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

Employing Pd­(OAc)<sub>2</sub>, a facile deprotonation route to access the highly basic tris­(alkylimido)­phosphate trianions, [(RN)<sub>3</sub>PO]<sup>3–</sup> (R = <sup>t</sup>Bu, <sup>c</sup>Hex, or <sup>i</sup>Pr), analogous to the orthophosphate (PO<sub>4</sub><sup>3–</sup>) ion in polar and in protic solvents has been achieved. Trinuclear and prismatic Pd­(II) clusters of these imido trianions having the formula {Pd<sub>3</sub>[(NR)<sub>3</sub>PO]­(OAc)<sub>3</sub>}<sub><i>n</i></sub> (<i>n</i> = 1 or 2) or as mixed-bridged clusters of the type {Pd<sub>3</sub>[(N<sup>i</sup>Pr)<sub>3</sub>PO]­(OAc)<sub>2</sub>(<i>OR</i>′)}<sub>2</sub> (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 Pd<sub>3</sub> unit. Reactivity studies aiming at the Pd­(II) atoms in these clusters with nucleophilic reagents, such as primary amines (R″NH<sub>2</sub>), have led to a new trimeric cluster with the formula {Pd<sub>3</sub>[(NR)<sub>3</sub>PO]­(OAc)<sub>3</sub>(R″NH<sub>2</sub>)<sub>3</sub>} in which the tripodal coordination of the Pd–N<sub>imido</sub> moieties remained unaffected, exemplifying the robustness of the Pd<sub>3</sub> 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)<sub>2</sub>.