Dinuclear Pd^Icomplexes with bridging allyl and related ligands

Abstract

There are many important synthetic methods that utilize palladium catalysts. In most of these reactions, the palladium species are proposed to exist exclusively in either the Pd(0) or Pd(II) oxidation states. However, in the last decade, dinuclear Pd(I) complexes have repeatedly been isolated from reaction mixtures previously suggested to involve only species in the Pd(0) and Pd(II) oxidation states. As a consequence, in order to design improved catalysts there is considerable interest in understanding the chemistry of dinuclear Pd(I) complexes. A significant proportion of the known dinuclear Pd(I) complexes are supported by bridging allyl or related ligands such as cyclopentadienyl or indenyl ligands. This review provides a detailed account of the synthesis, electronic structure and stoichiometric reactivity of dinuclear Pd(I) complexes with bridging allyl and related ligands. Additionally, it describes recent work where dinuclear Pd(I) complexes with bridging allyl ligands have been detected in catalytic reactions, such as cross-coupling, and discusses the potential implications for catalysis.

Dinuclear Nickel(I) and Palladium(I) Complexes for Highly Active Transformations of Organic Compounds

“…Catalytic transformations using these catalysts, such as addition, polymerization, allylic substitution, cross coupling, and C–H substitution reactions, significantly contribute to the production of useful organic chemicals in industry. Interestingly, several dinuclear Pd(I) and Ni(I) complexes have been reported to demonstrate notably higher activity as precatalysts compared to typical monomeric zerovalent or divalent metal complexes [ 11 , 12 , 13 , 14 , 15 , 16 ]. Detailed mechanistic studies revealed that dinuclear or mononuclear active catalysts are generated from the corresponding dinuclear precatalysts to achieve highly efficient and/or selective catalytic reactions.…”

“…Several other reports proposed that heterolytic or homolytic cleavage of the metal–metal bond of dinuclear Pd(I) or Ni(I) complexes could produce active metal species in situ, such as highly unsaturated “mono-ligated metal complexes”. However, the chemistries of dinuclear Ni(I) and Pd(I) complexes in catalysis have not been classified and compared with each other, although the chemistry of such nickel and palladium complexes has been summarized individually [ 11 , 12 , 13 , 14 , 15 , 16 ]. Therefore, the survey and comparison of the reactivity and catalytic performance of dinuclear nickel(I) and palladium(I) complexes, as well as their generation processes and structures, should be useful and informative.…”

Insights into the Catalytic Activity of [Pd(NHC)(cin)Cl] (NHC=IPr, IPrCl, IPrBr) Complexes in the Suzuki–Miyaura Reaction

“…The first description of the activation of Pd–allyl complexes, using an alternate weak base (K 2 CO 3 ), was performed by Colacot and co‐workers and was followed by similar reports . In the course of the preparation of the dinuclear Pd I complex [Pd 2 (IPr) 2 (η 3 ‐cin)Cl] (IPr=1,3‐bis(2,6‐diisopropyl‐phenyl)imidazol‐2‐ylidene; cin=cinnamyl), Hazari and co‐workers proposed an equilibrium between the Pd I ‐dimer and the catalytically active Pd 0 –NHC intermediate by a comproportionation/disproportionation reaction with unreactive [Pd(IPr)(cin)Cl] –. In this context, this study suggested the activation pathway of [Pd(NHC)(R‐allyl)Cl] to proceed as depicted in Scheme .…”

Hydrogenation of nitroarenes catalyzed by a dipalladium complex

“…In particular, chemists have great interest in the use of bimetallic compounds as catalysts to impart new reactivity of chemical reactions. Among various transition metal ions, dipalladium complexes have received much attention due to the remarkable activity of this metal ions . Few di‐nuclear palladium complexes exhibit the catalytic activities in cross‐coupling, olefin polymerization, and C‐H activation .…”