QUANTUM CHEMISTRY STUDIES ON THE Fe-Hg INTERACTIONS AND 31P NMR IN [Fe(CO)3(RPhPpy)2 (HgCl2)] (R = Me, Et, Ph)

In order to study the effects of R group on Fe-Hg interactions and 31P NMR, the structures of mononuclear complexes [Fe(CO)3(RPhPpy)2] (1: R = Me; 2: R = Et; 3: R = Ph) and binuclear complexes [Fe(CO)3(RPhPpy)2(HgCl2)] (4: R = Me; 6: R = Et; 6: R = Ph) were calculated by density functional theory (DFT) PBE0 method. Moreover, the 31P NMR chemical shifts were calculated by PBE0-GIAO method. The replacement of Ph group in Ph2Ppy ligands with Me or Et group results in higher stabilities and stronger Fe-Hg interactions. The stabilities of binuclear complexes follow the order of 5 > 4 >6. Although the electrostatic interactions in 5 are weaker, the weaker repulsion interactions and stronger orbital interactions lead to the highest stability. The strength of Fe → Hg interactions, which mainly attribute to σFe-P → nHg and σFe-C → nHg charge-transfer interactions, follows the order of 5 > 4 > 6. The 31P NMR chemical shifts in mononuclear complexes 1 ~ 3 or binuclear complexes 4 ~ 6 increase with the increase of electron-withdrawing effect of R group following the order of Me < Et < Ph. Due to Fe → Hg interactions, the charge-transfer from R groups towards the P, Fe and Hg atoms increases the electron density on P nucleus in binuclear complexes. Besides, the stronger σFe-C → nP charge-transfer in binuclear complexes can also increase the electron density of P nucleus. As a result, compared with corresponding mononuclear complexes, the 31P chemical shifts in binuclear complexes show some reduction.