Issue 10, 2018
From the journal:

Chemical Science

cis-Oxoruthenium complexes supported by chiral tetradentate amine (N4) ligands for hydrocarbon oxidations†

Chun-Wai Tse, ORCID logo ab   Yungen Liu, ORCID logo ac   Toby Wai-Shan Chow,a   Chaoqun Ma,c   Wing-Ping Yip,a   Xiao-Yong Chang, ORCID logo a   Kam-Hung Low,a   Jie-Sheng Huang ORCID logo a  and  Chi-Ming Che ORCID logo *abc  

* Corresponding authors

a State Key Laboratory of Synthetic Chemistry, Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, China
E-mail: cmche@hku.hk

b HKU Shenzhen Institute of Research and Innovation, Shenzhen, Guangdong 518053, China

c Department of Chemistry, Southern University of Science of Technology, Shenzhen, Guangdong 518055, China

Abstract

We report the first examples of ruthenium complexes cis-[(N4)RuIIICl2]+ and cis-[(N4)RuII(OH2)2]2+ supported by chiral tetradentate amine ligands (N4), together with a high-valent cis-dioxo complex cis-[(N4)RuVI(O)2]2+ supported by the chiral N4 ligand mcp (mcp = N,N′-dimethyl-N,N′-bis(pyridin-2-ylmethyl)cyclohexane-1,2-diamine). The X-ray crystal structures of cis-[(mcp)RuIIICl2](ClO4) (1a), cis-[(Me2mcp)RuIIICl2]ClO4 (2a) and cis-[(pdp)RuIIICl2](ClO4) (3a) (Me2mcp = N,N′-dimethyl-N,N′-bis((6-methylpyridin-2-yl)methyl)cyclohexane-1,2-diamine, pdp = 1,1′-bis(pyridin-2-ylmethyl)-2,2′-bipyrrolidine)) show that the ligands coordinate to the ruthenium centre in a cis-α configuration. In aqueous solutions, proton-coupled electron-transfer redox couples were observed for cis-[(mcp)RuIII(O2CCF3)2]ClO4 (1b) and cis-[(pdp)RuIII(O3SCF3)2]CF3SO3 (3c′). Electrochemical analyses showed that the chemically/electrochemically generated cis-[(mcp)RuVI(O)2]2+ and cis-[(pdp)RuVI(O)2]2+ complexes are strong oxidants with E° = 1.11–1.13 V vs. SCE (at pH 1) and strong H-atom abstractors with DO–H = 90.1–90.8 kcal mol−1. The reaction of 1b or its (R,R)-mcp counterpart with excess (NH4)2[CeIV(NO3)6] (CAN) in aqueous medium afforded cis-[(mcp)RuVI(O)2](ClO4)2 (1e) or cis-[((R,R)-mcp)RuVI(O)2](ClO4)2 (1e*), respectively, a strong oxidant with E(RuVI/V) = 0.78 V (vs. Ag/AgNO3) in acetonitrile solution. Complex 1e oxidized various hydrocarbons, including cyclohexane, in acetonitrile at room temperature, affording alcohols and/or ketones in up to 66% yield. Stoichiometric oxidations of alkenes by 1e or 1e* in tBuOH/H2O (5 : 1 v/v) afforded diols and aldehydes in combined yields of up to 98%, with moderate enantioselectivity obtained for the reaction using 1e*. The cis-[(pdp)RuII(OH2)2]2+ (3c)-catalysed oxidation of saturated C–H bonds, including those of ethane and propane, with CAN as terminal oxidant was also demonstrated.

Graphical abstract: cis-Oxoruthenium complexes supported by chiral tetradentate amine (N4) ligands for hydrocarbon oxidations

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Article information

DOI
https://doi.org/10.1039/C7SC05224C
Article type
Edge Article
Submitted
09 Dec 2017
Accepted
01 Feb 2018
First published
15 Feb 2018
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2018,9, 2803-2816

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cis-Oxoruthenium complexes supported by chiral tetradentate amine (N4) ligands for hydrocarbon oxidations

C. Tse, Y. Liu, T. Wai-Shan Chow, C. Ma, W. Yip, X. Chang, K. Low, J. Huang and C. Che, Chem. Sci., 2018, 9, 2803 DOI: 10.1039/C7SC05224C

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