Study On The Reaction Properties Of α - Diimine Nickel Metal Organic Compounds

This thesis reports the reaction of a Ni-Ni-bonded compound with a series of olefins to yield novel nickel olefin complexes. The products were characterized by single crystal structure analysis and NMR spectroscopy, and their electron configuration, the coordination and activation of C=C bond were studied by the methods of density functional theory (DFT). The full text is divided into three parts:Firstly, a brief introduction of the history and development of metal-metal bonded compounds is given and some representative metal-metal bonded compounds are summarized. In addition, an overview of the reactions of metal-metal bonded compounds with different kinds of small molecules is presented.Secondly, the reactions of ethylene, styrene,1-phenyl-l-propene, allylbenzene, and 1,4-diphenylerythrene, respectively, with the Ni-Ni-bonded compound 1 have been carried out and 5 products were obtained:LNi{η2-H2C=CH2}(2), LNi{η2-H2C=C(H)Ph} (3), LNi{η2-(CH3)(H)C=C(H)Ph} (4), LNi{η2-H2C=CH-CH2Ph} (5), and LNi{η2-PhC=CH-CH=CPh)} (6). The structures of the products show that after reacting with the olefin, the bridging coordination fashion of the ligands in compound 1 changed to the chelating coordination mode. In complex 2, because of the back-donation from the Ni atom to ethylene, the C=C bond is elongated by 0.06 A compared to free ethylene. The C=C bond in 3 is almost co-planar with the C2N2Ni ring as in the case of complex 2. With the phenyl substituent group in the styrene complex 3, the back π-bonding between the Ni atom and the C=C is stronger, yielding a much longer (the longest among the products) C=C bond. Due to the steric effect of the phenyl group. In the 1-phenyl-l-propene complex 4, the C=C bond coordinates to the Ni atom in a similar way. The Ni atom is three coordinated by the two N atoms of diimine L and the C=C bond. The C=C bond in 4 is longer than that in 2 but shorter than in 3, while the distance between the nickel atom and the C=C is increased even more. The structure of complex 5 is somewhat unexpected. When coordinating with the Ni atom, the position of C=C in allylbenzenemigrate to the next C atom, so the crystal structure turned out to be the same as 4. The diene complex 6 shows a similar structure with the others. The π-π conjugation affected the electron cloud density between the two C=C and further affected the back π-bonding between the Ni atom and the C=C which caused more elongation of C=C in 6 than in 2,4,5, but less than in 3.Thirdly, to get further insight about the electronic structure of the complexes, the DFT computations were carried out using model compounds in the singlet and triplet spin states. According to the results, the singlet state of 2,3,4,5 shows the lower energy and the calculated structures agree better with the experimental data. Moreover, clear NMR peaks of all 5 compounds also support a singlet state. Considering the data of NBO analysis and Mulliken atomic charges, we propose that all of the three components, both metal and the ligands, in 2-6 are in the oxidation state of 0.