Multimetal Complexes Research Articles

Excited-state energy- and electron-transfer reactions in multimetal systems

The ability of scientists to convert light into stored chemical potential energy has increased over the past ten years.1 A critical component of this development has been the sophistication of the synthesis of multi metal systems.1~2 Conceptually, the design of individual, but coupled, components in supramolecular systems with specific properties such as light absorption, light emission, chemical reaction, charge storage and conductivity are now possible through elaborate synthetic schemes.2 However, little is known about the coupling of these components. Extensive electronic coupling may perturb the desired characteristics of the mononuclear fragments. On the other hand, minimal coupling may preclude energyor electron-transfer processes within the lifetime of the excited state of the molecular ensemble. Our goal in this paper is to outline some of the design constraints present in supramolecular systems in terms of the coupling of metal centers in excited-state, energyand electrontransfer processes. Metal azine systems have been used extensively in the design of multimetal complexes. 13 One reason for this extensive use in the longlived excited state of complexes such as Ru(bpy)$+, where bpy = 2,2’bipyridine. Another reason is that polyazaaromatic ligands form stable, chelating, bridging ligands. The azines used as bridging and terminal ligands in this work are pictured in Figure 1.

Metal-organic ligand interaction in seawater: Multimetal complexation model for metal titration

A multimetal complexation model, consistent conceptually with the ligand-titration model has been developed for the metal titration. This model gives a similar relationship between total and free ion concentrations of an added metal to that derived from the discrete-ligand model in which the coexistence of strong and weak ligands is assumed. The conditional stability constant for organic complexes derived from the new model is in agreement with the strong-ligand conditional stability constant according to the discrete-ligand model; this constant also coincides with that obtained using the ligand-titration method.

Assemblage of multimetal complexes using the diphosphoxane (POP) linkage

Heterobimetallic complexes can be prepared using the monodentate diphosphoxane ligand in Mo(CO) 5PPh 2OPPh 2. Reactions with Cr(CO) 5CH 3CN and Fe 2(CO) 9 yielded the corresponding bimetallic products. The structure of Mo(CO) 5PPh 2OPPh 2Fe(CO) 4 was established by a single-crystal X-ray study. Cell data: Space group P 1 , monoclinic, a 10.533(2), b 10.993(2), c 16.439(3) Å; α 97.86(2), β 92.34(1), γ 116.20(1)°; Z = 2, D c 1.561 g cm −3 R F is 0.037 for 3830 observed reflections. The diphosphoxane ligand was found to bridge an octahedral Mo and the axial site of a trigonal bipyramidal Fe. Reaction of two equivalents of Mo(CO) 5PPh 2OPPh 2 with (PhCN) 2PdCl 2 produced the trimetallic complex trans-PdCl 2[PPh 2OPPh 2Mo(CO) 5] 2. The trimetallic complexes P[OPR 2Mo(CO) 5] 3 were prepared from the reaction of PCl 3 with Na[OPR 2Mo(CO) 5] (R = Ph, OEt). Similarly, a bimetallic complex PhP[OP(OEt) 2Mo(CO) 5] 2 can be prepared from PhPCl 2. These products illustrate the usefulness of the diphosphoxane linkage in the synthesis of multimetal complexes.

Alkali Metal‐Transition Metal π‐Complexes

AbstractIn this progress report a new principle is described for the synthesis of multimetal π‐complexes with hitherto unknown structural features. The nickel(0)‐olefin complexes 1,5,9‐cyclododecatrienenickel(0) and bis(1,5‐cyclooctadiene)nickel(0) react unexpectedly with main‐group metals, in particular alkali metals, their hydrides, and organometallic compounds, to give nickelligand species with a surplus charge. These species endeavor to transfer the excess charge onto π‐ligands such as olefins or dinitrogen. Multimetal complexes with electron rich transition metal π‐ligand units can, in addition, be prepared from metallocenes, alkali metals, and unsaturated compounds. The syntheses, structures, and reactions of this new class of substances will be summarized.

Nickel(O)-komplexe mit benzophenonimin-lithium und benzophenonimin

Lithium benzophenoneimide reacts with di-1,5cyclooctadienenickel in diethyl ether to yield a novel multi-metal complex, the structure of which has been characterized by spectroscopic and X-ray methods. (Cell data: a 14.013(1), b 13.817(1), c 33.147(1)Å, β 81.960(4)°, R  0.049). The main structural elements are a LiLi(2.542 Å) entity, connected by two Ph 2CN units, and two nickel atoms at nonbonding distance, bridged by another Ph 2CNLi molecule. In addtion, two benzophenoneimine Ph 2CNH molecules are π-bonded to the nickel atoms and also connected via a single lithium atom. Free coordination sites on all lithium atoms are occupied by ether molecules.