Room‐Temperature Palladium‐Catalyzed Negishi‐Type Coupling: A Combined Experimental and Theoretical Study

Abstract

An air-stable, bulky electron-accepting phosphine ligand (phosphabarrelene) allows the easy reduction of a Pd(II) precursor to a Pd(0) complex, highly active in room-temperature Negishi-type cross-coupling. DFT calculations show that the use of the electron-accepting ligand favors both transmetalation (TM) and reductive-elimination (RE) processes (see scheme; OA = oxidative addition).

Unexpected Substituent Effects in Aryl-Aryl Negishi Cross-Coupling Reactions Rationalized by Density Functional Theory and Natural Charges

“…Distances and barriers are explained by the bulky nature of the participating ligands. Values of Δ G ‡ (25.0–28.4 kcal/mol) are within the range of what is typically found for transmetalation reactions. ,, …”

“…Values of ΔG ‡ (25.0−28.4 kcal/mol) are within the range of what is typically found for transmetalation reactions. 39,41,42 The entire reaction (I → VI) produces a ΔG tot of around −5 kcal/mol on average. While ΔG tot seems to be independent of σ para , a correlation is found for the phenyl transfer TS, which shows an increase in ΔG ‡ with increasing σ para in agreement with our experimental results.…”

Computational Studies of Synthetically Relevant Homogeneous Organometallic Catalysis Involving Ni, Pd, Ir, and Rh: An Overview of Commonly Employed DFT Methods and Mechanistic Insights

“…The Pd-catalyzed coupling of aryl halides with organozinc reagents has been in the focus of some computational studies over these past few years. 210 A study of the transmetalation step in the Negishi reaction was undertaken in 2011 by Ujaque, Espinet, and co-workers at the SMD (THF) M06/TZVP (DGDZVP)//M06/6-31G(d)(LANL2DZ) level of theory. 211 They noted that the presence of additional ligand profoundly affects the reaction mechanism.…”

Formation of XPhos‐Ligated Palladium(0) Complexes and Reactivity in Oxidative Additions

“…The mechanism of the oxidative addition of aryl halidest o isolated Pd 0 complexes ligatedb yb ulky phosphines ligands has been widely investigated. [8,9] While the Pd 0 L 2 14-electron complex is usually the active catalytic species, [10] Pd 0 complexes ligatedb yb ulky phosphine ligandss uch as P(o-Tol) 3 and PtBu 3 reactvia the Pd 0 L12-electron complex after dissociation of one ligand. [8,11] First reported by the Buchwald group in 2003, [12] the XPhos ligand has found ab road range of applications( Scheme 2).…”