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

Abstract

Employing Pd(OAc)2, a facile deprotonation route to access the highly basic tris(alkylimido)phosphate trianions, [(RN)3PO](3-) (R = (t)Bu, (c)Hex, or (i)Pr), 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[(N(i)Pr)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-Nimido 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.