Ruddlesden Amy J, Duckett Simon B
Centre for Hyperpolarisation in Magnetic Resonance (CHyM), York Science Park, University of York, Heslington, York, YO10 5NY, UK.
Chem Commun (Camb). 2016 Jun 28;52(54):8467-70. doi: 10.1039/c6cc03185d.
A bidentate iridium carbene complex, Ir(κC,O-L1)(COD), has been synthesised which contains a strongly electron donating carbene ligand that is functionalised by a cis-spanning phenolate group. This complex acts as a precursor to effective magnetisation transfer catalysts which form after reaction with H2 and a suitable two electron donor. In solvents such as benzene, containing pyridine, they are exemplified by neutral, chiral Ir(H)2(κC,O-L1)(py)2 with inequivalent hydride ligands and Ir-O bond retention, whilst in methanol, Ir-O bond cleavage leads to zwitterionic Ir(H)2(κC,O(-)-L1)(py)3, with chemically equivalent hydride ligands. The active catalyst's form is therefore solvent dependent. Both these complexes break the magnetic symmetry of the hydride ligands and are active in the catalytic transfer of polarisation from parahydrogen to a loosely bound ligand. Test results on pyridine, nicotinaldehyde and nicotine reveal up to ≈1.2% single spin proton polarisation levels in their (1)H NMR signals which compare to the normal 0.003% level at 9.4 Tesla. These results exemplify how rational catalyst design yields a solvent dependent catalyst with good SABRE activity.
已合成一种双齿铱卡宾配合物Ir(κC,O-L1)(COD)，其含有一个通过顺式跨越酚盐基团功能化的强供电子卡宾配体。该配合物作为有效磁化转移催化剂的前体，在与H2和合适的双电子供体反应后形成。在含有吡啶的苯等溶剂中，它们以具有不等价氢化物配体且保留Ir-O键的中性手性Ir(H)2(κC,O-L1)(py)2为例，而在甲醇中，Ir-O键断裂导致两性离子Ir(H)2(κC,O(-)-L1)(py)3，具有化学等价的氢化物配体。因此，活性催化剂的形式取决于溶剂。这两种配合物都打破了氢化物配体的磁对称性，并且在将极化从仲氢转移到松散结合配体的催化过程中具有活性。对吡啶、烟醛和尼古丁的测试结果显示，其(1)H NMR信号中的单自旋质子极化水平高达约1.2%，而在9.4特斯拉时正常水平为0.003%。这些结果例证了合理的催化剂设计如何产生具有良好SABRE活性的溶剂依赖性催化剂。
