Facile Formation of Stable Tris(imido)phosphate Trianions as Their Tri- and Hexanuclear Pd(II) Complexes in Protic Solvents

Employing Pd­(OAc)₂, a facile deprotonation route to access the highly basic tris­(alkylimido)­phosphate trianions, [(RN)₃PO]^3– (R = ^tBu, ^cHex, or ⁱPr), analogous to the orthophosphate (PO₄^3–) ion in polar and in protic solvents has been achieved. Trinuclear and prismatic Pd­(II) clusters of these imido trianions having the formula {Pd₃[(NR)₃PO]­(OAc)₃}_n (n = 1 or 2) or as mixed-bridged clusters of the type {Pd₃[(NⁱPr)₃PO]­(OAc)₂(OR′)}₂ (R′ = Me or H) were isolated exclusively in all these reactions in which the trianionic species acts as a tripodal chelating ligand to the trinuclear Pd₃ unit. Reactivity studies aiming at the Pd­(II) atoms in these clusters with nucleophilic reagents, such as primary amines (R″NH₂), have led to a new trimeric cluster with the formula {Pd₃[(NR)₃PO]­(OAc)₃(R″NH₂)₃} in which the tripodal coordination of the Pd–N_imido moieties remained unaffected, exemplifying the robustness of the Pd₃ unit in all these clusters. We have also shown the catalytic activity of these Pd­(II) complexes in Mizoroki–Heck type coupling reactions in the presence of Cu­(OAc)₂.