科研之友
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摘要
The activation of the CH bond of 1-phenylpyrazole (2) and 2-phenyl-2-oxazoline (3) by [Ru(OAc)(2)(p-cymene)] is an autocatalytic process catalyzed by the co-product HOAc. The reactions are indeed faster in the presence of acetic acid and water but slower in the presence of a base K2CO3. A reactivity order is established in the absence of additives: 2-phenylpyridine>2-phenyl-2-oxazoline>1-phenylpyrazole (at RT). The accelerating effect of added acetate ions reveals an intermolecular deprotonation after C-H bond activation by a cationic RuII center (S(E)3 mechanism). The reactions of 1-phenylpyrazole and 2-phenyl-2-oxazoline first lead to the neutral cyclometalated complexes A(2) and A(3) ligated by one acetate. The latter dissociate to the cationic complexes B-2(+) and B-3(+), respectively, and acetate. A slow incorporation of one or two D atoms into 2, 3, and 2-phenylpyridine (1) was observed in the presence of deuterated acetic acid. The reversibility of the C-H bond activation/deprotonation takes place from the cationic complexes B-n(+) (n=1-3). They are also involved in oxidative additions to PhI, which are rate-determining and lead to the mono- and bis-phenylated products at high temperatures. A general mechanism is proposed for the arylation of arenes 13 catalyzed by [Ru(OAc)(2)(p-cymene)]. In contrast, the reaction of Pd(OAc)(2) with 2-phenylpyridine (1), is much faster: Pd(OAc)(2)>[Ru(OAc)(2)(p-cymene)]. Since the kinetics is not affected by added acetates, the reaction proceeds through a CMD mechanism assisted by a ligated acetate (intramolecular process) and is irreversible. A bis-cyclometalated Pd-II boolean AND Pd-II dimer D'(1) is formed whose bielectronic electrochemical oxidation leads to a [Pd-III boolean AND Pd-III](2+) dimer, in agreement with the result of a reported chemical oxidation used in arene functionalizations catalyzed by Pd(OAc)(2).
- 出版日期2013-6
