-aminopropyl)caprolactam or DBU to give the corresponding complexes [Pd(NH2(n)Bu)(H2L)] (4), (5), or [Pd(DBU)(H2L)] (7). The data suggest that hydrolysis of DBU to produce the N-(3-aminopropyl)caprolactam ligand in 5 is catalysed by the acetic acid formed during ligand metallation rather than by coordination to palladium. The X-ray crystal structures of H₄L, 5, and 6 are reported.

Complete photochromic structural changes in ruthenium(II)-diimine complexes, based on control of the excited states by metalation

The thermal and photochemical reactions of a newly synthesized complex, [Ru(II)(TPA)(tpphz)](2+) (1; TPA=tris(2-pyridylmethyl)amine, tpphz=tetrapyrido[3,2-a:2',3'-c:3'',2''-h: 2''',3'''-j]phenazine), and its derivatives have been investigated. Heating a solution of complex 1 (closed form) and its derivatives in MeCN caused the partial dissociation of one pyridylmethyl moiety of the TPA ligand and the resulting vacant site on the Ru(II) center was occupied by a molecule of MeCN from the solvent to give a dissociated complex, [Ru(II)(η(3)-TPA)(tpphz)(MeCN)](2+) (1', open form), and its derivatives, respectively, in quantitative yields. The thermal dissociation reactions were investigated on the basis of kinetics analysis, which indicated that the reactions proceeded through a seven-coordinate transition state. Although the backwards reaction was induced by photoirradiation of the MLCT absorption bands, the photoreaction of complex 1' reached a photostationary state between complexes 1 and 1' and, hence, the recovery of complex 1 from complex 1' was 67%. Upon protonation of complex 1 at the vacant site of the tpphz ligand, the efficiency of the photoinduced recovery of complex 1+H(+) from complex 1'+H(+) improved to 83%. In contrast, dinuclear μ-tpphz complexes 2 and 3, which contained the Ru(II)(TPA)(tpphz) unit and either a Ru(II)(bpy)2 or Pd(II)Cl2 moiety on the other coordination edge of the tpphz ligand, exhibited 100% photoconversion from their open forms into their closed forms (2'→2 and 3'→3). These results are the first examples of the complete photochromic structural change of a transition-metal complex, as represented by complete interconversion between its open and closed forms. Scrutinization by performing optical and electrochemical measurements allowed us to propose a rationale for how metal coordination at the vacant site of the tpphz ligand improves the efficiency of photoconversion from the open form into the closed form. It is essential to lower the energy level of the triplet metal-to-ligand charge-transfer excited state ((3)MLCT*) of the closed form relative to that of the triplet metal-centered excited state ((3)MC*) by metal coordination. This energy-level manipulation hinders the transition from the (3)MLCT* state into the (3)MC* state in the closed form to block the partial photodissociation of the TPA ligand.

Ion Translocation in Artificial Molecule-based Systems Induced by Light, Electrons, or Chemicals

Synthetic molecules and nanodevices, like their more elaborate biological counterparts, have been shown to perform several sophisticated functions, using even fairly simple molecular architectures. One limitation to developing artificial molecular arrays and networks from these miniscule building blocks is the lack of a unifying strategy whereby they can communicate or interact together, which has been successfully developed in natural systems. Understanding and harnessing these efficient biological processes could prove key in the development of future integrated molecule-based nanodevices and networks. Herein, we give a short overview of some manifestations of intra- and intermolecular communication based on chemical messengers in artificial systems, in some ways analogous to natural systems, which are in turn controlled by light, a redox process or a chemical reaction or interaction. Some advantages, limitations, and challenges are highlighted.