| Summary: | 碩士 === 國立清華大學 === 化學系 === 103 === This thesis focus on the study of the [2+2+2] cycloaddition reaction of the low-coordinate and steric hindrance quintuple bonded dimodybedenum complex Mo2[μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (1) with alkynes. It has produced six-membered complexes by head to tail C-C coupling and tail to tail C-C coupling. Further, explore the mechanism and regioseletivity.
The reactions of complex 1 with terminal alkynes othen give products by two terminal alkynes. For example, reaction of complex 1 with 4-fluorophenylacetylene, 4-methoxyphenylacetylene, cyclopropylacetylene, or ethyl propiolate can give six-membered complex of [2+2+2] cycloaddition reaction by head to tail C-C coupling Mo2[μ-κ2-3,5-R2C4H2][μ-κ2-HC(N-2,6-iPr2C6H3)2]2 and tail to tail C-C coupling Mo2[μ-κ2-3,6-R2C4H2][μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (R = 4-FPh (2, 3), 4-MeOPh (4, 5), cyclopropyl (6, 7), COOEt (8)). For Complexes 2-5, low yield by tail to tail coupling is observed reaction of 1 with para is electron donating group phenylacetylene. But, high yield by tail to tail coupling is observed reaction of complex 1 with para is electron withdrawing group phenylacetylene. In addition to experimental evidence, the mechanism of [2+2+2] cycloaddition reaction is affected by electronic effect for fuctional group of terminal alkynes. However, reaction of complex 1 with N-(methyl)-N-(p-toluenesulfonyl)-ethynylamine gives complex 9 which undergoes cleavage of nigrogen-sulfur bond and formed C4 ligand and tosylate ligand. So, if it has lone pair electron next to carbon-carbon triple bond, it can react with dimodybedenum quintuple bonded. However, reactions of complex 1 with internal alkyne and terminal alkyne are [2+2+2] cycloaddition reactions. First, reaction of complex 1 with diphenylacetylene or phenylpropyne gives four-membered complex for [2+2] cycloaddition reaction, Mo2(μ-κ2-RCCPh)[μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (R = Ph (10), Me (14)). Respectively, reactions of complex 10 or complex 14 with 1-pentyne, phenylacetylene, or ethyl propiolate always give six-member complexes, Mo2[μ-κ2-3,4-Ph2-6-RC4H][μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (R = Pr (11), Ph (12), COOEt (13)), Mo2[μ-κ2-3-Ph-4-Me-6-RC4H][μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (R = Pr (15), Ph (16)) and Mo2[μ-κ2-3-R-6-Me-5-PhC4H][μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (R = Ph (15), COOEt (16)). In addition to evidence of complex 11-13, the stereo orientation of terminal alkyne is affented by steric hindrance. In addition to evidence of complex 15-18, the stereo orientation of internal alkyne affected by electronic effect. In short, the electronic effect controls the stereo orientation of first alkyne and the steric effect controls the stereo orientation of second alkyne. In addition, the reaction of complex 10 with pivalonitrile gives complex, Mo2(trans-2-styryl-C6H5)[μ-κ2-HC(N-2,6-iPr2C6H3)(N-2-iPr-6-CH(κ1-CH2)CH3-C6H3)][μ-κ2-HC(N-2,6-iPr2C6H3)2] (21), in which the ortho-activated diphenylethene group coordinates to Mo center. The reaction of complex 10 with benzaldehyde gives six-membered complex, Mo2(H)[μ-κ2-O(PhC)2PhC][μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (22). From this reaction, we can know the electron-rich diphenylacetylene attacks to electron-withdrawing carbon of benzaldehyde by nucleophilic addition. Finally, The reaction of six-membered complex Mo2[μ-κ2-3,5-Pr2C4H2][μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (24a) with Fe2(CO)9 or acetonitrile give two complexes, Mo2(CO)[μ-κ2-3,5-Pr2C4H2][μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (24b), in which a carbon oxide coordinates to Mo center, and Mo2(MeCN)2[μ-κ2-3,5-Pr2C4H2][μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (24c), in which acetonitrile coordinates to Mo centers, respectively. Two reactions are reversible reaction. The molecular structures of complex 24b and complex 24c are determined by X-ray crystallography. The carbon-molybdenum bond is elongated. Because d-orbital electron contributes to back bonding of carbon oxide or acetonitrile, and little contributes to d-electron of six-membered ring.
In addition, the reaction of complex 1 with tetrachloroethylene gives complex, Mo2(Cl)2[μ-κ2-HC(N-2,6-iPr2C6H3)2][μ-κ2-HC(N-2,6-iPr2C6H3) (N-2-iPr-6-C(κ1-CCH)(CH3)2C6H3)] (26), in which bent vinylidene ligand coordinates to a Mo center. We are interested in reactivity of 26.
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