Configurational landscape of chiral iron(ii) bis(phosphane) complexes

Abstract

The reaction of a chiral [FeH(η²-H₂){(R,R)-Me-DuPhos}₂]⁺ ((R,R)-Me-DuPhos = (−)-1,2-bis[(2R,5R)-2,5-dimethylphospholano]benzene) complex with ethers and halides is investigated by NMR techniques. From this study, it is apparent that dihydrogen ligand exchange by poorly-coordinating donor molecules, such as THF or Et₂O, is feasible under mild conditions. The cis-[FeH(THF-d₈){(R,R)-Me-DuPhos}₂]⁺ complex is identified as the product in THF-d₈ solution. A mixture of cis- and trans-[FeH(ether){(R,R)-Me-DuPhos}₂]⁺ isomers is obtained after the addition of small quantities of THF or Et₂O to a CD₂Cl₂ solution of [FeH(η²-H₂){(R,R)-Me-DuPhos}₂]⁺. The reaction of [FeH(η²-H₂){(R,R)-Me-DuPhos}₂]⁺ with an excess of iodide or chloride salts in THF-d₈ or CD₂Cl₂ affords initially cis- and trans-[FeHX{(R,R)-Me-DuPhos}₂] (X = Cl or I) isomers. The trans complex is the thermodynamic product obtained when X = Cl, whereas the cis isomer is obtained when X = I. These complexes evolve with time, and the pentacoordinated [FeX{(R,R)-Me-DuPhos}₂](A) (X = Cl, A = BF₄; X = A = I) and hexacoordinated trans-[FeCl₂{(R,R)-Me-DuPhos}₂] compounds are obtained as air-stable crystals and identified by X-ray diffraction and NMR techniques. Experiments done with (S,S)-Me-DuPhos ((+)-1,2-bis[(2S,5S)-2,5-dimethylphospholano]benzene) gave similar results, and the [FeI{(S,S)-Me-DuPhos}₂](ClO₄) compound has been crystallographically characterized.