Understanding a Hydroformylation Catalyst that Produces Branched Aldehydes from Alkyl Alkenes

Abstract

This paper reports experimental and computational studies on the mechanism of a rhodium-catalyzed hydroformylation that is selective for branched aldehyde products from unbiased alkene substrates. This highly unusual selectivity relies on a phospholane-phosphite ligand prosaically called BOBPHOS. Kinetic studies using in situ high pressure IR (HPIR) and the reaction progress kinetic analysis methodology suggested two steps in the catalytic cycle were involved as turnover determining. Negative order in CO and positive orders in alkene and H were found and the effect of hydrogen and carbon monoxide partial pressures on selectivity were measured. Labeling studies found rhodium hydride addition to the alkene to be largely irreversible. Detailed spectroscopic HPIR and NMR characterization of activated rhodium-hydrido dicarbonyl species were carried out. In the absence of H, reaction of the rhodium-hydrido dicarbonyl with allylbenzene allowed further detailed spectroscopic characterization of four- and five-coordinate rhodium-acyl species. Under single-turnover conditions, the ratios of branched to linear acyl species were preserved in the final ratios of aldehyde products. Theoretical investigations uncovered unexpected stabilizing CH-π interactions between the ligand and substrate which influenced the high branched selectivity by causing potentially low energy pathways to become unproductive. Energy span and degree of TOF control analysis strongly support experimental observations and mechanistic rationale. A three-dimensional quadrant model was built to represent the structural origins of regio- and enantioselectivity.

Silicon-oriented regio- and enantioselective rhodium-catalyzed hydroformylation

“…As shown in Fig. 5 , the alkene insertion step was computed to be the rate-determining step, which is in agreement with the previous computational studies 51 – 56 and no observation of the H/D scrambling from the product (Fig. 7 ).…”

Metal-organic frameworks as kinetic modulators for branched selectivity in hydroformylation

“…Rh catalysts with bidentate ligands dominate the scene, especially with substrates with directing groups 22 . At present, the branched-selective hydroformylation of olefins without directing groups is still challenging and can be achieved only by complex Rh catalysts with a selectivity for 2-methylhexanale from 1hexene up to 75% 23,24 and up to 86% for 2-methylbutanale from 1-butene 25 . Supramolecular chemistry has also been used to tune regioselectivity in Rh-catalysed hydroformylation [26][27][28] .…”

Propene Hydroformylation Reaction Catalyzed by HRh(CO)(BISBI): A Thermodynamic and Kinetic Analysis of the Full Catalytic Cycle

“…In recent work, Clarke et al performed a computational study involving the hydroformylation of styrene catalyzed by a Rh‐BOBPHOS catalyst. [ 63 ] This study also investigated the possible origins of the regioselectivity observed in the reaction and identified, from a noncovalent interaction descriptor (NCI), that C‐H ··· π interactions between the olefin and specific phenyl rings of BOBPHOS are a possible factor responsible by the selectivity. Their main conclusion about the influence of C‐H ··· π interactions into the selectivity is that this interaction plays an essential role as a stabilizing factor.…”