Synthesis, Structure, And Reactivity Of (Dihydrogen)(Hydrido)Iron(Ii) Complexes Bearing Chiral Diphosphanes

The heterolytic cleavage of molecular hydrogen by [Fe(H2O)(6)][BF4](2) and the chiral phosphane (+)-1,2-bis[(2R,5R)-2,5-dimethylphospholano]benzene [(R,R)-Me-DuPhos] or its enantiomer [(S,S)-Me-DuPhos] yields the (dihydrogen)(hydrido)iron complexes [FeH((2)-H-2){(R,R)-Me-DuPhos}(2)]BF4 ([R,R-1]BF4) and [FeH((2)-H-2){(S,S)-Me-DuPhos}(2)]BF4 ([S,S-1]BF4), respectively. These complexes are fluxional in solution at room temperature, and the trans isomers are observed at 200 K. The ()-cis-[R,R-1]BF4 complex was identified crystallographically as the only stereoisomer at room temperature. The energetic and structural differences between the cis ( and ) and trans isomers were analyzed from a computational (DFT) perspective. The coordinated dihydrogen is displaced by CO or CH3CN ligands to form a mixture of cis and trans isomers of FeH(L)[(R,R)-Me-DuPhos](2)BF4 {L = CO ([R,R-2]BF4), CH3CN ([R,R-3]BF4)} or FeH(L)[(S,S)-Me-DuPhos](2)BF4 {L = CO ([S,S-2]BF4), CH3CN ([S,S-3]BF4)} complexes, and the cis isomers are the major ones. The formation of trans-[FeH(NMe3)(Me-DuPhos*)(2)]BF4 is suggested for the reaction of [R,R-1]BF4 and [S,S-1]BF4 with NMe3 {Me-DuPhos* = [(R,R)-Me-DuPhos] or [(S,S)-Me-Duphos]}.