Muhammad Safiyah R, Nugent Joseph W, Greer Rianna B, Lee Brian C, Mahmoud Jumanah, Ramirez Steven B, Goodson Boyd M, Fout Alison R
Department of Chemistry, University of Illinois at Urbana-Champaign, 601 S Goodwin Avenue, Urbana, Illinois, 61801, United States.
Department of Chemistry and Biochemistry and Materials Technology Center, Southern Illinois University, 1245 Lincoln Drive, Carbondale, Illinois, 62901, United States.
Chemphyschem. 2021 Jul 16;22(14):1518-1526. doi: 10.1002/cphc.202100178. Epub 2021 Jun 17.
The role of ligands in rhodium- and iridium-catalyzed Parahydrogen Induced Polarization (PHIP) and SABRE (signal amplification by reversible exchange) chemistry has been studied in the benchmark systems, [Rh(diene)(diphos)] and [Ir(NHC)(sub) (H) ] , and shown to have a great impact on the degree of hyperpolarization observed. Here, we examine the role of the flanking moieties in the electron-rich monoanionic bis(carbene) aryl pincer ligand, CCC (Ar=Dipp, 2,6-diisopropyl or Mes, 2,4,6-trimethylphenyl) on the cobalt-catalyzed PHIP and PHIP-IE (PHIP via Insertion and Elimination) chemistry that we have previously reported. The mesityl groups were exchanged for diisopropylphenyl groups to generate the ( CCC)Co(N ) catalyst, which resulted in faster hydrogenation and up to 390-fold H signal enhancements, larger than that of the ( CCC)Co-py (py=pyridine) catalyst. Additionally, the synthesis of the ( CCC)Rh(N ) complex is reported and applied towards the hydrogenation of ethyl acrylate with parahydrogen to generate modest signal enhancements of both H and C nuclei. Lastly, the generation of two ( CCC)Ir complexes is presented and applied towards SABRE and PHIP-IE chemistry to only yield small H signal enhancements of the partially hydrogenated product (PHIP) with no SABRE hyperpolarization.
在基准体系[Rh(diene)(diphos)]和[Ir(NHC)(sub)(H)]中，研究了配体在铑和铱催化的仲氢诱导极化（PHIP）和SABRE（通过可逆交换实现信号放大）化学中的作用，结果表明其对所观察到的超极化程度有很大影响。在此，我们研究了富电子单阴离子双（卡宾）芳基钳形配体CCC（Ar = Dipp，2,6 - 二异丙基或Mes，2,4,6 - 三甲基苯基）的侧翼部分在我们之前报道的钴催化的PHIP和PHIP - IE（通过插入和消除实现的PHIP）化学中的作用。将均三甲苯基换成二异丙基苯基以生成(CCC)Co(N)催化剂，这导致氢化速度加快，并且氢信号增强高达390倍，比(CCC)Co - py（py = 吡啶）催化剂的增强幅度更大。此外，还报道了(CCC)Rh(N)配合物的合成，并将其应用于用仲氢对丙烯酸乙酯进行氢化反应，以生成适度的氢和碳核信号增强。最后，展示了两种(CCC)Ir配合物的生成，并将其应用于SABRE和PHIP - IE化学中，结果仅产生部分氢化产物（PHIP）的小幅度氢信号增强，未出现SABRE超极化现象。
