Effects of a Tridentate Pincer Ligand on Parahydrogen Induced Polarization. Issue 14 (17th June 2021)

• Record Type: Journal Article
• Authors: Muhammad, Safiyah R.; Nugent, Joseph W.; Greer, Rianna B.; Lee, Brian C.; Mahmoud, Jumanah; Ramirez, Steven B.; Goodson, Boyd. M.; Fout, Alison R.
• Is Part Of: Chemphyschem. Volume 22:Issue 14(2021)
• Page Start: 1518
• Page End: 1526
• Publication Date: 2021-06-17
• Subjects: cobalt -- rhodium -- iridium -- PHIP -- parahydrogen; Chemistry, Physical and theoretical -- Periodicals; 541.05
• DOI: 10.1002/cphc.202100178
• Languages: English
• ISSNs: 1439-4235

Abstract

Abstract: The role of ligands in rhodium‐ and iridium‐catalyzed Para hydrogen 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)3 (H)2 ] +, 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, Ar 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 ( Dipp CCC)Co(N2 ) catalyst, which resulted in faster hydrogenation and up to 390‐fold 1 H signal enhancements, larger than that of the ( Mes CCC)Co‐py (py=pyridine) catalyst. Additionally, the synthesis of the ( Dipp CCC)Rh(N2 ) complex is reported and applied towards the hydrogenation of ethyl acrylate with para hydrogen to generate modest signal enhancements of both 1 H and 13 C nuclei. Lastly, the generation of two ( Mes CCC)Ir complexes is presented and applied towards SABRE and PHIP‐IE chemistry to only yield small 1 H signal enhancements of the partially hydrogenated product (PHIP) with no SABRE hyperpolarization. Abstract : The installation of diisopropylphenyl groups in the electron‐rich monoanionic bis(carbene) aryl pincer ligand is shown to increase the rate of olefin hydrogenation, leading to increased para hydrogen induced hyperpolarization (PHIP) of ethyl propionate and isoprene. Additionally, the synthesis and application of rhodium and iridium complexes towards this PHIP chemistry is explored.