Arylruthenium(III) Porphyrin-Catalyzed C–H Oxidation and Epoxidation at Room Temperature and [Ru^V(Por)(O)(Ph)] Intermediate by Spectroscopic Analysis and Density Functional Theory Calculations

Abstract

The development of highly active and selective metal catalysts for efficient oxidation of hydrocarbons and identification of the reactive intermediates in the oxidation catalysis are long-standing challenges. In the rapid hydrocarbon oxidation catalyzed by ruthenium(IV) and -(III) porphyrins, the putative Ru(V)-oxo intermediates remain elusive. Herein we report that arylruthenium(III) porphyrins are highly active catalysts for hydrocarbon oxidation. Using catalyst [Ru(TDCPP)(Ph)(OEt)] (HTDCPP = 5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrin), the oxidation of C-H bonds of various hydrocarbons with oxidant m-CPBA at room temperature gave alcohols/ketones in up to 99% yield within 1 h; use of [ BuN]IO as a mild alternative oxidant avoided formation of lactone from cyclic ketone in C-H oxidation, and the catalytic epoxidation with up to 99% yield and high selectivity (no aldehydes as side product) was accomplished within 5 min. UV-vis, electrospray ionization-mass spectrometry, resonance Raman, electron paramagnetic resonance, and kinetic measurements and density functional theory calculations lend evidence for the formation of Ru(V)-oxo intermediate [Ru(TDCPP)(O)(Ph)].

RuV‐Acylimido Intermediate in [RuIV(Por)Cl2]‐Catalyzed C–N Bond Formation: Spectroscopic Characterization, Reactivity, and Catalytic Reactions

“…We examined the X-band EPR spectrum of ar eaction mixture of [Ru III (TDCPP)(Cl)(THF)] with N 3 COC 6 H 4 -p-Cl (1d)i nC H 2 Cl 2 at 100 K( Figure S14), which shows an ew signal compared with the EPR spectrum of [Ru III (TDCPP)-(Cl)(THF)] in CH 2 Cl 2 under similar conditions;t he absence of an EPR signal for [Ru III (TDCPP)(Cl)(THF)],and also for previously reported [Ru III (TDFPP)(Cl)(THF)], [21] is possibly due to fast relaxation. [21] This new signal in the EPR spectrum, which features g values of 2.05, 1.97, 1.80 similar to those of Ru V species (S = 1/2), [21,39] disappeared upon addition of styrene to the reaction mixture (Figure S14). Theformulation of II as aRu V (NCOR) species,analogous to Ru V (O) species for oxidations by [Ru IV (Por)Cl 2 ]/2,6-Cl 2 pyNO via aR u III species generated in situ, [20,21] is based on the EPR studies and the following calculation results for II:i )a doublet ground state with single unpaired electron configuration (d xy ) 2 (d xz ) 1 (d yz ) 0 for Ru (d 3 , S = 1/2), ii)ashort Ru-N NCOR distance of 1.78 comparable to the experimental and calculated Ru VI -N NSO 2 Ar distances of 1.79(3) and 1.82-1.83 ,r espectively,i n[ Ru VI (TMP)(NSO 2 C 6 H 4 -p-OMe) 2 ], [40] Scheme 5.…”

“…[17] Herein we describe spectroscopic studies including ESI-MS and EPR, and also DFT calculations,o nR u(NCOR) species involved in CÀNb ond formation reactions catalyzed by ruthenium porphyrin (Ru(Por)) complexes;t hese Ru-(NCOR) species,g enerated in [Ru IV (Por)Cl 2 ]/N 3 COR(1) catalytic systems,c ould be formulated as Ru V -imido complexes,being different from the sulfonyl/arylnitrenoids [Ru VI -(Por)(NSO 2 Ar) 2 ] [18] and [Ru VI (Por)(NAr) 2 ] [19] involved in stoichiometric or [Ru II (Por)(CO)]-catalyzed reactions.T he [Ru IV (Por)Cl 2 ]/N 3 COR systems are applicable to catalytic CÀ Nbond formation reactions using substrates without DGs to transform i) alkenes 2 to aziridines 3 or oxazolines 4, ii)indoles 5 to C3-aminated derivatives 6,iii)silyl enol ethers 7 to a-amino ketones 8,i v) hydrocarbons 9 to C(sp 3 )-H amination products 10 (Figure 1b), together with functionalization of natural products and carbohydrate derivatives,with isolated product yields of up to 99 %(atotal of 75 examples). Notably,the Ru V (NCOR) species are unique examples of the nitrogen analogue of highly reactive Ru V (O) species [20,21] involved in, e.g.,[Ru IV (Por)Cl 2 ]-catalyzed oxygen atom transfer reactions (Figure 1aB).…”

Full use of factors promoting catalytic performance of chitosan supported manganese porphyrin

“…immobilized metalloporphyrins and their catalysis systems [31][32][33][34][35] adapting to the cleaner production process. However, the resulting yields (acetophenone and phenylethanol (ONE + OL), less than 25%) were lower than those obtained from the catalytic systems above [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] . In addition, RSM was also seldom used in the catalytic field of metalloporphyrins [14][15][16][17]19,20,[31][32][33][34][35] .…”

“…However, the resulting yields (acetophenone and phenylethanol (ONE + OL), less than 25%) were lower than those obtained from the catalytic systems above 7 – 25 . In addition, RSM was also seldom used in the catalytic field of metalloporphyrins 14 – 17 , 19 , 20 , 31 – 35 . Therefore, these are still a challenge.…”

Synthesis of Xanthones, Thioxanthones and Acridones by a Metal-Free Photocatalytic Oxidation Using Visible Light and Molecular Oxygen

“…Xanthone has been obtained by photocatalytic oxidation of the benzylic methylene position in 9H-xanthene. Thus, ruthenium complexes as catalysts have been used, the oxidant being oxygen [32] or iodate salts [33,34]. Iron complexes have also been employed as catalysts under aerobic conditions [35][36][37], as well as a copper complex [38] or copper(II) chloride [39].…”