Understanding Rh‐catalysed Hydroformylation with Phosphite Ligands through Catalyst Speciation Analysis by Operando FlowNMR Spectroscopy

Abstract

Phosphites are industrially important ligands for the Rhcatalysed hydroformylation of olefins because they produce more active catalysts than phosphines, which is mainly due to their strong π-acceptor properties facilitating CO dissociation from the metal centre. Herein, the effect of three prominent phosphite ligands (triphenylphosphite, Alkanox and BiPhePhos) on catalyst speciation during turnover is investigated using multi-nuclear operando FlowNMR spectroscopy. The quantita-tive catalyst distribution maps derived explain activity trends across a range of catalytic reaction conditions that show how phosphites produce more active catalysts, including reduced formation of inactive Rh 0 dimers in the absence of substrate during pre-activation and at the end of the reaction. Additionally, [(alkanox)Rh(acac)] complexes have been found to be of high stability which can be exploited for post-catalytic Rh recovery by simple addition of 2,4-pentanediones.

Twinned versus linked organometallics - bimetallic “half-baguette” pentalenide complexes of Rh(i)

“…S34†). 96 Two broad peaks at −16.2 ppm and −34.4 ppm were also observed suggesting some fluxionality within the product(s) formed. Although all attempts at isolating a clean sample lead to decomposition, standing of a 1 : 1 THF/pentane solution of the crude reaction mixture at −35 °C overnight led to the formation of crystals of the ion pair [Rh II (CO)(PMe 3 ) 4 ][Ph 4 Pn] ( 8 , Fig.…”

Paramagnetic Relaxation Agents for Enhancing Temporal Resolution and Sensitivity in Multinuclear FlowNMR Spectroscopy

“…Hydroformylation reactions catalysed by phosphine‐modified Rh complexes represent an industrially important application of homogeneous catalysis that has been extensively studied by in‐situ IR [66–68] and more recently also by operando FlowNMR spectroscopy [19,23,69] . Due to the excess ligand used and multiple coordination equilibria present during turnover, causing a dynamic distribution of various Rh/PR 3 intermediates of differing T 1 values, the application of an inert PRA that shortens and equalises all spin‐lattice relaxation times would be particularly beneficial in such systems.…”

Modular Synthesis of Phosphite and Phosphoramidite Ligands for Rh‐Catalyzed Hydroformylation

“…When the catalyst and ligand are in e, e configuration, high l/b ratio of 190 can be produced. [17] Based on the research of Van Leeuwen and Roobeek, this group explore and synthesize the phosphite ligand L1 and L2 [Chiraphite], which was derived from optically pure 2.4pentanediol, and was used in the hydroformylation of styrene to obtain high regioselectivity (b/l = 96 : 4), good enantioselectivity (ee% = 76 %). At the same time, the authors believed that the substrate, bisphosphine ligand and metal complex form an equatorial-equatorial space structure, which can obtain higher ee values (Scheme 3a).…”

“…The chelating effect and appropriate suitable bite angle can affect regioselectivity. When the catalyst and ligand are in e, e configuration, high l/b ratio of 190 can be produced [17] …”