- Email: [email protected]
Dimerization of methyl acrylate by homogeneous transition-metal catalysis. Part I. Activation of hydrido (carbonyl) chloro-[bis(triisopropylphosphane)] ruthenium by CF3SO3Ag
Journal of Molecular Catalysis, 85 (1993) 149-152 Elsevier Science Publishers B.V., Amsterdam
149
Dimerization of methyl acrylate by homogeneous transition-metal catalysis. Part I. Activation of hydrido (carbonyl)chloro[ bis (triisopropylphosphane ) ] ruthenium by CF,SO,Ag Reiner Sustmann*, Hermann Josef Hornung, Thomas Schupp and Barbara Patzke Institut fiir Organische Chemie der Uniuersitiit Essen, Postfach 103 764,46117 Essen (Germany) (Received March 26,1993; accepted July 8,1993)
Abstract The dimerization of methyl acrylate in the presence of RuH(CO)Cl[P(i-Pr),], and CF,SO,Ag to a mixture of linear tail-to-tail dimers is described. The mixture consists of 90% trans-2-hexene1,6-dioic acid dimethyl ester, of 6% ck-2-hexene-1,6-dioic acid dimethyl ester and of 3% truna-3hexene-1,6-dioic acid dimethyl ester. The reaction is carried out in neat methyl acrylate at 85 ’ C and displays turnover numbers of 600. Key words: dimerization; methyl acrylate; ruthenium
Introduction
The transition-metal catalyzed dimerization of olefins has been of continuing interest for several decades. In 1965 Alderson, Jenner, and Lindsey [ 1] described dimerizations of ethene, propene, and methyl acrylate (MA) by RhClB*3Hz0 and RuCls*3H20. At temperatures of 140°C RhC13*3Hz0 led to turnover numbers (TON) of 4 for methyl acrylate and ruthenium gave a TON of 26 at 150°C. In both cases 2-hexene-1,6-dioic acid dimethyl ester (d2-HDM) was the almost exclusive product. McKinney and Colton [ 21 showed that the use of RuC13*3H20 in the presence of zinc and further additives improved the TON for the formation of d2-HDM to 117. A [bis (dimethyl muconate) ] (trimethylphosphite)ruthenium complex which was isolated in these studies displayed similar catalytic activity in the dimerization of methyl acrylate at elevated temperatures. Ru3 (CO) 12was applied by Ren et al. [ 31 for the catalytic dimerization of methyl acrylate (maximum TON 320). Bis (benzoni*Corresponding author.
0304-5102/93/$06.00
0 1993 - Elsevier Science Publishers B.V. All rights reserved.
150
R. Sustmann et al. /J. Mol. Catal. 85 (1993) 149-152
trile)palladium dichloride as catalyst precursor was introduced by Barlow et al. [ 41 and by Pracejus and Oehme [ 51. In particular Pracejus and Oehme have studied this system in detail under various conditions [6-lo]. A maximum TON of 170 was reached. A similar catalyst was used by Nugent and Hobbs [ 111. Nugent and McKinney [ 121 investigated the addition of Lewis acids to palladium and rhodium catalyst precursors. Grenouillet, Neilbecker, and Tkatchenko [ 131 applied ($-allyl)palladium complexes (TON 170-180) and Wilke and Sperling [ 14,151 used similar nickel complexes. So far the best results were obtained by Brookhart et al. [ 16-181 who used cationic ($-pentamethylcyclopentadienyl)rhodium complexes. They improved this catalytic system to a TON of 6500. We have begun a more systematic study of the dimerization of methyl acrylate by homogeneous catalysis in order to delineate appropriate transition metals, their required oxidation state, and necessary additional ligands for the transition metal complexes. Our primary concept was that possible catalyst precursors should have at least one hydride ligand and the possibility to provide a ligand site for x-coordination of methyl acrylate prior to its insertion in the metal to hydrogen bond. If the catalyst precursor did not coordinate methyl acrylate directly suitable activators should be used to secure a ligand site. Here, we report on the use of hydrido (carbonyl) (chloro) [ bis (triisopropylphosphane ) ] ruthenium [ 191 as a possible catalyst precursor. It fulfils the requirement of having a hydride ligand and it offers a chloro ligand which might be removed by suitable additives.
Results and discussion HRu(CO)Cl[P(i-Pr),], (1) can be synthesized from RuC13*3Hz0 in methanol in the presence of tri (isopropyl)phosphane [ 191. The orange complex is insoluble in methyl acrylate at room temperature. At 80” C a homogeneous solution is obtained which produces traces of linear dimers but larger amounts of the branched dimer 2-methylene pentane-1,5dioic acid dimethyl ester. The formation of the latter can be attributed to a dimerization of methyl acrylate by free tri(isopropy1) phosphane which is formed in the solution by ligand dissociation. This type of reaction is known to take place with trialkyl phosphanes [20]. If, however, a suspension of 1 in methyl acrylate is stirred with a slightly more than equimolar amount of CF,SO,Ag at room temperature the complex dissolves and a precipitate of silver chloride is formed within five minutes. Heating the solution at 85°C leads to linear tail-to-tail dimers of methyl acrylate. The mixture consists of 90% trans-2-hexene-1,6dioic acid dimethyl ester, 6% of cis-2-hexene-1,6dioic acid dimethyl ester, 3% of trans3-hexene-1,6dioic acid dimethyl ester and traces of the &-&isomer. In contrast to other systems [2], trimers are observed only in traces. Within 24 h a turnover number of 600 is obtained. After this time the catalyst has become
R. Swtmann
151
et al. /J. Mol. Catal. 85 (1993) 149-152
inactive and excess methyl acrylate starts to polymerize. The initial turnover rate is 150 h-‘. The initial hypothesis, that the presence of a hydride ligand is important for a successful dimerization of methyl acrylate seems to be verified by these experiments. The feasibility of inserting a methyl acrylate molecule into a rubond has been demonstrated in hydrido (carthenium hydrogen bonyl) (chloro) [ tris (triphenylphosphane) ] ruthenium [ 211. After activation with CF3S03Ag this complex is also catalytically active in the dimerization of methyl acrylate but shows lower turnover numbers [ 221. The generation of a free ligand site by precipitation of chloride as AgCl and replacing the chloride ion by the less coordinating trifluoromethanesulfonic acid anion seems also to be a prerequisite. A 31P NMR spectroscopic study in methyl acrylate after addition of CF3S03Ag and removal of AgCl shows no free tri-isopropyl phosphane at room temperature where the catalytic dimerization already occurs slowly. Thus, the catalytic active species must retain two phosphane molecules. By IR spectroscopy in methyl acrylate it could be shown that also the carbonyl ligand is still present. From these observations an approximate mechanistic scheme based on Ru2+ as the formal metal oxidation state can be devised (Scheme 1) . A~-HDM A*-HDM
HCIRu11COIP(i-Pr),12
AZ-HDM
Ag+, MA
1 MA
AgCl “, [HRu”(MA)COIP(i-PrIa12]’
2
MA
7 IIi-Pr~,P12CO~MA~Ru~~~co2M~+ 3 MA H
[Ii-Pr),P12CO(MA)Ru” 4
Me02C~C02M~*
a I(i-Pr)3P12CO(MA)Ru
5
Me02CAC0
II
I-
+ 1
2 Me
Scheme 1.
At present, attempts are being made to isolate intermediate catalytically active complexes. Further experiments are also in progress to modify ruthenium hydride complexes in order to explore the influence of different phosphane ligands and to use other activators. Experimental
HRu(CO)Cl [P(i-Pr),], was prepared as described [ 191. Methyl acrylate was dried over calcium hydride, distilled, and kept under argon. Commercial
152
R. Sustmann et al. /J. Mol. Catal. 85 (1993) 149-152
CFBSOBAgwas dried in vacua and used without further purification. The reactions were carried out under argon in Schlenk vessels which were opened from time to time to follow product formation by GC (capillary column SE 52 (25 mX0.32 mm)). To a suspension of 58.0 mg (0.119 mmol) RuHCl(C0) [P (i-Pr)3]2 and 14.2 mg (0.114 mmol) hydroquinone monomethyl ether were added 20.0 ml (0.222 mol) of methyl acrylate and 44.9 mg (0.175 mmol) CF,SO,Ag. Within 5 min a yellow solution from which AgCl precipitated was formed. The solution was kept for 24 h at 85°C. After removal of methyl acrylate (6.5 g) fractional distillation gave 12.2 g (70.7 mmol) dimers (TON 600) as a mixture of trans2-hexene-1,6dioic acid dimethyl ester (90%), cis-2-hexene-1,6dioic acid dimethyl ester (6% ), truns-3-hexene-1,6dioic acid dimethyl ester (3% ), and traces of cis-3-hexene-1,6dioic acid dimethyl ester. The products were identified by 300 MHz ‘H NMR spectra, including (‘H,‘H) COSY spectra and by comparison with published MS data [ 231. References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
T. Alderson, E.L. Jenner, R.V. Lindsey, Jr., J. Am. Chem. Sot., 87 (1965) 5638. R.J. McKinney, M.C. Colton, Organometahics, 5 (1986) 1080. C.Y. Ren, W.C. Cheng, W.C. Chan, C.H. Yeung, C.P. Lau, J. Mol. Catal., 59 (1990) Ll. M.G. Barlow, M.J. Bryant, R.N. Haszeldine, A.G. Mackie, J. Organomet. Chem., 21 (1979) 215. G. Oehme, H. Pracejus, Tetrahedron Lett., (1979) 343. H. Pracejus, H.J. Krause, G. Oehme, Z. Chem., 20 (1980) 24. G. Oehme, H. Pracejus, J. Organomet. Chem., 320 (1987) C56. G. Oehme, J. Prakt. Chem., 326 (1984) 779. H. Pracejus, G. Oehme, J. Prakt. Chem., 320 (1980) 798. G. Oehme, I. Grassert, H. Mennenga, H. Baud&h, J. Mol. Catal., 37 (1986) 53. W.A. Nugent, F.W. Hobbs, Jr., J. Org. Chem., 48 (1983) 5364. W.A. Nugent, R.J. McKinney, J. Mol. Catal., 29 (1985) 65. P. Grenouihiet, D. Neilbecker, I. Tkatchenko, J. Chem. Sot., Chem. Commun. (1989), 1850. G. Wilke, Angew. Chem., 100 (1988) 189; Angew. Chem. Int. Ed. Engl., 27 (1988) 185. K. Sperling, Dissertation Ruhr-Universitlit Bochum 1983. M. Brookhart, S. Sabo-Etienne, J. Am. Chem. Sot., 113 (1991) 2777. M.Brookhart,D.M. Lincoln, M.A. Bennent, S. Pelling, J. Am. Chem. Sot., 112 (1990) 2691. M. Brookhart, E. Hauptmann, J. Am. Chem. Sot., 114 (1992) 4437. M.A. Eateruelas, H. Werner, J. Organomet. Chem., 303 (1986) 221. U.S. Patent 3,074,999 (1963) to M.M. Rauhut, H. Currier (Chem. Abstr., 58 (1963) 11224B). K. Hiraki, N. Ochi, Y. Sasada, H. Hayashida, Y. Fuchita, S. Yamamoto, J. Chem. Sot., Dalton Trans., (1985), 873. Th. Schupp, unpublished results. F.W. McLafferty, D.B. Stauffer, The Wiley/NBS Registry of Mass SpectralData, Vol 1, John Wiley and Sons, New York, 1989.
149
Dimerization of methyl acrylate by homogeneous transition-metal catalysis. Part I. Activation of hydrido (carbonyl)chloro[ bis (triisopropylphosphane ) ] ruthenium by CF,SO,Ag Reiner Sustmann*, Hermann Josef Hornung, Thomas Schupp and Barbara Patzke Institut fiir Organische Chemie der Uniuersitiit Essen, Postfach 103 764,46117 Essen (Germany) (Received March 26,1993; accepted July 8,1993)
Abstract The dimerization of methyl acrylate in the presence of RuH(CO)Cl[P(i-Pr),], and CF,SO,Ag to a mixture of linear tail-to-tail dimers is described. The mixture consists of 90% trans-2-hexene1,6-dioic acid dimethyl ester, of 6% ck-2-hexene-1,6-dioic acid dimethyl ester and of 3% truna-3hexene-1,6-dioic acid dimethyl ester. The reaction is carried out in neat methyl acrylate at 85 ’ C and displays turnover numbers of 600. Key words: dimerization; methyl acrylate; ruthenium
Introduction
The transition-metal catalyzed dimerization of olefins has been of continuing interest for several decades. In 1965 Alderson, Jenner, and Lindsey [ 1] described dimerizations of ethene, propene, and methyl acrylate (MA) by RhClB*3Hz0 and RuCls*3H20. At temperatures of 140°C RhC13*3Hz0 led to turnover numbers (TON) of 4 for methyl acrylate and ruthenium gave a TON of 26 at 150°C. In both cases 2-hexene-1,6-dioic acid dimethyl ester (d2-HDM) was the almost exclusive product. McKinney and Colton [ 21 showed that the use of RuC13*3H20 in the presence of zinc and further additives improved the TON for the formation of d2-HDM to 117. A [bis (dimethyl muconate) ] (trimethylphosphite)ruthenium complex which was isolated in these studies displayed similar catalytic activity in the dimerization of methyl acrylate at elevated temperatures. Ru3 (CO) 12was applied by Ren et al. [ 31 for the catalytic dimerization of methyl acrylate (maximum TON 320). Bis (benzoni*Corresponding author.
0304-5102/93/$06.00
0 1993 - Elsevier Science Publishers B.V. All rights reserved.
150
R. Sustmann et al. /J. Mol. Catal. 85 (1993) 149-152
trile)palladium dichloride as catalyst precursor was introduced by Barlow et al. [ 41 and by Pracejus and Oehme [ 51. In particular Pracejus and Oehme have studied this system in detail under various conditions [6-lo]. A maximum TON of 170 was reached. A similar catalyst was used by Nugent and Hobbs [ 111. Nugent and McKinney [ 121 investigated the addition of Lewis acids to palladium and rhodium catalyst precursors. Grenouillet, Neilbecker, and Tkatchenko [ 131 applied ($-allyl)palladium complexes (TON 170-180) and Wilke and Sperling [ 14,151 used similar nickel complexes. So far the best results were obtained by Brookhart et al. [ 16-181 who used cationic ($-pentamethylcyclopentadienyl)rhodium complexes. They improved this catalytic system to a TON of 6500. We have begun a more systematic study of the dimerization of methyl acrylate by homogeneous catalysis in order to delineate appropriate transition metals, their required oxidation state, and necessary additional ligands for the transition metal complexes. Our primary concept was that possible catalyst precursors should have at least one hydride ligand and the possibility to provide a ligand site for x-coordination of methyl acrylate prior to its insertion in the metal to hydrogen bond. If the catalyst precursor did not coordinate methyl acrylate directly suitable activators should be used to secure a ligand site. Here, we report on the use of hydrido (carbonyl) (chloro) [ bis (triisopropylphosphane ) ] ruthenium [ 191 as a possible catalyst precursor. It fulfils the requirement of having a hydride ligand and it offers a chloro ligand which might be removed by suitable additives.
Results and discussion HRu(CO)Cl[P(i-Pr),], (1) can be synthesized from RuC13*3Hz0 in methanol in the presence of tri (isopropyl)phosphane [ 191. The orange complex is insoluble in methyl acrylate at room temperature. At 80” C a homogeneous solution is obtained which produces traces of linear dimers but larger amounts of the branched dimer 2-methylene pentane-1,5dioic acid dimethyl ester. The formation of the latter can be attributed to a dimerization of methyl acrylate by free tri(isopropy1) phosphane which is formed in the solution by ligand dissociation. This type of reaction is known to take place with trialkyl phosphanes [20]. If, however, a suspension of 1 in methyl acrylate is stirred with a slightly more than equimolar amount of CF,SO,Ag at room temperature the complex dissolves and a precipitate of silver chloride is formed within five minutes. Heating the solution at 85°C leads to linear tail-to-tail dimers of methyl acrylate. The mixture consists of 90% trans-2-hexene-1,6dioic acid dimethyl ester, 6% of cis-2-hexene-1,6dioic acid dimethyl ester, 3% of trans3-hexene-1,6dioic acid dimethyl ester and traces of the &-&isomer. In contrast to other systems [2], trimers are observed only in traces. Within 24 h a turnover number of 600 is obtained. After this time the catalyst has become
R. Swtmann
151
et al. /J. Mol. Catal. 85 (1993) 149-152
inactive and excess methyl acrylate starts to polymerize. The initial turnover rate is 150 h-‘. The initial hypothesis, that the presence of a hydride ligand is important for a successful dimerization of methyl acrylate seems to be verified by these experiments. The feasibility of inserting a methyl acrylate molecule into a rubond has been demonstrated in hydrido (carthenium hydrogen bonyl) (chloro) [ tris (triphenylphosphane) ] ruthenium [ 211. After activation with CF3S03Ag this complex is also catalytically active in the dimerization of methyl acrylate but shows lower turnover numbers [ 221. The generation of a free ligand site by precipitation of chloride as AgCl and replacing the chloride ion by the less coordinating trifluoromethanesulfonic acid anion seems also to be a prerequisite. A 31P NMR spectroscopic study in methyl acrylate after addition of CF3S03Ag and removal of AgCl shows no free tri-isopropyl phosphane at room temperature where the catalytic dimerization already occurs slowly. Thus, the catalytic active species must retain two phosphane molecules. By IR spectroscopy in methyl acrylate it could be shown that also the carbonyl ligand is still present. From these observations an approximate mechanistic scheme based on Ru2+ as the formal metal oxidation state can be devised (Scheme 1) . A~-HDM A*-HDM
HCIRu11COIP(i-Pr),12
AZ-HDM
Ag+, MA
1 MA
AgCl “, [HRu”(MA)COIP(i-PrIa12]’
2
MA
7 IIi-Pr~,P12CO~MA~Ru~~~co2M~+ 3 MA H
[Ii-Pr),P12CO(MA)Ru” 4
Me02C~C02M~*
a I(i-Pr)3P12CO(MA)Ru
5
Me02CAC0
II
I-
+ 1
2 Me
Scheme 1.
At present, attempts are being made to isolate intermediate catalytically active complexes. Further experiments are also in progress to modify ruthenium hydride complexes in order to explore the influence of different phosphane ligands and to use other activators. Experimental
HRu(CO)Cl [P(i-Pr),], was prepared as described [ 191. Methyl acrylate was dried over calcium hydride, distilled, and kept under argon. Commercial
152
R. Sustmann et al. /J. Mol. Catal. 85 (1993) 149-152
CFBSOBAgwas dried in vacua and used without further purification. The reactions were carried out under argon in Schlenk vessels which were opened from time to time to follow product formation by GC (capillary column SE 52 (25 mX0.32 mm)). To a suspension of 58.0 mg (0.119 mmol) RuHCl(C0) [P (i-Pr)3]2 and 14.2 mg (0.114 mmol) hydroquinone monomethyl ether were added 20.0 ml (0.222 mol) of methyl acrylate and 44.9 mg (0.175 mmol) CF,SO,Ag. Within 5 min a yellow solution from which AgCl precipitated was formed. The solution was kept for 24 h at 85°C. After removal of methyl acrylate (6.5 g) fractional distillation gave 12.2 g (70.7 mmol) dimers (TON 600) as a mixture of trans2-hexene-1,6dioic acid dimethyl ester (90%), cis-2-hexene-1,6dioic acid dimethyl ester (6% ), truns-3-hexene-1,6dioic acid dimethyl ester (3% ), and traces of cis-3-hexene-1,6dioic acid dimethyl ester. The products were identified by 300 MHz ‘H NMR spectra, including (‘H,‘H) COSY spectra and by comparison with published MS data [ 231. References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
T. Alderson, E.L. Jenner, R.V. Lindsey, Jr., J. Am. Chem. Sot., 87 (1965) 5638. R.J. McKinney, M.C. Colton, Organometahics, 5 (1986) 1080. C.Y. Ren, W.C. Cheng, W.C. Chan, C.H. Yeung, C.P. Lau, J. Mol. Catal., 59 (1990) Ll. M.G. Barlow, M.J. Bryant, R.N. Haszeldine, A.G. Mackie, J. Organomet. Chem., 21 (1979) 215. G. Oehme, H. Pracejus, Tetrahedron Lett., (1979) 343. H. Pracejus, H.J. Krause, G. Oehme, Z. Chem., 20 (1980) 24. G. Oehme, H. Pracejus, J. Organomet. Chem., 320 (1987) C56. G. Oehme, J. Prakt. Chem., 326 (1984) 779. H. Pracejus, G. Oehme, J. Prakt. Chem., 320 (1980) 798. G. Oehme, I. Grassert, H. Mennenga, H. Baud&h, J. Mol. Catal., 37 (1986) 53. W.A. Nugent, F.W. Hobbs, Jr., J. Org. Chem., 48 (1983) 5364. W.A. Nugent, R.J. McKinney, J. Mol. Catal., 29 (1985) 65. P. Grenouihiet, D. Neilbecker, I. Tkatchenko, J. Chem. Sot., Chem. Commun. (1989), 1850. G. Wilke, Angew. Chem., 100 (1988) 189; Angew. Chem. Int. Ed. Engl., 27 (1988) 185. K. Sperling, Dissertation Ruhr-Universitlit Bochum 1983. M. Brookhart, S. Sabo-Etienne, J. Am. Chem. Sot., 113 (1991) 2777. M.Brookhart,D.M. Lincoln, M.A. Bennent, S. Pelling, J. Am. Chem. Sot., 112 (1990) 2691. M. Brookhart, E. Hauptmann, J. Am. Chem. Sot., 114 (1992) 4437. M.A. Eateruelas, H. Werner, J. Organomet. Chem., 303 (1986) 221. U.S. Patent 3,074,999 (1963) to M.M. Rauhut, H. Currier (Chem. Abstr., 58 (1963) 11224B). K. Hiraki, N. Ochi, Y. Sasada, H. Hayashida, Y. Fuchita, S. Yamamoto, J. Chem. Sot., Dalton Trans., (1985), 873. Th. Schupp, unpublished results. F.W. McLafferty, D.B. Stauffer, The Wiley/NBS Registry of Mass SpectralData, Vol 1, John Wiley and Sons, New York, 1989.