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  • Developing ligands for palladium(II)-catalyzed C-H functionalization: intimate dialogue between ligand and substrate.

Developing ligands for palladium(II)-catalyzed C-H functionalization: intimate dialogue between ligand and substrate.

The Journal of organic chemistry (2013-04-10)
Keary M Engle, Jin-Quan Yu
ABSTRACT

Homogeneous transition-metal-catalyzed reactions are indispensable to all facets of modern chemical synthesis. It is thus difficult to imagine that for much of the early 20th century, the reactivity and selectivity of all known homogeneous metal catalysts paled in comparison to their heterogeneous and biological counterparts. In the intervening decades, advances in ligand design bridged this divide, such that today some of the most demanding bond-forming events are mediated by ligand-supported homogeneous metal species. While ligand design has propelled many areas of homogeneous catalysis, in the field of Pd(II)-catalyzed C-H functionalization, suitable ligand scaffolds are lacking, which has hampered the development of broadly practical transformations based on C-H functionalization logic. In this Perspective, we offer an account of our research employing three ligand scaffolds, mono-N-protected amino acids, 2,6-disubstituted pyridines, and 2,2'-bipyridines, to address challenges posed by several synthetically versatile substrate classes. Drawing on this work, we discuss principles of ligand design, such as the need to match a ligand to a particular substrate class, and how ligand traits such as tunability and modularity can be advantageous in reaction discovery.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Palladium, nanopowder, <25 nm particle size (TEM), ≥99.5%
Sigma-Aldrich
Palladium, foil, thickness 1.0 mm, 99.9% trace metals basis
Sigma-Aldrich
Palladium, foil, thickness 0.25 mm, 99.98% trace metals basis
Sigma-Aldrich
Palladium, powder, <75 μm, 99.9% trace metals basis
Sigma-Aldrich
Palladium, powder or granules, 99.99% trace metals basis
Sigma-Aldrich
Palladium, powder, 99.995% trace metals basis
Sigma-Aldrich
Palladium, wire, diam. 0.5 mm, 99.9% trace metals basis
Sigma-Aldrich
Palladium, sponge, 99.9% trace metals basis
Sigma-Aldrich
Palladium, wire, diam. 1.0 mm, 99.9% trace metals basis
Sigma-Aldrich
Palladium, foil, thickness 0.025 mm, 99.9% trace metals basis
Sigma-Aldrich
Palladium, foil, thickness 0.5 mm, 99.9% trace metals basis
Sigma-Aldrich
Palladium, evaporation slug, diam. × L 0.6 cm × 0.6 cm, 99.95% trace metals basis
Palladium, foil, not light tested, 50x50mm, thickness 0.03mm, as rolled, 99.95%
Palladium, foil, light tested, 50x50mm, thickness 0.075mm, as rolled, 99.95%
Palladium, foil, not light tested, 25x25mm, thickness 0.0125mm, 99.95%
Palladium, foil, not light tested, 100x100mm, thickness 0.005mm, 99.95%
Palladium, foil, not light tested, 150x150mm, thickness 0.025mm, as rolled, 99.95%
Palladium, foil, not light tested, 50x50mm, thickness 0.005mm, 99.95%
Palladium, rod, 100mm, diameter 2.0mm, 99.95%
Palladium, wire reel, 0.1m, diameter 0.5mm, as drawn, 99.95%
Palladium, foil, not light tested, 150x150mm, thickness 0.03mm, as rolled, 99.95%
Palladium, foil, light tested, 25x25mm, thickness 0.03mm, as rolled, 99.95%
Palladium, rod, 25mm, diameter 6.0mm, 99.95%
Palladium, wire reel, 1m, diameter 0.05mm, as drawn, 99.9%
Palladium, wire reel, 0.2m, diameter 0.25mm, as drawn, 99.99+%
Palladium, wire reel, 0.5m, diameter 0.125mm, hard, 99.95%
Palladium, foil, not light tested, 100x100mm, thickness 0.006mm, 99.95%
Palladium, wire reel, 2m, diameter 0.25mm, hard, 99.95%
Palladium, microfoil, disks, 25mm, thinness 0.5μm, specific density 303.4μg/cm2, permanent mylar 3.5μm support, 99.99%
Palladium, foil, not light tested, 50x50mm, thickness 0.0025mm, 99.95%