Peripheral ligands

It is becoming increasingly apparent that a very extensive chemistry is associated with the dimetal species (1), and (3) - (13). Three types of reaction may be identified (i) aSTdition of other metal ligand fragments, discussed in the next Section, (ii) replacement of peripheral ligands on the metal centres, and (iii) reactions at the bridging carbon atom. One example of (ii) and (iii) will suffice to illustrate the scope and potential for new chemistry. 

This compound can be considered as a precursor of more elaborate bpym-based magnetic systems so that formal substitution of the water molecules by more appropriate peripheral ligands, such as bpym and 2,2 -bithi-azoline (bt) together with NCS" or NCSe" counter-ions, allows us to fine tune the ligand field strength around the iron(II) atom, resulting in a rich variety of magnetic behaviour in the [Fe(L)(NCX)2]2(bpym) series. 

As Table XVIII shows, the solitaire pzs, 66a and 67b have reductions very close to those reported for H2(pc) and are more negative than those reported for 47. Additionally, for solitaire porphyrazines 67b-67d, which have a [l,T-(diphenylphosphino) ferrocene] palladium(II) peripheral ligand, a reversible one-electron oxidation due to the ferrocene was measured at +0.18 V. 

REVERSIBLE MIGRATION OF A HYDROGEN ATOM FROM A METAL CENTRE TO A PERIPHERAL LIGAND... 

Figure 8. The structure of Mne02(piv)io(pivH)4 only portions of the peripheral ligands are shown. (Reproduced with permission from ref. 32. Copyright 1986 Royal Society of Chemistry).

Giuffrida, G. and Campagna, S. (1994) Influence of peripheral ligands on the metal-metal interaction in dinuclear metal complexes with V-heterocyclic bridging ligands, Coord. Chem. Rev. 135/136, 517-531. 

The dinuclear complex [(bpy)2Ru(bpt)Ir(ppy)2]2+ was reported by Haas-noot et al., Fig. 22b [ 124], In this complex the two metal centers are linked via a bpt bridging ligand containing a mono anionic triazole unit. Because of this electronic feature, the MLCT states localized on the two moieties involve the peripheral ligands and not the bridging ligand. In [(bpy)2Ru(bpt)Ir(ppy)2]2+, emission is only observed from the Ru-based unit and the direction of intercomponent energy transfer is Ir - Ru, i.e., in the opposite direction from that observed for [(bpy)2Ru(HAT)Ir(ppy)2]3+. 

In coordinately unsaturated molecular metal complexes, carbon-hydrogen bonds of the peripheral ligands may, if the stereochemistry allows, closely approach a metal center so as to develop a three-center two-electron bond between the carbon, the hydrogen, and the metal atoms, C-H-M. In some instances, the interaction is followed by a scission of the C-H bond whereby the metal is effectively oxidized and discrete M-H and M-C a bonds are formed. This class of metal-liydrogen-carbon interactions and reactions is shown to be a common phenomenon in metal surface chemistry. 

Coordination of a metal to the itt-orbitals of an arene opens pathways for nncleophile addition to the arene. The power of the effect is related to the oxidation state (Cr , Mn , Fe ) and peripheral ligands (Cp or CO). Under snitable conditions, both heteroatom and carbon-based nncleophiles add rapidly under mild conditions. The fate of the cyclohexadienyl intermediate depends on the conditions of the next stage of the batch-wise process. Loss of an electronegative leaving group leads to an analog of... 

Fig. 6. Formula of a decanuclear Ru " " metal complex with 2,3-bis (2 -pyridyl) pyrazine (dpp) bridging ligands and 2,2 - bipyridine (bpy) peripheral ligands, and the corresponding scheme (Fig. 2b).

Catalytic behavior of lanthanide imine complexes with varied peripheral ligands... 

Another important consideration concerns the peripheral ligands. Figure 2 shows the peripheral ligands that are employed in the systems discussed here. 

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