| There is currently considerable interest in binuclear complexescontaining metal-metal interactions, because of their unique structures andproperties including catalysis and spectroscopy. Most of the complexesbridging with 2-(diphenylphosphino) pyridine (Ph2Ppy) or its analogs canform donor-acceptor bond between two metal atoms. And the metal-matalinteractions have notable effects on catalytic behaviour and spectroscopy.Theoretical study on the structure, the nature of the metal-metal interactions,catalytic mechanism and spectroscopy of these complexes is practicallyuseful.In the present work, the metal-metal interactions and their effects on 31PNMR chemical shifts and catalytic activities have been investigated byquantum chemistry calculations. This theoretical work will be helpful fordesign of novel organic materials. The discussions are as follow:1. By density functional theory (DFT) PBE0 method, the stabilities, thenature of Fe-Cu interactions, the effects on 31P NMR and catalytic activityof Fe(CO)3(Ph2Ppy)2(CuXn) (Xn=Cl22-, Cl-, Br-) have been investigated. Thestability of [Fe(CO)3(Ph2Ppy)2(CuCl2)] is higher than that of[Fe(CO)3(Ph2Ppy)2(CuX)] (X=Cl-, Br-), so it is stable and could besynthesized experimentally. The Fe-Cu interactions (including Fe→Cu andFe→Cu interactions) mainly exhibit the indirect interactions. The Fe-Cu(â… )interactions (mostly in Fe→Cu interactions, acting asσFe-P→4sCu andσFe-C→4sCu) are stronger than Fe-Cu(â…¡) interactions (mostly in Feâ†Cuinteractions, acting asσFe-C*→4sCu andσFe-P*→4sCu). While N-Cu(â…¡) interactions, which plays an important role in the stabilities for[Fe(CO)3(Ph2Ppy)2(CuCl2)], are much stronger than N-Cu(â… ) interactions.TheσFe-P*→4sCu charge transfer in [Fe(CO)3(Ph2Ppy)2(CuCl2)] and thestrongerσFe-C→nP charge transfer in [Fe(CO)3(Ph2Ppy)2(CuX)] (X=Cl-, Br-),increase the electron density on P nucleus of binuclear complexes. As aresult, an upfield 31P chemical shift is observed, compared withmononuclear complex. Because the delocalization ofσFe-C→4sCu andσFe-C→πC-O* weakens Fe-C bond andÏ€bond of CO, it is favorable toincrease the catalytic activity of binuclear complexes.2. To study the effects of R group on Fe-Hg interactions and 31P NMR,the binuclear complexes [Fe(CO)3(RPhPpy)2(HgCl2)] (R=Me, Et, Ph) arestudied by density functional theory (DFT) PBE0 method. Replacing the Phgroup in Ph2Ppy ligands with Me or Et group results in higher stability andstronger Fe-Hg interactions. The stabilities of binuclear complexes followthe order of Et＞Me＞Ph. Although the electrostatic interactions between[Fe(CO)3(EtPhPpy)2] and HgCl2 are weaker, the weaker repulsioninteractions and stronger orbital interactions lead to the higher stability. Thestrength of Fe→Hg interactions follows the order of Et≈Me＞Ph. TheFe→Hg interactions mainly act asσFe-P→nHg andσFe-C→nHg charge transfer.The 31P NMR chemical shifts in mononuclear complexes and binuclearcomplexes increase as the strength of electron-withdrawing effect of groupR increases in the order of Me＜Et＜Ph. Through Fe→Hg interactions, thecharges transfer from R groups towards the P, Fe and Hg atoms. Thisincreases the electron density on P nucleus in binuclear complexes. Besides,the strongerσFe-C→nP charge transfer in binuclear complexes can alsoincrease the electron density of P nucleus. As a result, compared with theirmononuclear complexes, the 31P chemical shifts in binuclear complexesshow some reduction. 3. To study the effects of R' group on Fe-Hg interactions and 31P NMR,The binuclear complexes [Fe(CO)3(Ph2PR')2(HgCl2)] (R'=pym, fur, py, thi;pym=pyrimidine, fur=furyl, py=pyridine, thi=thiazole) and are studied bydensity functional theory (DFT) PBE0 method. The conclusions can bedrawn as follow: The stabilities of binuclear complexes follow the order ofpym＞py＞thi＞fur. The complexes with nitrogen donor atoms are more stablethan those with O or S atoms. The Fe-Hg interactions play a dominant rolein the stability of the complexes. The strength of Fe-Hg interactions followsthe order of pym＞fur＞py＞thi. In complexes [Fe(CO)3(PPh2R)2(HgCl2)](R=pym, fur), there is aσbond between Fe and Hg, resulting from theoverlap of 4s orbital of Hg and the hybrid orbital (formed by 4s and 3dz2) ofFe. While in complexes [Fe(CO)3(PPh2R)2(HgCl2)] (R=py, thi), the Fe-Hginteractions mainly act asσP-Fe→-nHg andσC-Fe→-nHg charge transfer. ThroughFe→Hg interactions, the charges transfer from R' groups towards the P, Feand Hg atoms. This increases the electron density on P nucleus in binuclearcomplexes. Besides, the charge transfer ofσFe-Hg→-σP-Fe* and the strongσFe-C→-σFe-P* charge transfer can also increase the electron density of Pnucleus. As a result, compared with their mononuclear complexes, the 31Pchemical shifts in binuclear complexes show some reduction.
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