Structurally-Responsive Ligands for High-Performance Catalysts

Abstract

Hemilabile ligands that undergo reversible changes in denticity have long been exploited to enable catalyst activation and to increase lifetime. However, this common description does not fully reflect reality with respect to the diversity of known ligand types, modes of action, and impacts on catalysis. The term structurally responsive ligand (SRL) is employed here to encompass ligands that exhibit selftuning denticity, hapticity, or versatile coordination. This Perspective covers case study examples of SRLs in catalysis and their influence on catalyst lifetime, rate, and selectivity. The examples include leading and emerging catalysts for enabling transformations, which emphasizes both the breadth and significance of this class of ligands.

Cooperative approaches in catalytic hydrogenation and dehydrogenation

“…1,2,6 The aims of the coverage here are to present an overview of key features of MLC, illustrated with characteristic examples, and provide the context to frame MMC. MLC reactivity and so-called non-innocent ligands fall into a range of classes, with redox-active ligands, 14 structurally-responsive ligands 15 and bifunctional systems 1,2,6 being the most common. The latter is the focus of this work, wherein bifunctional or multisite reactivity across the metal and ligand occur on-cycle.…”

Development and Molecular Understanding of a Pd‐Catalyzed Cyanation of Aryl Boronic Acids Enabled by High‐Throughput Experimentation and Data Analysis

“…Hence, both terms potentially describe the necessity of at least one weakly binding phosphine of the bidentate Xantphos-type ligand, in line with the well-known hemi-lability exhibited by those ligands. [83,84] To gain further insight into the key parameters required for high yields in the bisphosphine group B, a more general statistical analysis encompassing non-Xantphos-like ligands was carried out (see Figure 5). After performing a classification with the same parameter used for the Xantphos ligand subset, the threshold value for Eσ* (PÀ C)max L remained at 0.237 Hartree (Figure 5,a).…”

“…In this arena, structurally-responsive ligands (SRL) like Buchwald dialkyl biaryls and Xantphos-type ligands excel as they are able to stabilize the metal in their L2 state while their well-known hemilability opens up a coordination site (L1 state) that may be needed to enable catalysis (see Scheme 2). [83,84]…”

Changes in ligand coordination mode induce bimetallic C–C coupling pathways

“…In response to the steric and electronic demands of the metal, the 1-azaallyl fragment in L1 switches from μ-N in 1 to μ-[η 2 -CC;κ 1 -N] and κ 1 -N modes in products 2 and 3 , respectively, which indicates that L1 is structurally responsive. 37 We previously hypothesized that the capacity of L1 to adopt these different coordination modes may induce C–C bond formation. This premise has been exploited extensively for decades with hemilabile ligands that promote substitution chemistry and other organometallic reactions via changes in ligand denticity.…”

“…This premise has been exploited extensively for decades with hemilabile ligands that promote substitution chemistry and other organometallic reactions via changes in ligand denticity. 37–41 Indeed, one of the viable catalytic pathways for bimetallic α-arylation, noted above, involves a switch between κ 2 -P,N and κ 1 -P 2-phosphinoimidazole coordination. 22…”