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 (PO43–) 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–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.