含磷硫多牙基鎳錯合物之硫醇與腈類分子轉換成硫亞胺酯之反應機制與腈水解酶相關之研究

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2008

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將[Ni(CH3CN)6](ClO4)2與兩當量的P(C6H5)(o-C6H4SH)2在不同的腈類溶劑(像是乙腈、丙腈、異丁腈以及苯甲腈)下反應,可以得到一系列鎳錯合物,其含磷配子之硫醇會與腈類結合形成硫亞胺酯,此硫亞胺酯的生成與所推測腈水解酶在催化過程中的中間體相似。在先前所提到的反應中會先形成一個中間體[Ni(P(C6H5)(o-C6H4S)(o-C6H4SH))2]的綠色沉澱,這個中間體上帶有未配位的硫醇,會進一步與腈類上不飽和的碳原子進行親核性加成反應而形成硫亞胺酯的結構,我們推測在反應過程中形成無水的過氯酸來促使這樣的結構生成,這個無水過氯酸會將腈類分子質子化使得硫醇容易轉換為硫亞胺酯。 當[Ni(CH3CN)6](ClO4)2與三當量的P(C6H5)2(o-C6H4SH)反應,可以生成並分離出一個帶有硫胺基陽離子的化合物 [P((o-C6H4SC(CH3)NH3)- (C6H5)2)]2+。這樣的結果也進一步支持在反應中會形成無水過氯酸的可能。假如將反應的溶劑換成異丁腈,則會有兩種產物的生成,分別是[P((o-C6H4SC((CH3)2CH)NH2)(C6H5)2)][ClO4]和[P((o-C6H4SC(CH3)2- (C6H5)2))[ClO4]。有趣的是在異丁腈的異丙基及氰基之間會發生碳碳鍵的斷裂。更令我們感興趣的是將親核基加入帶有硫亞胺酯結構的鎳錯合物[Ni(P(C6H5)(o-C6H4S)(o-C6H4SC(CH3)NH2))2](BF4)2後會產生正四價的鎳錯合物[Ni(P(C6H5)(o-C6H4S)2)2]。
The reaction of [Ni(CH3CN)6][ClO4]2 and two equivalents of P(C6H5)(o-C6H4SH)2 in different nitriles, such as acetonitrile, propylnitrile, isobutronitrile and benzonitrile, produced a series of nickel complexes having a nitrile molecule incorporated with a thiol group of phosphine ligand to form a thioiminoester group. The resulting thioiminoester group is similar to the intermediate proposed in the catalytic cycle of nitrilase. An intermediate, [Ni(P(C6H5)(o-C6H4S)(o-C6H4SH))2], was formed first in the previous reactions, and precipitated as a green solid. The uncoordinated thiol groups of the intermediate will further nucleophilic attack to the unsaturated carbon of nitriles to generate complexes with thioiminoester groups. An anhydrous perchlorate acid were suspected to be generated in the reactions. The anhydrous acid will protonate on a nitrile molecule to facilitate the conversion of nitrile and thiol to thioiminoester. When [Ni(CH3CN)6][ClO4]2 reacted with three equivalents of P(C6H5)2(o-C6H4SH), a thioester ammonium cation, [P((o-C6H4SC(CH3)- NH3)(C6H5)2)]2+, was formed and isolated from the reaction mixture. This result further supports the formation of the anhydrous perchlorate acid in the reaction. If isobutronitrile was employed as the solvent, two products, [P((o-C6H4SC((CH3)2CH)NH2)(C6H5)2)][ClO4] and [P((o-C6H4SC(CH3)2- (C6H5)2))[ClO4], were obtained. Interestingly, the cleavage of carbon carbon bond between isopropyl and nitrile groups in isobutronitrile was occured. More interestingly, a Ni(Ⅳ) complex, [Ni(P(C6H5)(o-C6H4S)2)2], was generated by the addition of a nucleophile to the nickel thioiminoester complex, [Ni(P(C6H5)(o-C6H4S)(o-C6H4SC(CH3)NH2))2](BF4)2.

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腈水解酶, 鎳錯合物, 腈類化合物轉換, Nitriles, Nickel complexes, Conversion of nitriles

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