Organometallics 1996, 14, 80-82
80
Oxidative Carbonylation of Aliphatic Mono-, Di-, and Triamines Catalyzed by Montmorillonite-Bipyridinylpalladium(11) Acetate V. L. K. Valli and Howard Alper* Ottawa-Carleton Chemistry Institute, Department of Chemistry, University of Ottawa, 10 Marie Curie, Ottawa, Ontario, Canada K I N 6N5 Received June 24, 1994@ A simple, efficient, and highly selective non-phosgene route h a s been developed for the preparation of aliphatic, alicyclic, and/or aromatic mono-, di-, and triurethanes from the corresponding amines using montmorillonite-bipyridinylpalladium(I1) acetate (Pd-Clay) in the presence of NaI as a promoter. The catalytic activity of other palladium catalysts was studied and compared with Pd-Clay. The difference in reactivity, as well as the selectivity between the immobilized palladium catalyst, i.e., Pd-Clay, and the homogeneous catalyst systems is accounted for in terms of the position and t h e electronic environment of the metal i n t h e interlayers of the clay system surrounded by t h e surface Bransted acidic sites. The versatility of t h e present catalytic system was demonstrated by the synthesis of commercially important isocyanate precursors, including those of Dytek-A-diurethane and isophorone diurethane.
Introduction
amine^.',^*^ A report by Chaudhari and co-workers showed that palladium on carbon in the presence of NaI Alkyl isocyanates such as methyl N-methyl isocyanate as a promoter can catalyze the conversion of aliphatic have industrial applications in the preparation of variamines to urethanes. The reaction proceeds well for ous insecticides and pesticides.' Also, the major demethylamine, but higher amines gave low conversion mand for aliphatic and/or alicyclic diisocyanates is for to products. Recently, we described the use of a transithe production of polyurethane elastomers. Polyuretion-metal complex immobilized on a smectite clay, Le., thanes based on aromatic diisocyanates turn yellow montmorillonite-bipyridinylpalladiu(I1) acetate (Pdupon exposure to extended sunlight. As a result, alkyl Clay), for the reductive carbonylation of aromatic monodiisocyanates are used almost exclusively in the synand dinitro arenes to the corresponding mono- and thesis of high-performance polyurethane elastomers diurethanes in good to excellent yield^.^ We now wish which require light stability and weatherability. Phosto report the highly selective oxidative carbonylation of gene has been used to prepare isocyanates on a comaliphatic and alicyclic mono-, di-, and triamines to their mercial basis, and less hazardous non-phosgene routes corresponding mono-, di-, and triurethanes using catahave attracted considerable attention in the last two lytic amounts of Pd-Clay, a nitrogen-containing donor d e c a d e ~ . ~One a of the approaches being advanced is to ligand, and NaI added as a promoter. Pd-Clay is first synthesize the urethane, either by oxidative carprepared by anchoring 2,2'-bipyridine in the interlayers bonylation of amine^^-^ or by reductive carbonylation of montmorillonite and subsequent complexation with of nitro compounds in the presence of an a l c ~ h o l , ~ - l ~ Pd(OAc)2.l6 followed by the thermal elimination of alcohol to form isocyanates. Results and Discussion The oxidative carbonylation of aromatic amines to Treatment of aliphatic and/or alicyclic monoamines form arylurethanes can be realized quite easily using with carbon monoxide (70 atm) and oxygen (11atm) in various transition-metal However, the methanol in the presence of catalytic amounts of Pdsynthesis of aliphatic urethanes and, in particular, aliphatic diurethanes by a non-phosgene route is not (7) Leung, T. W.; Dombek, B. D. J. Chem. SOC.,Chem. Commun. as facile due to the reduced reactivity of the aliphatic 1992, 205 and references therein. reactants. As a result, there are few publications in the (8)Giannoccaro, P.; Nobile, C. F.; Mastrorilli, P.; Ravasio, N. J. Organomet. Chem. 1991,419,251. literature on the oxidative carbonylation of aliphatic Abstract published in Advance ACS Abstracts, October 15, 1994. (1) Kelkar, A. A.; Kohle, D. S.; Kanagasabhapathy, S.; Chaudhari, R. V. Ind. Eng. Chem. Res. 1992,31, 172. (2) Senekar, S. D.; Rosthauser, J. W.; Markusch, P. H. 34th Annual Polyurethane TechnicallMarketing Conference; Oct 21-24,1992; p 588. (3) Cenini, S.; Pizzotti, M.; Crotti, C.; In Aspects of Homogeneous Catalysis; Ugo, R., Ed.; Reidel: Dordrecht, The Netherlands, 1988; Vol. 6, p 97. (4) Fukuoka, S.; Chono, M.; Khono, M. CHEMTECH 1984,670. (5) Alper, H.; Hartstock, F. W. J. Chem. Soc., Chem. Commun. 1985, 1141. (6) Benedini, F.; Nali, M.; Rindone, B.; Tollari, S.; Cenini, S.; La, G. M.; Porta, F. J. Mol. Catal. 1986, 34, 155. @
(9)Valli, V. L. K.; Alper, H. J. Am. Chem. SOC.1993,115, 3778. (10) Gargulak, J. D.; Berry, A. J.; Noirot, M. D.; Gladfelter, W. L. J . Am. Chem. SOC.1992,114,8933. (11) Gargulak, J. D.; Noirot, M. D.; Gladfelter, W. L.; J.Am. Chem. SOC.1991, 113, 1054. (12) Cenini, S.; Ragaini, F.; Pizzotti, M.; Porta, F.; Mestroni, G.; Alessio, E. J. Mol. Catal. 1991, 64, 179. (13) Bhaduri, S.; U. S. Patent 4,491,670, 1985. (14) Cenini, S.; Pizzotti, M.; Crotti, C.; Porta, F. J . Org. Chem. 1988, 53, 1243. (15) Balabanov, G. P.; Dergunov, Y. I.; Khoshdurdyev, K. 0.;Manov-
Yu-Vunskii, V. I.; Neredov, B. K ; Rysikhin, A. I. US. Patent4,207,212, 1980. (16) Choudary, B. M.; Bharati, P. J. Chem. SOC.,Chem. Commun. 1987, 1505.
0276-7333/95/2314-0080~09.00/0 0 1995 American Chemical Society
Carbonylation of Mono-, Di-, and Triamines
_
Organometallics, Vol. 14,No. I , 1995 81
Table 1. Effect of NaI on the Carbonylation of n-Hexvlamine Catalvzed bv Pd-Clav~ with 23’-b~v“ _ _ ~ ~ yield (%) by NMR
Table 2. Comparison of Various Palladium Catalysts for the Carbonylation of n-Hexylamind
~
yield (%) by NMR
expt no.
substrate:NaI
conversion (%)
urethane
urea
expt no.
catalyst
conversion
urethane
urea
1 2 3 4 5 6
no NaIb 1:l 3: 1 5: 1 1O:l 5:Id
100 72 100 100 100 100
80 68 91 99c 75 50
20 4 9 traces 25 50
1 2 3 4 5 6 7
Pd(PPhs)4 Pd(PPh3)4’ Pd(OAc)zC PdC Pd-Clay Pd-Clayd Pd-Clayb
100 89 52 94 100 100 100
78 12 0 73 85 50 80
22 77 12 11 traces 50 20
Reaction conditions for expt 4: substrate (2 mmol), Pd-Clay (20 mg, 0.004 mmol), 2,2’-bpy (16 mg, 0.1 mmol), NaI (60mg, 0.4 mmol), methanol
(6 mL), CO/Oz (70/11 am), 210 “C, 8 h. Ratio of substrate to NaI changes as indicated above. Carried out for 36 h. Isolated yield. Carried out without 2,2’-bpy.
For reaction conditions, see footnote a of Table 1, the amount of Pd catalyst being 0.004 ”01. Without NaI. Catalyst decomposed. Without 2,y-b~~.
Table 3. Oxidative Carbonylation of Mono-, Di-, and Triamines Catalyzed by Pd-Clay, 2,2’-bps, and NaP
Clay, NaI as promoter, and a nitrogen donor ligand, 2,2’bipyridine, a t 210 “C for 6-12 h afforded the corresponding urethanes in 62-91% isolated yield (eq 1).
yield (a)by NMR (isolated) expt
RNH,
+ CO + 1/202 + MeOH
Pd-Clay, bpy, NaI 210 oc,
RNHC0,Me
,.
+ H20 (1)
The reaction is highly selective, and only trace amounts of ureas were obtained as byproducts. However, the formation of urea is dependent on the amount of NaI used as a promoter. The best ratio of substrate to NaI is 51. In the presence of more NaI, i.e., using a substrate to NaI ratio of 3:1, the results were comparable to the 5:l ratio of substrate to NaI. However, when the ratio of the substrate to NaI was l O : l , the selectivity toward urethanes was inferior, affording 75% urethane and 25% urea when n-hexylamine was used as the substrate. This result can be compared with the control experiment performed in the absence of NaI. Using n-hexylamine as a model reactant, a control experimental run without NaI afforded complete conversion t o give 80% urethane and 20% urea. Although the conversion of n-hexylamine was 100%in the absence of 2,2’-bipyridine, virtually no selectivity was observed with urethane to urea formed in a 1:l ratio (Table 1). Thus, the nitrogen donor, i.e., 2,2’-bipyridine, and the amount of NaI play important roles in the selectivity of the reaction. Use of a monodentate nitrogen donor requires longer reaction time for complete conversion and gave poor selectivities. Thus, using N-methylpyrrolidine as a donor, carbonylation of n-hexylamine required 18 h, affording 69% of the corresponding urethane and 31%urea, while 1,lO-phenanthroline can be used instead of 2,2’-bipyridine, affording 82% urethane and 18%urea when n-hexylamine is the model substrate. The use of Pd(PPh)r in place of Pd-Clay afforded complete conversion with slightly inferior selectivities (78% urethane, 22% urea) compared with the clay system. In the absence of NaI, Pd(PPh)r gave poor selectivity toward urethane (12%)formation, with ureas obtained as the major compounds. Other palladium catalysts, for example Pd/C, gave a result comparable to that for Pd(PPh)r. However, when homogeneous Pd(0Ac)n was used instead of Pd-Clay, decomposition of Pd(OAc)2 was observed, resulting in poor yields (12%) of ureas, and no urethane was obtained in the case of n-hexylamine a s the starting amine (Table 2). The method reported herein shows excellent selectivity for the formation of aliphatic and alicyclic diure-
amine
urethane
urea
1 2 3 4 5 6 7 8 9 10
85 (83) 2-3 (traces) n-C6H13NH2 91 (81) 6 (traces) n-ClZH25h% ieC3H7NH2 79 (62) 20 (18) cyclo-CsH11NH2 99 (91) 89 (72) HzN(CHz)sNHz H~NCHZ(CH~)CH(CH~)~NH~’ 100 (88) HzNCHz(CH3)CH(CH2)3NHzc 100 (94) HZNCHZ(CH~)CH(CH~)~NH~~ 91 l,4-(NH2)2-cyclo-cd-Ilo 32 l-NHz-3-CHzNH2-3,5,5100 (96) (CH3)-CyClO-C6H7 11 1,3-(NHz)z-4-CH&jH3 98 (69) 12 HzNCH(CH~)CHZ[OCHZCH(CH~)],NHZ~ quantitative 13 H2NCH(CH3)CH2[0CH2CH(CH3)1,” quantitative CH3
I
CH3
I
H2CO[CH2CHO],&H2CHNH2
14
I
quantitative
HCO[CH~CHO]PH~CHNHZ
I
I
LH3 CH3 H2CO[CH2CHO]&H&HNH2
I
CH3
I
CH3
For reaction conditions, see footnote a of Table 1. The amounts of catalyst, promoter, donor, and solvent are double and triple in case of diand triamines, respectively. Reaction time for di- and triamines is 18 h. Dytek-A. Pd-Clay, 2,2’-bpy, NaI, EtOH. Pd(PPh3)4, 2,2’-bpy, NaI. e Jeffamine-D-400,x = 5-6. fJeffamine-D-2000, y = 33 (av). g JeffamineT-5000, x y z = 83.
+ +
thanes directly by the carbonylation of the corresponding diamines (eq 2). H2N-ONH,
+
2CO
+
O2
+
2MeOH
p d ~ ~ ~ ~ c B ~ ~ h N k
MeO,CNH0NHCO2Ms
+
2H20 (2)
To our knowledge, there are no efficient catalysts described in the literature for the preparation of diurethane precursors of isophorone diisocyanate (IPDI) and Dytek-A-diisocyanate (DDI) by direct oxidative carbonylation methods. A method reported by Leung and Dombek claimed 73% selectivity toward the IPDI precursor using complex metallamacrocycliccompounds as catalysts.7 A series of diamines was subjected to carbonylation in the same manner as for n-hexylamine to give diurethanes in good to excellent yields (Table 3). Of particular note are the preparation of the diurethane precursors to isophorone diisocyanate (IPDI), Dytek-A-diisocyanate (DDI), and 2,4-toluene diisocyanate (TDI). Diand triamines of Jeffamine 400, 2000, and T-5000 (Jeffamines are poly(propy1eneoxy) amines) were also
Valli and Alper
82 Organometallics, Vol. 14,No. 1, 1995 carbonylated efficiently, affording the corresponding diand triurethanes in quantitative yields. Attempts to prepare trans,truns-( 1,4-cyclohexanediyl)diurethane(convertible to trczns,trans-CDI) resulted in complete conversion of the starting material, but the yield of the diurethane was moderate, with the balance of the product being an uncharacterized polymer. The recycling capacity of Pd-Clay was examined for the carbonylation of n-hexylamine. It was found that Pd-Clay is active for u p to three cycles, affording 68% conversion in the third run. Addition of 2,2'-bipyridine and NaI is necessary in each run. However, the selectivity toward the formation of urethane was unchanged, affording 55% urethane (81% selectivity). After the third cycle, no considerable amount of conversion was noticed, indicating the loss of activity. Use of a high reaction temperature and pressure might have caused the gradual leaching of the palladium metal from the interlayers of the clay. It is conceivable that, in these reactions, the surface Bransted and Lewis acidities of the smectite clay can promote carbon monoxide insertion to generate the intermediate species RNHZ+(CO)MHLn, bound to the silicate sheets of montmorillonite, which in turn can react with alcohol to give urethanes. The superior selectivity of Pd-Clay over other palladium catalysts could be due to the change in electronic environment around the palladium in the clay interlayers. ESCA studies reported on Pd-Clay indicated that palladium is present as a divalent palladium species in the interlayers of clay.16 However, the corresponding homogeneous Pd(OAc)s afforded only ureas as t h e major products under the same experimental conditions. This confirms the difference in electronic environment around palladium in Pd-Clay. Also, the presence of surface Bransted and Lewis acidic centers in the smectite clay can enhance the polarization of carbon monoxide and result in a more selective r e a ~ t i 0 n . l ~
Conclusion A simple, efficient, and highly selective non-phosgene route was developed for the preparation of-&pWkand/ or alicyclic mono-, di-, and triurethanes from the corresponding amines in good to excellent yields. This methodology, coupled with the recently developed conversion of urethanes to isocyanates by using chlorocatecholborane18 constitutes an attractive route for the preparation of commercially important isocyanates from amines by carbonylation.
Experimental Section General Considerations. The following spectrometers were used to obtain spectral data: Bomem MB100-Cl5 (FTIR), Varian XL-300 and/or Gemini 200 (NMR),and VG 7070E (MS). X-ray basal spacings of Pd-Clay were determined with a Philips PW 3710 based analytical difiactometer using Nifiltered Cu Ka radiation. Pd-Clay was synthesized by a known method,16 and the d(oo1) expansion of Pd-Clay was determined to be 5.3 A . Organic solvents were dried and distilled prior to use. General Procedure for the Pd-Clay-Catalyzed Oxidative Carbonylationof Amines. A mixture of the substrate (2 mmol), Pd-Clay(20 mg, contains 0.004 mmol of Pd), 2 3 (17) Pinnavaia, T. J.; Raythatha, R.; Lee, J. G. S.; Hollaran, L. J.; Hoffman, J. F. J.Am. Chem. SOC.1979,101, 6891. (18)Valli, V. L. K.; Alper, H. J. Org. Chem., in press.
bipyridine (16 mg, 0.1 mmol),NaI (60 mg, 0.4 mmol), and dry methanol (6 mL) was charged in a 30 mL autoclave. The autoclave was flushed with carbon monoxide, pressurized t o 70 atm, and then carefully pressurized with 11atm of oxygen. (Caution! Reverse addition, i.e., 0 2 before CO, is dangerous.) The autoclave was transferred to a preheated oil bath at 210 "C and stirred for 6-18 h. The reaction mixture was cooled to room temperature, filtered through neutral alumina, and then concentrated by rotary evaporation. The crude material was washed with pentane and further purified by column chromatography (neutral alumina, eluant 9:1pentane/chloroform). Di- and triamines were also reacted in a similar procedure using amounts of catalyst and NaI proportional to the number of amine groups(e.g.,in the case of Dytek-A, double the amount of catalyst, promoter and solvents were used compared t o the case for n-hexylamine). Preparation of n-Hexylmethylurethane Using Pd(PPh)4, 2,8'-Bipyridine,and NaI. A mixture of n-hexylamine (2 mmol), Pd(PPh)r(4.6 mg, 0.004 mmol), 2,Y-bipyridine (16 mg, 0.1 mmol), and dry methanol (6 mL) was charged in a 30 mL autoclave. The autoclave was flushed with carbon monoxide, pressurized to 70 atm, and then pressurized with 11 atm of oxygen. The autoclave was transferred to a preheated oil bath at 210 "C and stirred for 6 h. The reaction mixture was cooled t o room temperature, filtered through neutral alumina, and then concentrated by rotary evaporation. Urea was separated as a solid material from the reaction mixture and was isolated by filtration. The crude n-hexylmethylurethane was purified by column chromatography (neutral alumina, with 9:1pentane/chloroformas the eluant). The isolated yield of urethane was 78%. IR v(C0) 1718 cm-l. lH NMR (CDCl3): 6 0.80 (t,3H, CH3), 1.25 (m, 6H, CHd, 1.48 (m, 2H, CHz), 3.11 (9, 2H, CHz), 3.60 (8, 3H, OCH3), 4.72 (br, lH, NH). 13CNMR (CDC13): 6 12.9,21.5,25.3,28.9,30.4,40.1, 51.3, 156.8; MS ( d e ) : 159 (M+). The same procedure was followed for other palladiumcatalyzed carbonylation reactions using 0.004 mmol of the respective palladium catalyst. The urethanes 1-11 (Table 3) were characterized by comparisonwith literature data.4-12J9-26 The following urethanes are new. 12, Jeffamine-D4OO methyl diurethane: IR v(C0) 1712 cm-l; 'H NMR (CDC13)6 1.12 (d, CH3), 2.31 (m, CH), 3.48 (m, OCH), 3.75 (s, OCH3), 5.18 (br, NH),5.52 (br, NH); 13CNMR (CDC13) 6 51.68 (OCH3), 156.52 (carbonyl). 13,Jeffamine-D-2000methyl diurethane: IR v(C0) 1714 cm-'; 'H NMR (CDC13)6 1.12 (d, CH3), 2.32 (m, CHI, 3.48 (m, OCH), 3.78 ( 8 , OCH3), 5.20 (br, NH),5.49 (br, NH); 13C NMR (CDCl3) 6 51.64 (OCH3), 156.60 (carbonyl). 14,Jeffamine-T-5000methyl triurethane: IR v(C0) 1720 cm-l; lH NMR (CDCl3) 6 1.19 (6, CH3), 2.34 (m, CHI, 3.49 (m, OCH), 3.62 (m, OCH3), 5.32 (br, NH), 5.50 (br, NH);13C NMR (CDCls) 6 51.70 (OCH3), 55.07 (OCH3), 155.20 (carbonyl), 156.48 (carbonyl).
Acknowledgment. We are indebted to the Institute for Chemical Science and Technology and the University Research Incentive Fund for financial support of this research. We are grateful to DuPont, Dow Chemical Canada Inc., and Texaco for providing samples of Dytek A and Jeffamines. OM9404947 (19) Merger, F.; Nestler, G.; Towae, F.; Hellbach, H.; Eur. Pat. Appl. E P 100 047; Chem. Abstr. 1984,100,157138g. (20) Disteldorf, J.; Huebel, W.; Reiffer, J. Eur. Pat. Appl. E P 106 138; Chem. Abstr. 1984,101, 170702b. (21) Disteldorf, J.; Huebel, W.; Wolf, E. Ger. Offen. DE 3 151 855; Chem. Abstr. 1983,99, 176959~. (22) Burgess, E. M.; Penton, H. R., Jr.; Taylor, E. A.; Williams, W. M. Org. Synth. 1973,53,1857. (23) Zhou, X.; Huang, Z. Synth. Commun. 1989,19, 1347. (24) Alper, H.; Vasapollo, G.; Hartstock, F. W.; Mlekuz, M.; Smith, D. J. H.; Morris, G. E.; Organometallics 1987,6, 2391. (25) Wallace, G. C.; Zerba, E. N. Pestic. Sci. 1989,26, 215. (26) Crosby, J.; Paton, R. M.; Rennie, R. A. C. Ger. Offen. DE 2 336 403; Chem. Abstr. 1974,81, 49257a.
