Base-Promoted Carbon−Hydrogen Bond Activation of Alkanes with Rhodium(III) Porphyrin Complexes

Chan, Yun Wai; Chan, Kin Shing

doi:10.1021/om800397p

Cited by 32 publications

(61 citation statements)

References 49 publications

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“…The residue was purified by pipet column chromatography on silica gel with a hexane/CH 2 Cl 2 solvent mixture (7/1) as eluent. The red solid Rh(ttp)(n-pentyl) 23 Typical Procedures for the Reaction of Rh(ttp)Cl with Cyclohexyl Bromide and KOH in Air. Rh(ttp)Cl (1a; 7.8 mg, 0.0097 mmol), aqueous KOH (5.5 M, 0.0175 mL, 0.096 mmol), and cyclohexyl bromide (2a; 0.012 mL, 0.097 mmol), were added to benzene (2.0 mL).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Facile Aerobic Alkylation of Rhodium Porphyrins with Alkyl Halides

et al. 2015

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Alkylation of rhodium porphyrins was achieved in moderate to high yields in the presence of air and water. With this facile alkylation method, various alkyl Rh III (por) species, including those with tertiary alkyl, were synthesized. Mechanistic investigations suggest a parallel S N 2 via [Rh I (ttp)] − with halogen atom transfer pathway via [Rh II (ttp)] • . ■ INTRODUCTIONRhodium porphyrin alkyls ( Figure 1) play an important role in catalysis. They are precursors of [Rh II (por)] • (por = porphyrinato dianion) metalloradicals for carbon−hydrogen bond 1 and carbon−carbon single bond activation. 1d,2 Activation of these strong bonds has gained much current interest for more efficient utilization of hydrocarbons. 3 To the best of our knowledge, only primary and secondary alkyl Rh III (por) species have been reported so far. Tertiary alkyl Rh III (por) species remain unknown, which may be of great interest in investigating its role in catalysis. Hence, developing robust methods to access alkyl Rh III (por) species, especially tertiary alkyl Rh III (por) species, is important.The synthesis of rhodium porphyrin alkyls was first reported by Ogoshi in 1972 by the reaction between Rh III (oep)Cl (oep =2,3,7,8,12,13,17,18-octaethylporphyrinato dianion) and MeLi (Scheme 1a). 4 A more versatile method involves the reduction of Rh III (por)Cl by NaBH 4 to generate [Rh I (por)] − . [Rh I (por)] − then undergoes nucleophilic substitution with alkyl halides to give the corresponding rhodium porphyrin alkyls (Scheme 1b). 5 In 1986, Kadish and co-workers reported the Rh−C bond formation by the electrochemically generated monomeric species [Rh II (tpp)] • (tpp = 5,10,15,20-tetraphenylporphyrinato dianion) (Scheme 1c). 6 In 1990, Wayland discovered the formation of Rh−C bond by carbon−hydrogen bond activation of CH 4 and toluene to give Rh(por)Me and Rh(por)Bn (Scheme 1d). 1a,b The carbon−oxygen bond cleavage of methanol by Rh III (ttp)Cl (ttp =5,10,15,20-tetratolylporphyrinato dianion) in alkaline media was discovered to give a high yield of Rh III (ttp)Me and was reported by Chan in 2009 (Scheme 1e). 7 In 2010, Chan and co-workers found the formation of the Rh−C bonds by carbon−nitrogen bond activation (CNA) of amines (Scheme 1f). 8 This CNA method, further developed by the Dong group, tolerates air and water by utilizing ammonium salts as the alkylating agents (Scheme 1g). An S N 2-like reaction pathway involving a [Rh I (por)] − intermediate was proposed. 9 These reported methods are unlikely to prepare a tertiary alkyl Rh III (por) species due to the steric hindrance. Herein, we disclose a facile Figure 1. Structure of rhodium porphyrin alkyls. Scheme 1. Synthesis of Rhodium Porphyrin AlkylsArticle pubs.acs.org/Organometallics

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Section: ■ Results and Discussionmentioning

confidence: 99%

Facile Aerobic Alkylation of Rhodium Porphyrins with Alkyl Halides

et al. 2015

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“…The base-promoted alkane CHA by Rh(ttp)Cl [20] and other base-promoted bond activation by transition metal complexes [19,21], have prompted us to examine the promoting effect of base on the CNA of amines. However, it was found that the addition of a base was not beneficial to product yield with only 25% and 43% yields of Rh(ttp) n Bu obtained in the presence of KOH and K 2 CO 3 , respectively for the reactions between Rh(ttp)Cl and n Bu 3 N (Table 1, entries 7 and 8).…”

Section: ð1þmentioning

confidence: 99%

“…To gain an idea of the reactive intermediate and the reaction mechanism of CNA of amine, several reactive rhodium porphyrin species such as [Rh(ttp)] À , [Rh(ttp)] 2 and Rh(ttp)H were treated to react with tri-n-butylamine under the same reaction conditions [20].…”

Section: ð1þmentioning

confidence: 99%

“…The solvent was then removed under vacuum and the red crude mixture was purified by silica gel column chromatography eluting with a solvent mixture of hexane: CH 2 Cl 2 (1:1). A red product Rh(ttp) n Pent [20] …”

Section: Reaction Between Rh(ttp)cl and Tripentylamine In Benzenementioning

confidence: 99%

“…However, CNA by high valent transition metal complexes are rarely reported, examples include CNA of pyridine by thorium(IV) complexes [14] and CNA of amines by a rhodium(III) corrole complex [15] (corrole = tetradehydrocorrin). Previously we have reported a series of bond activation chemistry with Group 9 metalloporphyrin complexes, including the carboncarbon bond activation (CCA) of nitroxides [16], nitriles [17], esters and amide [18], base-promoted carbon-hydrogen bond activation of toluenes [19] and alkanes [20]. In expanding the substrate scope in bond activation chemistry, we have examined the reactions of amines with rhodium porphyrin complexes and discovered the CNA of amines to give rhodium(III) porphyrin alkyls.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Carbon–nitrogen bond activation of amines by rhodium(III) porphyrin complexes

Lai

Chan

2010

Journal of Organometallic Chemistry

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Cyclometalated Iridium(III) Complexes with Ligand Effects on the Catalytic C–H Bond Activation of Toluene

et al. 2017

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New cyclometalated iridium(III) complexes have been designed, prepared and applied as catalytic systems for the C-H bond activation (CHA) of toluene through a clean, highly efficient, and environmentally friendly process. The complexes have the general formula [(C^N) 2 Ir(N^O)]. The C^N ligands are the monoanionic bidentate cyclometalating ligands 2-phenylpyridinato (ppy), 2-phenylbenzoxazolato (pbo), and 2-(3.5-difluorophenyl)benzoxazolato (dfpbo). The (N^O) ligand is also a monoanionic bidentate cyclometalating ligand, namely picolinato (pic). The complexes [(ppy) 2 Ir(pic)] (1), [(pbo) 2 Ir(pic)] (2), and [(dfpbo) 2 -Ir(pic)] (3) were structurally characterized by 1 H and 13 C NMR spectroscopy, FAB-MS, and X-ray crystallography. The activation [a] 2023 Scheme 1. Synthetic route to the C^N ligands and complexes 1-3.

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Base-Promoted Carbon−Hydrogen Bond Activation of Alkanes with Rhodium(III) Porphyrin Complexes

Cited by 32 publications

References 49 publications

Facile Aerobic Alkylation of Rhodium Porphyrins with Alkyl Halides

Facile Aerobic Alkylation of Rhodium Porphyrins with Alkyl Halides

Carbon–nitrogen bond activation of amines by rhodium(III) porphyrin complexes

Cyclometalated Iridium(III) Complexes with Ligand Effects on the Catalytic C–H Bond Activation of Toluene

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