Chirality-Guided Isomerization of Mn2S2 Diamond Core Complexes: A Mechanistic Study

Occasioned by the discovery of a ligand transfer from M(N2S2) to MnI in Mn(CO)5Br, the resulting H2N2S2 ligand-tethered dimanganese complex, (mu 4-N,N '-ethylenebis( merc aptoacet amide ) )-[Mn2(CO)6], was found to have myriad analogues of the type (mu-S- E)2[Mn2(CO)6], making up an under-studied class containing Mn2S2 rhombs. The attempt to synthesize a nontethered version resulted in a solid-state structure in an anti-conformation. However, a direct comparison of the Fourier-transform infrared spectra of the tethered versus nontethered complexes in combination with theoretical frequency calculation suggested the coexistence of syn- and anti-isomers and their interconversion in solution. Analysis of the syn- versus anti-version of the dimanganese components led to the understanding that whereas the anti-form exists as centrosymmetric RS isomers, the syn-form is restricted by C2 symmetry to be either RR or SS. Molecular scrambling experiments indicated monomeric, pentacoordinate, 16-e- (S-O)Mn(CO)3 intermediates with lifetimes sufficiently long to sample R and S monomers. Density functional theory analysis of the mechanistic pathway and a kinetic study corroborated that the proposed isomerization involves the cleavage and reformation of the dimeric structures.

Automated summary

The discovery of ligand transfer from M(N2S2) to MnI in Mn(CO)5Br led to the synthesis of a ligand-tethered dimanganese complex, (mu 4-N,N'-ethylenebis(mercaptoacetamide))-[Mn2(CO)6], which has numerous analogues of the type (mu-S-E)2[Mn2(CO)6]. These complexes constitute an understudied class with Mn2S2 rhomb structures. Comparison of the infrared spectra and frequency calculation of the tethered and nontethered complexes suggested the existence of both syn- and anti-isomers and their interconversion in solution. The analysis of the dimanganese components revealed that the anti-form is centrosymmetric RS isomer, while the syn-form is limited by C2 symmetry to be either RR or SS.