Electrophilic phosphinidene complexes play a central role in organophosphorus chemistry. The chemistry of transient phosphinidene complexes has been well studied, but stable, cationic phosphinidene complexes are not as well understood. Therefore the reactivity of a cationic phosphinidene complex [CpFe(CO)2{PNiPr2}]+ (Cp = η5-cyclopentadienyl, iPr = isopropyl), toward bond activation, cycloaddition and nucleophilic addition has been examined. The complex [CpFe(CO)2{PNiPr2}]+ reacts with primary, secondary, and tertiary silanes to form the silyl phosphine complexes [CpFe(CO)2{P(H)(SiR3)NiPr2}]+ (SiR3 = SiPhH2, SiPh2H, Si(C2H5)3), in which the phosphinidene has inserted into the Si-H bond. A computational study shows that the insertion is concerted. The same phosphinidene complex reacts with HPPh2 to form the phosphine-coordinated phosphinidene complex [CpFe(CO)2{P(PHPh2)NiPr2}]+, which rearranges to the phosphino-phosphine complex [CpFe(CO)2{P(PPh2)(H)NiPr2}]+. Reaction of [CpFe(CO)2{PNiPr2}]+ with H2 at high pressure leads to the primary phosphine complex [CpFe(CO)2{PH2(NiPr2)}]+. The phosphinidene complex [CpFe(CO)2{PNiPr2}]+ reacts with alkenes and alkynes via (1+2) cycloaddition to form phosphiranes and phosphirenes respectively. Conjugated alkenes react to initially form phosphiranes, which rearrange to phospholenes via a [1+3] sigmatropic shift. Reaction with an α, β unsaturated ketone gives an oxo-3-phospholene complex. Reaction with azobenzene forms a benzodiazophosphole via C-H activation. Addition of HCl or HBF4·O(CH3CH2)2 to the phosphirene and benzodiazophosphole complexes results in P-N bond cleavage, yielding the respective chlorophosphorus heterocyclic complexes. The heterocycles can be removed from the metal complexes by addition of trimethylphosphine or triethylphosphine. The phosphinidene complex [CpFe(CO)2{PNiPr2}]+, reacts with trialkylphos-phines to form the phosphine-coordinated phosphinidene complexes [CpFe(CO)2-{P(PR3)NiPr2]+ (R = CH3, C2H5, C4H9). Phosphines act as a protecting group and allow amine cleavage via reaction with HBF4·O(CH3CH2)2 to form phosphine-coordinated chlorophosphinidene complexes. The resulting chloro group can be displaced by an additional phosphine, leading to novel bisphosphoniophosphido complexes [CpFe(CO)2{P(PR3)}]2+, which rapidly dissociates to form [PR3-P-PR3]+. Reaction of [CpFe(CO)2{PNiPr2}]+ with bis(dimethylphosphino)methane forms [CpFe(CO)-{P(NiPr2)P(Me2)CH2P(Me2)-κ2P1,P4}]+. P-N cleavage of the bridging complex [CpFe(CO){P(NiPr2)P(Me2)CH2P(Me2)-κ2P1,P4}]+ with HCl leads to [CpFe(CO)-{P(Cl)P(Me2)CH2P(Me2)-κ2P1,P4}]+. Phosphine addition to [CpFe(CO){P(Cl)-P(Me2)CH2P(Me2)-κ2P1,P4}]+ gives the bisphosphoniophosphido complex [CpFe(CO)-{P(PR3)P(Me2)CH2P(Me2)-κ2P1,P4}]2+, which is stable to dissociation. The reactivity studies of [CpFe(CO)2{PNiPr2}]+ have shown that it can be used to activate non-polar bonds like Si-H, P-H and H-H to form P-Si, P-P and P-H bonds, but is not electrophilic enough to activate C-H bonds. [CpFe(CO)2{PNiPr2}]+ undergoes cycloaddition reactions with a wide range of unsaturated substrates leading to phosphorus heterocycles, and shows the typical reactivity expected for electrophilic phosphinidene complexes. Novel complexes with P-P-P ligands and P-P bonds have been formed via phosphine addition reactions of [CpFe(CO)2{PNiPr2}]+.