Abstract:
Polarized unsaturated functional groups is directly reduced by using metal amidoborane or derivatives thereof through double hydrogen transfer process. Over 99% conversion of reagents and high isolated yield of products can be achieved after reaction.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to a method of reducing polarized unsaturated functional groups by using metal amidoboranes and their derivatives. 
       BACKGROUND OF THE INVENTION 
       [0002]    Metal amidoboranes and their derivatives are attractive new materials for chemical hydrogen storage. Because of co-exist of hydridic B—H and protic N—H bonds, the materials can release hydrogen below 100° C. without the assistance of catalysis. 
         [0003]    Transfer hydrogenation is a useful method to reduce unsaturated functional group. Hydrogen donor, DH 2 , as a reducing reagent, is utilized in the process. The hydrogens of the donor are nonequivalent and transfer sequentially to unsaturated functional group. Different kind of hydrogen will transfer from hydrogen donor to unsaturated functional group in the reduction process to realize the purpose. 
         [0004]    Ammonia borane (NH 3 BH 3 )has been reported to reduce imines by double hydrogen transfer process. However, the reducing abilities of metal amidoborane compounds have not been studied yet. 
       SUMMARY OF THE INVENTION 
       [0005]    The invention is related to the process of reducing organic compound having polarized unsaturated functional groups by metal amidoboranes and their derivatives, wherein the organic compound having the formula which include R 1 —C(=X 1 )—R 2 , R 3 —C(R 4 )=N—R 5 , R 6 —C≡N, wherein R 1 , R 2 , R 3 , R 4 , R 5 , and R 6  are selected from the group consisting of hydrogen, substituted or unsubsituted alkyl, aryl, amine and alkoxyl groups; X1 is selected from O or S; metal amidoborane has a formula of M(NH 2 BH 3 ) x , wherein x is valence of M, M is at least one metal elements selected from the group 1 to 13 (standard period table, IUPAC system), the metal amidoborane is preferable selected from the group consisting of LiNH 2 BH 3 , NaNH 2 BH 3 , KNH 2 BH 3 , Mg(NH 2 BH 3 ) 2 , Ca(NH 2 BH 3 ) 2 , Sr(NH 2 BH 3 ) 2  and ternary or multinary amidobrane such as Li 2 Mg(NH 2 BH 3 ) 4  etc. The its derivative has a formula of X 2 —nY, wherein X 2  is the metal amidoborane and Y is the ligand such as ammonia borane, NH 3 , THF, etc which can form complex with metal amidoborane or ammonia borane, n is the number of ligand. The derivative is selected from the group consisting of LiNH 2 BH 3 .NH 3 BH 3 , NaNH 2 BH 3 .NH 3 BH 3 , KNH 2 BH 3 .NH 3 BH 3 , RbNH 2 BH 3 .NH 3 BH 3 , CsNH 2 BH 3 .NH 3 BH 3 , Be(NH 2 BH 3 ).NH 3 , Mg(NH 2 BH 3 ).NH 3 , Ca(NH 2 BH 3 ).NH 3 , Sr(NH 2 BH 3 ).NH 3  and Ba(NH 2 BH 3 ).NH 3 . 
         [0006]    Preferably, the derivative is selected from the group consisting of LiNH 2 BH 3 .NH 3 BH 3 , NaNH 2 BH 3 .NH 3 BH 3 , Mg(NH 2 BH 3 ) 2 .NH 3  and Ca(NH 2 BH 3 ) 2 .NH 3  or mixture thereof. 
         [0007]    The organic compound having polarized unsaturated functional groups is R 1 —C(=O)—R 2  or R 3 —C(R 4 )=N—R 5  , wherein R 1  and R 2  are selected from substituted and unsubsituted alkyl, or substituted and unsubsituted aryl; R 4  is selected from the group consisting of hydrogen, substituted and unsubsituted alkyl, substituted and unsubsituted aryl groups; R 3  and R 5  are substituted aryl or unsubsituted aryl. 
         [0008]    When R 1 , R 2 , R 3 , R 4 , R 5  and R 6  are selected from substituted and unsubsituted alkyl, or substituted and unsubsituted alkoxyl, the carbon atoms is less than 10; when R 1 , R2, R 3 , R 4 , R 5  and R 6  are selected from substituted and unsubsituted aryl, the carbon atoms is less than 60. 
         [0009]    Alkyl is selected from the group consisting of methyl, ethyl, propyl, isopropyl, butyl, s-butyl, isobutyl, pentyl, neopentyl, hexyl, heptyl, isoheptyl, 2-ethylhexyl, cyclohexyl and octyl. Alkoxyl is selected from the group consisting of methoxyl, ethoxyl, propoxyl, isopropoxyl, butoxyl, s-butoxyl, isobutoxyl, pentoxyl, neopentoxyl, hexoxyl, heptoxyl, isoheptoxy, 2-ethylhexoxyl, or octoxyl. 
         [0010]    Aryl is selected from phenyl, biphenyl, naphthyl, anthryl, phenanthryl, and heterocyclic compound having aromaticity which is select from furyl, thienyl, pyrryl, oxazolyl, thiazolyl, imidazolyl, pyrazolyl, or pyridyl. 
         [0011]    “substituted” refers to the addition of one or more substituted groups to a compound or functional group. Substituent groups in the invention do not cause the compounds to be unstable or unsuitable for use in an intended reaction and are inert under reaction conditions. 
         [0012]    The substituent groups are selected from the group consisting of alkyl, alkoxyl, halogen, or nitrato. 
         [0013]    Compounds for formula R 1 —C(=O)—R 2  are one or more compounds selected from the group consisting of cyclohexanone, acetophenone 4-methylacetophenone, 4-methoxyacetophenone, 4-nitroacetophenone, benzylacetone, 4-phenyl-3-buten-2-one, benzophenone and 4-chloroacetophenone. 
         [0014]    Compounds for formula R 3 —C(R 4 )=N—R 5  are one or more compounds selected the group consisting of N-benzylideneaniline, N-(4-methylbenzylidene)aniline, 4-methyl-N-benzylidene aniline, N-(4-chlorobenzylidene)aniline, N-(4-methoxybenzylidene)aniline, and N-(4-nitrobenzylidene)aniline. 
         [0015]    The temperature for the invention is in the rang of 20° C. to 60° C. . 
         [0016]    The suitable solvent is needed in the process of the invention, which is selected from the group consisting of THF, glyme, diglyme, triglyme, crown ether, dichloromethane and dioxane. 
         [0017]    The molar ratio of metal amidobrane or derivatives to polarized unsaturated functional group is 1:1 to 1:2. 
         [0018]    The compounds with the formula R 1 —C(=O)—R 2 , to become corresponding secondary alcohol after reaction, and compounds with the formula R 3 —C(R 4 )=N—R 5 , to become corresponding secondary amine in the process. 
         [0019]    Y is the ligand selected from the group consisting of NH 3 BH 3 , NH 3 , pyridine, quadrol, triphenylphosphine or THF. 
         [0020]    Comparing to the traditional boron hydride (such as LiBH 4 ), the metal amidoboranes and their derivatives having positively charged atom of hydrogen and electronegative atom of hydrogen which can transfer to the unsaturated functional group simultaneously in the reaction can avoid the steps of hydrolysis and solvolysis in traditional boron hydride reaction, and can be more convenient than the traditional method. Meanwhile, the metal amidoboranes and their derivatives have more reactivity than other reagent used in double hydrogen transfer reactions. For example, it is reported in the literature that amidoboranes (NH 3 BH 3 ) reducing N-benzylideneaniline (imine) in the reaction with THF as reagent at the temperature of 60° C., the proportion of materials is 1:1, the reaction time is 7 hs, while it takes 2 hs in the reaction of lithium amidoboranes (LiNH 2 BH 3 ) reducing N-benzylideneaniline with proportion of materials being 1:1 at the room temperature, the conversion rate is more than 99%. 
         [0021]    Amidoboranes and their derivatives can reduce unsaturated organic polar functional groups directly by double hydrogen transfer reactions, the conversion of reactants can be over 99% after the reaction, and the product of higher yield can be obtained. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1 . In-situ FTIR for reaction between LiNH3BH3 and benzophenone at room temperature, 
           [0023]      FIG. 2 . In-situ FTIR for reaction between LiNH 3 BH 3  and N-benzylideneaniline at room temperature. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Example 1 
       [0024]    Reducing benzophenone into α-phenylbenzenemethanol with LiNH 2 BH 3  5 ml solution of 0.1 M LiNH 2 BH 3  in THF was slowly added into 1 ml solution of 1 M benzophenone in THF under room temperature in a closed glass bottle. FT—IR spectrometer was used to observe the consumption of carbonyl group and formation of OH group. Stirring the solution and finish the reaction after the reaction was stopped one hour later. Analysis indicated conversion of benzophenone is over more than 99%. THF was evaporated by rotary, then 10 ml hexane was added into the glass bottle to extract residues alcohol formed for two times. Then, clear hexane solution was collected after centrifugation. Next, hexane was removed with the rotary evaporation evaporated to leave rude product. In the end, further column chromotrography was utilized to purify alcohol rude product to obtain the end product. The isolated yield of α-phenylbenzenemethanol is 94%. 
         [0025]    As can be seen from the  FIG. 1  that In-situ FTIR show that during the reaction, absorption of C= 0  stretch vibration at 1664 cm −1  was decreasing accompanied with increasing absorption of OH stretch vibration at 3401 cm −1 during the reaction. 
         [0026]    Characteristic data of product(see  FIG. 1 ):  1 H NMR (500 MHz, CDCl 3 ): δ (ppm) 2.22-2.23 (d, J=3.58 Hz, O—H), 5.73-5.74 (d, J=3.42 Hz, 1H), 7.15-7.30 (m, 10H); 13C NMR (500 MHz, CDCl 3 ) : δ (ppm) 76.29, 126.55, 127.58, 128.50, 143.82; FT—IR (neat): 3259, 1017 cm −1 . 
       Example 2 
       [0027]    Reducing N-benzylideneaniline into N-benzylaniline with LiNH 2 BH 3    
         [0028]    5 ml solution of 0.1 M LiNH 2 BH 3  in THF was slowly added into lml solution of  0 . 5  M N-benzylideneaniline in THF under room temperature in a closed glass bottle. FTIR spectrometer was used to observe the consumption of imine group and formation of amine group. The reaction was stopped two hours later. Analysis indicated conversion of N-benzylideneaniline is over more than 99%. THF was evaporated by rotary, then 10 ml hexane was added into the glass bottle to extract amine formed residues for two times. Then, clear hexane solution was collected after centrifugation. Next, hexane was removed with the rotary evaporation evaporated to leave rude product. In the end, further column chromotrography was utilized to purify rude amine product to obtain the end product. The isolated yield of N-benzylaniline is more than 93%. In-situ FTIR (in  FIG. 2 ) show that during the reaction, absorption of C=N stretch vibration at 1631 cm −1  was decreasing accompanied with increasing absorption of NH stretch vibration at 3369 cm −1 . (see  FIG. 2 ) Characteristic data of product:  1 H NMR (500 MHz, CDCl 3 ): δ≢(ppm) 4.05 (s, N—H), 4.36 (s, 2H), 6.67-6.78 (m, 3H), 7.20-7.42 (m, 7H);  13 C NMR (500 MHz, CDC13): δ (ppm) 48.31, 112.84, 117.55, 127.19, 127.48, 128.60, 129.23, 139.45, 148.15;FT—IR (neat): 3419, 2920, 1602, 1505, 750 cm −1 . 
       Example 3 
       [0029]    Reducing benzophenone into α-phenylbenzenemethanol with Ca(NH 2 BH 3 ) 2    
         [0030]    5 ml solution of 0.1 M Ca(NH 2 BH 3 ) 2  in THF was slowly added into 1 ml solution of  1 M benzophenone in THF under room temperature in a closed glass bottle. FTIR spectrometer was used to observe the consumption of carbonyl group and formation of OH group. The reaction was stopped one hour later. Analysis indicated conversion of benzophenone is more than over 99%. THF was evaporated by rotary, then 10 ml hexane was added into the glass bottle to extract alcohol formed for two times. Then, clear hexane solution was collected after centrifugation. Next, hexane was evaporated to leave rude product. In the end, further column chromotrography was utilized to purify alcohol product. The isolated yield of α-phenylbenzenemethanol is 90%. 
         [0031]    Characteristic data of product:  1 H NMR (500 MHz, CDCl 3 ): δ (ppm) 2.22-2.23 (d, J=3.58 Hz, O—H), 5.73-5.74 (d, J=3.42 Hz, 1H), 7.15-7.30 (m, 10H);  13 C NMR (500 MHz, CDCl 3 ) : δ (ppm) 76.29, 126.55, 127.58, 128.50, 143.82; FT—IR (neat): 3259, 1017 cm −1 . 
       Example 4 
       [0032]    Reducing N-benzylideneaniline into N-benzylaniline with Ca(NH 2 BH 3 ) 2    
         [0033]    5 ml solution of 0.1 M Ca(NH 2 BH 3 ) 2  in THF was slowly added into lml solution of 0.5 M N-benzylideneaniline in THF under room temperature in a closed glass bottle. FTIR spectrometer was used to observe the consumption of imine group and formation of amine group. The reaction was stopped two hours later. Analysis indicated over 99% conversion of N-benzylideneaniline. THF was evaporated, then 10 ml hexane was added into the glass bottle to extract amine formed for two times. Then, clear hexane solution was collected after centrifugation. Next, hexane was evaporated to leave liquid residue. In the end, further column chromotrography was utilized to purify amine product. The isolated yield of N-benzylaniline is 87%. 
         [0034]    Characteristic data of product:  1 H NMR (500 MHz, CDCl 3 ): δ (ppm) 4.05 (s, N—H), 4.36 (s, 2H), 6.67-6.78 (m, 3H), 7.20-7.42 (m, 7H);  13 C NMR (500 MHz, CDCl 3 ): δ (ppm) 48.31, 112.84, 117.55, 127.19, 127.48, 128.60, 129.23, 139.45, 148.15; FT—IR (neat): 3419, 2920, 1602, 1505, 750 cm −1 . 
       Example 5 
       [0035]    Reducing benzophenone into α-phenylbenzenemethanol with LiNH 2 BH 3 .NH 3 BH 3    
         [0036]    5 ml solution of 0.1 M LiNH 2 BH 3 .NH 3 BH 3  in THF was slowly added into lml solution of  1 M benzophenone in THF under room temperature in a closed glass bottle. FTIR spectrometer was used to observe the consumption of carbonyl group and formation of OH group. The reaction was stopped one hour later. Analysis indicated over 99% conversion of benzophenone. THF was evaporated, then 10 ml hexane was added in the glass bottle to extract alcohol formed for two times. Then, clear hexane solution was collected after centrifugation. Next, hexane was evaporated to leave rude product. In the end, further column chromotrography was utilized to purify rude product. The isolated yield of α-phenylbenzenemethanol is 95%. 
         [0037]    Characteristic data of product:  1 H NMR (500 MHz, CDCl 3 ): δ (ppm) 2.22-2.23 (d, J=3.58 Hz, O—H), 5.73-5.74 (d, J=3.42 Hz, 1H), 7.15-7.30 (m, 10H);  13 C NMR (500 MHz, CDCl 3 ) : δ (ppm) 76.29, 126.55, 127.58, 128.50, 143.82; FT—IR (neat): 3259, 1017 cm −1 . 
       Example 6 
       [0038]    Reducing N-benzylidene aniline into N-benzylaniline with LiNH 2 BH 3 .NH 3 BH 3    
         [0039]    5 ml solution of 0.1 M LiNH 2 BH 3 .NH 3 BH 3  in THF was added into 1 ml solution of 0.5 M N-benzylideneaniline in THF under room temperature in a closed glass bottle. FTIR spectrometer was used to observe the consumption of imine group and formation of amine group. The reaction was stopped two hours later. Analysis indicated over 99% conversion of N-benzylideneaniline. THF was evaporated, then 10 ml hexane was added into the glass bottle to extract amine formed for two times. Then, clear hexane solution was collected after centrifugation. Next, hexane was evaporated to leave rude product. In the end, further column chromotrography was utilized to purify rude product. The isolated yield of N-benzylaniline is 93%. 
         [0040]    Characteristic data of product:  1 H NMR (500 MHz, CDCl 3 ): δ (ppm) 4.05 (s, N—H), 4.36 (s, 2H), 6.67-6.78 (m, 3H), 7.20-7.42 (m, 7H);  13 C NMR (500 MHz, CDC13): δ (ppm) 48.31, 112.84, 117.55, 127.19, 127.48, 128.60, 129.23, 139.45, 148.15; FT—IR (neat): 3419, 2920, 1602, 1505, 750 cm −1 .