Rong Dongsheng, Gong Shida, Wang Chaoyang, Luo Qiong, Li Qian-Shu, Xie Yaoming, King R Bruce, Schaefer Henry F
MOE Key Laboratory of Theoretical Environmental Chemistry, Center for Computational Quantum Chemistry, South China Normal University , Guangzhou 510631, P. R. China.
School of Chemistry and Chemical Engineering, Qingdao University , Qingdao 266071, P. R. China.
Inorg Chem. 2017 Dec 4;56(23):14486-14493. doi: 10.1021/acs.inorgchem.7b02064. Epub 2017 Nov 15.
The photochromic dithionite complex CpRh(μ-CH)(μ-OSSO) (Cp = η-MeC) is of interest because it undergoes an unusual fully reversible unimolecular photochemical rearrangement to the isodithionite complex CpRh(μ-CH)(μ-OSOSO). In order to obtain more insight into these systems, a comprehensive density functional theory study has been carried out on isomeric CpM(CH)(SO) (M = Rh, Ir) derivatives. The experimentally observed rhodium complexes with coupled sulfur dioxide (SO) units to give dithionite or isodithionite ligands are surprisingly high-energy kinetic isomers in our analysis, reflecting the need for dithionite rather than SO for their synthesis. Many isomeric structures containing two separate SO ligands are found to lie at lower energies than these dithionite and isodithionite complexes. In the lowest-energy CpM(CH)(SO) isomers, the two methylene groups couple to form an ethylene ligand that can be either terminal or bridging. In slightly higher energy structures, a formal hydrogen shift is predicted to occur within the ethylene ligand to give a methylcarbene CHCH ligand. Isomers with a bridging methylcarbene ligand are energetically preferred over isomers with a terminal methylcarbene ligand. Generation of the lower-energy CpRh(CH)(SO) isomers containing separate SO ligands should be achievable through reactions of SO with more highly reduced cyclopentadienylrhodium methylene complexes such as CpRh(μ-CH).
光致变色连二亚硫酸盐配合物CpRh(μ-CH)(μ-OSSO)（Cp = η-MeC）备受关注，因为它会发生一种不寻常的完全可逆单分子光化学重排，生成异连二亚硫酸盐配合物CpRh(μ-CH)(μ-OSOSO)。为了更深入了解这些体系，我们对异构体CpM(CH)(SO)（M = Rh，Ir）衍生物进行了全面的密度泛函理论研究。在我们的分析中，实验观察到的带有偶联二氧化硫（SO）单元以生成连二亚硫酸盐或异连二亚硫酸盐配体的铑配合物是高能动力学异构体，这反映了它们合成时需要连二亚硫酸盐而非SO。许多含有两个独立SO配体的异构体结构的能量比这些连二亚硫酸盐和异连二亚硫酸盐配合物更低。在能量最低的CpM(CH)(SO)异构体中，两个亚甲基偶联形成一个乙烯配体，该配体可以是端基的或桥连的。在能量稍高的结构中，预计乙烯配体内会发生形式上的氢迁移，生成甲基卡宾CHCH配体。具有桥连甲基卡宾配体的异构体在能量上优于具有端基甲基卡宾配体的异构体。通过SO与还原程度更高的环戊二烯基铑亚甲基配合物如CpRh(μ-CH)反应，应该能够生成含有独立SO配体的能量较低的CpRh(CH)(SO)异构体。
