the chemical, physicochemical, theoretical and metal coordination studies of phospholes which have so far appeared in the literature are reviewed briefly with particular reference to the electronic structure of the system. the coordinating properties of the simple phospholes 1-phenylphosphole (pp), 3-methyl-1-phenylphosphole (mpp), 3,4- dimethyl-l-phenylphosphole (dpp) and 3,4-dimethyl-1-rwbutylphosphole (dbp) with the metal ions re(iii), ru(iii), ru(ii), co{ii), rh(iii), ir(iii), ni(ii), pd(ii), pt(ii), cu(i) and hg(ii) and also with carbonyl complexes of ru(ii) and rh(i) have been studied. ... differences in the behavior of the various phospholes studied here, and also other phospholes, in complex formation are attributed to variations in the substitution pattern with the type of substitution at the phosphorus atom being apparently of particular importance. the results are discussed in terms of orbital perturbation of a pyramidal phosphole in which the homo may not be the lone-pair orbital and also in terms of a pyramidal but aromatic phosphole system.