Unsaturated organic ligands

Fluxionality. The fluxional behavior of unsaturated organic ligands in mono- and oligonuclear organometallic complexes was well documented 109a) as a result of extensive NMR spectroscopic investigations. The advent of pulse Fourier transform... 

The Bonding of Unsaturated Organic Ligands to a Metal Centre... 

A useful synthetic route to specific carbonyl-PF3 transition metal complexes (method C) involves displacement of relatively weakly bound ligands such as ammonia, iodide ion, or unsaturated organic ligands (e.g., dienes, arenes) from suitable metal carbonyl complexes. 

Photolytic and chemical methods of activation have also been employed in the reactions of clusters with unsaturated organic ligands. The photochemical activation of compounds containing metal-metal bonds has not received much attention until relatively recently (127). However, it is now being investigated in some detail. In some cases the photochemical products differ from those obtained by thermal activation alone (127). The reaction of Ru3(CO)12 with ethylene is an example of such behavior (128). 

Few other reactions between higher clusters and unsaturated organic ligands have been carried out (231, 232), but there are a number of studies which involve group IB organometallic derivatives (233-236). There are also a few high-nuclearity mixed-metal cluster alkynes which are the products of reactions between two heterometal complexes (237-242). 

Since the discovery of Zeise s salt, K[Pt(ri2-C2H4)Cl3], the first organometallic complex of a transition element, and particularly since the first reported synthesis of ferrocene, [Fe(r 5-C5H5)2], the number and variety of organometallic compounds with unsaturated organic ligands has increased enormously. 

In Section 4.4, we survey systems in which unsaturated organic ligands coordinate with two or more metal atoms, and show how their skeletons place their carbon atoms in similar bonding environments to those in carboranes. 

COMPLEXES OF UNSATURATED ORGANIC LIGANDS WITH TWO OR MORE METAL ATOMS MIXED METAL-CARBON CLUSTERS... 

The bonding description for a coordinated alkene can be extended to other unsaturated organic ligands. Polyalkenes may be non-conjugated or conjugated. In complexes of non-conjugated systems (e.g. cycloocta-1,5-diene (cod), 23.20, or... 

Reactions of metal carbonyls with unsaturated organic ligands are discussed in later sections. 

Considerable efforts are now being devoted to many other bipy-type complexes with transition metals, trying to prepare new electrocrystalline materials, solve their X-ray stmctures, and measure their conductivities as a function of temperature. It is possible that some of these materials will have similar propoerties to those of the endohedral fullerenes and the cryptatium species described above. After all, they also contain metal cation centers sorrounded by highly unsaturated organic ligands that are capable of easy reduction. As such, all of these systems, if appropriately designed and manipulated, could yield novel conducting materials widi unusual properties. 

The lanthanides and actinides also form a wide range of complexes with unsaturated organic ligands including allyls, cyclopentadienyls and cycloocta-tetraene derivatives. The bonding is strongly polar. Coordination numbers are determined largely by steric requirements around the metal centre. 

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