Oxorhenium(V) Complexes with Phenolate鈥揙xazoline Ligands: Influence of the Isomeric Form on the O-Atom-Transfer Reactivity

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• 作者：J枚rg A. Schachner ; Belina Terfassa ; Lydia M. Peschel ; Niklas Zwettler ; Ferdinand Belaj ; Pawel Cias ; Georg Gescheidt ; Nadia C. M枚sch-Zanetti
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：December 15, 2014
• 年：2014
• 卷：53
• 期：24
• 页码：12918-12928
• 全文大小：572K
• ISSN：1520-510X

文摘

The bidentate phenolate鈥搊xazoline ligands 2-(2鈥?hydroxyphenyl)-2-oxazoline (1a, Hoz) and 2-(4鈥?4鈥?dimethyl-3鈥?4鈥?dihydrooxazol-2鈥?yl)phenol (1b, Hdmoz) were used to synthesize two sets of oxorhenium(V) complexes, namely, [ReOCl₂(L)(PPh₃)] [L = oz (2a) and dmoz (2b)] and [ReOX(L)₂] [X = Cl, L = oz (3a or 3a鈥?/b>); X = Cl, L = dmoz (3b); X = OMe, L = dmoz (4)]. Complex 3a鈥?/b> is a coordination isomer (N,N-cis isomer) with respect to the orientation of the phenolate鈥搊xazoline ligands of the previously published complex 3a (N,N-trans isomer). The reaction of 3a鈥?/b> with silver triflate in acetonitrile led to the cationic compound [ReO(oz)₂(NCCH₃)](OTf) ([3a鈥?/b>](OTf)). Compound 4 is a rarely observed isomer with a trans-O鈺怰e鈥揙Me unit. Complexes 3a, 3a鈥?/b>, [3a鈥?/b>](OTf), and 4 were tested as catalysts in the reduction of a perchlorate salt with an organic sulfide as the O acceptor and found to be active, in contrast to 2a and 2b. A comparison of the two isomeric complexes 3a and 3a鈥?/b> showed significant differences in activity: 87% 3a vs 16% 3a鈥?/b> sulfoxide yield. When complex [3a鈥瞉(OTf) was used, the yield was 57%. Density functional theory calculations circumstantiate all of the proposed intermediates with N,N-trans configurations to be lower in energy compared to the respective compounds with N,N-cis configurations. Also, no interconversions between N,N-trans and N,N-cis configurations are predicted, which is in accordance with experimental data. This is interesting because it contradicts previous mechanistic views. Kinetic analyses determined by UV鈥搗is spectroscopy on the rate-determining oxidation steps of 3a, 3a鈥?/b>, and [3a鈥?/b>](OTf) proved the N,N-cis complexes 3a鈥?/b> and [3a鈥?/b>](OTf) to be slower by a factor of 鈭?.