Homo- and Heterobimetallic Precursor Catalysts for the Heck Reaction, and a Proposal for a General Catalytic Cooperativity Index

Abstract

Homo‐ (Pd2) and heterobimetallic (PtPd) complexes supported by a P,P‐bridging, bis(P,N‐chelating) coordination mode of the potentially hexadentate ligand 1,1‐bis[di(o‐N,N‐dimethylanilinyl)phosphino]methane (dmapm) are effective catalyst precursors for the aerobic Heck coupling of iodobenzene and styrene at 100 °C in DMF/H2O solution containing K2CO3. This medium allows for trivial separation of the trans‐stilbene product which precipitates after the reaction mixture is cooled. The bimetallic precursors are more active than predicted from the sum of the activities of complexes chosen to mimic their mono‐metallic “half units,” suggesting some degree of intermetallic cooperativity during the reaction. A non‐linear dependence of initial rate on catalyst concentration implies, however, that the complexes do not remain intact, and may be involved in dissociative equilibria with non‐dmapm containing monometallic components that are more active species for the Heck coupling. The complexes are slowly degraded by oxidation at a phosphorus centre. A general index for quantifying the degree of intermetallic cooperativity during a catalytic cycle is proposed and its utility and limitations are discussed.

Simultaneous Functionalization of Carbon Surfaces with Rhodium and Iridium Organometallic Complexes: Hybrid Bimetallic Catalysts for Hydroamination

“…On the other hand, homogeneous bimetallic complexes containing two metal centers tethered in close proximity by a bridging unit, have been shown to catalyze a range of reactions more efficiently than the analogous mixtures of the monometallic “half-units”. − They can also offer alternative or enhanced selectivity, by facilitating different mechanistic pathways. , While in separate studies bimetallic complexes and organometallic complexes on carbon surfaces have performed as excellent catalysts, ,,,, the combination of these two approaches provides opportunities to explore more advanced catalysts.…”

Synthesis, structure and catalytic activity of dicarbene dipalladium complexes with different substituents

“…However, bimetallic palladium complexes in which the bidentate ligand bridges the two metal centers are not very much [11][12][13]. The design and synthesis of binuclear complexes with di-NHC are of considerable interest because the adjacent metals could function in a synergic manner in their interactions with substrate molecules [14]. In addition, the electronic and steric properties can be modified by substituents attached to the nitrogen atoms of the NHC ring, which is important for their utilization as ligands in catalytic reactions [15,16].…”

Kinematic molecular manufacturing machines

“…Jones and James have recently also proposed a "cooperativity catalytic index" to evaluate the cooperative effect in bi-or poly-metallic catalysts of organic transformations [69]. It should be noted however, that this index is limited by the fact that it is based only on kinetic data that assumes the reaction to be first-order in a catalyst.…”