A Single Bioinspired Hexameric Nickel Catechol-Alloxazine Catalyst Combines Metal and Radical Mechanisms for Alkene Hydrosilylation.

Mechanisms combining organic radicals and metallic intermediates hold strong potential in homogeneous catalysis. Such activation modes require careful optimization of two interconnected processes: one for the generation of radicals and one for their productive integration towards the final product. We report that a bioinspired polymetallic nickel complex can combine ligand- and metal-centered reactivities to perform fast hydrosilylation of alkenes under mild conditions through an unusual dual radical- and metal-based mechanism. This earth-abundant polymetallic complex incorporating a catechol-alloxazine motif as redox-active ligand operates at low catalyst loading (0.25 mol%) and generates silyl radicals and a nickel-hydride intermediate through a hydrogen atom transfer (HAT) step. Evidence of an isomerization sequence enabling terminal hydrosilylation of internal alkenes points towards the involvement of the nickel-hydride species in chain walking. This single catalyst promotes a hybrid pathway by combining synergistically ligand and metal participation in both inner- and outer- sphere processes.

Molecular Tectonics: Design of Enantiopure Luminescent Heterometallic Ir(III)-Cd(II) Coordination Network.

With the aim of combining luminescence and chirality in heterometallic Ir(III)-Cd(II) coordination networks, synthetic strategies for the formation of new Ir(III)-based chiral metallatectons ([Ir(dFppy)2(1)][PF6]), both as a racemic mixture of Δ and Λ enantiomers (rac-[Ir(dFppy)2(1)][PF6]) and as enantiopure complexes (Δ-[Ir(dFppy)2(1)][PF6] and Λ-[Ir(dFppy)2(1)][PF6]), were developed. The final compounds were characterized both in solution and in the crystalline phase. Notably, their crystal structures were determined by single crystal X-ray diffraction, and their photophysical properties in solution and in the solid state were investigated. Combination of the cationic linear metallatecton with Cd(2+) iodide salt ([CdI3](-)), behaving as an anionic two-connecting node, leads to the formation of 1D chiral and neutral heterometallic Ir(III)-Cd(II) luminescent coordination networks both as a racemic mixture and as enantiomerically pure infinite architectures. The latter have been structurally studied in the solid state by X-ray diffraction both on single crystals and on microcrystalline powders. The infinite coordination networks display phosphorescence in the solid state at ca. 600 nm upon excitation at 400 nm.

Cyclodextrin polyrotaxanes as a highly modular platform for the development of imaging agents.

Selectively functionalized cyclodextrins with a bodipy fluorescent tag or Gd(3+) complex were synthetized and threaded onto a polyammonium chain to form polyrotaxanes. This modular supramolecular assembly makes an ideal platform for bimodal (fluorescent and MRI) imaging applications.

Luminescent coordination polymers based on self-assembled cadmium dipyrrin complexes.

A series of novel Cd(II) complexes based on α,ß-unsubstituted dipyrrin ligands (dpm) has been prepared and characterised both in solution and in the solid state. These compounds are of the [Cd(dpm)(2)] type, with the coordination sphere of the metal centre occupied by two dpm chelates. Interestingly, in contrast to what has been reported for the Zn(II) analogues, in the presence of a pyridyl- or imidazolyl-appended dpm ligand, the coordination number of the Cd(II) cation can be increased to six, leading to an octahedral coordination sphere. As a consequence, the formation of 1-, 2-, and 3D coordination polymers by self-assembly is observed. Photophysical investigations of the discrete complexes and self-assembled networks have demonstrated that both types of compounds are luminescent in the solid state.

Excited state properties and energy transfer within dipyrrin-based binuclear iridium/platinum dyads: the effect of ortho-methylation on the spacer.

Luminescent cyclometalated iridium complexes based on pyridyl appended dipyrrin ligands were prepared and characterized both in the solid state and in solution. The functionalization of the peripheral pyridyl moiety causes dramatic changes on the emission properties of both mono- and hetero- binuclear complexes. A detailed photophysical investigation of the two mononuclear derivatives of the [(Ppy)(2)Ir(dpm-py)] family (Ppy=2-phenylpyridine, dpm-py=5-(4-pyridyl)dipyrrin) was carried out. Introduction of methyl groups at the 3 and 5 positions on the pyridyl unit diminishes the non-radiative rate constant by locking the peripheral pyridyl group orthogonally to the dipyrrinato plane. Thus, they limit the rotational degree of freedom, as well as the charge-transfer character of the excited state. The coordination of these two complexes to a cyclometalated [(dppy)Pt] fragment (dppy=2,6-diphenylpyridine) led to the formation of binuclear species in which the iridium and platinum complexes behave as acceptors and donors, respectively. In these heterobinuclear compounds, the methyl groups do not influence the energy transfer efficiency, which is estimated to be above 90 %. However, they do limit the charge-transfer character of the acceptor's excited state, as well as its rotational degree of freedom, thus avoiding the detrimental effect upon the photophysical performance.

Sensitisation of the near-infrared emission of Nd(III) from the singlet state of porphyrins bearing four 8-hydroxyquinolinylamide chelates.

The α(4) atropoisomer of a tetraaryl porphyrin and its Pd(II) complex, both bearing four hydroxyquinolinyl chelating units pre-organised on the same face of the porphyrin backbone, bind a Nd(III) centre thus affording either a mononuclear or a heterobinuclear anionic species, respectively. The near-infrared emission of the lanthanide centred at 1064 nm is observed upon excitation of the Soret band at 425 nm. Sensitisation proceeds mainly from the singlet state of the porphyrin.

Porphyrin-based switchable molecular turnstiles.

The design, synthesis and structural characterisation, in solution, of two new molecular turnstiles based on Sn-porphyrin derivatives are described. The system is composed of a stator (5-(4-pyridyl)-10,15,20-triphenylporphyrin), a hinge (Sn(IV)) and a rotor (handle equipped with 2,6-pyridinedicarboxamide as a tridentate coordinating site or its Pd(II) complex). The presence of interaction sites, both on the stator and the rotor, offers the possibility of switching between an open state (free rotation of the handle around the porphyrin) and a closed state (blockage of the rotation) by either establishment of hydrogen bonds between the stator and the rotor or by the simultaneous binding of Pd by both coordinating groups.

Luminescent 1D heterometallic (Ir,Cd) coordination polymers based on bis-cyclometalated Ir(III) metallatectons and trinuclear Cd(II) dianionic nodes.

Seven isostructural heterometallic luminescent (Ir,Cd) coordination polymers were prepared upon the combination of tris-chelate cationic Ir(III) complexes behaving as metalloligands with Cd(II) salts. Three octahedral Ir(III) complexes have been considered in the present report. They consist of a bipyridine unit functionalised with 3-pyridyl moieties as peripheral coordinating sites and two 2-phenylpyridyl cyclometalating derivatives. Three cadmium halide salts CdX2 (X = Cl, Br, I) were used and rearranged themselves during the self-assembly process with the metallatectons to afford a dianonic trinuclear Cd node [Cd3X8]2-. Seven out of the nine possible metallotecton-metal salt combinations could be characterised in the crystalline phase by X-ray diffraction on single crystals proving the isostructurality of the seven extended architectures studied. All of the CPs are luminescent with small shifts observed in the emission wavelength compared to the discrete complexes. Depending on the degree of fluorination of the two cyclometalating units, tuning of the emission wavelength of the discrete complexes as well as of the resulting coordination polymers is achieved.

Design and synthesis of sn-porphyrin based molecular gates.

The design, synthesis, and structural characterization, both in solution by (1)H NMR and in the solid state by X-ray diffraction on single crystals, of a series of molecular gates based on Sn-porphyrin derivatives are presented. The molecular system is based on a porphyrin core bearing at the meso positions either phenyl or pyridyl groups as a stator, octahedral Sn(IV) cation located at the center of the porphyrin as a hinge, and different handles connected to the porphyrin through Sn-O axial bonds. The stability of the complexes in the presence of different acids is also reported.

A molecular gate based on a porphyrin and a silver lock.

A Sn(IV) metallaporphyrin bearing a 4-pyridyl group on one meso position and a handle equipped also with a pyridyl unit functions in solution as a molecular gate in the presence of silver cation: the complexation-decomplexation of Ag(I) corresponds to the opening and closing motions of the gate.

Molecular tectonics: heterometallic (Ir,Cu) grid-type coordination networks based on cyclometallated Ir(III) chiral metallatectons.

A chiral-at-metal Ir(III) organometallic metallatecton was synthesised as a racemic mixture and as enantiopure complexes and combined with Cu(II) to afford a heterobimetallic (Ir,Cu) grid-type 2D coordination network.

Energy Transfer at the Zeolite†L Boundaries: Towards Photo- and Electroresponsive Materials.

A series of iridium(III) compounds have been used as stopper molecules at the pore openings of zeolite L and act as effective donor units for transferring excitation energy to dye molecules entrapped within the zeolite channels. The synthesis and photophysical characterization of the new iridium(III) complexes are described, along with Förster resonance energy-transfer experiments. Transfer efficiencies for the studied systems are discussed on the basis of the role played by the localization of the donor excited state and the acceptor distribution in the channels. Because iridium(III) complexes can also be electrically excited, the electroluminescent behavior of donor-acceptor zeolite systems can be explored, by embedding them into a polymeric active layer and constructing light-emitting devices (LEDs). Novel hybrid LEDs can be fabricated with emission from the dyes entrapped into the zeolites and sensitized by the electro-responsive iridium(III) complex.

A platinum based organometallic turnstile.

The synthesis of an organometallic turnstile based on a Pt(II) centre as a hinge was achieved. Its dynamic behaviour in solution was investigated using 1D and 2D NMR techniques. Using Ag(I) cation as an effector, the switching between its open and closed states in solution was demonstrated.

A platinum turnstile with a palladium lock.

An organometallic molecular turnstile composed of a stator based on an α,ω-diphosphine bearing, in a symmetric fashion, the 2,6-pyridyl diamide moiety as a central tridentate chelating unit and a rotor composed of Pt(II) equipped with two pyridyl groups in trans configuration was designed. The switching between its open and closed states using Pd(II) was investigated both in solution and in the solid state.

Porphyrin based molecular turnstiles.

Molecular turnstiles, based on a hinge composed of a Sn-porphyrin bearing coordinating sites at the meso positions and a handle, equipped with a tridentate coordinating pole or its Pd(ii) complex, connected to the porphyrin through Sn-O bonds, offering open (free rotation of the handle around the hinge) and close states (blockage of rotation through binding of Pd(ii)) were designed, prepared and studied both in solution and in the solid state.

Sensitization of the NIR emission of Nd(III) by the alpha4 atropoisomer of a meso-tetraphenyl porphyrin bearing four 8-hydroxyquinolinylamide chelates.

The alpha4 atropoisomer of the meso tetrakis 8-hydroxyquinolinylamide porphyrin and its Pd complex binds Nd(iii) and sensitizes efficiently its near infrared (NIR) emission when excited in the visible domain.

Dipyrrin based luminescent cyclometallated palladium and platinum complexes.

A series of complexes based on the combination of cyclometallated palladium or platinum moieties with functionalized dipyrrin ligands bearing mesityl- or benzonitrile groups have been prepared and characterized both in the solid state and in solution; these compounds exhibit a characteristic dipyrrin-centered luminescence with an emission intensity modulated by the degree of rotational freedom of the aromatic group attached to the dipyrrin chelate.