Synthesis and Function of Crystalline-state Photoresponsive Metal Complexes with Active S-S Bond

点击翻译按钮获取中文摘要

In the crystalline state, the rhodium dinuclear complex[(RhCp^*)_2(μ-CH_2)_2(μ-O_2SSO_2)] (1) with a photoresponsive dithionite group (μ-O_2SSO_2) and two pentamethylcyclopentadienyl ligands (Cp^*=η^5-C_5Me_5) undergoes a 100% reversible unimolecular type T inverse photochromism upon interconversion to [(RhCp^*)_2(μ-CH_2)_2(μ-O_2SOSO)] (2). The photochromism can be followed directly by using stepwise crystal structure analysis.In this study, we found that the photoreaction of 1 was triggered by absorption of the 510 nm light (charge transfer band from σ(S-S)to σ^*(S-S)and σ^*(Rh-Rh)orbitals assigned by DFT calculation) and included two important processes:kinetically controlled oxygen-atom transfer to produce four stereoisomers of 2 and thermodynamically controlled isomerization between the four stereoisomers of 2 to afford the most stable isomer. Although the formation rate of the four stereoisomer products was kinetically controlled and the population of the four stereoisomers produc … More ed in the system was thermodynamically controlled, both processes were regulated by the steric hindrance between the μ-O_2SSO_2 or μ-O_2SOSO ligand and the reaction cavity formed by the Cp^* ligands. The cooperation of both processes achieved an intriguing stereospecific oxygen-atom rearrangement to produce only one stereoisomer of 2 at the final stage of the photoreaction at room temperature.We also determined the effect of the oxygen-atom rearrangement on the rotational motion of the two crystallographibally independent Cp^* ligands (parallel and perpendicular arrangement). Using variable-temperature ^13C CP/MAS NMR and quadrupolar echo solid-state ^2H NMR spectroscopies, before photoirradiation, the activation energies for the rotation of the parallel and perpendicular Cp^* ligands in 1 were determined to be 30±3 and 10±1 kJ/mol, respectively, and after photoirradiation, in 2, they were much lower than those in 1 (20±2 and 8±1 kJ/mol, respectively). The large decrease in the activation energy for the parallel Cp^* in 2 is attributed to the relaxation of molecular stress via a stereospecific oxygen-atom rearrangement, which suggests that the rotational motion of the Cp^* ligands is coupled to the photochromism.Furthermore, we have found an absolute asymmetric photoisomerization of a new achiral photochromic dithionite complex having n-propyl moieties [(RhCp^<Pro>)_2(μ-CH_2)(μ-O_2SSO_2)] (Cp^<Pro>=η^5-C_5Me_4n-Propyl) in chiral crystals. This complex is crystallized in the space group of P2_12_12_1 and gives both crystals containing the helical isomers of P and M.We performed a crystalline-state photoreaction by using these chiral crystals in similar way to [(RhCp^*)_2(μ-CH_2)(μ-O_2SSO_2)] and obtained [RhCp^<Pro>)_2(μ-CH_2)(μ-OSOSO_2)] almost quantitatively. The obtained μ-OSOSO_2 complex has an e.e value of 95%. Less