Amine-catalyzed substitution in CpFe(CO)2I by phosphine and bisphosphine ligands.

Abstract

We have found that amines significantly accelerate iodide substitution in CpFe(CO)2I (1) (Cp = η5-cyclopentadienyl) with phosphines and allow the synthesis of new complexes that are not available through reactions carried out without an amine. The reaction of equimolar amounts of 1 and triphenylphosphine in toluene containing DIPA afforded [CpFe(CO)2PPh3]+I- within 5 min at room temperature in 72% yield (90% after 24 h). DIPA and pyrrolidine gave the highest yields of the tested amines. We performed a similar reaction using model bisphosphines 1,3-bis(diphenylphosphino)ethane (dppe) and 1,1'-bis(diphenylphosphino)ferrocene (dppf). The products depended on the reagent ratio and bore the CpFe(CO)2 moiety coordinated to one or two phosphine phosphorus atoms. Chelates [CpFe(CO)(dppe)]+I- (4) and [Cp2Fe2(CO)4(dppe)]2+2I- (5) were formed in 72% and 98% yield, respectively. We also performed the DIPA-catalyzed reaction of 1 with triethyl phosphite and obtained the product of an Michaelis-Arbuzov-like rearrangement, CpFe(CO)2[P(O)(OCH2CH3)2] (11). All complexes were characterized with spectroscopic analysis by NMR, FT-IR, and ESI-MS, and by XRD for three complexes. To clarify the reaction mechanism, we performed theoretical calculations of the intermolecular interactions between 1 and amine molecules. We propose two possible reaction mechanisms to explain the formation of products.