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

[Image: see text] [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.