Computational and Experimental Study on Selective sp2/sp3 or Vinylic/Aryl Carbon鈥揌ydrogen Bond Activation by Platinum(II): Geometries and Relative Stability of Isomeric Cycloplat

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• 作者：Yumin Li ; Jeffrey Carroll ; Bradley Simpkins ; Deepak Ravindranathan ; Christopher M. Boyd ; Shouquan Huo
• 刊名：Organometallics
• 出版年：2015
• 出版时间：July 13, 2015
• 年：2015
• 卷：34
• 期：13
• 页码：3303-3313
• 全文大小：523K
• ISSN：1520-6041

文摘

Cyclometalating ligands 6-(1-phenylethyl)-2,2鈥?bipyridine (L4), 6-(1-phenylvinyl)-2,2鈥?bipyridine (L5), and 6-(prop-1-en-2-yl)-2,2鈥?bipyridine (L6) were synthesized by the Negishi coupling of 6-bromo-2,2鈥?bipyridine with the corresponding organozinc reagents. The reaction of L4 with K₂PtCl₄ produced only the cycloplatinated compound 4a via sp² C鈥揌 bond activation. The reactions of L5 and L6 produced exclusively the cycloplatinated compounds 5b and 6a, respectively, via vinylic C鈥揌 bond activation. DFT calculations were performed on 12 possible cycloplatination products from the reaction of N-alkyl-N-phenyl-2,2鈥?bipyridin-6-amine (alkyl = methyl (L1), ethyl (L2), and isopropyl (L3)) and L4鈥?b>L6. The results show that compounds 1b鈥?b>3b resulting from the sp³ C鈥揌 bond activation of L1鈥?b>L3 are thermodynamic products, and their relative stability is attributed to the planar geometry that allows for a better conjugation. Similar reasoning also applies to the stability of products from vinylic C鈥揌 bond activation of L5 and L6. The relative stability of isomeric cycloplatinated compounds 4a and 4b may be due to the different strengths of C鈥揚t bonds. The steric interaction is the major cause of severe distortion from a planar coordination geometry in the cycloplatinated compounds, which leads to instability of the corresponding cyclometalated products and a higher kinetic barrier for C鈥揌 bond activation.