The coordination behaviour of 1,2,4-triphosphaferrocenes [FeCpR(eta(5)-P(3)C(2)tBu(2))] [Cp-R = Cp (1), Cp''' (2)] towards Cu-I chloride is significantly influenced by the substitution pattern of the cyclopentadienyl ring attached to iron. The dimeric copper complexes [{FeCP(eta(5):eta(1):eta(1)-p(3)tBu(2)C(2))} {mu-CuCl-(MeCN)}(2) (3) and [{FeCp''' (eta(5):eta(1):eta(1)-P(3)tBu(2)C(2))}(mu-CuCl)](2) (4), in which two 1,2,41-triphosphaferrocenes are linked by two CuCl centres to form dimeric complexes were obtained in reactions using a 1:1 stoichiometry. Whereas in 3 a tetracoordinated Cu atom is revealed, 4 possesses a threefold-coordinated Cu atom due to the steric influence of the bulkier Cp'''. ligand. However, if the reaction is carried out with an excess of CuCl in a 1:2 stoichiometry for the Cp derivative 1 the same product 3 is obtained, whereas in the case of a tri-tert-butyl-substituted Cp''' ligand complex 2 the triphospholyl ring is fragmented tinder mild conditions to a tetrdphosphabutadiene moiety within an iron triple-decker sandwich complex [{FeCp''')(2) (mu,eta(4):eta(4):eta(1):eta(1)-P-4)}(mu-CuCl(MeCN)}](infinity) (5) embedded in a CuCl polymer matrix. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)