US010618878B1

(12 ) United States Patent ( 10 ) Patent No.: US 10,618,878 B1 Shaikh et al. (45 ) Date of Patent: Apr. 14 , 2020

(54 ) CATALYTIC REDUCTION OF AROMATIC in Water ; ACS Sustainable Chemistry Energy 4 ( 3) ; pp . 1834-1839 ; RING IN AQUEOUS MEDIUM Feb. 16 , 2016 ; Abstract Only ; 2 Pages. Biswas , et al. , A Mild Rhodium Catalyzed Direct Synthesis of ( 71) Applicant: King Fahd University of Petroleum Quinolones from Pyridones: Application in the Detection ofNitroaromat and Minerals , Dhahran (SA ) ics ; The Journal of Organic Chemistry 82 ( 20 ); pp . 10989-10996 ; Sep. 13 , 2017 ; Abstract Only ; 2 Pages. (72 ) Inventors: M. Nasiruzzaman Shaikh , Dhahran Laska , et al .; Rhodium Containing Magnetic Nanoparticles: Effec (SA ) ; Zain H. Yamani, Dhahran (SA ) tive Catalysts for Hydrogenation and the 1,4 - Addition of Boronic Acids ; Catalysis Letters vol. 122 , Issue 1-2 ; pp . 68-75 ; Dec. 1, 2007 ; (73 ) Assignee : King Fahd University of Petroleum Abstract Only ; 5 Pages . and Minerals , Dhahran (SA ) Shaikh , et al.; Sub -nanometric Rh decorated magnetic nanoparticles as reusable catalysts for nitroarene reduction in water ; Catalysis ( * ) Notice : Subject to any disclaimer , the term of this Communications vol. 119 ; pp . 134-138 ; Jan. 10 , 2019 ; Abstract patent is extended or adjusted under 35 Only ; 2 Pages . U.S.C. 154 ( b ) by 0 days. Baralt, et al .; Homogeneous Catalytic Hydrogenation . 6. Synthetic and Mechanistic Aspects of the Regioselective Reductions ofModel ( 21) Appl. No .: 16 /366,586 Coal Nitrogen , Sulfur, and Oxygen Heteroaromatic Compounds Using the ( ~ 5 Pentamethylcyclopentadienyl) rhodiu?m ris( acetonitrile ) ( 22 ) Filed : Mar. 27 , 2019 Dication Complex as the Catalyst Precursor ; J. Am . Chem . Soc . 114 ; pp . 5187-5196 ; 1992 ; 10 Pages . (51 ) Int. Ci. Konnerth , et al. , Selective hydrogenation of N -heterocyclic com C07D 295/023 ( 2006.01 ) pounds using Ru nanocatalysts in ionic liquidst ; Green Chemistry ; CO7D 209/08 ( 2006.01) Mar. 24 , 2017 ; 6 Pages . C07D 215/06 (2006.01 ) Wen , et al. , Strong Brønsted acid promoted asymmetric hydroge C07C 5/10 ( 2006.01 ) nation of isoquinolines and quinolines catalyzed by a Rh -thiourea B01J 23/46 chiral phosphine complex via anion bindingt ; Chemical Science 7 ; ( 2006.01 ) Jan. 24 , 2016 ; 5 Pages . B01J 35/00 (2006.01 ) Rahi , et al ., Hydrogenation of quinolines, alkenes, and biodiesel by B01J 37/04 (2006.01 ) palladium nanoparticles supported on magnesium oxideti; Dalton BOIJ 37/03 ( 2006.01 ) Transactions 41 ; Sep. 26 , 2012 ; 8 Pages . B01J 23/745 (2006.01 ) Fang , et al. , Ruthenium nanoparticles supported on magnesium (52 ) U.S. CI. oxide: A versatile and recyclable dual - site catalyst for hydrogena CPC C07D 295/023 ( 2013.01) ; B01J 23/464 tion of mono- and poly -cyclic arenes, N -heteroaromatics , and ( 2013.01) ; BOIJ 23/745 (2013.01 ) ; B01J S -heteroaromatics ; Journal of Catalysis 311 ; pp . 357-368 ; Jan. 29 , 35/0013 (2013.01 ) ; B01J 35/0033 ( 2013.01 ); 2014 ; 12 Pages. Zhang , et al.; Cooperation between the surface hydroxyl groups of B01J 377035 ( 2013.01) ; B01J 37/04 Ru — SiO2 @ mSiO2 and water for good catalytic performance for ( 2013.01) ; C07C 5/10 (2013.01 ) ; C07D 209/08 hydrogenation of quinolinet; Catalysis Science & Technology 4 ; (2013.01 ) ; C07D 215/06 ( 2013.01 ) Jan. 14 , 2014 ; 10 Pages. (58 ) Field of Classification Search Karakulina, et al. , A Rhodium Nanoparticle — Lewis Acidic Ionic CPC CO7D 295/023 ; CO7D 2097008 ; CO7D Liquid Catalyst for the Chemoselective Reduction of Heteroarenes; 215/06 ; B01J 23/464 ; B01J 23/745 ; B01J Angew . Chem . Int. Ed . 55 ; pp . 292-296 ; 2016 ; 5 Pages . 35/0013 ; B01J 35/0033 ; B01J 37/035 ; B01J 37/04 ; C07C 5/10 See application file for complete search history . Primary Examiner Timothy R Rozof (74 ) Attorney, Agent, or Firm — Oblon , McClelland , (56 ) References Cited Maier & Neustadt, L.L.P. U.S. PATENT DOCUMENTS (57 ) ABSTRACT 5,753,584 A 5/1998 Paez et al. 7,732,634 B2 6/2010 Soled et al. A method of reducing an aromatic ring under relatively mild 8,211,486 B2 7/2012 Beers et al. condition using sub -nano particles of a transition metal 9,480,978 B1 11/2016 Shaikh et al . supported on super paramagnetic iron oxide nanoparticles (SPIONs ). The catalyst is efficient for catalyzing the reduc FOREIGN PATENT DOCUMENTS tion of both carbocyclic and heterocyclic compound. In CN 1272308 C 8/2006 compound comprising both carbocyclic and heterocyclic aromatic rings , the catalyst displays high regioselectivity for OTHER PUBLICATIONS the heterocyclic ring . Pelisson , et al.; Magnetically Retrievable Rh ( 0 ) Nanocomposite as Relevant Catalyst for Mild Hydrogenation of Functionalized Arenes 20 Claims, 15 Drawing Sheets U.S. Patent Apr. 14 , 2020 Sheet 1 of 15 US 10,618,878 B1

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10 nm US 10,618,878 B1 1 2 CATALYTIC REDUCTION OF AROMATIC 2221-2228 ; Wang et al. Chem . Rev. 2012 , 112 , 2557-2590 ; RING IN AQUEOUS MEDIUM Wen et al. Chem . Sci. , 2016 , 7 , 3047-3051 ; and Zhang et al. Chem . Sci. , 2016 , 7 , 4594-4599 ) . For example , Fish and STATEMENT OF FUNDING co -worker reported Rh -based catalyst ( n -pentamethylcy 5 clopentadienyl) rhodium dicationic complex , [Cp * Rh ACKNOWLEDGEMENT (CH2CN ) 2] 2+ for the regioselective reduction of nitrogen This project was funded by the Center of Research containing model compounds such as quinoline ( Konnerth Excellence in Nanotechnology (CENT ) of King Fahad Uni et al. Green Chem . , 2017 , 19 , 2762-2767; Xia et al. Catal. Sci. Technol ., 2017 , 7 , 5515-5520 ; and Baralt et al. J. Am . versity of Petroleum and Minerals (KFUPM ) , the Kingdom 10 Chem . Soc. , 1992 , 114 , 5187-5196 ). An iridium complex of of Saudi Arabia ; Award number NT- 2018 -MNS . BINOL - derived phosphoramidite PipPhos was used for the STATEMENT REGARDING PRIOR hydrogenation of a series of quinolones (Fish et al. Orga DISCLOSURE BY THE INVENTORS nometallics, 1991, 10 , 54-56 ). Unfortunately, these homo geneous catalytic procedures suffer from serious drawbacks Aspects of this technology are described in an article 15 of employing harsh reaction conditions accompanied by a “ Sub -nanometric Rh decorated magnetic nanoparticles as tedious and cumbersome purification process . The combi reusable catalysts for nitroarene reduction in water ” pub nation of low catalytic efficiency and restricted reusability lished in Catalysis Communications, 2019 , 119 , 134-138 , on was an impediment to wide use in industrial application . Sep. 11 , 2018 , which is incorporated herein by reference in Recent focus on the production of chemicals by environ its entirety . 20 mentally friendly methods has required the development of recyclable and more efficient catalysts . Heterogeneous BACKGROUND OF THE INVENTION catalysis provides the advantage of easy separation of the catalyst from the reaction mixture and hence , the catalyst Field of the Disclosure may be recycled (Fish et al. J. Catal. 1986 , 102 , 270-273 ; 25 Mrsaic et al. Adv. Synth . Catal. 2008 , 350 , 1081-1089 ; and The present invention relates to a method of catalytic Wang et al. J. Mater. Chem ., 2009 , 19 , 8009-8014 , each reduction of carbocyclic and heterocyclic aromatic rings incorporated herein by reference in their entirety ) . Accord using a catalyst having subnano -particles of transition metal ingly , numerous heterogeneous catalytic systems based on supported on superparamagnetic iron oxide nanoparticles Ru , Rh , Ir , Pt, Pd and Au have been developed for the ( SPIONs) . 30 reduction of heterocylic compounds such as quinoline ( Abu Reziq et al. J. Am . Chem . Soc. , 2006 , 128 , 5279-5282 ; Description of Related Art Polshettiwar et al. Green Chem . , 2010 , 12 , 743-754 ; Fang et al. J. Catal . 2014 , 311 , 357-368 ; Zhang et al. Catal. Sci. The “ background " description provided herein is for the Technol. 2014, 4 , 1939-1948; Zhu et al . ChemCatChem purpose of generally presenting the context of the disclo- 35 2014 , 6 , 2954-2960; Wang et al. Catal. Sci. Technol. 2015, sure . Work of the presently named inventors , to the extent it 5,4746-4749 ; Karakulina et al. Angew . Chem . Int. Ed . 2016 , is described in this background section , as well as aspects of 55 , 292-296 ; Fan et al. Catal. Commun . 2013 , 31, 81-85 ; the description which may not otherwise qualify as prior art Campanati et al. J. Mol. Catal. A 2002 , 184 , 267; Barbaro et at the time of filing , are neither expressly or impliedly al. Green Chem . 2012 , 14 , 3211-3219 ; Ge et al. Chem admitted as prior art against the present disclosure . 40 CatChem 2013, 5 , 2183-2186 ; Gong et al. J. Catal. 2013 , Catalytic reduction of organic functional groups, such as 297 , 272-280 ; Dell'Anna et al. Appl. Catal. , A 2014 , 481, alkene , alkyne , carbonyl, imine , and nitro is an important 89-95 ; and Mao et al . Catal. Sci. Technol. 2013 , 3 , 1612 tool in organic synthesis (Minnaard et al. Acc . Chem . Res. 1617 ) . Although complete conversion of quinoline with 2007 , 40 , 1267-1277 ; Co et al. Organometallics , 2005, 24 , good regioselectivity was observed at 50 bar or more of H2 4824-4831 ; Farrar- Tobar et al . Chem . Eur. 1 2018 , 24 , 1-11 ; 45 pressure and about 200 ° C. in some cases, the reaction Sridharan et al. Chem . Rev. 2011, 111, 7157-7259 ; Zhou et progressed at a very slow rate . Also , the reaction involved al. Angew . Chem . Int. Ed . 2010 , 49 , 8121-81251 ; and Song ] the use of environmentally unfriendly and toxic organic et al . Appl. Catal. B , 2018 , 227, 386-408 ; each incorporated solvents . Thus, there is a need for an alternative recyclable herein by reference in their entirety ]. For example , reduction catalyst, where the reaction could be conducted at low of N -heterocycle compounds, such as quinoline to 1,2,3,4- 50 temperature without employing hydrogen gas at high pres tetrahydroquinoline (bz - THQ ) is of interest because bz sure in a green solvent such as water . To achieve such goals , THQ is a building block for the synthesis of agrochemicals , judicious choice of a catalyst and a solid support would be pharmaceuticals , dyes , alkaloids and numerous other fine required to obtain efficient regioselective reduction . Also , products [Sridharan et al. Chem . Rev. 2011, 111, 7157-7259 , the catalyst should be separable from the reaction mixture and Guthertz et al . J. Am . Chem . Soc . ( 2018 ) , 140 , 3156- 55 and be reusable with relative ease . A number of precious 3169 (DOI : 10.1021/ jacs.8600665 ) ]. Heteroarene hydroge metal- impregnated solid supports such as zeolite , polymer , nation is challenging due to their relatively low reactivity silica, and cellulose have been investigated as catalytic and the presence of a pair of electrons on heteroatoms such systems (Fish et al.; Mrsaic et al .; Wang et al. , Abu - Reziq et as nitrogen which deactivates the catalysts (Rahi et al. al.; Polshettiwar et al .; Fang et al.; Zhang et al.; Zhu et al.; Dalton Trans. 2012 , 41 , 14490-14497 ) . Three reduction 60 Niu et al. , Karakulina et al. , Fan et al.; Campanati et al.; products of quinoline are possible which are 1,2,3,4 - tetra Barbaro et al .; Ge et al.; Gong et al.; Dell'Anna et al. , and hydroquinoline (bz - THQ ) , 5,6,7,8 -tetrahydroquinoline (py Mao et al. ] . However , a ligand - free metal supported on THQ) , and decahydroquinoline (DHQ ) . Driving the reduc SPIONs has been rarely explored . It should be noted that tion reaction to produce selectively one major product such solid - supported catalysts require post -reaction separation as bz - THQ is challenging. Homogeneous catalysts of Ru , 65 from the products . The separation is generally achieved by Rh , Ir and Pd have been used in the reduction of quinoline filtration , centrifugation , or precipitation , each of which with good results (Guo et al. Catal. Sci . Technol. , 2017 , 7 , severely affects the prospects of reusing the catalyst as a US 10,618,878 B1 3 4 result of gradual loss of catalyst with each cycle [ Tao et al. In the most preferred embodiment, the nitrogen hetero Adv. Synth . Catal. 2015, 357 , 753-760 ). cyclic ring is a five membered ring or six membered ring . Superparamagnetic iron oxide nanoparticles ( SPIONS) In another preferred embodiment, the nitrogen heterocy have attracted a great deal of attention because they have clic ring is in a compound selected from the group consisting desirable physical characteristics and are easily obtainable 5 of optionally substituted or unsubstituted pyrrole , pyridine, from low cost precursors . They are insoluble in water and pyrazol, imidazole , triazol, tetrazol , indole , quinoline, iso other common solvents , and have magnetic characteristics quinoline , pyrimidine , pyridazine, pyrazine , purine , oxazol, that render their separation from reaction mixtures by an thiazol , isothiazol, 1,2 -oxazine , 1,3 - oxazine, 1,4 -oxazine , external magnet effortless . Magnetically separable catalysts 1,2 -thiazine , 1,3- thiazine, 1,4 - thiazine, 1,2,3 - triazine , 1,2,4 have been utilized in the syntheses of biphenyl and higher 10 triazine , and 1,3,5 - triazine . olefins , and in the asymmetric hydrogenation of ketones and In another preferred embodiment the aromatic ring is transesterification of triglycerides to produce biodiesel [ Yan carbocyclic ring . et al . Org. Lett . 2013 , 15 , 1484-1487 ; McDonald et al . Green In another preferred embodiment, the carbocyclic aro Chem ., 2008, 10, 424-432; Wang et al. Tetrahedron Lett. , 15 maticconsisting ring ofis optionallya in a compound substituted selected or unsubstituted from the groupben 2013 , 54 , 238-241 ; and Zhu et al. Adv. Synth . Catal. , 2007 , zene , biphenyl, naphthalene, anthracene, pyrene , benz [ a ] 349, 1917-1922 ]. anthracene , benzo [a ]pyrene , or the like . U.S. Pat . No. 9,480,978B1 discloses a catalyst comprising In a more preferred embodiment, the compound is iron oxide (Fe2O4 ) nanoparticle core and bis ( diarylphosphi selected from optionally substituted or unsubstituted ben nomethyl dopamine anchored on the surface as a ligand to 20 zene , toluene, and xylene. a metal catalyst. Also , it discloses that the metal catalyst is In another preferred embodiment, the reducing reagent is selected from nickel, platinum , palladium , rhodium , iron , hydrogen gas , tetrahydroxydiboron ( THDB ) , sodium boro gold , silver, ruthenium , and iridium . In particular, the patent hydride , lithium borohydride , lithium aluminum hydride , discloses that the metal catalyst is rhodium ( III ) chloride or diborane , calcium hydride, sodium hydride , potassium 2,5 -norbornadiene - rhodium ( 1) chloride. The patent further 25 hydride, or disobutylaluminum hydride. discloses the use of the coordinated rhodium catalyst in In another preferred embodiment, the reducing reagent is hydroformylating an olefin to the corresponding aldehyde . THDB . Pelisson et al. [ ACS Sustainable Chem . Eng . ( 2016 ) 4 , 3 , In another preferred embodiment, the reducing reagent is 1834-1839 ] disclose the preparation of Rhº /yFe2O3 nano pressurized hydrogen gas in the range of 2 bar to 100 bar. composite by depositing metal nanoparticles on non - func- 30 In another preferred embodiment the solvent is a com tionalized magnetic support through a wet impregnation pound containing the aromatic ring . method . The nanocomposite is shown to be an effective In another preferred embodiment, the solvent is water , an catalyst at room temperature for hydrogenation of nitroben lcohol, a carbocyclic aromatic solvent, a polar aprotic polar zene to aniline and dechlorination of chloroarene com solvent or a mixture thereof . pounds and can be magnetically retrieved from reaction 35 In another preferred embodiment , the solvent is an alco mixtures . hol selected from methanol, ethanol, propanol , isopropanol, Laska et al . [ Catal. Letters (2008 ) 122 (1-2 ), 68-75 ] butanol, isobutanol, t- butyl alcohol, dimethyl ether , diethyl disclose rhodium catalyst supported on SPIONs prepared by ether, and the like . a method involving sulfonated triphenylphosphoine ligands. In another preferred embodiment, the polar aprotic polar The catalyst promoted the hydrogenation of olefins and the 40 aprotic solvent is selected form tetrahydrofurane , dioxane , addition of arylboronic acids to dimethyl itaconate in water. dimethylformamide, acetonitrile , dimethylacetamide , and Accordingly one object of the present disclosure is to the like . provide a regioselective reduction method for aromatic In another preferred embodiment , the method comprises : compounds in general and aromatic heterocyclic compounds suspending a catalyst in a solvent selected from the group in particular using an efficient and recyclable catalyst that 45 consisting of water , methanol, ethanol , propanol, iso can be removed from a reaction mixture by a magnet . propanol , butanol, a compound comprising the N -het erocyclic ring , and a mixture thereof to form a catalyst SUMMARY mixture , wherein the catalyst consists of superparamag netic iron oxide nanoparticles (SPIONs ) and rhodium A first aspect of the invention is directed to a method of 50 particle of less than 1 nm deposited on the SPIONS , hydrogenating an aromatic ring in a compound comprising : mixing the catalyst mixture with a compound comprising suspending a catalyst in a solvent to form a catalyst an N -heterocyclic aromatic ring and tetrahydroxydibo mixture ,wherein the catalyst consists of superparamag ron ( THDB ) , and netic iron oxide nanoparticles (SPIONs ) and transition heating to a temperature in the range of 40 to 100 ° C. metal particles of less than 1 nm deposited on the 55 In a more preferred embodiment, the solvent is water . superparamagnetic iron oxide nanoparticles , In another preferred embodiment, the N -aromatic hetero mixing the catalyst mixture with a compound comprising cycle is selected from pyrrole , pyridine, pyrazol , imidazole , an aromatic ring and a reducing agent, and triazol, tetrazol, indole , quinoline, isoquinoline, pyrimidine , heating to a temperature in the range of 40 to 200 ° C. pyridazine , pyrazine , purine, oxazol , thiazol, isothiazol, 1,2 In a preferred embodiment, the transition metal is selected 60 oxazine, 1,3 -oxazine , 1,4 - oxazine, 1,2 -thiazine , 1,3 - thiaz from rhodium (Rh ), platinum ( Pt) , palladium (Pd ) , ruthe ine , 1,4 - thiazine , 1,2,3 - triazine , 1,2,4 - triazine , and 1,3,5 nium (Ru ), nickel (Ni ) , copper (Cu ) , osmium (Os ) , iridium triazine . ( Ir ) , rhenium (Re ) , gold (Au ) , and silver ( Ag ) . In another preferred embodiment, the method comprises : In another preferred embodiment, the aromatic ring is suspending a catalyst in a solvent selected from the group heterocyclic ring or a carbocyclic ring . 65 consisting of water, methanol, ethanol , propanol , iso In a more preferred embodiment, the aromatic ring is a propanol , butanol, a compound comprising the carbo nitrogen heterocyclic ring . cyclic aromatic ring , and a mixture thereof to form a US 10,618,878 B1 5 6 catalyst mixture, wherein the catalyst consists of super accompanying drawings, in which some, but not all embodi paramagnetic iron oxide nanoparticles (SPIONs ) and ments of the disclosure are shown . The present disclosure rhodium particle of less than 1 nm deposited on the will be better understood with reference to the following SPIONS, definitions. mixing the catalyst mixture with a compound comprising 5 All publications mentioned herein are incorporated herein a carbocyclic aromatic ring and hydrogen gas at a by reference in full for the purpose of describing and pressure in the range of 2 bar to 100 bar, and disclosing the methodologies , which are described in the heating to a temperature in the range of 40 to 100 ° C. publications , which might be used in connection with the In another preferred embodiment , the solvent is the aro description herein . Nothing herein is to be construed as an matic compound 10 admission that the inventors are not entitled to antedate such In another preferred embodiment , the aromatic compound disclosure by virtue of prior disclosure . Also , the use of “ or ” is selected from benzene , toluene , and xylene . means “ and /or ” unless stated otherwise . Similarly , " com The foregoing paragraphs have been provided by way of prise, " " comprises, " " comprising " " include, " " includes, " general introduction , and are not intended to limit the scope and “ including” are interchangeable and not intended to be togetherof the withfollowing further claims advantages. The , will described be best understoodembodiments by , 15 limiting. reference to the following detailed description taken in As used herein , the term " compound” is intended to refer conjunction with the accompanying drawings. to a chemical entity , whether in a solid , liquid or gaseous phase , and whether in a crude mixture or purified and BRIEF DESCRIPTION OF THE DRAWINGS isolated . 20 As used herein , the term “ salt ” refers to derivatives of the A more complete appreciation of the disclosure and many disclosed compounds , monomers or polymers wherein the of the attendant advantages thereof will be readily obtained parent compound is modified by making acid or base salts as the same becomes better understood by reference to the thereof. Exemplary salts include , but are not limited to , following detailed description when considered in connec mineral or organic acid salts of basic groups such as amines , tion with the accompanying drawings, wherein : 25 and alkali or organic salts of acidic groups such as carbox FIG . 1 shows pictorial representation of quinoline hydro ylic acids. The salts of the present disclosure can be syn genation using catalyst, Rh @ Fe3O4, and THDB as hydrogen thesized from the parent compound that contains a basic or source in water . acidic moiety by conventional chemicalmethods . Generally FIG . 2 shows XRD spectra of a ) Fe3O4 and b ) Rh @ Fe304. such salts can be prepared by reacting the free acid or base FIG . 3a3b showsshows TEM TEM imagesimages of of Rh Fe304 @ Fe304. . Insets FIG . 3c 30 forms of these compounds with a stoichiometric amount of shows magnified image of Rh nanoparticles decorating the the appropriate base or acid in water or in an organic solvent, Fe3O4 particles. Inset , FIG . 3d shows particle size distribu or in a mixture of the two; generally non -aqueous media like tion curve of Rh @ Fe304 , and circled STEM image of ether , ethyl acetate , ethanol, isopropanol , or acetonitrile are Rh @ Fe304 particles shows Rh nanoparticle with a size : ~ < 1 preferred . nm . 35 As used herein , the term “ about” refers to an approximate FIG . 3e shows HRTEM image of Rh @ Fe304. number within 20 % of a stated value , preferably within 15 % FIG . 3F show a TEM image Rh @ Fe304; inset 3g shows of a stated value , more preferably within 10 % of a stated the selected area electron diffraction (SAED ) pattern of value, and most preferably within 5 % of a stated value . For Fe3O4 from Rh @ Fe3O4. example , if a stated value is about 8.0 , the value may vary FIG . 4a showsmagnetic hysteresis loops of Rh @ Fe3O4 at 40 in the range of 8 + 1.6 , +1.0 , +0.8 , +0.5 , +0.4 , +0.3 , +0.2 , or room temperature with 1 tesla magnet. +0.1 . FIG . 4b shows recycling the catalyst in the hydrogenation As used herein , the term “ alkyl” unless otherwise speci reaction of quinoline at 50 ° C. in water . fied refers to both branched and straight chain saturated FIG . 5a shows SEM image of Fez04. aliphatic primary , secondary , and / or tertiary hydrocarbons of FIG . 5b shows SEM image of Rh @ Fe304. FIG . 6a shows Fe mapping of Rh @ Fe304 45 typically Ci to C10 , and specifically includes , but is not FIG . 6b shows Rh mapping of Rh @ Fe304. limited to , methyl, trifluoromethyl, ethyl, propyl, isopropyl, FIG . 7 shows STEM image of Rh @ Fe304 (top ) and cyclopropyl, butyl, isobutyl , t -butyl , pentyl, cyclopentyl, elemental identification of Rh . isopentyl, neopentyl , hexyl , isohexyl , cyclohexyl, cyclohex FIG . 8 shows ' H NMR of Bz - THQ obtained from the ylmethyl, 3 -methylpentyl , 2,2 - dimethylbutyl, and 2,3 - dim Quinoline hydrogenation in water. 50 ethylbutyl . As used herein , the term optionally includes FIG . 9 shows 13C NMR of Bz - THQ obtained from the substituted alkyl groups . Exemplary moieties with which the Quinoline hydrogenation in water . alkyl group can be substituted may be selected from the FIG . 10 shows ' H NMR of Bz - THQ obtained from the group including , but not limited to , hydroxyl, alkoxy, ary Quinoline hydrogenation in D20 . loxy, or combination thereof. FIG . 11 shows 13C NMR of BZ - THQ obtained from the 55 As used herein , the term " substituted ” refers to at least Quinoline hydrogenation in D20 . one hydrogen atom that is replaced with a non -hydrogen FIG . 12a shows MS spectra of reduced product bz - THQ group , provided that normal valences are maintained and in presence of tetrahydroxydiboron in H20 . that the substitution results in a stable compound . When a FIG . 12b shows MS spectra of reduced product deuterated substituent is noted as “ optionally substituted ” , the substitu Bz- THQ in presence of tetrahydroxydiboron in D20 . 60 ents are selected from the exemplary group including , but FIG . 13 shows TEM image of Fe304 @ Rh after 16 con not limited to , halo , hydroxyl , alkoxy , oxo , alkanoyl , ary secutive catalytic cycles. loxy, alkanoyloxy, amino , alkylamino , arylamino , arylalky lamino , disubstituted amines ( e.g. in which the two amino DETAILED DESCRIPTION substituents are selected from the exemplary group includ 65 ing , but not limited to , alkyl, aryl or arylalkyl) , alka Embodiments of the present disclosure will now be nylamino, aroylamino , aralkanoylamino , substituted described more fully hereinafter with reference to the alkanoylamino , substituted arylamino , substituted aral US 10,618,878 B1 7 8 kanoylamino , thiol, alkylation , arylthio , arylalkylthio , alky nm . In a particularly preferred embodiment the SPIONS Ithiono , arylthiono , aryalkylthiono , alkyl sulfonyl, aryl sul have an average diameter in the range 7 nm to 10 nm . In one fonyl, arylalkylsulfonyl , sulfonamide ( e.g. -SO2NH2) , or more embodiments , the transition metal is present in an substituted sulfonamide , nitro , cyano , carboxy, carbamyl amount in the range of 1-20 wt. % , preferably in the range ( e.g. CONH2) , substituted carbamyl ( e.g. CONHalkyl, 5 of 3-15 wt. % , more preferably in the range of 4-10 wt. % CONHaryl, CONHarylalkyl or cases where there are relative to a total weight of the supported catalyst. For two substituents on one nitrogen from alkyl, aryl, or alky example , the rhodium is present in an amount of about 4.2 lalkyl) , alkoxycarbonyl, aryl, substituted aryl, guanidine, wt. % , about 6.5 wt. % , or about 8.2 wt. % relative to a total heterocyclyl ( e.g. indolyl , imidazoyl, furyl, thienyl, thiaz weight of the supported catalyst . In a most preferred olyl, pyrrolidyl , pyridyl, pyrimidiyl , pyrrolidinyl , piperidi- 10 embodiment , the transition is present in an amount of about nyl, morpholinyl , piperazinyl, homopiperazinyl and the 8.2 wt. % relative to a total weight of the supported catalyst, like ), substituted heterocyclyl and mixtures thereof and the and metal particles are dispersed on the surface of the like . SPIONs. The transition metal of the catalyst may be any As used herein , the term " cycloalkyl ” refers to cyclized transition metal that is able to catalyze the reduction reaction alkyl groups . Exemplary cycloalkyl groups include , but are 15 of an aromatic and / or heteraromatic ring. Examples of not limited to , cyclopropyl, cyclobutyl, cyclopentyl, cyclo transition metals useful as catalysts include , but are not hexyl , norbornyl, and adamantyl. Branched cycloalkyl limited to , rhodium , platinum (Pt ), palladium (Pd ) , ruthe groups such as exemplary 1 -methylcyclopropyl and 2 -meth nium (Ru ), nickel (Ni ) , copper (Cu ), osmium (Os ) , iridium ylcyclopropyl groups are included in the definition of ( Ir ) , rhenium (Re ), gold (Au ) , silver (Ag ) and mixtures or cycloalkyl as used in the present disclosure . 20 alloys thereof. In a particularly preferred embodiment , the As used herein , the term “ aryl” unless otherwise specified transition metal is rhodium . refers to functional groups or substituents derived from an The aromatic compound to be reduced can be any com aromatic ring including , but not limited to , phenyl, biphenyl, pound comprising an aromatic ring. In some embodiments , naphthyl, thienyl, and indolyl. As used herein , the term the aromatic compound is an optionally substituted hetero optionally includes both substituted and unsubstituted moi- 25 cyclic compound. As used herein the term “ aromatic het eties . Exemplary moieties with which the aryl group can be erocyclic compound ” has the established meaning in the substituted may be selected from the group including , but chemical art and is intended to refer to an aromatic com not limited to , hydroxyl, amino , alkylamino , arylamino , pound comprising a heterocyclic aromatic ring . The hetero alkoxy, aryloxy, nitro , cyano , sulfonic acid , sulfate , phos cyclic ring has one or more heteroatom . The heteroatoms phonic acid , phosphate or phosphonate or mixtures thereof. 30 include are but not limited to , nitrogen , oxygen , sulfur , or The substituted moiety may be either protected or unpro combination thereof. Examples of nitrogen containing het tected as necessary , and as known to those skilled in the art . erocyclic aromatic compounds include , but are not limited As used herein , the term " alcohol" unless otherwise to , pyrol, imidazole, pyrazol, triazol, tetrazol, pyridine , specified refers to a chemical compound having an alkyl pyrazine, pyrimidine, purine , quinoline, quinolin2( 1H ) -one, group bonded to a hydroxyl group . Many alcohols are 35 isoquinoline, isoquinolin - 1 ( 2H ) -one , phathalazine, quinazo known in the art including, but not limited to , methanol, line, cinnoline , quinoxaline, carbazol, 1,8 -naphtharidine , ethanol, propanol, isopropanol, butanol, isobutanol and t- bu pyrido [3,2 - d ]pyrimidine , acridine , phenazine, phenoxazine tanol, as well as pentanol, hexanol, heptanol and isomers and the like. Examples of oxygen containing heterocyclic thereof. Since the alkyl group may be substituted with one aromatic compounds include, but are not limited to , furan , or more hydroxyl group , the term “ alcohol” includes diols , 40 benzofuran , 2 -pyrone , 4 -pyrone , coumarin , 7- methoxycou triol, and sugar alcohols such as, but not limited to , ethylene marin , chromone, and dibenzofurane. Examples of sulfur glycol , propylene glycol, glycerol, and polyol. containing heterocyclic aromatic compounds include, but As used herein the terms “ reduction ” and “ reducing are not limited to , thiophen , benzothiophene, and dibenzo agent” have the well accepted meaning in the chemical art . thiophene . Examples ofheterocyclic compounds comprising So a reducing agent causes the reduction of an organic 45 a combination ofhetero atoms include, but are not limited to , compound by decreasing its oxidation state . For example , thiazol, oxazol, isoxazole , isothiazol, 1,2,5 -oxadiazole , phe the addition of hydrogen atoms to aromatic ring by a noxazine , phenothiazine , and phinoxathiin . reducing agent is a reduction reaction . In some preferred embodiment, the heterocyclic aromatic The disclosure is directed to a method of hydrogenating compound may be substituted with a substituents which may an aromatic ring in a compound comprising : 50 be reduced along with the heteraromatic ring . Such a sub suspending a catalyst in a solvent to form a catalyst stituents include , but not limited to nitro , chloro , and iodo mixture ,wherein the catalyst consists of superparamag substituent. For example, the nitro group is reduced to amino netic iron oxide nanoparticles (SPIONs ) and transition group and the chloro substituent is replaced by a hydrogen . metal particles of less than 1 nm deposited on the In some more preferred embodiments of the method , a superparamagnetic iron oxide nanoparticles , 55 heterocyclic aromatic ring may be regioselectively reduced mixing the catalyst mixture with a compound comprising in a heterocyclic compound comprising a carbocyclic aro an aromatic ring and a reducing agent , and matic ring under relatively mild condition in aqueous solu heating to a temperature in the range of 40 to 200 ° C. tion . For example , quinoline and isoquinoline are reduced The catalyst of the invention contains and preferably regiospecifically to 1,2,3,4 -tetrahydroquinoline and 1,2,3,4 consists of transition metal particles having a diameter of 60 tetrahydroisoquinoline , respectively , in aqueous medium . less than 1 nm , preferably less 0.8 nm , more preferably less In other preferred embodiments, the aromatic compound than 0.7 nm , and most preferably about 0.5 nm deposited on is an optionally substituted carbocyclic aromatic compound superparamagnetic iron oxide nanoparticles ( SPIONS) . The such as but not limited to benzene , naphthalene , anthracene, SPIONs are iron oxide (Fe2O4 ) nanoparticles having an phenanthrene , pyrene , benz[ ajanthracene, benzo [ a ]pyrene , average diameter in the range of 3 nm to 100 nm , preferably 65 and the like . There are large numbers of substituted carbo in the range 4 nm to 50 nm , more preferably in the range of cyclic aromatic compounds known in the art. For example , 5 to 25 nm , and most preferably in the range of 6 nm to 15 substituted benzene compounds such as , but not limited to US 10,618,878 B1 9 10 toluene , o -xylene , m -xylene , p -xylene , anisol, phenol, The examples below are intended to further illustrate hydroxyanisol isomers, dihydroxyphenol isomers , trihy protocols for preparing , characterizing transition metal sup droxybenzene , polyphenols , halogenated benzene such as ported SPIONs, and uses thereof, and are not intended to chlorobenzene , dichlorobenzene and isomers thereof, bro limit the scope of the claims. mobenzene , dibromobenzene and isomers thereof, tribro- 5 mobenzene and isomers thereof, fluorinated benzene , and Example 1 iodinated benzene can be reduced by the method of inven tion . Other well - known substituted carbocyclic aromatic Materials : compounds include , but not limited to methylated , hydroxy All chemicals were purchased from Sigma- Aldrich and lated , and halogenated naphthalene, methylated , hydroxy- 10 were used without further purification unless otherwise lated , and halogenated anthracene, methylated , hydroxy indicated . Standard procedures were followed for drying and lated , and halogenated phenanthrene , methylated , deoxygenating solvents . Schlenk line techniques were used hydroxylated , and halogenated benz [a ]anthracene , and to carry out reactions under inert atmosphere wherever methylated , hydroxylated , and halogenated pyrene and ben needed . Deionized (DI ) water (specific conductivity : 18.2 zo [ a ]pyrene . 15 m2) was used in all the experiments . In some preferred embodiment, the carbocyclic aromatic Methods : compound may be substituted with a substituents which may Fourier - Transform Infrared (FTIR ) spectroscopic data be reduced along with the carbocyclic aromatic ring . Such a were obtained on a Nicolet 720 in the wave number range of substituents include, but not limited to nitro , chloro , and 400 to 4000 cm- using KBr as the IR transparent window iodo substituent. For example , the hydrogenation of 20 material. X -ray diffraction data were collected on Rigaku nitrobenzene would produce cyclohexyl amine and chlo model Ultima -IV diffractometer employing Cu — K? radia robenzene would produce hexane . tion (a = 1.5405 Å ) at 40 kV and 25 mA over a 20 range Any reducing agent may be utilized with the catalyst of between 20 and 90 ° . The Transmission Electron Microscopy the invention in the reduction method . Example of reducing images were acquired at the Instituto de Nanociencia de agents suitable to use with the catalyst of the invention 25 Aragón (LMA - INA ) , University of Zaragoza , Spain , on a include , but not limited to hydrogen gas, sodium borohy TEM ( Joel, J E M 2011 ) operated at 200 kV with 4kx4k dride , lithium borohydride , lithium aluminum hydride, tet CCD camera (Ultra Scan 400SP ,Gatan ). The TEM samples rahydroxydiboron , diborane , calcium hydride, sodium were prepared by dropping on a copper grid from an hydride, potassium hydride, disobutylaluminum hydride , ethanolic suspension and drying at room temperature . The and combination thereof. 30 amount of Rh in the catalyst was determined by Inductively Any liquid may be utilized as a solvent in the method of Coupled Optical Emission Spectrometry ( ICP -OES ; Plas the invention including the aromatic compound to be maQuant PO 9000 - Analytik Jena ). The samples were reduced . Examples of the solvent to be used in the method dissolved in a dilute HNO3 and HCl mixture. Calibration include, but are not limited to water, alcohol such as, but not curves were prepared for Rh and Fe using standard solutions limited to , methanol, ethanol, propanol, isopropanol , 1 - bu- 35 ( ICP Element Standard solutions, Merk ). Samples for Scan tanol and isomers thereof, ethers such as, but not limited to , ning Electron Microscopy ( SEM ) were prepared from etha dimethyl ether , diethyl ether, methylethyl ether, dimethyl nolic suspensions on alumina stubs and coated with gold in formamide , tetrahydrofurane , dioxane , benzene, toluene, an automatic gold coater (Quorum , Q150T E ) . For the xylenes, hexane , cyclopentane, hexane, cyclohexane , and elemental analysis and mapping , the energy dispersive the like . Since some reducing agents may react violently 40 X - ray spectra (EDS ) were collected on a Lyra 3 attachment with water and alcohols , care should be taken in selecting to the SEM . The magnetic susceptibilities were measured at the combination of a solvent and a reducing agent so that the room temperature using a vibrating sample magnetometer solvent does not inactivate the reducing agent. For example (VSM ,model PMC Micromag 3900 ) equipped with a 1 tesla hydrogen gas or tetrahydroxydiborn may be utilized in a magnet . Catalytic reactions were performed in Teflon lined method using any solvent, whereas lithium aluminum 45 autoclaves from HiTech , USA (model MOLOSSG0010 hydride or diborane would be used with non -polar or polar E129A - 00022-1D1101 ) , fitted with a pressure gauge and a aprotic solvents such as dioxane , tetrahydrofurane , benzene mechanical stirrer . Catalytic products were identified by a and toluene . Shimadzu 2010 Plus ( Japan ) gas chromatograph equipped The use of hydrogen gas as a reducing agent in the method with a mass spectrometer . The disappearance of the reactant of the invention may require pressurizing the hydrogen gas 50 and sequential appearance of the product was recorded in at a pressure in the range 1 to 200 bars , preferably in the real- time , identifying the species in terms of their molecular range 5 to 100 bars, more preferably in the range of 10 to 75 ion ( M + ) by comparing and matching them with the avail bars , and most preferably in the range of 15 to 50 bars . able Willey library of the mass spectrum database , in addi In some preferred embodiments , the molar ratio of aro tion to the identification of mass fragmentation . Solution ' H matic compound to reducing agent is in the range of 1 to 50 , 55 and 13C NMR experiments were performed on a Bruker preferably in the range 2 to 25 ,more preferably in the range Ascend 400 spectrometer at Saudi International Petrochemi 3 to 25 , and most preferably in the range of 4 to 10 . cal Company (SIPCHEM ) in Dhahran Techno Valley (DTV ) Since the catalytic reduction method of the invention is and chemical shifts ( 8 ) values were referenced to tetram sensitive to solvent used in the method and the reactivity of ethylsilane ( TMS ) as an internal standard . the aromatic compound to reduction , the temperature of the 60 reaction may be set to produce the desired product in a Example 2 reasonable amount of time. One of ordinary skill in the art would be able to determine the appropriate temperature and Synthesis of Rh @ Fe2O4 Catalyst : the reasonable time for the reaction of interest. In some The catalyst was prepared as described in a co - pending embodiments , the reaction temperature is in the range of 40 65 application Ser . No. 16 /359,409 titled " [ An Iron Oxide to 80 ° C., whereas in some other embodiments the reaction Supported Rhodium Catayst for Nitroarene Reduction ]” ) temperature is in the range of 80 to 200 ° C. which is incorporated herein by reference in its entirety . US 10,618,878 B1 11 12 Magnetite ( Fe304) nanoparticles in the range of 7-9 nm were 30.22 ° , 35.70 ° , 43.10 ° , 53.40 ° , 57.10 ° and 63.20 ° demon prepared according to a procedure described elsewhere strated the purity and formation of single phase nanomate [Panella et al. J. Catal. , 2009 , 261, 88-93 ; and Tang et al. rials with cubic structure ( JCPDS card No. 01-075-0449 ) of Fuel Process . Technol. , 2012 , 95 , 84-89_each incorporated magnetite (Fe304 ) [Shaikh et al. New J. Chem ., 2015 , 39 , herein by reference in its entirety ] . In a typical preparation , 5 7293-7299 ] . It is noteworthy that there was no observed nanostructured magnetite was prepared from an alkaline recognizable peak (s ) of Rh in the diffraction pattern , prob solution containing Fe( II ) and Fe ( III) precursors in themolar ably due to the low concentration of Rh and the sub ratio of 1: 2 . The black powder (200 mg) was suspended in nanometer particle size of Rh . The size of magnetite crys ethanol, sonicated for 3 h . An aqueous solution containing tallites was estimated to be less than 10 nm from Debye 0.019 g of Rh( NO3 ) 3 (0.19 mmol was added and the mixture 10 Scherrer equation ; which was validated from the FESEM stirred overnight. The mixture was heated to 50 ° C. for 3 h , (See FIGS. 5a and 5b ) and TEM images of the catalyst and 27 M ammonium hydroxide solution was slowly added specimen (FIGS . 3a to 3g ) . The structural refinement per to pH > 12 with continued stirring for additional 4 h to insure formed by using the Rietveld method (see Table 1 ) which uniform dispersion of the catalytic species on the magnetic confirmed the formation of the desired phase in high purity support. The resulting black solid was precipitated and 15 with a goodness of fit close to the unity (GoF = 1.07-1.13) . separated by placing a magnet at the bottom of the flask , and This suggests that incorporation of Rh particles did not alter washed with several aliquots of DI water ( 5x30 mL ) and the structure nor dilate the lattice of the parent support , finally with ethanol. suggesting that SPIONs remained stable during the Rh particles decoration process. Example 3 20 TABLE 1 Quinoline Reduction with THDB : The catalytic reduction of quinoline was performed in a Structure and microstructural parallel 10 - place reaction tube reactor fitted with a magnetic parameters obtained by Rietveld refinements . stirrer and a Teflon stopper. To a suspension of 2.0 mg 25 Lattice Rh @ Fe3O4 in 2 mL DIwater , quinoline ( 0.5 mmol, 0.65 uL ) Crystallite Micro parameter was added and the system flushed with N2 gas 3 times . Phase size strain Space ( a = b = c ) Tetrahydroxydiboron ( THDB , 4 mmol) was added . The tube Material ( % ) (nm ) ( % ) group GoF was capped tightly with Teflon stopper and heated at 80 ° C. Fe304 100 8.24 0.68 Fd - 3m 8.349 1.13 The reaction progress was monitored by TLC ( thin layer 30 ( 227 ) chromatography ) . The product was extracted from the aque Rh @ Fe304 100 8.40 0.54 Fd - 3m 8.362 1.08 ous medium with ethyl acetate and the ethyl acetate solution (227 ) dried with sodium sulfate and the solvent evaporated under reduced pressure . The residue containing the product was The morphological and nanostructural features of Fe304 eluted from a short silica gel column using a mixture of ethyl 35 and Rh @ Fe3O4 particles were investigated by transmission acetate and hexane ( 8 : 2 ) . Conversion was measured by GC electron microscopy ( TEM ) , which revealed the formation and identified by the GC -MS . of well -dispersed spherical particles of about 7-9 nm in size with narrow size distribution ( FIGS . 3a - g) , which was Example 4 confirmed by measurement with a particle size analyzer 40 (FIG . 3d ). Furthermore , the surface magnetite (7-9 nm ; FIG . Aromatic Compounds Reduction with Hydrogen Gas: 3a ) is uniformly decorated with Rh particles that are < 1 nm Rh @ Fe3O4 catalyst ( 5 mg) and the selected reactant ( for in size ( Figure . 3b ) ; as corroborated by the confined area of example , pyridine , 0.5 mL ) mixture was placed in a Teflon elemental mapping (see FIGS. 6a and 6b ). It is reasonable to lined autoclave fitted with a pressure gauge , mechanical assume that during the process of decorating the magnetite stirring and automatic temperature controller. The reactor 45 with Rh particles, increase in surface potential led to was flushed repeatedly with H ,, filled with H , up to 40 bars , decrease in the size of the Rh particles to the sub -nano and the reaction initiated with heating and stirring and region . The scanning tunneling electron microscopy continued for 10 h . Then , the reactor was allowed to cool (STEM ) was used to investigate the local physical and down to room temperature, depressurized , and opened . The electronic structure of surfaces, which led to the identity of degree of conversion was determined by GC and the product 50 Rh particles in the sample ( FIG . 2e and FIG . 7 ) . The was identified by the NMR or GC -MS . HRTEM image (FIG . 27) confirms high crystallinity of Similar methods were used for the hydrogenation of Fe3O4 nanoparticles, which was also concluded from the aromatic hydrocarbons such as benzene, toluene and xylene . powder XRD pattern shown earlier in FIG . 2. FIG . 2f and the Bragg reflections in the corresponding SAED pattern (FIG . Example 5 55 2g) yielded a d - value of 0.249 nm which could be assigned to the < 311 > reflection ofmagnetite in the specimen in cubic Structure Characterization of the Catalyst : phase . However, ICP -OES data demonstrates that the ratio Structural characterization of the catalyst was carried out of Fe / Rh was found to be 94 : 6 which was further confirmed by a number of analytical and spectroscopic techniques. The by both EDS studies, SEM and TEM . FTIR of Rh @ Fe304 phase analysis was investigated by X - ray diffraction . FIG . 2 60 showed a vibrational red shift of 7 nm from 586 nm for the shows the XRD signature ofmagnetite with Rh line (a ) and Fe O bond in the parent magnetite . without Rh line ( b ) . High crystallinity of the freshly pre The magnetization (M ) vs. applied magnetic field (H ) pared Rh @ F204 is evident from the diffraction pattern , measurements was conducted by vibrating sample magne which corresponds to that ofmagnetite spinel structure and tometery at room temperature . FIG . 4a shows that both superimposition with the pure Fe3O4 peaks indicates the 65 samples of Fe304 and Rh @ Fe304 display superparamag preservation of Fe3O4 structural lattice arrangement upon netic behavior as no hysteresis loop was observed in the decoration of sub -nanosized Rh particles. XRD angle at ( 20 ) recorded curve . It is important to highlight that slight US 10,618,878 B1 13 14 reduction of saturation magnetization establishes the viabil Scheme 1 shows the possible reaction products of quino ity of the surface decoration with non - magnetic element, Rh . line reduction using tetrahydroxydiboron in water. To preparationFrom the techniqueforegoing offersdiscussion an excellent , it is clear pathway that the to reporteddesign explore the catalytic reduction activity of Rh @ Fe304, qui ing catalysts with well -dispersed sub -nanometer Rh par- 5 noline and THDB were selected as a model nitrogen het ticles on nanostructured magnetic support and can be erocyclic reactant and reducing agent, respectively ( Table extended to other solid surfaces to develop catalysts for 1 ). Samples were taken out periodically and analyzed by thin other organic transformations. layer chromatography ( TLC ) and gas chromatography (GC ) Example 6 to evaluate conversion and selectivity . Based on preliminary 10 results , the reaction solvent, time, temperature , amount of Catalytic Reduction: catalyst , and the concentrations quinolone and THDB were The conversion and regioselectivity of the reduction of optimized . Reduction reactions were carried out in water, quinoline catalyzed by Rh @ Fe3O4 was evaluated as a model IPA , methanol, THF, 1,4 -dioxane and cyclohexane , and the reactionEfficacy forof thethe magneticreduction catalystof N -heterocyclic towards reduction compounds was. 15 results are summarized in Table 1.No reduction product was tested by using tetrahydroxydiboron ( THDB ) and hydrogen observed in methanol, dioxane, cyclohexane and THF even gas as examples of reducing agents . after long reaction time for up to five hours ( Table 1 ) . The (a ) Rh @ Fe304- Catalyzed Reduction of Quinolone with reaction progress in IPA was much slower than in water and THDB : No reduction product was observed from a reaction 20 was completed in 5 h . In contrast , quantitative conversion mixture comprising quinolone and without teterhydroxydi quinolone to reduced product was observed in water . Also , boron . Thus, the combination of Rh @ Fe3O4 and a reducing the effect of temperature was briefly examined . In water, no agent such as tetrahydroxydiboron is required to carry out conversion was observed at room temperature , but the the reduction process. Table 1 summarizes the experimental conversion was appreciable at 50 and 80 ° C. ( Table 1 ) . In parameters and the results of quinoline hydrogenation in 25 fact, it took only 10 min . at 80 ° C. to achieve > 99 % various media . conversion with 100 % selectivity . The product selectivity Scheme 1 was maintained even at 80 ° C. ( see Table 1 ) . The effect of relative concentration of tetrahydroxydiboron ( THDB ) on Quinoline Reduction in Water 30 quinoline reduction in water is shown in Table 2. The amount of THDB was varied systematically from 2 to 8 molar equivalent of quinoline . The conversion was observed increase steadily with increasing THDB and 97 % con Rh @ Fe304 version into bz- THQ was achieved with 6 equivalents (OH ) 2B - B (OH )2 + 35 THDB after 30 min . of reaction time. But the optimum H20 , 80 ° C. conversion of ~ 99 % was achieved with 8 equivalent of THDB (Table 2 ) in just 10 min . Hence , quinoline can be bz - THQ smoothly reduced to bz - THQ in water at 80 ° C. by adding eight equivalent of tetrahydroxydiboron as reducing agent to + 40 selectively produce Bz - THQ in 10 minutes without any N other products . In contrast , bz - THQ , py - THQ and DHQ py -THQ have been observed in a conventional hydrogenation . DHQ The reduction of heterocyclic rings in comparison to 45 carbocyclic rings depends on the nature of interaction of quinoline with the metal center of the catalyst (Konnerth et TABLE 1 al. and Xia et al.each incorporated herein by reference in their entirety ). The observed exclusive regioselectivity for Rh @ Fe304- mediated hydrogenation of the reduction of the heterocyclic aromatic ring could be quinoline “ using THDB as H , source 50 explained by quinoline interaction with or absorption to the Temp Time Conversion Selectivity activemetal through the ring nitrogen , which can impact the Entry Solvent (° C.) (min . ) ( % ) ( % ) instantaneous microenvironment generated around the metal 1 Water Rt 30 center [Shaikh et al. RSC Adv. , 2016 , 6 , 41687-41695— 50 10 88 100 incorporated herein by reference in its entirety ] . The inter 20 94 100 80 10 > 99 100 55 action between the ring nitrogen and the metal ion is 2 IPA 80 10 15 100 enhanced by the basic nature of the support which plays an 60 67 100 essential role in directing the reaction pathway [Pinna et al. 300 94 100 Chem .Mater . , 2005, 17 , 3044-3049 — incorporated herein by 3 THF 80 300 4 Cyclohexane 80 300 reference in its entirety ). Earlier reports described that 5 Methanol 80 300 nd nd 60 hydroxylated basic supports , such as magnesium oxide or 6 80 300 magnetite , have been shown to be capable of engaging 1,4 - dioxane N - bearing heterocyclic moieties via hydrogen bonding [ Der 40.5 mol of quinoline mmol of THDB 2 mL water were used ; bmeasured by GC ; aedt et al . J. Am . Chem . Soc. 2017 , 139, 18084-18092 ; identified by GC -MS and NMR ; Sanchez et al. Applied Catalysis A : General 477 ( 2014 ) rt : room temperature ; 65 117-124 ; and Bai et al. Angew . Chem ., Int. Ed . 2016 , 55 , nd : not determined . 15656-15661_each incorporated herein by reference in their entirety ]. US 10,618,878 B1 15 16 TABLE 2 were improved using quinoline as model substrate with various solvents , pressures, and temperatures . The solvent Effect of the relative concentration of tetrahydroxydiboron ( THDB ) on quinoline hydrogenation in has a large effect on the reduction -catalyzed reaction . Qui water as a function of on -stream reaction time. noline is reduced in 2 h to bz - THQ (Scheme 1 ) in water 5 under 20 bar hydrogen pressure . In less polar solvent such THDB Time Conv. Sel. as toluene and methanol, a significant decrease in conver Entry (mmol ) (min ) ( % ) ( % ) sion was observed ( Table 3 ) . At room temperature , no 1 2 10 57 100 detectable product was observed ( Table 3 ). But on increas 20 59 100 ing the temperature to 50 ° C., quinoline was quantitatively 30 64 100 10 converted to bz - THQ. The effect of pressure on the conver 2 4 10 62 100 sion and selectivity were studied and summarized . At 115 ° 20 87 100 30 93 100 C., neat pyridine was converted quantitatively to piperidine 3 6 10 96 100 in 10 h . Similar results were observed in the hydrogenation 20 97 100 of pyrazine in IPA ( Table 3 ). Also , the hydrogenation 30 97 100 15 activity of the catalyst was evaluated for the five -membered 4 8 10 >99 100 ring heterocycles ( Table 3 ), and pyrrole was found to be the asubstrate 1 mmol; most reactive among the hetrocyclic compounds tested bmeasured by GC ; ( Table 3) . At 130 ° C./40 bar , indole hydrogenation attained identified by GC -MS and NMR . 70 % conversion with 100 % selectivity after 24 h in THF , 20 whereas only 12 % of 2 -methylindol is converted to the (b ) Rh @ Fe304- Catalyzed Reduction of Quinolone with hydrogenation product at 150 ° C./40 bar in 24 h of reaction Hydrogen Gas: time. This observation could be partly ascribed to the The catalytic performance of Rh @ Fe304 catalyst towards presence of electron -donating group in the 5 -membered ring the reduction of a series of N -heterocyclic compounds with that tends to increase the electron density around nitrogen hydrogen gas was evaluated in water and THF as well as 25 atom , thereby effectively binding its lone pair with Rh metal without a solvent. The reaction variables and the results are in the catalyst, causing deactivation of the active metal summarized in Table 3. Initially , the reaction conditions centers . TABLE 3 Rh @ Fe304- mediated hydrogenation of N -heteroarene by hydrogen gas Time Temp Pres. Convb . Sel.. Entry Substrate Product Solv. (h ) ( ° C .) ( bar) ( % ) ( % )

1 Water 2 rt 20 2 40 20 > 67 100 2 50 20 > 99 100

2 Methanol 2 50 30 61 100

NH 3 Toluene 2 50 30 36 100

2d None 10 115 40 > 99 100

NH 3e C HN IPA 14 130 30 > 99 100

4 None 10 120 30 > 97 100 US 10,618,878 B1 17 18 TABLE 3 - continued Rh @ Fe30 , -mediated hydrogenation of N -heteroarene by hydrogen gas Time Temp Pres . Convb . Sel.. Entry Substrate Product Solv . ( h ) (° C . ) (bar ) ( % ) ( % ) 5 THF 24 140 40 70 100

6 THF 24 150 40 12 100

amount of substrate used 0.5 mmol; bmeasured by GC ; identified by GC -MS and NMR; dsubstrate used 12 mmol, 1 mL ; e substrate used 6 mmol.

Hydrogenation of aromatic compounds such as benzene , Scheme 2 toluene, xylenes and the like were carried out with pressur ized hydrogen gas without any solvent. Again , the reaction 25 Isotopic Mechanistic Experiment temperature is an important determining factor for driving the reaction toward formation of the reduction product. For instance , it was observed that benzene could be rapidly H H (D ) hydrogenated to cyclohexane at 100 ° C. and a pressure of 30 30 H bar ( Table 4 ). At 115º C. and 50 bar hydrogen gas pressure , Rh @ Fe304 H ( D ) 51 % of toluene was converted to methylcyclohexane in 24 (OH ) 2B - B (OH ) 2 H hours, and the conversion is increased to 70 % when tem D20 , 80 ° C. perature was raised to 130 ° C. The observed increased 35 H ( D ) activity implies that the catalyst is stable at higher tempera bz - THQ ture. In the case of p -xylene , the hydrogenation propensity decreased relative to toluene due to the increase of methyl Mass spectrometric and NMR spectroscopic studies indi substituents ( Table 4 ). Only 22 % conversion of p -xylene to cated that quinoline was deuterated at the C ( 2 ), C ( 3 ) and 1,4 -dimethyl cyclohexane was observed in 24 hours . 40 C ( 4 ) positions of the N -bearing heterocyclic ring ( see FIGS. 8-11) . Also , nitrogen should be deuterated . However , the TABLE 4 possibility of rapid exchange of deuterium with water during the process of isolating the product precluded the observa Rh @ Fe304- mediated hydrogenation of aromatic 45 tion of deuterated nitrogen ( see FIGS. 12a and 12b )) [Mao compounds by hydrogen gas without solvent et al . J. Mol. Catal. A : Chem . 2011 , 341 , 51-56 — incorpo rated herein by reference in its entirety ]. From the foregoing discussion , it is evident that quinoline can be quantitatively Time Conv . Sel. and selectively reduced to bz - THQ in water by THDB . Also , Entry Substrate Product ( h ) ( % ) ( % ) 50 the results highlight the definite role of water molecules in the hydrogenation process . On the basis of above discussion , 1 Benzene Cyclohexane 8 > 99 100 wepropose a plausible route for the catalytic hydrogenation 2 Toluene Methycyclohexane 51 100 of quinoline in the following sequence (Scheme 3 ) . 24 70 100 Scheme 3 is a proposed mechanism for quinolone reduc 3 p - Xylene 1,4 - Dimethylcyclohexane 24 22 100 55 tion with THDB catalyzed by Rh @ Fe304. Initially , Rh undergoes oxidative addition to THDB to produce 1 , fol lowed by the coordination of water molecule to boron atom ameasured by GC ; to form adduct 2. The Rh -hydride complex 3 is produced by bidentified by GC -MS ; the elimination of boric acid (H2B03 ) . Quinoline which is in Cused 1 mL benzene ; 60 contact with the magnetite support through hydrogen bond dused 0.5 mL toluene and p -xylene . ing , enter into the catalytic cycle and forms intermediate 4 . The intermediate is formed by the transfer ofhydrogen from Based on the observed activity and selectivity of the Rh- hydride to C ( 2 ) of quinolone, the most electrophilic catalyst, a reaction pathway is proposed in Scheme 2 . center in quinolone leading to the reduction of C ( 2 ) -N bond Deuterium isotope labelling studies were performed by 65 [Dell'Anna et al. J. Mol. Catal A : Chem . 2015 , 402, 83-91– using D20 as and identifying the location of additional incorporated herein by reference in its entirety ]. Since the hydrogen in the hydrogenated quinoline . reduction of the C2 - N bond disrupts the aromaticity of the US 10,618,878 B1 19 20 heterocyclic ring , the reduction of C2 - N is probably the rate catalytic reaction scheme, at least four equivalents ofwater determining step [Eros et al. Chem . Eur . 1 2012, 18 , 574 molecules are required for the hydrogenation of one mol 585 ] . Coordination of THDB to Rh particles produces 7 ecule of quinoline, producing bz - THQ . followed by addition of another water molecule to a boron atom of THDB generates produces intermediate 8 , and 5 another hydrogen transfer and liberating boric acid to pro Scheme 3 duces 9. Elimination of boric acid from 9 to produce 11 which rearranges to produce 1,2,3,4 - tetrahydroquinolin (bz Proposed Catalytic Cycle for the Reduction of THQ ) and free Rh . As can be readily seen from the proposed Quinoline in Water with THD

H H

N H

H ( OH )2B - B (OH ) 2 -B (OH ) 3 [Rh ] H— [Rhy H (HO ) 2B— [ Rh ] — B (OH ) 2 1 H2O

H -OH 0 N H H - OH HO B [ Rh ] O ( HO )2B- [Rh ] B - OH OH H 11 OH 2 N H -B (OH )3 H20 H 10 ( HO) 2B- [ R1] -H 3

B ( HO2- ) [ R ] -H

H

H o H - OH O — B (OH )3 B ( HO2–) [ R1 ] B OH (HO ) 2B- [ Rh ] OH H

H H - OH 4 8 B (HO )2- [ Rh ]—B ( OH ) 2 lo HO -B- [Rh ] || H2O H20 H H- [Rh ] OH N H N H H 7

(OH )2B - B (OH ) 2 6 - B (OH )3 US 10,618,878 B1 21 22 To examine recycling the catalyst in subsequent hydro oxazine , 1,2 - thiazine , 1,3 - thiazine, 1,4- thiazine, 1,2,3 - triaz genation reactions, the catalyst was isolated from a reaction ine , 1,2,4 - triazine , and 1,3,5 - triazine . mixture for reduction of quinolone and recycled . After each 6. The method of claim 1 , wherein the aromatic ring is a reduction cycle , the catalyst was removed from the reaction carbocyclic aromatic ring . mixture by putting a magnet at the bottom of the flask and 5 7. The method of claim 6 , wherein the carbocyclic aro decanting the liquid . The catalyst was thoroughly washed matic ring is in a compound selected from the group several times with methanol and dichloromethane , and dried consisting of optionally substituted or unsubstituted ben for use in subsequent reduction cycles without adding any zene , biphenyl, naphthalene , anthracene , pyrene , benz [ a ] fresh catalyst . It was found that the catalyst could be used in anthracene, benzo [ a ]pyrene , or the like . 16 consecutive cycles without significant loss of catalytic 10 8. The method of claim 7 , wherein the compound is activity . The catalytic activity declined slightly with increas selected from optionally substituted or unsubstituted ben ing the number of cycles as about 93 % of the catalytic zene , toluene , and xylene . activity was observed after 16 cycles (FIG . 46 ). The used 9. The method of claim 1 , wherein the reducing reagent is thecatalyst metal was content collected was at quantified the end ofby cumulative ICP -OES .cycles The usedand 15 at least one of hydrogen gas , tetrahydroxydiboron (THDB ) , catalyst showed 6.1 % loss of Rh as a result of leaching from sodium borohydride, lithium borohydride, lithium alumi the surface of magnetic nanoparticles . This was corrobo num hydride , diborane , calcium hydride, sodium hydride , rated by the HRTEM and STEM investigations on the potassium hydride, and disobutylaluminum hydride. recycled catalyst , which showed no severe damage to the 10. The method of claim 1 , wherein the reducing reagent magnetite surface ; no sign of surface agglomeration was 20 is THDB . observed either ( see FIG . 13) . 11. The method of claim 1 , wherein the reducing reagent The disclosure describes a facile synthesis of sub -nano is pressurized hydrogen gas in the range of 2 bars to 100 sized Rh particles supported on superparamagnetic iron bars . oxide nanoparticles (SPIONs , Fe3O4) , for efficient hydro 12. The method of claim 1 , wherein the solvent is a genation and of a series of N -bearing heterocyclic and 25 compound containing the aromatic ring . carbocyclic aromatic compounds under mild experimental 13. The method of claim 1 , wherein the solvent is water, conditions in environmentally friendly solvent such as an alcohol, a carbocyclic aromatic solvent, a polar aprotic water . The results showed that the regioselective reduction polar solvent or a mixture thereof. of quinoline in water was complete in about 10 min . using 14. Themethod of claim 1 , wherein the solvent is a polar THDB as the hydrogen source. The Rh @ Fe304 construct 30 aprotic solvent is selected from the group consisting of was a stable and versatile catalyst in the reduction of other tetrahydrofuran , dioxane, dimethylformamide , acetonitrile , aromatic and heterocycles compounds, such as but not and dimethylacetamide. limited pyridine , pyrazine, indole , nzene , toluene , and 15. A method of hydrogenating an N -heterocyclic aro xylene with hydrogen gas under moderate pressure and matic ring comprising : temperature . Isotopic labelling studies were successfully 35 suspending a catalyst in a solvent selected from the group revealed the source ofhydrogen and the role of THDB in the consisting of water , methanol, ethanol, propanol, iso reaction . The catalyst was shown to possess excellent activ propanol , butanol, a compound comprising the N -het ity towards reduction reaction for 16 consecutive cycles. The erocyclic ring, and a mixture thereof to form a catalyst combination of water as a green solvent and tetrahydroxy mixture , wherein the catalyst consists of superparamag diboron as reducing agent offers an environmentally benign 40 netic iron oxide nanoparticles (SPIONS ) and rhodium synthesis strategy for industrial relevant compounds particle of less than 1 nm deposited on the SPIONS, The invention claimed is : mixing the catalyst mixture with a compound comprising 1. A method of hydrogenating an aromatic ring compris an N -heterocyclic aromatic ring and tetrahydroxydibo ing : ron ( THDB ), and suspending a catalyst in a solvent to form a catalyst 45 heating to a temperature in the range of 40 to 100 ° C. mixture, wherein the catalyst consists of superparamag 16. The method of claim 14 , wherein the solvent is water . netic iron oxide nanoparticles (SPIONs ) and transition 17. The method of claim 15 , wherein the N -aromatic metal particles of less than 1 nm deposited on the heterocycle is selected from pyrrole , pyridine , pyrazol, imi superparamagnetic iron oxide nanoparticles , dazole , triazol , tetrazol, indole , quinoline , isoquinoline, mixing the catalyst mixture with a compound comprising 50 pyrimidine , pyridazine, pyrazine , purine , oxazol, thiazol , an aromatic ring and a reducing agent, and isothiazol, 1,2 - oxazine, 1,3 - oxazine, 1,4 - oxazine, 1,2 - thiaz heating to a temperature in the range of 40 to 200 ° C. ine , 1,3 -thiazine , 1,4 - thiazine , 1,2,3 - triazine, 1,2,4 - triazine , 2. The method of claim 1 , wherein the transition metal and 1,3,5 - triazine . particles are at least one selected from the group consisting 18. A method of hydrogenating a carbocyclic aromatic of rhodium (Rh ), platinum ( Pt) , palladium (Pd ) , ruthenium 55 ring comprising : (Ru ), nickel (Ni ) , copper (Cu ), osmium ( Os ), iridium ( Ir ), suspending a catalyst in a solvent selected from the group rhenium (Re ) , gold ( Au ), and silver ( Ag) . consisting of water , methanol, ethanol, propanol, iso 3. The method of claim 1 , wherein the aromatic ring is a propanol, butanol, a compound comprising the carbo heterocyclic ring or a carbocyclic ring . cyclic aromatic ring, and a mixture thereof to form a 4. The method of claim 1 , wherein the aromatic ring is a 60 catalyst mixture , wherein the catalyst consists ofsuper nitrogen heterocyclic five or six membered ring . paramagnetic iron oxide nanoparticles (SPIONS ) and 5. The method of claim 4 , wherein the nitrogen hetero rhodium particle of less than 1 nm deposited on the cyclic ring is in a compound selected from the group SPIONS, consisting of optionally substituted or unsubstituted pyrrole , mixing the catalyst mixture with a compound comprising pyridine , pyrazol, imidazole , triazol, tetrazol, indole , quino- 65 a carbocyclic aromatic ring and hydrogen gas at a line , isoquinoline , pyrimidine , pyridazine , pyrazine , purine , pressure in the range of 2 bar to 100 bar , and heating to oxazol, thiazol, isothiazol, 1,2 - oxazine , 1,3 -oxazine , 1,4 a temperature in the range of 40 to 100 ° C. US 10,618,878 B1 23 24 19. The method of claim 18 , wherein the solvent is the aromatic compound. 20. The method of claim 19 , wherein the aromatic com pound is selected from benzene, toluene, and xylene . 5