Nucleophilicity and P–C Bond Formation Reactions of a Terminal Phosphanido Iridium Complex

The diiridium complex [{Ir­(ABPN2)­(CO)}2(μ-CO)] (1; [ABPN2]− = [(allyl)­B­(Pz)2(CH2PPh2)]−) reacts with diphenylphosphane affording [Ir­(ABPN2)­(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 O2. Products from the reaction of 2 with methyl chloroacetate were found to be either [Ir­(ABPN2)­(CO)­(H)­(PPh2CH2CO2Me)]­[PF6] ([6]­PF6) or [Ir­(ABPN2)­(CO)­(Cl)­(H)] (7) and the free phosphane (PPh2CH2CO2Me), both involving P–C 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(ABPN2)­{CHC­(CO2Me)–CO}­{PPh2–CHCH­(CO2Me)}] (10), which bears the functionalized phosphane PPh2–CHCH­(CO2Me) and an iridacyclobutenone fragment. Related model reactions aimed to confirm mechanistic proposals are also studied.