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Palladium-catalyzed carboxylation of allyl stannanes and carboxylative coupling of allyl stannanes and allyl halides
T. Inui, M. Anpo, K. Izui, S. Yanagida, T. Yamaguchi (Editors) Advances in Chemical Conversions for Mitigating Carbon Dioxide
165
Studies in Surface Science and Catalysis, Vol. 114 9 1998 Elsevier Science B.V. All rights reserved.
Palladium-catalyzed carboxylation of allyl stannanes and carboxylative coupling of allyl stannanes and allyl halides Min Shi, Russell Franks and Kenneth M. Nicholas* Department of Chemistry and Biochemistry, University of Oklahoma, Norman, OK, 73019 U.S.A. Abstract. The reaction of allyl stannanes with CO 2 to form stannyl carboxylates (esters) is catalyzed by Pd(PR3) 4 complexes.
Thus, R 3 S n C H 2 C H = C H 2 [R-Me and Ph] are converted to
R3SnO2CCH2CH=CH 2 and R3SnO2CCH=CHCH 3 under 33 atm of CO 2 (70 ~ THF) in moderate to excellent yield in the presence of 8 mol% Pd(PPh3)4; polycarboxylation of diallyldibutyltin and tetraallyltin
also
is effected,
producing
the respective
di-
and
tetracarboxylates,
Bu2Sn(O2CCH2CH=CH2) 2 and Sn(O2CCH2CH=CH2) 4, along with the corresponding isomeric crotyl derivatives. In the presence of allyl halides, allyl stannanes and CO 2 undergo carboxylative coupling to produce allyl esters. Under these conditions other Sn-C (Sn-alkyl, -awl, -vinyl) and Si-C (Si-allyl, -alkyl, -aryl, -vinyl) bonds are inert to carboxylation and carboxylative coupling with allyl halides. A tentative mechanism is proposed to account for this catalytic carboxylation of a main group metal-carbon bond.
Introduction The world's dwindling petroleum reserves and increasing atmospheric concentrations of carbon dioxide have stimulated considerable interest in the capture and chemical conversion of carbon dioxide. Among several approaches being examined towards this objective is the activation of carbon dioxide by transition metal complexes. 1 Reactions of CO2 which result in carbon-carbon bond formation are especially synthetically attractive, e.g. the classic carboxylation of Grignard reagents. Indeed, insertions of CO2 into the metal-carbon bonds of electropositive main group metals 1b,2 and many transition metals 1 are common but corresponding reactions with less polar organometaUics, though still thermodynamically favorable, 3 are rarer. Promoting such transformations would be highly desirable since the resulting metal carboxylates should be more amenable to subsequent transformation of the weaker M-O bond, enhancing the prospects for catalytic conversions to organic products. We report here the first examples of transition metal catalyzed insertion of CO2 into otherwise unreactive tin-carbon bonds and a catalytic coupling reaction between allylstannanes and allyl halides.
166 Results
and D i s c u s s i o n
Although allyltributyltin does not react with CO2 in THF even at 70 ~ and 33 atm (24 hr), under the same conditions in the presence of 8 mol % Pd(PPh3) 4 or Pd(PPh3)2C12/PPh 3 this stannane is quantitatively converted to the isomeric tin esters (eq. 1).4,5 Under the same carboxylation conditions a 30% conversion of allyltriphenyltin to isomeric insertion products (7:3) was found. Surprisingly, crotyltributyltin failed to undergo carboxylation entirely. 9, R,Sn.CH2.CH=CHR,
CO 2 (30 a t m ) .__ pd(PPh3)4 o r ~
RsSn-O-C-CH2-CH=CHR'
+
I R3Sn-O-C-CH=CH-CH2R'
(R=Bu, R'=H)
Pd(PPhs)2CI2/PPh 3
(90 %)
(R=Bu, R'=H)
(10 %)
(R=Ph, R'=H)
THF, 70 ~
(70 %)
(R=Ph, R'=H)
(30 %)
24 h
(R=Bu, R'=Me)
no reaction
(R=Bu, R'=Me)
Multiple carboxylation of poly(allyl)stannanes also can be effected with Pd(0) catalysis. Thus, diallyldibutyltin reacted completely with CO 2 under the standard conditions to afford dicarboxylates (overall yield >90%). In the Pd-catalyzed reaction of tetraallyltin with CO 2 a complex mixture of
Bu2Sn(CH2-CH=CH2)2
co,
>
~
Bu2Sn(O-C-CH2-CH=CH2)2
Pd(PPh3)4, THF, 70 oC, 24 h
+
f'
Bu2Sn(O-C-CH=CH-CH3) 2
( 2.2 : 1 )
? [ Bu2(CH2=CHCH2)SnOCCH2CH=CH,]
O-C-CH2-CH=CH2 I 0
Sn(CH2-CH=CH2)4
C02
-~
(i) Sn(O-C-CH2-CH=CH2) 4
Oi Sn(O-C-CH=CH-CH3) 4
Pd(PPh3)4, THF, 70 ~ 72 h
Sn(O-C-CH2-CH=CH2)4.~O.C-CH=CH-CH3)n
(n=l, 2, 3, 4)
carboxylates (allyl)4_nSn(O2C-allyl) n (n=l-4) was produced after 24 hr. However, if the reaction time was extended to 72 h, the major products (ca. 80 % yield) were the isomeric tetracarboxylates, i.e. all four Sn-allyl bonds had inserted CO2. Under these conditions double bond isomerization products dominated ca. 4:1. Of the various stannanes tested thus far only those possessing allyl-tin bonds were found to undergo carboxylation. Thus, tetrabutyltin, tetraphenyltin, vinyltributyltin, and benzyltributyltin each
167 were recovered unchanged after contact with CO2/Pd(PPh3) 4 under the previous conditions. The failure of the crotyl- and benzyl-tin derivatives to react with CO 2 and the diminished reactivity of allyltriphenyltin suggests that a specific Pd-allyl interaction may play an important role in catalysis. The allyl silanes aUyltrimethylsilane, allyltriphenylsilane, and allyltrimethoxysilane also did not react. These observed structure/reactivity features in combination with the established reactivity of Pdallyl complexes with CO26 lead us to propose Scheme 1 as a tentative catalytic mechanism: Scheme 1
stannaneactivation/f----'~ ~
~-~
PPh3/Pd~SnR3
"~
• ' •~'snR3 Pd(PPh3)2
(PPh3)2Pd-- SnR3
coJ R3Sn
17~
Pd(PPh3)n
~ , ~ . . ~
(PPh3)2Pd"1~: 0"~ Sn
(PPh3)2Pd-- SnR3 Pd(PPh3)n +
C02
C02 activation
_
~_] R3Sn
",--- (PPha)2Pd :'? "C~0
i) oxidative addition of allylstannane to Pd(0)L n gives rl 3- and 1"11-allyl palladium complexes; ii) insertion of CO2 into the 111-allyl palladium bond (or the Pd-Sn bond); and iii) reductive elimination of the carboxylate and organotin groups to give the product and regenerate Pd(0). The sensitivity of the reaction to substitution on or adjacent to the Sn-allyl unit suggests that an initial rl2-complex may precede the oxidative addition step but no indication of complexation of the allyl stannane by Pd(PPh3) 4 was provided by 1H NMR analysis. Although transmetalation from Sn to Pd(II) 7 and the
168 activation of allyl electrophiles (e.g. halides, carbonates) by Pd(0) complexes 8 are both well documented, Pd(0) activation of aUyl tin reagents has little precedent. 9 However, the viability of an (rl3-allyl)Pd(stannyl) intermediate is supported by formation of a Pt analog in the reaction of Pt(ethylene)2(PPh3) with (allyl)SnMe3 .10 The possibility of CO 2 insertion into the Pd-C bond of the latter is bolstered by prior examples of CO 2 insertion reactions of ri 1_ and rl3-allyl-Pd complexes. 6 Since neither starting material nor product isomerization occurs under the reaction conditions (op cit), isomerization of the intermediate CO 2 inserted species apparently occurs prior to product release. 11 An alternative mechanistic pathway involving reaction of an intermediate Pd(rl2-CO2) complex 12 with the allyl stannane cannot be excluded at this time. However, IR spectra of Pd(PPh3)4/CO 2 solutions (1 atm, THF) showed no absorptions in the 1625-1700 cm- 1 region expected for such a species. We have also begun to investigate the possibilites for modifying the stannane carboxylation to produce wholly organic products. Bond energy considerations suggested that metathesis of the tin carboxylate with an alkyl halide might be possible. Although no reaction was observed betweeen the tin carboxylate and 2-methallyl chloride (65 ~ THF), in the presence of Pd(PPh3) 4 under the same conditions, clean conversion to the corresponding allyl ester (below) was observed. Moreover, combined reaction of allylSnBu 3, CO 2 and methallyl chloride in the presence of Pd(0) or Pd(II) complexes produced a mixture of organic esters (below) in moderate (unoptimized) yield. A major component was that expected from allyl-Sn carboxylation followed by metathesis with the allylic halide; a second major product, however, appears to be derived from initial carboxylation of the methallyl chloride. c..3 + 0
co= Bu3Sn~,~
BuaSnCI
Pd(PPha)4 THF, 65 ~ 12 h
+
~
Cl
.tm)
Pd(PPh3)4 or Pd(PPha)2CI2/PPh3 THF, 70 ~ 24 h
+
Bu3SnCl
U ( 50 % isolated yield )
As in the direct stannane carboxylation the carboxylative coupling is thus far limited to allyl stannanes; RSnBu 3 with R = PhCH 2, Ph, vinyl, PhC-C- all fail to react. The structure of the
169 isomeric ester (propenyl 3-methyl-3-butenoate) and existing precedents for the formation of allyl-Pd species 8 and their insertion reactions with CO2 6 suggest the involvement of a second pathway. involving initial carboxylation of the aUyl halide (Scheme 2). Scheme 2
I C'l
cl~Pd~ppha
co2
R3Sn"~'~
~,~pph P~snR3 ~ Pd(PPh3)n
o3-.A I
(PPh3)2Pd--Cl RzSn,/",,~
]
I
O ) CO2 I
(PPh3)2Pd~SnR3
~,~
C.H3
-vc,
In conclusion we have reported on two new reactions relevant to the goal of carbon dioxide utilization. In the first, Pd complexes catalyze the net insertion of CO 2 into otherwise unreactive Snallyl bonds. The product organotin carboxylates, especially diorganotin esters, have a wide range of commercial applications. 13 In the second reaction the same Pd complexes catalyze the coupling of allyl stannane, allyl halide and CO 2 to produce allyl esters. Efforts are underway to further elucidate the mechanistic details of these reactions and to extend their scope to include a range of organometals and organic halides. Acknowledgments. We are grateful for financial support provided by the U.S. Department of Energy, Office of Basic Energy Sciences.
170 References.
1)
2) 3)
a) Behr, A. "Carbon Dioxide Activation by Metal Complexes", VCH publ., Weinheim, Germany, 1988; b) Ito, T.; Yamamoto, A. "Organometallic Reactions of Carbon Dioxide", chap. 3 of Organic and Bio-organic Chemistry of Carbon Dioxide, Inoue, S.; Yamazaki, N., ed. Kodansha Ltd., Tokyo, Japan, 1982; c) Gibson, D.H. Chem. Rev. 1996, 96, 2063. Sanderson, R.T.J. Am. Chem. Soc. 1955, 77, 4531. Bond enthalpy considerations for M-CR 3 + CO 2 ---> M-OC(=O)-CR 3 indicate an exothermic
4)
C bond and a C-C c-bond is formed at the expense of a comparably strong C-O re-bond. The following procedure is representative. Allyltributyltin (0.33 g, 1.0 mmol), Pd(Ph3P) 4
process for virtually all metals since a strong M-O bond is formed at the expense of a weaker M-
(0.093 g, 0.08 mmol), 20 mL of dry THF, and a magnetic stir bar were placed in the 50 mL glass liner of a stainless steel autoclave under a nitrogen purge. After the autoclave was purged several times with CO 2, it was pressurized with CO 2 (33 atm), sealed, and heated at 70 ~ for
5) 6)
7) 8) 9)
24 h with stirring. After cooling and release of the pressure, the solvent was removed under reduced pressure and the residue was passed through a short column of flash silica (1:1 ethyl acetateJhexane) to afford a spectroscopically pure mixture of the tin carboxylates. A preliminary report of this study has appeared recently: Shi, M.; Nicholas, K.M.J. Am. Chem. Soc. 1997, 119, 5057. a) ref. la, p. 54-60; b) Ito, T.; Kindaichi, Y.; Takami, Y. Chem. Ind (London), 1980, 19, 83; c) Hung, T.; Jolly, P.W.; Wilke, G. J. Organomet. Chem. 1980, 190, C5; d) Santi, R.; Marchi, M. J. Organomet. Chem. 1979, 182, 117; e) ref. la, p. 56; f) Behr, A.; Ilsemann, G. v.; Keim, W.; Kruger, C.; Tsay, Y.-H. Organometallics, 1986, 5, 514; g) Behr, A.; Ilsemann, G. j. Organomet. Chem. 1984, 276, C77. Stille, J.K. Angew. Chem. Int. Ed. Eng. 1986, 25, 508. Trost, B.M. Acc. Chem. Res. 1980, 13, 385; Tsuji, J. Pure Appl. Chem. 1982, 54, 197. Catalysis of allyl-Sn additions to aldehydes by Pd(II)L2C12 complexes recently has been
reported; one, less efficient example using Pd(PPh3) 4 was included. Nakamura, H.; Iwama, H.; Yamamoto, Y. J. Am. Chem. Soc. 1996, 118, 6641. 10) Christofides, A.; Ciriano, M.; Spencer, J.L.; Stone, F.G.A.J. Organomet. Chem. 1979, 178, 273. 11) Extensive double bond isomerization has been found in the reactions of (rl3-allyl)Pd complexes with CO2; ref. 6 c-f. 12) Sakamoto, M.; Shimizu, I.; Yamamoto, A. Organometallics, 1994, 13, 407. 13) Kirk-Othmer Concise Encyclopedia of Chemical Technology, Grayson, M. and Eckroth, D. eds., 1985, Wiley, NY, pp. 1179-1181; Sijpesteijn, A. K.; Luijten, J. G. A.; van der kerk, G. J. M. in Fungicides, An Advanced Treatise, Torgeson, D. C., ed., Academic Press, New York, 1969, Vol. 2, p. 331; Evans, C. J. Tin and Its Uses, 1976, 110, 6; van der kerk, G. J. M.; Luijten, J. G. A. J. Appl. Chem. 1954, 4, 31.
165
Studies in Surface Science and Catalysis, Vol. 114 9 1998 Elsevier Science B.V. All rights reserved.
Palladium-catalyzed carboxylation of allyl stannanes and carboxylative coupling of allyl stannanes and allyl halides Min Shi, Russell Franks and Kenneth M. Nicholas* Department of Chemistry and Biochemistry, University of Oklahoma, Norman, OK, 73019 U.S.A. Abstract. The reaction of allyl stannanes with CO 2 to form stannyl carboxylates (esters) is catalyzed by Pd(PR3) 4 complexes.
Thus, R 3 S n C H 2 C H = C H 2 [R-Me and Ph] are converted to
R3SnO2CCH2CH=CH 2 and R3SnO2CCH=CHCH 3 under 33 atm of CO 2 (70 ~ THF) in moderate to excellent yield in the presence of 8 mol% Pd(PPh3)4; polycarboxylation of diallyldibutyltin and tetraallyltin
also
is effected,
producing
the respective
di-
and
tetracarboxylates,
Bu2Sn(O2CCH2CH=CH2) 2 and Sn(O2CCH2CH=CH2) 4, along with the corresponding isomeric crotyl derivatives. In the presence of allyl halides, allyl stannanes and CO 2 undergo carboxylative coupling to produce allyl esters. Under these conditions other Sn-C (Sn-alkyl, -awl, -vinyl) and Si-C (Si-allyl, -alkyl, -aryl, -vinyl) bonds are inert to carboxylation and carboxylative coupling with allyl halides. A tentative mechanism is proposed to account for this catalytic carboxylation of a main group metal-carbon bond.
Introduction The world's dwindling petroleum reserves and increasing atmospheric concentrations of carbon dioxide have stimulated considerable interest in the capture and chemical conversion of carbon dioxide. Among several approaches being examined towards this objective is the activation of carbon dioxide by transition metal complexes. 1 Reactions of CO2 which result in carbon-carbon bond formation are especially synthetically attractive, e.g. the classic carboxylation of Grignard reagents. Indeed, insertions of CO2 into the metal-carbon bonds of electropositive main group metals 1b,2 and many transition metals 1 are common but corresponding reactions with less polar organometaUics, though still thermodynamically favorable, 3 are rarer. Promoting such transformations would be highly desirable since the resulting metal carboxylates should be more amenable to subsequent transformation of the weaker M-O bond, enhancing the prospects for catalytic conversions to organic products. We report here the first examples of transition metal catalyzed insertion of CO2 into otherwise unreactive tin-carbon bonds and a catalytic coupling reaction between allylstannanes and allyl halides.
166 Results
and D i s c u s s i o n
Although allyltributyltin does not react with CO2 in THF even at 70 ~ and 33 atm (24 hr), under the same conditions in the presence of 8 mol % Pd(PPh3) 4 or Pd(PPh3)2C12/PPh 3 this stannane is quantitatively converted to the isomeric tin esters (eq. 1).4,5 Under the same carboxylation conditions a 30% conversion of allyltriphenyltin to isomeric insertion products (7:3) was found. Surprisingly, crotyltributyltin failed to undergo carboxylation entirely. 9, R,Sn.CH2.CH=CHR,
CO 2 (30 a t m ) .__ pd(PPh3)4 o r ~
RsSn-O-C-CH2-CH=CHR'
+
I R3Sn-O-C-CH=CH-CH2R'
(R=Bu, R'=H)
Pd(PPhs)2CI2/PPh 3
(90 %)
(R=Bu, R'=H)
(10 %)
(R=Ph, R'=H)
THF, 70 ~
(70 %)
(R=Ph, R'=H)
(30 %)
24 h
(R=Bu, R'=Me)
no reaction
(R=Bu, R'=Me)
Multiple carboxylation of poly(allyl)stannanes also can be effected with Pd(0) catalysis. Thus, diallyldibutyltin reacted completely with CO 2 under the standard conditions to afford dicarboxylates (overall yield >90%). In the Pd-catalyzed reaction of tetraallyltin with CO 2 a complex mixture of
Bu2Sn(CH2-CH=CH2)2
co,
>
~
Bu2Sn(O-C-CH2-CH=CH2)2
Pd(PPh3)4, THF, 70 oC, 24 h
+
f'
Bu2Sn(O-C-CH=CH-CH3) 2
( 2.2 : 1 )
? [ Bu2(CH2=CHCH2)SnOCCH2CH=CH,]
O-C-CH2-CH=CH2 I 0
Sn(CH2-CH=CH2)4
C02
-~
(i) Sn(O-C-CH2-CH=CH2) 4
Oi Sn(O-C-CH=CH-CH3) 4
Pd(PPh3)4, THF, 70 ~ 72 h
Sn(O-C-CH2-CH=CH2)4.~O.C-CH=CH-CH3)n
(n=l, 2, 3, 4)
carboxylates (allyl)4_nSn(O2C-allyl) n (n=l-4) was produced after 24 hr. However, if the reaction time was extended to 72 h, the major products (ca. 80 % yield) were the isomeric tetracarboxylates, i.e. all four Sn-allyl bonds had inserted CO2. Under these conditions double bond isomerization products dominated ca. 4:1. Of the various stannanes tested thus far only those possessing allyl-tin bonds were found to undergo carboxylation. Thus, tetrabutyltin, tetraphenyltin, vinyltributyltin, and benzyltributyltin each
167 were recovered unchanged after contact with CO2/Pd(PPh3) 4 under the previous conditions. The failure of the crotyl- and benzyl-tin derivatives to react with CO 2 and the diminished reactivity of allyltriphenyltin suggests that a specific Pd-allyl interaction may play an important role in catalysis. The allyl silanes aUyltrimethylsilane, allyltriphenylsilane, and allyltrimethoxysilane also did not react. These observed structure/reactivity features in combination with the established reactivity of Pdallyl complexes with CO26 lead us to propose Scheme 1 as a tentative catalytic mechanism: Scheme 1
stannaneactivation/f----'~ ~
~-~
PPh3/Pd~SnR3
"~
• ' •~'snR3 Pd(PPh3)2
(PPh3)2Pd-- SnR3
coJ R3Sn
17~
Pd(PPh3)n
~ , ~ . . ~
(PPh3)2Pd"1~: 0"~ Sn
(PPh3)2Pd-- SnR3 Pd(PPh3)n +
C02
C02 activation
_
~_] R3Sn
",--- (PPha)2Pd :'? "C~0
i) oxidative addition of allylstannane to Pd(0)L n gives rl 3- and 1"11-allyl palladium complexes; ii) insertion of CO2 into the 111-allyl palladium bond (or the Pd-Sn bond); and iii) reductive elimination of the carboxylate and organotin groups to give the product and regenerate Pd(0). The sensitivity of the reaction to substitution on or adjacent to the Sn-allyl unit suggests that an initial rl2-complex may precede the oxidative addition step but no indication of complexation of the allyl stannane by Pd(PPh3) 4 was provided by 1H NMR analysis. Although transmetalation from Sn to Pd(II) 7 and the
168 activation of allyl electrophiles (e.g. halides, carbonates) by Pd(0) complexes 8 are both well documented, Pd(0) activation of aUyl tin reagents has little precedent. 9 However, the viability of an (rl3-allyl)Pd(stannyl) intermediate is supported by formation of a Pt analog in the reaction of Pt(ethylene)2(PPh3) with (allyl)SnMe3 .10 The possibility of CO 2 insertion into the Pd-C bond of the latter is bolstered by prior examples of CO 2 insertion reactions of ri 1_ and rl3-allyl-Pd complexes. 6 Since neither starting material nor product isomerization occurs under the reaction conditions (op cit), isomerization of the intermediate CO 2 inserted species apparently occurs prior to product release. 11 An alternative mechanistic pathway involving reaction of an intermediate Pd(rl2-CO2) complex 12 with the allyl stannane cannot be excluded at this time. However, IR spectra of Pd(PPh3)4/CO 2 solutions (1 atm, THF) showed no absorptions in the 1625-1700 cm- 1 region expected for such a species. We have also begun to investigate the possibilites for modifying the stannane carboxylation to produce wholly organic products. Bond energy considerations suggested that metathesis of the tin carboxylate with an alkyl halide might be possible. Although no reaction was observed betweeen the tin carboxylate and 2-methallyl chloride (65 ~ THF), in the presence of Pd(PPh3) 4 under the same conditions, clean conversion to the corresponding allyl ester (below) was observed. Moreover, combined reaction of allylSnBu 3, CO 2 and methallyl chloride in the presence of Pd(0) or Pd(II) complexes produced a mixture of organic esters (below) in moderate (unoptimized) yield. A major component was that expected from allyl-Sn carboxylation followed by metathesis with the allylic halide; a second major product, however, appears to be derived from initial carboxylation of the methallyl chloride. c..3 + 0
co= Bu3Sn~,~
BuaSnCI
Pd(PPha)4 THF, 65 ~ 12 h
+
~
Cl
.tm)
Pd(PPh3)4 or Pd(PPha)2CI2/PPh3 THF, 70 ~ 24 h
+
Bu3SnCl
U ( 50 % isolated yield )
As in the direct stannane carboxylation the carboxylative coupling is thus far limited to allyl stannanes; RSnBu 3 with R = PhCH 2, Ph, vinyl, PhC-C- all fail to react. The structure of the
169 isomeric ester (propenyl 3-methyl-3-butenoate) and existing precedents for the formation of allyl-Pd species 8 and their insertion reactions with CO2 6 suggest the involvement of a second pathway. involving initial carboxylation of the aUyl halide (Scheme 2). Scheme 2
I C'l
cl~Pd~ppha
co2
R3Sn"~'~
~,~pph P~snR3 ~ Pd(PPh3)n
o3-.A I
(PPh3)2Pd--Cl RzSn,/",,~
]
I
O ) CO2 I
(PPh3)2Pd~SnR3
~,~
C.H3
-vc,
In conclusion we have reported on two new reactions relevant to the goal of carbon dioxide utilization. In the first, Pd complexes catalyze the net insertion of CO 2 into otherwise unreactive Snallyl bonds. The product organotin carboxylates, especially diorganotin esters, have a wide range of commercial applications. 13 In the second reaction the same Pd complexes catalyze the coupling of allyl stannane, allyl halide and CO 2 to produce allyl esters. Efforts are underway to further elucidate the mechanistic details of these reactions and to extend their scope to include a range of organometals and organic halides. Acknowledgments. We are grateful for financial support provided by the U.S. Department of Energy, Office of Basic Energy Sciences.
170 References.
1)
2) 3)
a) Behr, A. "Carbon Dioxide Activation by Metal Complexes", VCH publ., Weinheim, Germany, 1988; b) Ito, T.; Yamamoto, A. "Organometallic Reactions of Carbon Dioxide", chap. 3 of Organic and Bio-organic Chemistry of Carbon Dioxide, Inoue, S.; Yamazaki, N., ed. Kodansha Ltd., Tokyo, Japan, 1982; c) Gibson, D.H. Chem. Rev. 1996, 96, 2063. Sanderson, R.T.J. Am. Chem. Soc. 1955, 77, 4531. Bond enthalpy considerations for M-CR 3 + CO 2 ---> M-OC(=O)-CR 3 indicate an exothermic
4)
C bond and a C-C c-bond is formed at the expense of a comparably strong C-O re-bond. The following procedure is representative. Allyltributyltin (0.33 g, 1.0 mmol), Pd(Ph3P) 4
process for virtually all metals since a strong M-O bond is formed at the expense of a weaker M-
(0.093 g, 0.08 mmol), 20 mL of dry THF, and a magnetic stir bar were placed in the 50 mL glass liner of a stainless steel autoclave under a nitrogen purge. After the autoclave was purged several times with CO 2, it was pressurized with CO 2 (33 atm), sealed, and heated at 70 ~ for
5) 6)
7) 8) 9)
24 h with stirring. After cooling and release of the pressure, the solvent was removed under reduced pressure and the residue was passed through a short column of flash silica (1:1 ethyl acetateJhexane) to afford a spectroscopically pure mixture of the tin carboxylates. A preliminary report of this study has appeared recently: Shi, M.; Nicholas, K.M.J. Am. Chem. Soc. 1997, 119, 5057. a) ref. la, p. 54-60; b) Ito, T.; Kindaichi, Y.; Takami, Y. Chem. Ind (London), 1980, 19, 83; c) Hung, T.; Jolly, P.W.; Wilke, G. J. Organomet. Chem. 1980, 190, C5; d) Santi, R.; Marchi, M. J. Organomet. Chem. 1979, 182, 117; e) ref. la, p. 56; f) Behr, A.; Ilsemann, G. v.; Keim, W.; Kruger, C.; Tsay, Y.-H. Organometallics, 1986, 5, 514; g) Behr, A.; Ilsemann, G. j. Organomet. Chem. 1984, 276, C77. Stille, J.K. Angew. Chem. Int. Ed. Eng. 1986, 25, 508. Trost, B.M. Acc. Chem. Res. 1980, 13, 385; Tsuji, J. Pure Appl. Chem. 1982, 54, 197. Catalysis of allyl-Sn additions to aldehydes by Pd(II)L2C12 complexes recently has been
reported; one, less efficient example using Pd(PPh3) 4 was included. Nakamura, H.; Iwama, H.; Yamamoto, Y. J. Am. Chem. Soc. 1996, 118, 6641. 10) Christofides, A.; Ciriano, M.; Spencer, J.L.; Stone, F.G.A.J. Organomet. Chem. 1979, 178, 273. 11) Extensive double bond isomerization has been found in the reactions of (rl3-allyl)Pd complexes with CO2; ref. 6 c-f. 12) Sakamoto, M.; Shimizu, I.; Yamamoto, A. Organometallics, 1994, 13, 407. 13) Kirk-Othmer Concise Encyclopedia of Chemical Technology, Grayson, M. and Eckroth, D. eds., 1985, Wiley, NY, pp. 1179-1181; Sijpesteijn, A. K.; Luijten, J. G. A.; van der kerk, G. J. M. in Fungicides, An Advanced Treatise, Torgeson, D. C., ed., Academic Press, New York, 1969, Vol. 2, p. 331; Evans, C. J. Tin and Its Uses, 1976, 110, 6; van der kerk, G. J. M.; Luijten, J. G. A. J. Appl. Chem. 1954, 4, 31.