Quantum chemistry studies on the Ru–M interactions and the 31P NMR in [Ru(CO)3(Ph2Ppy)2(MCl2)] (M = Zn, Cd, Hg)

To study the Ru–M interactions and their effects on 31P NMR, complexes [Ru(CO)3(Ph2Ppy)2] (py = pyridine) (1) and [Ru(CO)3(Ph2Ppy)2MCl2] (M = Zn, 2; Cd, 3; Hg, 4) were calculated by density functional theory (DFT) PBE0 method. Moreover, the PBE0-GIAO method was employed to calculate the 31P chemical shifts in complexes. The calculated 31P chemical shifts in 1–3 follow 2 > 3 > 1 which are consistent to experimental results, proving that PBE0-GIAO method adopted in this study is reasonable. This method is employed to predict the 31P chemical shift in designed complex 4. Compared with 1, the 31P chemical shifts in 2–4 vary resulting from adjacent Ru–M interactions. The Ru → M or Ru ← M charge-transfer interactions in 2–4 are revealed by second-order perturbation theory. The strength order of Ru → M interactions is the same as that of the P–Ru → M delocalization with Zn > Cd > Hg, which coincides with the order of 31P NMR chemical shifts. The interaction of Ru → M, corresponding to the delocalization from 4d orbital of Ru to s valence orbital of M2+, results in the delocalization of P–Ru → M, which decreases the electron density of P nucleus and causes the downfield 31P chemical shifts. Except 2, the back-donation effect of Ru ← M, arising from the delocalization from s valence orbital of M2+ to the valence orbital of Ru, is against the P–Ru → M delocalization and results in the upfield 31P chemical shifts in 4. Meanwhile, the binding energies indicate that complex 4 is stable and can be synthesized experimentally. However, as complex [Ru(CO)3(Ph2Ppy)2HgCl]+5 is more stable than 4, the reaction of 1 with HgCl2 only gave 5 experimentally.