Reactions of the Mo-Mo Quintuple Bond with Main Group Reagents

• Main Authors: Lee, Wei-Ting, 李威廷
• Other Authors: Tsai, Yi-Chou
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/17726704473648735650

碩士 === 國立清華大學 === 化學系 === 100 === The low-coordinate and low-valent quintuple bonded dimolybdenum complex, Mo2[μ-η2-HC(N-2,6-iPr2C6H3)2]2 (1), displays remarkable reactivity toward main group reagents. Undergo an oxidative addition of 1 equiv of diphenylzinc to the Mo-Mo quintuple bond of 1, the dimolybdenum complex, (m-ZnC6H5)(1-C6H5)Mo2[m-2-HC(N-2,6-iPr2C6H3)2]2 (2) is afforded. Subsequent treatment of 2 with 1 equiv of benzyl bromide gives a novel dimolybdenum complex, [m-2-HC(N-2,6-iPr2C6H3)2]Mo[-2:2-C6H5Zn(C6H5)Br]Mo[m-2-HC(N-2,6-iPr2C6H3)(N-2-iPr-6-CH(1-CH2)CH3-C6H3)] (3), where one Br atom coordinates between molybdenum and zinc and the molybdenum center accompanies with C-H bond activation of methyl groups. Addition of 4 equiv of diphenylzinc to 1 leads to the formation of the quadruply-bonded dimolybdenum complex, (1-C6H5)2Mo2[m-2-HC(N-2,6-iPr2C6H3)2]2 (5), which functionalized of the Mo-Mo quintuple bond by two phenyl groups. Reaction of 1 with 2 equiv of dimethylzinc affords (m-2:1-Zn(CH3)2)2Mo2[m-2-HC(N-2,6-iPr2C6H3)2]2 (6), which is unstable in solvent at room temperature, it transforms into (1-CH3)2(THF)Mo2[m-2-HC(N-2,6-iPr2C6H3)2]2 (7) quickly. Each molybdenum has one phenyl group coordinates on it, and there is weak agostic interaction between the hydrogen atom of methyl group and the molybdenum center. Treatment of 1 with 2 equiv of trimethylaluminum gives the unstable complex, [m-(CH3)2Al(CH3)2]Mo[m-2-HC(N-2,6-iPr2C6H3)(N-2-iPr-6-CH(1-CH2)CH3-C6H3)] (m-H)Al(CH3)[m-2-HC(N-2,6-iPr2C6H3)2]Mo(1-CH3) (8). The formation of 8 is through the carboalumination of 1 equiv of trimethylaluminum to the Mo-Mo quintuple bond accompanies with a C-H bond activation of methyl group. Complex 8 changes into the intermediate complex 9, which then transforms into Mo(Solvent)[m-2-HC(N-2,6-iPr2C6H3)2](m-CH3)Mo[m-2-HC(N-2,6-iPr2C6H3)(N-2- iPr-6-CH(1-CH2)CH3-C6H3)] (Solvent = THF (10), Et2O (11)) when it contacts solvents like tetrahydrofuran or ether. Complex 10 and 11 contain one methyl group bridging between two molybdenum centers and there is C-H bond activation of methyl group to the molybdenum. Reaction of 1 with 4 equiv of triethylaluminum gives (2-C2H4)Mo[m-2-HC(N-2,6-iPr2C6H3)(N-2-iPr-6-CH(1-CH2)CH3-C6H3)](m- H)Al(C2H5)[m-2-HC(N-2,6-iPr2C6H3)2]Mo(2-C2H4) (12). The formation of 12 is through the carboalumination of 1 equiv of triethylaluminum to the Mo-Mo quintuple bond accompanies with a C-H bond activation of methyl group, and there are two vinyl groups coordinate to the molybdenum centers. Treatment of 1 equiv of phenylsilane to 1 gives rise to the formation of [m-Si(H)C6H5]Mo2[m-2-HC(N-2,6-iPr2C6H3)2]2 (13), which is formed via an oxidative addition of one molecular phenylsilane to the dimolybdenum quintuple bond, and then releases one molecular hydrogen gas. Besides, Complex 13 can activate a small amount of water to give the novel product, (1-H)(1-OH)[m-Si(H)C6H5]Mo2[m-2-HC(N-2,6-iPr2C6H3)2]2 (14). Complex 13 and 14 exhibit the fluxional behavior, which have been characterized by variable temperature NMR. Introduction of 1 equiv of diphenylgermane to 1 leads to the formation of a lantern-type quadruply-bonded dimolybdenum complex, [m-Ge(C6H5)2]Mo2[m-2-HC(N-2,6-iPr2C6H3)2]2 (15). Treatment of 1 with 3 equiv and 4 equiv of phenylisocyanate affords (m-1:2-PhNCO)(m-2:2-CON(Ph)CONPh)Mo2[m-2-HC(N-2,6-iPr2C6H3)2]2 (16) and [m-2:2-CON(Ph)C(O)NPh][m-2:2-CON(Ph)CONPh]Mo2[m-2-HC (N-2,6-iPr2 C6H3)2]2 (17), respectively. Complex 16 is formed via a C-N coupling in a “head-to-tail” mode, and one molecular phenylisocyanate coordinates on molybdenum centers. On the other hand, via C-N coupling, complex 17 has two pairs of two molecules of phenylisocyanate coordinate to the molybdenum centers. Beside, 1 can effectively catalyzes the cyclotrimerization of phenylisocyanate under mild conditions, affords high yield of 1,3,5-triphenylisocyanurate.