Carbene vs Olefin Products of C-H Activation on Ruthenium via Competing - and <img src="http://pubs.acs.org/images/gifchars/beta2.gi

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• 作者：Vladimir F. Kuznetsov ; Kamaluddin Abdur-Rashid ; Alan J. Lough ; Dmitry G. Gusev
• 刊名：Journal of the American Chemical Society
• 出版年：2006
• 出版时间：November 8, 2006
• 年：2006
• 卷：128
• 期：44
• 页码：14388 - 14396
• 全文大小：262K
• 年卷期：v.128,no.44(November 8, 2006)
• ISSN：1520-5126

文摘

Bulky pincer complexes of ruthenium are capable of C-H activation and H-elimination from thepincer ligand backbone to produce mixtures of olefin and carbene products. To characterize the productsand determine the mechanisms of the C-H cleavage, reactions of [RuCl₂(p-cymene)]₂ with N,N'-bis(di-tert-butylphosphino)-1,3-diaminopropane (L1) and 1,3-bis(di-tert-butylphosphinomethyl)cyclohexane (L2)were studied using a combination of X-ray crystallography, NMR spectroscopy, and DFT computationaltechniques. The reaction of L1 afforded a mixture of an alkylidene, a Fischer carbene, and two olefin isomersof the 16-e monohydride RuHCl[^tBu₂PNHC₃H₄NHPBu^t₂] (2), whereas the reaction of L2 gave two olefinand two alkylidene isomers of 16-e RuHCl[2,6-(CH₂PBu^t₂)₂C₆H₈] (3), all resulting from dehydrogenationsof the ligand backbone of L1 and L2. The key intermediates implicated in the C-H activation reactionswere identified as 14-electron paramagnetic species RuCl(PCP), where PCP = cyclometalated L1 or L2.Thus the <IMG SRC="/images/gifchars/alpha.gif" BORDER=0>- and -H elimination reactions of RuCl(PCP) involved spin change and were formally spin-forbidden. Hydrogenation of 2 and 3 afforded 16-electron dihydrides RuH₂Cl(PCP) distinguished by a largequantum exchange coupling between the hydrides.