Reactivity of iron complexes containing monodentate aminophosphine ligands – Formation of four-membered carboxamido-phospha-metallacycles

Treatment of [FeCp(CO)2Cl] with 1 equiv of the amidophosphine ligands Li[R2PNR′] (R = Ph, iPr, R′ = iPr, tBu, Cy) afforded complexes of the type [FeCp(CO)(κ2(C,P)-(Cdouble bond; length as m-dashO)–NiPr-PPh2)] (1a), [FeCp(CO)(κ2(C,P)-(Cdouble bond; length as m-dashO)-NtBu-PPh2)] (1b), and [FeCp(CO)(κ2(C,P)-(Cdouble bond; length as m-dashO)-NCy-PiPr2)] (1c) in 40–50% yields. Complex 1a was also formed when [FeCp(CO)2(PPh2NHiPr)]+ (2) was reacted with 1 equiv of KOtBu. These complexes feature a four-membered carboxamido-phospha-ferracycle as a result of an intramolecular nucleophilic attack of the amidophosphine ligand on coordinated CO. Upon treatment of 1a with the electrophile [Me3O]BF4 the aminocarbene complex [FeCp(CO)(κ2(C,P)double bond; length as m-dashC(OMe)-NiPr-PPh2)]+ (3) was obtained bearing an aza-phospha-carbene moiety. Upon treatment of cis,trans,cis-[Fe(CO)2(Ph2PNHiPr)2(Br)2] (4a) and cis,trans,cis-[Fe(CO)2(Ph2PNHtBu)2(Br)2] (4b) with KOtBu the carboxamido-phospha-ferracycles trans-[Fe(CO)2(κ2(C,P)-(Cdouble bond; length as m-dashO)-NiPr-PPh2)(Ph2PNHiPr)Br] (5a) and trans-[Fe(CO)2(κ2(C,P)-(Cdouble bond; length as m-dashO)-NtBu-PPh2)(Ph2PNHtBu)Br] (5b) were formed in moderate yield. Finally, representative structures were determined by X-ray crystallography.