Dynamic Pd^II/Cu^IMultimetallic Assemblies as Molecular Models to Study Metal–Metal Cooperation in Sonogashira Coupling

Abstract

Cooperation between two different metals plays a crucial role in many synergistic catalytic reactions, such as the Sonogashira C−C cross‐coupling reaction, where an interaction between the Pd and Cu centers is proposed in the transmetalation step. Although several heterobimetallic Pd/Cu complexes were proposed as structural models of the active species in Sonogashira coupling, the detailed understanding of the metal–metal cooperation in transmetalation is still lacking in current systems. In this work, we report a stepwise and systematic approach to building heteromultimetallic Pd/Cu assemblies as a tool to study metal–metal cooperativity. We obtained fully characterized Pd/Cu multimetallic assemblies that show reactivity in alkyne activation, formation of catalytically relevant aryl/acetylide species, and C−C elimination, serving as functional models for Sonogashira reaction intermediates. The combined experimental and DFT studies highlight the importance of ligand‐controlled coordination geometry, metal–metal distances and dynamics of the multimetallic assembly for transmetalation step.

Heteropolymetallic Architectures as Snapshots of Transmetallation Processes at Different Degrees of Transfer

“…[5] Besides, Lledós and Khusnutdinova found that subtle changes in PdÀ Cu distances have a large effect in the efficiency of the Sonogashira coupling, the shorter the better. [6] Similar results were described by Espinet and coworkers in Pd arylation processes by Au aryls, [7] by Zhang and coworkers in the cross coupling reaction of iodobenzene facilitated by PdÀ Au species, [8] and by Hashmi and coworkers in several PdÀ Au transmetallation scenarios. [9] On the other hand, Takita, Uchiyama and coworkers used PdÀ Cu catalysts in cross coupling reactions for CÀ C bonds on highly sterically hindered structures by taking advantage of the lowered activation energy for the transmetallation process due to the presence of the intermetallic interactions.…”

“…below) Crystal structure of the cation complex of 5. Relevant distances (Å) and angles (°): Pd(1)-Ag, 2.8597(2); Pd(1)À C( 13), 2.072(2); Pd(1)À C(7), 2.143(2); AgÀ C(7), 2.239(2); C(7)À Pd(1)À Ag, 50.73 (6); Pd(1)À AgÀ Pd(2), 132.774 (8).…”

“…(left) Crystal structure of the complex 1. Relevant distances (Å) and angles (°): PdÀ C(7) 2.0007(19), PdÀ N 2.1034(17), PdÀ P 2.2497(5), PdÀ Cl(1) 2.4182(5); C(7)À PdÀ N 80.99(7), C(7)À PdÀ P 97.47(6), NÀ PdÀ P 173.90(5), C(7)À PdÀ Cl(1) 153.80(6), NÀ PdÀ Cl(1) 96.04(5), PÀ PdÀ Cl(1) 87.932(18). (right) Crystal structure of the complex 2.…”

Bimetallics in a Nutshell: Complexes Supported by Chelating Naphthyridine-Based Ligands

“…Similarly, Khusnutdinova and co-workers employed related unsymmetrical naphthyridine-based ligands containing a BPMAN side arm to support multinuclear Cu chains (2–4 Cu atoms) synthesized in a stepwise, selective, and reversible fashion, lengthening the chain by adding more equivalents of Cu I or shortening it through chemical reduction . They also employed similar ligands to synthesize Cu–Pd multimetallic species as functional models for reaction intermediates in the Sonogashira reaction . In addition, their use of an unsymmetrical diamine-OP t Bu 2 naphthyridine ligand afforded a Cu–Pt heterobimetallic system that appears to exhibit metal–metal cooperativity in alkyne C–H activation and aryl abstraction from the BArF 24 anion, as was observed for 7 (Scheme ).…”

Combining metal–metal cooperativity, metal–ligand cooperativity and chemical non-innocence in diiron carbonyl complexes

“… 7 The utilization of synthetic complexes wherein multiple metals work together to activate chemical bonds is a promising avenue to stabilize reactive species or develop new chemical transformations. 8 The increased popularity for studying multimetallic complexes is evident by a wide range of ligand scaffolds designed to accommodate multiple metal centers that have recently been reported. 7–9 Ligands based on 1,8-naphthyridine have been shown to be highly suitable for the synthesis of bimetallic complexes capable of MMC.…”