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

Abstract To study the Ru–M interactions and their effects on 31 P NMR, complexes [Ru(CO) 3 (Ph 2 Ppy) 2 ] (py = pyridine) ( 1 ) and [Ru(CO) 3 (Ph 2 Ppy) 2 MCl 2 ] (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 31 P chemical shifts in complexes. The calculated 31 P 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 31 P chemical shift in designed complex 4 . Compared with 1 , the 31 P 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 31 P NMR chemical shifts. The interaction of Ru → M, corresponding to the delocalization from 4d orbital of Ru to s valence orbital of M 2+ , results in the delocalization of P–Ru → M, which decreases the electron density of P nucleus and causes the downfield 31 P chemical shifts. Except 2 , the back-donation effect of Ru ← M, arising from the delocalization from s valence orbital of M 2+ to the valence orbital of Ru, is against the P–Ru → M delocalization and results in the upfield 31 P 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 (Ph 2 Ppy) 2 HgCl] + 5 is more stable than 4 , the reaction of 1 with HgCl 2 only gave 5 experimentally.