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Reactivity of a Dinuclear PdIComplex [Pd2(μ-PPh2)(μ2-OAc)(PPh3)2] with PPh3: Implications for Cross-Coupling Catalysis Using the Ubiquitous Pd(OAc)2/nPPh3Catalyst System

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JournalOrganometallics
DateAccepted/In press - 10 Aug 2021
DatePublished (current) - 13 Sep 2021
Issue number17
Volume40
Number of pages8
Pages (from-to)2995-3002
Original languageEnglish

Abstract

[PdI2(μ-PPh2)(μ2-OAc)(PPh3)2] is the reduction product of PdII(OAc)2(PPh3)2, generated by reaction of ‘Pd(OAc)2’ with two equivalents of PPh3. Here, we report that the reaction of [PdI2(μ-PPh2)(μ2-OAc)(PPh3)2] with PPh3results in a nuanced disproportionation reaction, forming [Pd0(PPh3)3] and a phosphinito-bridged PdI-dinuclear complex, namely [PdI2(μ-PPh2){κ2-P,O-μ-P(O)Ph2}(κ-PPh3)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 PdIIdisproportionation species to the observed PdIcomplex is postulated. Upon reaction of the mixture of [Pd0(PPh)3] and [PdI2(μ-PPh2){κ2-P,O-μ-P(O)Ph2}(κ-PPh3)2] with 2-bromopyridine, the former Pd0complex undergoes a fast oxidative addition reaction, while the latter dinuclear PdIcomplex converts slowly to a tripalladium cluster, of the type [Pd3(μ-X)(μ-PPh2)2(PPh3)3]X, with an overall 4/3 oxidation stateperPd. Our findings reveal complexity associated with the precatalyst activation step for the ubiquitous ‘Pd(OAc)2’/nPPh3catalyst system, with implications for cross-coupling catalysis.

Bibliographical note

Funding Information:
We are grateful to Bayer AG (Ph.D. studentship to N.W.J.S.) for funding this study. D.R.H. is funded by an EPSRC iCASE award (voucher number 19000077) with GlaxoSmithKline. We thank the University of York for supporting NMR spectrometers and X-ray equipment, and EPSRC for NMR upgrades (EP/K039660/1). We thank Karl Heaton (MS), Dr. Alex Heyam and Heather Fish (NMR) for their guidance and support.

Publisher Copyright:
© 2021 American Chemical Society

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