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.