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

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.