By reacting [{Cp"'Fe(CO)(2)}(2)(mu,eta(1:1)-P-4)] (1) with in situ generated phosphenium ions [Ph2P][A] ([A](-) = [OTf](-) = [O3SCF3](-), [PF6](-)), a mixture of two main products of the composition [{Cp"'Fe(CO)(2)}(2)(mu,eta(1:1)-P-5(C6H5)(2))][PF6] (2a and 3a) could be identified by extensive P-31 NMR spectroscopic studies at 193 K. Compound 3a was also characterized by X-ray diffraction analysis, showing the rarely observed bicyclo[2.1.0]pentaphosphapentane unit. At room temperature, the novel compound [{Cp"'Fe}(mu,eta(4:1)-P5Ph2){Cp"'(CO)(2)Fe}][PF6] (4) is formed by decarbonylation. Reacting 1 with in situ generated diphenyl arsenium ions gives short-lived intermediates at 193 K which disproportionate at room temperature into tetraphenyldiarsine and [{Cp"'Fe(CO)(2)}(4)(mu(4),eta(1:1:1:1)-P-8)][OTf](2) (5) containing a tetracyclo[3.3.0.0(2,7).0(3,6)]octaphosphaoctane ligand.