Group 10 metal catalysts have shown much promise for the copolymerization of nonpolar with polar alkenes to directly generate functional materials, but access to high copolymer molecular weights nevertheless remains a key challenge toward practical applications in this field. In the context of identifying new strategies for molecular weight control, we report a series of highly polarized P(V)-P(III) chelating ligands that manifest unique space filling and electrostatic effects within the coordination sphere of single component Pd polymerization catalysts and exert important influences on (co)polymer molecular weights. Single component, cationic phosphonic diamide-phosphine (PDAP) Pd catalysts are competent to generate linear, functional polyethylenes with M up to ca. 2 × 10 g mol, significantly higher than prototypical catalysts in this field, and with polar content up to ca. 9 mol %. Functional groups are positioned by these catalysts almost exclusively along the main chain, not at chain ends or ends of branches, which mimics the microstructures of commercial linear low-density polyethylenes. Spectroscopic, X-ray crystallographic, and computational data indicate PDAP coordination to Pd manifests cationic yet electron-rich active species, which may correlate to their complementary catalytic properties versus privileged catalysts such as electrophilic α-diimine (Brookhart-type) or neutral phosphine-sulfonato (Drent-type) complexes. Though steric blocking within the catalyst coordination sphere has long been a reliable strategy for catalyst molecular weight control, data from this study suggest electronic control should be considered as a complementary concept less prone to suppression of comonomer enchainment that can occur with highly sterically congested catalysts.

Fast, base-promoted protodeboronation of polyfluoroaryl and heteroaryl boronic acids complicates their use in Suzuki-Miyaura coupling (SMC) because a base is generally required for catalysis. We report a "cationic" SMC method using a PAd-Pd catalyst that proceeds at rt in the absence of a base or metal mediator. A wide range of sensitive boronic acids, particularly polyfluoroaryl substrates that are poorly compatible with classic SMC conditions, undergo clean coupling. Stoichiometric experiments implicate the intermediacy of organopalladium cations, which supports a long-postulated cationic pathway for transmetalation in SMC.

The use of fluorinated arylboronic acid building blocks in cross-coupling has remained challenging, because of their acute base sensitivity. We report a general solution to this problem using a true catalytic intermediate, Pd­(PAd3)­(p-FC6H4)­Br, as a uniquely effective “on-cycle” precatalyst that allows Suzuki–Miyaura coupling to occur much faster than even the most severe protodeboronation side reactions. Control of boron speciation between the active acid and dormant ester forms was also found to play a critical role in balancing the rates of catalysis versus reagent decomposition. This method is compatible with any fluorination pattern, base-labile functional groups, and a range of bromo­(hetero)­arenes.

Substituted 1,3-dienes are valuable synthetic intermediates used in myriad catalytic transformations, yet modern catalytic methods for their preparation in a highly modular fashion using simple precursors are relatively few. We report here an aerobic boron Heck reaction with cyclobutene that forms exclusively linear 1-aryl-1,3-dienes using (hetero)arylboronic acids, or 1,3,5-trienes using alkenylboronic acids, rather than typical Heck products (i.e., substituted cyclobutenes). Experimental and computational mechanistic data support a pericyclic mechanism for C−C bond cleavage that enables the cycloalkene to circumvent established limitations associated with diene reagents in Heck-type reactions.

Tri(1-adamantyl)phosphine, a simple yet long-absent homoleptic phosphine, has finally been prepared. The simplicity of this compound beguiles its exceptional properties. The electron-releasing character eclipses all other alkylphosphines. The phosphine geometry and overall size are also more compact than anticipated, which may occur as a result of dispersion forces. We believe the donicity, marked resistance towards cyclometallation or P−C bond scission, and also substantial polarizability engendered by the three diamondoid fragments together account for the phenomenal performance of Pd-PAd 3 catalysts during Suzuki-Miyaura coupling reactions. A correlation analysis is also described that provides support for polarizability as a potentially general influence on the properties of tertiary phosphines. 1 Introduction 2 Synthesis of Tri(1-adamantyl)phosphine 3 Reactions of Tri(1-adamantyl)phosphine Palladium Complexes 4 Electronic and Steric Properties of Tri(1-adamantyl)phosphine 5 Conclusion Key words phosphine, ligand, catalysis, cross-coupling, palladium, diamondoid Liye Chen (right) is originally from Dalian, China. In 2008, he obtained a BS in chemistry from Tsinghua University in Beijing, China and then completed post-undergraduate research at the Shanghai Institute of Organic Chemistry. Currently, Liye is a Ph.D. candidate at Princeton in Brad Carrow's laboratory and is pursuing catalyst and reaction discovery and development. Brad Carrow (left) obtained his B.S. in chemistry from the Missouri University of Science and Technology in 2003. He received his in Ph.D. in 2011 from the University of Illinois at Urbana-Champaign following work in the laboratories of John F. Hartwig. After completing his graduate studies, he was a postdoctoral fellow and then an assistant professor in the laboratories of Kyoko Nozaki at the University of Tokyo. Since Fall 2013, he has been an assistant professor of chemistry at Princeton University. His research interests revolve around transition-metal catalysis in the context of sustainable organic synthesis, polymer synthesis, and strong bond activation.