MAJUMDER ARPI

Article富山大学地域連携推進機構産学連携部門ベンチャー・ビジネス・ラボラトリー年報, 平成20年度, 2008, Page 86-87departmental bulletin pape

MAJUMDER, ARPI

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Mechanistic Studies on ChalcogerトAtomReplacement Reactions of Phosphine Chalcogenides and Separation of the Intermediate Phosphine V. B. L. Dr. ARPI MAJUMDER Back2round Phosphines are effective ligands to stabilize the Pd0, therefore, phosphine-assisted Pd0 complexes have been widely employed as catalysts in the coupling reactions. However, phosphines are toxic, expensive and because of their air-sensitivity, they get oxidized very easily during the catalytic reactions. Therefore it is necessary to regenerate and reuse these catalysts. On solving this problem, I have found a new catalysis of Pd0 (and Pt0) for chalcogen replacement reactions of phosphine chalcogenides which is a new catalytic activity of Pd0. The mechanism of these replacement reactions has been observed to be dissociative企omthe kinetic investigation. On the basis of this mechanism, it is very easy to recover and reuse those phosphine catalysts which are elaborative and valuable. Results It has been observed that, phosphine－圃freePd0 catalysts either blocks the catalytic cycles kinetically or decomposed into inactive palladium black. To overcome these problems of phosphine ligands, we have prepぽedphosphine sulfides which can stabilize the Pd0 thermodynamically to form air-stable Pd0 catalysts even a白erconsumption of the substrates and do not deactivate the catalytic cycle kinetically. Thus, we are able to prepare air-stable Pd0-phosphine sulfide complexes as the catalysts. However, by a number of repetitions of the reaction, the sulfur atoms in the phosphine-sulfide groups are gradually replaced with oxygen atoms by the catalysis of Pd0 to give the phosphine oxides, which deactivate the Pd0 catalysts by precipitation of Pd sediment. This problem can be solved by the reaction of these phosphine oxides with excess sulfur in DMF at 125°C for 2h in presence of Pd0 . This is the catalytic replacement of chalcogen atoms of phosphine chalcogenides. In the absence of Pd0, this conversion can hardly proceed under the above conditions. So far, two associative mechanisms have been proposed for the chalcogen仕ansfer企omphosphine chalcogenides to phosphines by theoretical calculations as shown in Scheme 1. Mechanism 1 involves a nucleophilic attack of the phosphine phosphorus on the phosphine-chalcogenide phosphorus via a three回memberedcyclic transition state and Mechanism 2 isan X-philic attack via a linear transition state. 面髄倒閣院陰m1符〈つこ込芝一．司畠R＂、滴 t R〆~＞R‘｜正 iR ヰ＋；R' R、，W~ ,.-;;x-P~~’一 γ叫やマ’M岳d官an除m2酔 崎宇R、／一、 ｝＇ 鈴、量‘ /t' I除、 F I ＂：ア ＋ X出陀沼市唱a R:;P·一知P~R＇一 i Rフp.－柑.Pcf’iR 荷’ R "R' I R R I 曹也軒そごf>....X~－~＇ = R~＝＝X + pふ符符en＂＇》了. R"' ~ T ・＇n:・Scheme 1 86 From the thorough kinetic investigation, it reveals that the chalcogen atom replacement (R3P=X1 +X2→ R3P=X2 +Xi, where X1 and X2 are two different chalcogen)) proceeds via dissociation of X in conflict with the above theoretical investigation. For the study of the reaction mechanism, we considered the reaction of phosphine selenide with sulfur. I have taken simple monodentate triphenylphosphine selenide, which was allowed to react with excess sulfur in presence of [Pd( dba)2] ( dba = dibenzylideneacetone ).I have carried out the kinetic experiments both in presence and absence of Pd0 and found that the rate constants of chalcogen replacement reactions for both these kinds remain almost unchanged on varying the sulfur concentration. This results indicates that the rate constants does not depend on sulfur concentration ie, rate constant is zeroth order w工t.sulfur concentration and the mechanism may be the dissociative in nature. I have also carried out the catalytic reactions in presence of Pt0. Activation enthalpy (&ft) and entropy (LlSt) for both catalytic and non-catalytic reactions have been estimated (Table 1）企omthe Eyring plot (Figure 1). The dissociation is enthalpically promoted by the catalysis of Pd0 (and also Pt0). Positive LlSt value also indicates the dissociative mechanism. ・38＼・k、'*, •,"-Pd ＼、、－'* ', 丹＼＼、．、＇－＊，.，、、世Table 1: ・3611r !:. Ht (kJ/mol) ムS/(J/mol/K) Catalytic reaction by 110.46 ± 0.54 26士1.72~d(O) Catalytic reaction by 116.2 ±0.63 32 ±2.00 ~t(O) IN on-catalytic 158.5 ±0.60 102士1.731reaction i:--40 ぎ－41．ミcy 岨-39-l .＂貝"・ ＼ Non-catalytヘ··~ -44 .45 0.0026 0.0027 0.0028 0 0029 0.0030 0.0031 0.0032 0.0033 ? ?? ????』 ?? ? ??I have also attempted to separate the intermediate phosphine as the evidence of the dissociative mechanism. The p2S2 complex, [Pd(p2S2)(dba)] was reacted with an excess of iodobenzene in DMF at 70°C for 48 h under N2 and the phosphine intermediate, 1,2-bis( diphenylphosphino )ethane (p2), was successfully separated as the chelate compound of Pdn by employing the novel catalysis of Pd0. This result gave us evidence of the dissociation of the chalcogen atom from the phosphine chalcogenides and revealed that the phosphine can be regenerated easily from the phosphine sulfide by the catalysis of Pd0. The novel catalytic replacement and dissociation of chalcogen atom are applicable to regeneration of phosphines from their oxides via the phosphine sulfides. We can conclude that the chalcogen atom replacement of phosphine chalcogenides proceeds by dissociation of the chalcogen atoms, which is enthalpically promoted by the catalytic interaction of Pd0 (and also Pt0). Taking advantage of this catalysis, it is possible to regenerate phosphines from phosphine oxides via phosphine sulfide formation. This catalytic conversion will be significant especially for the regeneration and reuse of other elaborative and expensive phosphines四catalystswhich gets oxidized during the coupling reaction. 87 

Mechanistic Studies on Chalcogen-Atom Replacement Reactions of Phosphine Chalcogenides and Separation of the Intermediate Phosphine

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Mechanistic Studies on Chalcogen-Atom Replacement Reactions of Phosphine Chalcogenides and Separation of the Intermediate Phosphine

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