Late Transition Metal Complexes Based On Functionalized Carborane Ligands:Synthesis, Reactivity And Catalytic Activity

Carborane chemistry has become one of the hotspot in modern chemistry research because of its particular structure property and corresponding high thermal and chemical stability. Since the discovery of 1,2-dicarba-closo-dodecaborane in the 1960s, carborane derivatives have been widely utilized in the fields of catalysis, radiopharmaceutical, and polymer chemistry, as well as their great influence in the molecular recognition, non-linear optical materials, and liquid crystal materials. In this dissertation, we focus on the study of carborane ligands containing N, P, and S donors. Reactivity of these ligands with late transition metal complexes has been systemic explored, and the application of the corresponding obtained metal complexes in olefin polymerization and small molecular activation has been also studied.1. Reactivity of carboranylamidine ligand (CabN-DI(C)C)H with half-sandwich iridium and rhodium complexes [Cp*MCl2]2 (M=Ir, Rh) was explored. A series of 18-electron imine-coordinated complexes and 16-electron amine-coordinated complexes were obtained by the reaction of the lithium salt of carboranylamidine with transition metal precursors under different conditions. Crystal structure of the product indicated that the imine group has the stronger coordination ability than the amine group. Further study revealed that the 18-electron iridium complexes showed good catalytic activity for norbornene polymerization in the presence of MAO, and the iridium complex exhibits high polymerization activity (up to 2.69 × 106 gPNB mol-1 Ir h-1) with viscosity-average molecular weight (Mv) of the polymer is 106 gPNB mol-1. The microstructure of the obtained polynorbornene characterized by NMR and IR shows that the polymer is typical of vinyl-type products. All polynorbornenes are soluble at room temperature in chlorobenzene, and show well thermal stability.2. Besides the half-sandwich transition metal precursors, We also studied the reactivity of non-Cp late transition metals (such as MCl2, M=Ni, Co, Cu) with carboranylamidine under the similar reaction condition. A series of bis-C, N-chelated mode transition metal complexes were obtained based on carboranylamidinate ligand. Crystal structure also indicated that the imine group has the stronger coordination ability than the amine group. Different from our previous similar complex, the C, N-chelated nickel complexes exhibit poor catalytic activity for the norbornene polymerization. The reason may be ascribed to the nonplanar geometry of the metal center (the dihedral angles of C-N-Ni in two nickel complexes are both approximate 35°), which indicates that the d orbital of the metal was occupied by a single electron. This also explains why the Ni2+ complex is paramagnetic.3. Carboranylamidinate thiol was obtained by the insertion of sulfur powder to the lithium salt of carboranylamidine followed by the hydrolysis procedure. Reaction of carboranylamidinate thiolate with half-sandwich iridium and rhodium complexes afforded B-H bond activation complexes. The possible reason for B-H bond activation may be due to the insertion of the sulfur or selenium bridge, which caused the electron-deficient metal center to be located very close to the B(3/6) vertices. Synthesis of carboranylamidinate selenol was failed due to its air and moisture sensitivity. So the analogous B-H bond activation complexes were obtained through the reaction of half-sandwich iridium and ruthenium compounds with carboranylamidinate selenolate which was formed in situ by the insertion of selenium to carboranylamidinate lithium. Surprisingly, the reaction of [Cp*RhCl2]2 with carboranylamidinate selenol afforded unexpected oxidative and reductive products, respectively. However, the reason is still unknown. On the other hand, binuclear copper complexes were obtained by using the strong coordination ability and the filled pz orbital of sulfur atom.4. Upon heating in neat methanol, nido-carboranylamidine was successfully prepared through the selective removal of B(3/6) atom of closo-carboranylamidine without addition of any base because of the basic imine group in the ligand. Because of the electronic and steric effects, C-C bond cleavage of zwitterionic carborane cage promoted by half-sandwich iridium complex was achieved, and the first pesudocloso mono-substituted carborane complex was reported. There are two reasons for the formation of the product:i) The steric crowd between amidinate group and Cp*, and this was confirmed by the parallel reaction of nido ligand with Ni(acac)2 which the c/oso-metallacarborane was afforded; ii) The iridium(III) center may reduce the carborane cage, and the redox process induces opening of the bond in the cage. DFT study also confirmed that the the energy of pseudocloso structure is lower than that of the closo isomer by 5.0 kcal mol-1.5. Reactivity of carboranyl phosphine with half-sandwich complex was systemically studied. Monophosphine-o-carborane sulfide LPS was obtained in high yield by the oxidation reaction of monophosphine-o-carborane with sulfur powder, and we found that the addition of a small amount of weak base such as Et3N could largely prompt this oxidation process. Treatments of [Cp*MCl2]2 with the lithium salt of LPS generated the C,S-coordinated complexes, the C,S-chelated iridium complex exhibited catalytic activity for the polymerization of norbornene in the presence of MAO as cocatalyst (highest activity up to 1.40 × 106 gpNB mol-1 Ir h-1). The spectroscopy data of the polymer indicate that the polynorbornene is also typical of vinyl-type products. Lps can be modified to give the corresponding thiol LpsSH. The unexpected B,S,S-coordination mode iridium product through B-H activation was obtained by the reaction of [Cp*IrCl2]2 with the lithium salt of LpS SH. However, [Cp*RhCl2]2 gave the product with the S,S-mode under the same conditions. The reactions between nucleophilic reagent containing carborane cage and three kinds of coordination modes metal products were investigated. Metal reduction complex and salt metathesis complex have been obtained by using different types of nucleophiles. Moreover, using biphosphine-o-carborane as the ligand, the structure transformation of closo to zwitterionic, zwitterionic to zwitterionic, and zwitterionic to pseudocloso was studied; some of nido-metal complexes can activate H2 to form the metal hydride complexes.