Chirality-Guided Isomerization of Mn 2 S 2 Diamond Core Complexes: A Mechanistic Study.

Occasioned by the discovery of a ligand transfer from M(N 2 S 2 ) to Mn I in Mn(CO) 5 Br, the resulting H 2 N 2 S 2 ligand-tethered dimanganese complex, (μ 4 - N , N '-ethylenebis(mercaptoacetamide))[Mn 2 (CO) 6 ], was found to have myriad analogues of the type (μ-S-E) 2 [Mn 2 (CO) 6 ], making up an under-studied class containing Mn 2 S 2 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 C 2 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.