Other Conjugated Metal Coordination

They do, however, stand as examples of the role that a transition metal can play as part of a delocalized, conjugated S3rstem. 

1 example illustrates only one of the many conjugated counterions that have been employed. 

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A photoactive metal center is introduced in these systems. The ruthenium bipyridyl complexes are coordinated to the emeraldine base to form the corresponding polymer complexes as described above." The incorporation of the ruthenium centers to the pyridyl backbone has been also reported to give the ruthenium complexes Conjugated ruthenium bipyridine complexes thus obtained are evaluated to be photorefractive materials. Other transition metal complexes can be employed to form the corresponding polymer complexes. The pyridine unit is replaced by bithienyl, 1,4-diazabutadiene, ethylene, benzimidazole or thiazole. ... 

For this reason, several reversible chemistries that are efficient in organic phase (e.g., catalyzed by acids or bases) are less convenient in aqueous media. Instead, reactions occurring under sufficiently mild conditions need to be employed. These restrictions have led to the preference of but a few different reaction types, and, to date, mainly imines (including hydrazones, oximes, etc.), disulfides, and metal coordination are employed in these systems. However, other reaction types, such as transthiolesterification, conjugate addition, aUcene metathesis, and aldol addi-tion/condensation, have been demonstrated, but are so far less preferred in these systems. 

In the case of r)2-coordination of the exocyclic C=C bond, it becomes substantially elongated compared with the double bond of free alkenes, as a result of back donation from the metal to the 7t orbitals of the double bond. For instance, in complex 17b the coordinated bond length is 1.437 A (see Fig. 3.2).18 This is also reflected in the loss of planarity around the quaternary exocyclic carbon, the methylenic carbon being bent out of the ring plane by 10.78°.18 Similar structural features were also observed with other P2Pd conjugated olefin complexes.39... 

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