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      Reactivity of a Dinuclear Pd I Complex [Pd 2(μ-PPh 2)(μ 2-OAc)(PPh 3) 2] with PPh 3: Implications for Cross-Coupling Catalysis Using the Ubiquitous Pd(OAc) 2/nPPh 3 Catalyst System

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          Abstract

          [Pd I 2(μ-PPh 2)(μ 2-OAc)(PPh 3) 2] is the reduction product of Pd II(OAc) 2(PPh 3) 2, generated by reaction of ‘Pd(OAc) 2’ with two equivalents of PPh 3. Here, we report that the reaction of [Pd I 2(μ-PPh 2)(μ 2-OAc)(PPh 3) 2] with PPh 3 results in a nuanced disproportionation reaction, forming [Pd 0(PPh 3) 3] and a phosphinito-bridged Pd I-dinuclear complex, namely [Pd I 2(μ-PPh 2){κ 2-P,O-μ-P(O)Ph 2}(κ-PPh 3) 2]. The latter complex is proposed to form by abstraction of an oxygen atom from an acetate ligand at Pd. A mechanism for the formal reduction of a putative Pd II disproportionation species to the observed Pd I complex is postulated. Upon reaction of the mixture of [Pd 0(PPh) 3] and [Pd I 2(μ-PPh 2){κ 2-P,O-μ-P(O)Ph 2}(κ-PPh 3) 2] with 2-bromopyridine, the former Pd 0 complex undergoes a fast oxidative addition reaction, while the latter dinuclear Pd I complex converts slowly to a tripalladium cluster, of the type [Pd 3(μ-X)(μ-PPh 2) 2(PPh 3) 3]X, with an overall 4/3 oxidation state per Pd. Our findings reveal complexity associated with the precatalyst activation step for the ubiquitous ‘Pd(OAc) 2’/nPPh 3 catalyst system, with implications for cross-coupling catalysis.

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          Most cited references38

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          Anionic Pd(0) and Pd(II) intermediates in palladium-catalyzed Heck and cross-coupling reactions.

          The anions of PdCl(2)L(2) and Pd(OAc)(2), precursors of palladium(0) used in cross-coupling and Heck reactions, play a crucial role in these reactions. Tricoordinated anionic complexes Pd(0)L(2)Cl(-) and Pd(0)L(2)(OAc)(-) are the effective catalysts instead of the usually postulated Pd(0)L(2) complex. The anion ligated to the palladium(0) affects the kinetics of the oxidative addition to ArI as well as the structure and reactivity of the arylpalladium(II) complexes produced in this reaction. Thus, pentacoordinated anionic complexes are formed, ArPdI(Cl)L(2)(-) or ArPdI(OAc)L(2)(-), the precursor of neutral trans-ArPd(OAc)L(2), instead of the usually postulated trans-ArPdIL(2) complex (L = PPh(3)).
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            Unparalleled Rates for the Activation of Aryl Chlorides and Bromides: Coupling with Amines and Boronic Acids in Minutes at Room Temperature

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              Solvent Effect on Palladium-Catalyzed Cross-Coupling Reactions and Implications on the Active Catalytic Species

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                Author and article information

                Journal
                Organometallics
                Organometallics
                om
                orgnd7
                Organometallics
                American Chemical Society
                0276-7333
                1520-6041
                19 August 2021
                13 September 2021
                : 40
                : 17
                : 2995-3002
                Affiliations
                []Department of Chemistry, University of York , Heslington, York, North Yorkshire YO10 5DD, United Kingdom
                []Bayer AG , Alfred-Nobel-Strasse 50, 40789 Monheim, Germany
                Author notes
                Author information
                https://orcid.org/0000-0002-5132-5468
                Article
                10.1021/acs.organomet.1c00347
                8441971
                34539028
                fc1ce5c8-a9ba-454c-ae47-2aec44687e0e
                © 2021 American Chemical Society

                Permits the broadest form of re-use including for commercial purposes, provided that author attribution and integrity are maintained ( https://creativecommons.org/licenses/by/4.0/).

                History
                : 11 June 2021
                Funding
                Funded by: Bayer, doi 10.13039/100004326;
                Award ID: NA
                Funded by: Engineering and Physical Sciences Research Council, doi 10.13039/501100000266;
                Award ID: EP/K039660/1
                Funded by: Engineering and Physical Sciences Research Council, doi 10.13039/501100000266;
                Award ID: 19000077
                Funded by: University of York, doi 10.13039/100009001;
                Award ID: NA
                Funded by: GlaxoSmithKline, doi 10.13039/100004330;
                Award ID: NA
                Categories
                Article
                Custom metadata
                om1c00347
                om1c00347

                Inorganic & Bioinorganic chemistry
                Inorganic & Bioinorganic chemistry

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