Using para hydrogen induced polarization to study steps in the hydroformylation reaction

Abstract

Para-hydrogen assisted NMR spectroscopy allows the detection of an array of reaction intermediates during iridium catalyzed hydroformylation.

Data-powered augmented volcano plots for homogeneous catalysis

“…S3 †). This nding is fully consistent with experimental observations regarding the generally enhanced stability of iridium catalysts used in hydroformylation, [45][46][47] as well as additional ancillary evidence regarding the isolation of acyl dihydro iridium intermediates 48,49 (i.e., I7) during the same process. It has been postulated that this extra stability arises from relativistic effects that stabilize the 6s electron level relative to the 5d level thereby inducing stronger bonding in third row relative to second row transition metals.…”

Advancing homogeneous catalysis for parahydrogen-derived hyperpolarisation and its NMR applications

“…The use of para-H 2 to enhance NMR signal intensity is a versatile platform that allows the hyperpolarisation of a range of different functionalities including metal complexes, 14,30,36,38,45 alkenes, 14,30,57 alkanes, 14,30 esters, 88 aldehydes, [23][24][25][26][27]114 carboxylic acids, 126,192 N-heterocycles, 17,29 amines, 58,193 diazirines, 124,194,195 nitriles, 167 silanes, 132 sulfoxides, 147,172 a-ketoacids, 125,146,147,157,196 amino acids, 197 peptides 78,80,82,198 and many others. Enhanced NMR signals can be achieved most commonly for 1 H, 13 C and 15 N sites, although PHIP and SABRE-enhanced 2 H, 199,200 11 B, 28,64,66 19 F, 85,128,129,…”

“…1a). 9,24,25 These newly introduced protons can exhibit dramatically enhanced 1 H NMR signals. The nuclear hyperpolarisation, however, is typically short-lived and decays reaching the thermal equilibrium level due to nuclear spin relaxation which is typically characterised by the time taken to establish thermal longitudinal magnetisation, T 1 .…”

“…At the same time, PHIP can be observed for catalytic intermediates if initial para-H 2 activation by the catalyst active centre is pairwise, although the full cycle can be non-pairwise. Based on this possibility, effects such as oneH-PHIP [23][24][25][26][27][28] can be observed wherein only one of the para-H 2 originating protons ends up in the hyperpolarised product. There are also reactions in which molecules can become hyperpolarised without chemical incorporation of para-H 2 into the target structures, as takes place in SABRE.…”

“…Nevertheless, strongly enhanced NMR signals for metal hydride intermediates has been of great use in mapping hydroformylation reaction pathways. [23][24][25][26][27]114 OneH-PHIP has expanded the types of reactions that can be examined using para-H 2 and has been of tremendous value in probing inorganic reaction mechanisms.…”