The diiridium complex [{Ir(ABPN(2))(CO)}(2)(mu-CO)] (1; [ABPN(2)]- = [(allyl)B(Pz)(2)(CH2PPh2)]-) reacts with diphenylphosphane affording [Ir(ABPN(2))(CO)(H) (PPh2)] (2), the product of the oxidative addition of the P-H bond to the metal. DFT studies revealed a large contribution of the terminal phosphanido lone pair to the HOMO of 2, indicating nucleophilic character of this ligand, which is evidenced by reactions of 2 with typical electrophiles such as H+, Me+, and O-2. Products from the reaction of 2 with methyl chloroacetate were found to be either [Ir(ABPN(2))(CO)(H)(PPh2CH2CO2Me)][PF6] ([6]PF6) or [Ir(ABPN2)(CO)(Cl)(H)] (7) and the free phosphane (PPh2CH2CO2Me), both involving PC bond formation, depending on the reaction conditions. New complexes having iridacyclophosphapentenone and iridacyclophosphapentanone moieties result from reactions of 2 with dimethyl acetylenedicarboxylate and dimethyl maleate, respectively, as a consequence of a further incorporation of the carbonyl ligand. In this line, the terminal alkyne methyl propiolate gave a mixture of a similar iridacyclophosphapentanone complex and [Ir(ABPN(2)){CH-C(CO2Me)CO}{PPh2CH-CH(CO2Me)}] (10), which bears the functionalized phosphane PPh2CH-CH(CO2Me) and an iridacyclobutenone fragment. Related model reactions aimed to confirm mechanistic proposals are also studied.