Cyclobutadiene complexes with nucleophiles

Tetraphenylcyclobutadienepalladium and -nickel complexes and tetra-methylcyclobutadienenickel chloride react readily with nucleophilic reagents to give 7r-cyclobutenyl complexes 12, 30, 31, 65, 91), a reaction reminiscent of those described by Chatt et al. for diene-palladium and diene-platinum halide complexes (Section VI, F). Non-halogen-containing cyclobutadiene complexes, however, appear inert under similar conditions so that this reaction is very dependent on the other ligands present. Some similarity between cyclobutadiene-metal and diene-metal complexes appears to exist but how far the parallel can be drawn remains to be seen. The reactions are fully discussed in Section VI. 

Isocyanides, being nucleophilic, and having a greater proton affinity than the corresponding cyanides, add readily to carbocations, though the acid sensitivity of isocyanides limits the reaction to those carbocations which can be prepared under non-acidic conditions. The complex of cyclobutadiene with AICI3 provides a useful example of this type of reaction. The isocyanide can also insert into the C—Cl bond of 143. 

Novel organometallic poly(arylene)s with 1,3-type (cyclobutadiene)cobalt moieties 27 in the main chain are prepared by Ni(0)-mediated dehalogenative polycondensation of monomers having (cyclobutadiene)cobalt moieties [51], The polymers with of 20 kDa exhibit thermotropic liquid crystallinity. The synthesis of a variety of homometallic and heterometallic oligomers and polymers such as 28 is possible via nucleophilic aromatic substitution reactions of dichlorophenylene-Fe Cp and dihydroxyphenylene-Ru Cp complexes in DMF in the presence of K2CO3 [52]. 

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