Bridging of bipyridine units by phenylphosphine links: linear and cyclic oligomers and some acid derivatives.

[structures: see text] Reaction of 6,6'-dibromo-2,2'-bipyridine with phenylphosphine under palladium-promoted cross-coupling conditions provides a variety of linear oligomers bearing two reactive bromo substituents as well as a cyclic dimer, characterized by X-ray crystallography, in which the bipyridine units are constrained to a cis configuration by two phenylphosphine oxide bridges. Derivatives of the linear species containing both carboxylate and phosphonate substituents are readily obtained.