Das Sandip, Ray Soumyadip, Devi Tarali, Ghosh Somnath, Harmalkar Sarvesh S, Dhuri Sunder N, Mondal Padmabati, Kumar Pankaj
Department of Chemistry, Indian Institute of Science Education and Research (IISER) Tirupati 517507 India
Humboldt-Universität zu Berlin, Institut für Chemie Brook-Taylor-Straße 2 D-12489 Berlin Germany.
Chem Sci. 2022 Jan 11;13(6):1706-1714. doi: 10.1039/d1sc06803b. eCollection 2022 Feb 9.
Small molecule activation and their transfer reactions in biological or catalytic reactions are greatly influenced by the metal-centers and the ligand frameworks. Here, we report the metal-directed nitric oxide (NO) transfer chemistry in low-spin mononuclear {Co(NO)}, [(12-TMC)Co(NO)] (1-CoNO, = 0), and {Cr(NO)}, ([(BPMEN)Cr(NO)(Cl)]) (4-CrNO, = 1/2) complexes. 1-CoNO transfers its bound NO moiety to a high-spin [(BPMEN)Cr(Cl)] (2-Cr, = 2) and generates 4-CrNO an associative pathway; however, we did not observe the reverse reaction, , NO transfer from 4-CrNO to low-spin [(12-TMC)Co] (3-Co, = 1/2). Spectral titration for NO transfer reaction between 1-CoNO and 2-Cr confirmed 1 : 1 reaction stoichiometry. The NO transfer rate was found to be independent of 2-Cr, suggesting the presence of an intermediate species, which was further supported experimentally and theoretically. The experimental and theoretical observations support the formation of μ-NO bridged intermediate species ({Cr-NO-Co}). Mechanistic investigations using N-labeled-NO and tracking the N-atom established that the NO moiety in 4-CrNO is derived from 1-CoNO. Further, to investigate the factors deciding the NO transfer reactivity, we explored the NO transfer reaction between another high-spin Cr-complex, [(12-TMC)Cr(Cl)] (5-Cr, = 2), and 1-CoNO, showing the generation of the low-spin [(12-TMC)Cr(NO)(Cl)] (6-CrNO, = 1/2); however, again there was no opposite reaction, , from Cr-center to Co-center. The above results advocate clearly that the NO transfer from Co-center generates thermally stable and low-spin and inert {Cr(NO)} complexes (4-CrNO & 6-CrNO) from high-spin and labile Cr-complexes (2-Cr & 5-Cr), suggesting a metal-directed NO transfer (cobalt to chromium, not chromium to cobalt). These results explicitly highlight that the NO transfer is strongly influenced by the labile/inert behavior of the metal-centers and/or thermal stability rather than the ligand architecture.
在生物或催化反应中，小分子的活化及其转移反应会受到金属中心和配体骨架的显著影响。在此，我们报道了低自旋单核{Co(NO)}、[(12 - TMC)Co(NO)]（1 - CoNO，S = 0）和{Cr(NO)}、([(BPMEN)Cr(NO)(Cl)])（4 - CrNO，S = 1/2）配合物中的金属导向一氧化氮（NO）转移化学。1 - CoNO将其结合的NO部分通过缔合途径转移至高自旋的[(BPMEN)Cr(Cl)]（2 - Cr，S = 2）并生成4 - CrNO；然而，我们未观察到反向反应，即NO从4 - CrNO转移至低自旋的[(12 - TMC)Co]（3 - Co，S = 1/2）。1 - CoNO与2 - Cr之间NO转移反应的光谱滴定证实了1∶1的反应化学计量比。发现NO转移速率与2 - Cr无关，这表明存在一种中间物种，实验和理论均进一步支持了这一点。实验和理论观察结果支持形成μ - NO桥连的中间物种({Cr - NO - Co})。使用N标记的NO并追踪N原子进行的机理研究表明，4 - CrNO中的NO部分源自1 - CoNO。此外，为了研究决定NO转移反应活性的因素，我们探索了另一种高自旋Cr配合物[(12 - TMC)Cr(Cl)]（5 - Cr，S = 2）与1 - CoNO之间的NO转移反应，结果显示生成了低自旋的[(12 - TMC)Cr(NO)(Cl)]（6 - CrNO，S = 1/2）；然而，同样没有观察到从Cr中心到Co中心的反向反应。上述结果清楚地表明，从Co中心转移NO可从高自旋且不稳定的Cr配合物（2 - Cr和5 - Cr）生成热稳定、低自旋且惰性的{Cr(NO)}配合物（4 - CrNO和6 - CrNO），这表明存在金属导向的NO转移（从钴到铬，而非从铬到钴）。这些结果明确突出了NO转移受金属中心的不稳定/惰性行为和/或热稳定性的强烈影响，而非配体结构。
