N-Phosphino-amidines and -guanidines: synthesis, structure and P,N-chelate chemistry

Abstract

The syntheses of the cyclic N-phosphino-amidines and -guanidines Ph₂PN(Prⁱ)C(NPrⁱ₂)N(Prⁱ) (1) and Ph₂PN(c-Hex)C(R)N(c-Hex) [R = piperazino (2), morpholino (3), Me (4), and Ph (5)] are reported. DFT studies have identified the preferred structures for compounds 1–5 with the E-configuration being the most stable form for the N-phosphino-amidines, while the Z-conformation is preferred for the N-phosphino-guanidines something that highlights the potential of such systems to act as κ²-P,N-chelates. The differences in donor characteristics of 2–5 have been probed through the study of their corresponding P(V) selenide derivatives (6–9) and their complexes with the cis-RhCl(CO) (10–12) and cis-PdCl₂ (13–17) fragments. In line with the DFT studies both the amidines and guanidines are found to coordinate as κ²-P,N-chelates, with the latter being moderately weaker donor ligands. The molecular structures of compounds 3 and 4, together with those of the Rh and Pd complexes 10 and 15, respectively, have been determined in the solid state by X-ray crystallography, the latter confirming bidentate κ²-P,N-chelation.