Begum Shahin A, Chowdhury Md Arshad H, Ghosh Shishir, Tocher Derek A, Richmond Michael G, Yang Li, Hardcastle K I, Rosenberg Edward, Kabir Shariff E
Department of Chemistry, Jahangirnagar University Savar Dhaka-1342 Bangladesh
Department of Chemistry, University College London 20 Gordon Street London WC1H OAJ UK.
RSC Adv. 2018 Sep 21;8(57):32672-32683. doi: 10.1039/c8ra07400c. eCollection 2018 Sep 18.
The site preference for ligand substitution in the benzothiazolate-bridged cluster HOs(CO)(μ-1,2-N,C-η,κ-CHNS) (1) has been investigated using PPh. 1 reacts with PPh in the presence of MeNO to afford the mono- and bisphosphine substituted clusters HOs(CO)(PPh)(μ-1,2-N,C-η,κ-CHNS) (2) and HOs(CO)(PPh)(μ-1,2-N,C-η,κ-CHNS) (3), respectively. 2 exists as a pair of non-interconverting isomers where the PPh ligand is situated at one of the equatorial sites syn to the edge-bridging hydride that shares a common Os-Os bond with the metalated heterocycle. The solid-state structure of the major isomer establishes the PPh regiochemistry at the N-substituted osmium center. DFT calculations confirm the thermodynamic preference for this particular isomer relative to the minor isomer whose phosphine ligand is located at the adjacent C-metalated osmium center. 2 also reacts with PPh to give 3. The locus of the second substitution occurs at one of the two equatorial sites at the Os(CO) moiety in 2 and gives rise to a pair of fluxional stereoisomers where the new phosphine ligand is scrambled between the two equatorial sites at the Os(CO)P moiety. The molecular structure of the major isomer has been determined by X-ray diffraction analysis and found to represent the lowest energy structure of the different stereoisomers computed for HOs(CO)(PPh)(μ-1,2-N,C-η,κ-CHNS). The fluxional behavior displayed by 3 has been examined by VT NMR spectroscopy, and DFT calculations provide evidence for stereoselective tripodal rotation at the Os(CO)P moiety that serves to equilibrate the second phosphine between the two available equatorial sites.
使用三苯基膦（PPh₃）研究了苯并噻唑酸盐桥连簇合物HOs(CO)(μ-1,2-N,C-η,κ-CHNS)（1）中配体取代的位点偏好性。1在亚硝酸甲酯（MeNO₂）存在下与三苯基膦反应，分别生成单膦和双膦取代的簇合物HOs(CO)(PPh₃)(μ-1,2-N,C-η,κ-CHNS)（2）和HOs(CO)(PPh₃)₂(μ-1,2-N,C-η,κ-CHNS)（3）。2以一对非互变异构体形式存在，其中三苯基膦配体位于与桥连氢化物共边且与金属化杂环共享一个Os-Os键的赤道位点之一。主要异构体的固态结构确定了在N-取代锇中心的三苯基膦区域化学。密度泛函理论（DFT）计算证实了相对于次要异构体（其膦配体位于相邻的C-金属化锇中心），该特定异构体的热力学偏好性。2也与三苯基膦反应生成3。第二次取代的位点发生在2中Os(CO)部分的两个赤道位点之一，并产生一对互变立体异构体，其中新的膦配体在Os(CO)P部分的两个赤道位点之间无序排列。主要异构体的分子结构已通过X射线衍射分析确定，并发现其代表了为HOs(CO)(PPh₃)(μ-1,2-N,C-η,κ-CHNS)计算的不同立体异构体中的最低能量结构。通过变温核磁共振（VT NMR）光谱研究了3表现出的互变行为，DFT计算为Os(CO)P部分发生立体选择性三脚架旋转提供了证据，该旋转用于使第二个膦在两个可用的赤道位点之间达到平衡。
