The ubiquitous P(o-tol)3 ligand promotes formation of catalytically-active higher order palladacyclic clusters.

The Herrmann-Beller catalyst, Pd[(C^P)(μ2-OAc)]2, is readily formed by reaction of the cyclic trimer of 'Pd(OAc)2' with P(o-tol)3. In the presence of hydroxide, Pd(C^P)(μ2-OAc)]2 converts to [Pd(C^P)(μ 2 -OH)]2. Here, we report how this activated Pd precatalyst species, and related species, serve as a conduit for formation of higher order Pd n clusters containing multiple cyclopalladated P(o-tol)3 ligands. The catalytic competency of a Pd4-palladacyclic cluster is demonstrated in an arylated Heck cross-coupling, which is comparable to the base-activated form of Herrmann's catalyst, namely [Pd(C^P)(μ2-OH)]2. The findings show that 'simple' ubiquitous phosphine ligands can promote higher order Pd speciation, moving beyond well-known phosphine-ligated Pd1 and Pd2 complexes. The findings challenge the status quo in the field, in that phosphine ligands can ligate higher order Pd n species which are catalytically competent species in cross-coupling reactions.