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

Occasioned by the discovery of a ligand transfer from M(NS) to Mn in Mn(CO)Br, the resulting HNS ligand-tethered dimanganese complex, (μ-,'-ethylenebis(mercaptoacetamide))[Mn(CO)], was found to have myriad analogues of the type (μ-S-E)[Mn(CO)], making up an under-studied class containing MnS rhombs. The attempt to synthesize a nontethered version resulted in a solid-state structure in an -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 - and -isomers and their interconversion in solution. Analysis of the - versus -version of the dimanganese components led to the understanding that whereas the -form exists as centrosymmetric RS isomers, the -form is restricted by C symmetry to be either RR or SS. Molecular scrambling experiments indicated monomeric, pentacoordinate, 16-e (S-O)Mn(CO) 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.