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Dioxotungsten(VI) complexes with tetradentate [O,N,N,O] ligands: syntheses, spectral characterisation and catalytic applications
Inorganic Chemistry Communications 8 (2005) 122–124 www.elsevier.com/locate/inoche
Dioxotungsten(VI) complexes with tetradentate [O,N,N,O] ligands: syntheses, spectral characterisation and catalytic applications Ari Lehtonen
*
Department of Chemistry, University of Turku, Vatselantie, FIN-20014 Turku, Finland Received 10 November 2004; accepted 19 November 2004
Abstract Two new tungsten(VI) complexes of the type WO2(ONNOR) (ONNOR = tetradentate diaminobis(phenolate) ligand) were prepared by the reaction of trisdiolatetungsten(VI) complex W(eg)3 (eg = 1,2-ethanediolate) and diaminobis(phenol)s in the presence of water. Studied complexes catalysed ROMP of norbornene when activated by Et2AlCl. They also catalysed oxotransfer reaction between DMSO and benzoin. Ó 2004 Elsevier B.V. All rights reserved. Keywords: Alkoxide complexes; Oxo complexes; Phenolate ligands; Tungsten; Catalysis
High-valent molybdenum and tungsten complexes with oxo ligands have attracted considerable interest due to their applications in organometallic and catalytic chemistry. In particular, these complexes are known to catalyse olefin metathesis reaction [1] and are also used in various industrial and biological oxidation processes [2,3]. Numerous dioxomolybdenum(VI) complexes with a variety of supporting ligands have been prepared and studied as catalyst model compounds [4,5], whereas the chemistry of analogous tungsten complexes is still inadequately studied [5–7]. One reason for the relatively little number of known dioxotungsten(VI) complexes is the poor availability of suitable starting materials, since typical synthetic routes start from soluble derivatives of
*
Tel.: +358 2 3336733; fax: +358 2 3336700. E-mail address: ari.lehtonen@utu.fi.
1387-7003/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2004.11.021
WO2Cl2, i.e., WO2Cl2(dme) [8] and WO2(acac)2 [9]. Trisdiolatotungsten(VI) complex W(eg)3 (1) (eg = ethylene glycolate) [10] is a straightforwardly available, stable and moderately soluble compound, which can be easily converted to different tungsten(VI) alkoxide and phenoxide complexes [11]. We have earlier found that 1 can react with tridentate aminobis(phenol)s (H2ONOR; R = Me, tert-Bu) to produce mixed ligand oxotungsten(VI) complexes [WO(eg)(ONOR)] [12]. The current paper presents reactions of 1 with tetradentate diaminobis(phenol)s. Syntheses and spectral characterization of two new dioxotungsten(VI) complexes with [O,N,N,O] donor ligands have been reported. Trisdiolato complex 1 was treated with tetradentate ligands, N,N 0 -bis(2-hydroxy-3,5-dimethylbenzyl)-N,N 0 dimethylethane-1,2-diamine (H2ONNOMe) and N,N 0 bis(2-hydroxy-3,5-di-tert-butylbenzyl)-N,N 0 -dimethylethane-1,2-diamine (H2ONNOtBu), in watery methanol and the reaction mixtures were stirred under reflux.
A. Lehtonen / Inorganic Chemistry Communications 8 (2005) 122–124
Scheme 1. Formation of complexes [WO2(ONNOR)].
The reaction yielded monomeric complexes [WO2(ON NOMe)] (2) and [WO2(ONNOtBu)] (3), respectively (see Scheme 1). 1 Presumably, the mechanism for the formation of these complexes includes ligand displacement in association with hydrolytic cleavage of two diolato groups. Complex 2 deposited as pale yellow microcrystals upon cooling to the room temperature, whereas complex 3 was obtained as white crystalline solid. Both compounds were characterised by spectral methods and ele-
1 1.00 mmol (364 mg) of 1 and equivalent amount of ligand precursor H2ONNOMe (356) or H2ONNOtBu (525 mg) were suspended in 20 ml of moist MeOH. The reaction mixtures were stirred under reflux for 6 h to obtain pale yellow solutions. Complexes 2 and 3 crystallised upon cooling to the room temperature. Crystalline products were washed with cold methanol and dried under ambient atmosphere. [WO2(ONNOMe)] (2): Pale yellow crystalline solid. Yield 310 mg (54%). IR: 1316(m), 1271(s), 1252(vs), 1231(vs), 1163(vs), 1144(m), 1061(s), 995(s), 959(m), 934(vs), 899 (vs), 868(m), 843(vs), 808(m), 774(m), 739(w), 688(m), 617(m), 588(m), 554(m). NMR: dC 153.88, 131.49, 129.95, 127.98, 127.31, 121.21, 64.01, 62.89, 53.09, 52.24, 48.71, 47.75, 20.41, 16.30. dH 6.98 (2H, ArH), 6.66 (2H, ArH), 5.08 (d, J = 14 Hz, 2H, NCH2), 3.51 (d, J = 14 Hz, 2H, NCH2), 3.18 (d, J = 13 Hz, 2H, NCH2), 2.74 (s, 6H, NCH3), 2.24 (s, 6H, ArCH3), 2.22 (d, J = 10 Hz, 2H, NCH2), 2.09 (s, 6H, ArCH3). Found: C, 40.29; H, 5.32; N, 4.71. C22H30N2O4W requires: C, 46.33; H, 5.30; N, 4.91. [WO2(ONNOtBu)] (3): White crystalline solid. Yield 275 mg (37%). IR: 1304(s, br), 1263(vs), 1253(vs), 1238(vs), 1204(s), 1171(s), 1132(s), 1063(m), 1015(m), 993(m), 937(s), 901(vs), 876(s), 855(s), 812(m), 785(m), 756(s), 692(w), 617(m), 557(s), 475(m). NMR: dC 155.56, 142.75, 138.80, 124.29, 123.83, 121.35, 65.64, 53.59, 49.49, 35.15, 34.24, 31.58, 30.63. dH 7.36 (d, J = 3 Hz, 2H, ArH), 6.86 (d, J = 3 Hz, 2H, ArH), 4.94 (d, J = 14 Hz, 2H, NCH2), 3.62 (d, J = 14 Hz, 2H, NCH2), 3.29 (d, J = 10 Hz, 2H, NCH2), 2.81 (s, 6H, NCH3), 2.40 (d, J = 10 Hz, 2H, NCH2), 1.45 (s, 18H, C(CH3)3), 1.29 (s, 18H, C(CH3)3). Found: C, 55.13; H, 7.29; N, 3.69. C34H54WN2O4 requires: C, 55.29; H, 7.37; N, 3.79.
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mental analyses. IR and NMR data of these complexes were practically identical with those recorded earlier for their molybdenum analogues [13]. Both studied compounds show two characteristic cis-WO2 vibrational bands at around 900 and 935 cm1 in their IR spectra. The latter bands occur at 20 cm1 higher frequencies than those for the molybdenum congeners [13]. 1H and 13 C NMR spectra in CDCl3 show expected resonances for octahedral complexes with C2 rotation axis. Catalytic activities of complexes 2 and 3 were investigated using ROMP of norbornene as a test reaction. Sixcoordinated tungsten complexes (10 lmol) were dissolved in 6 ml of CH2Cl2/norbornene (2 mmol of cycloalkene monomer) mixture to form colourless solutions, which were treated with 1.8 M toluene solution of Et2AlCl. As a result, the solutions changed rapidly to an orange colour and simultaneous gel-formation started leading quickly to the completeness of reactions, which produced mainly insoluble, rubber-like polymers in high yields. However, polymerisations were difficult to control, whereas product outcome seems to depend predominately on the amount of used cocatalyst. The activation mechanism is not known, but the colour change of catalyst precursors upon addition of Et2AlCl is probably related to the reduction of W(VI) centres. Similar activation by reducing aluminium compounds has earlier been used in heterogeneous polymerisation of norbornene, which was catalysed by single crystals of (Bu4N)2[W6O19] [14]. The utility of studied dioxotungsten(VI) complexes to catalyse oxo-transfer reactions was investigated using DMSO as the oxygen donor and benzoin as the reductant. In a typical test reaction, 0.10 mmol of benzoin was dissolved in 0.7 ml of DMSO in a NMR tube and subsequently treated with 0.01 mmol of catalyst. The reaction mixture was kept at 100 °C for 48 h. Both complexes catalysed these oxidation reactions, since detected yields of oxidised products (benzil) were 50–60%, whereas in control experiments without catalysts no reactions between substrates and DMSO were observed. On the grounds of comparable molybdenum and tungsten based catalyst systems, it is supposed that the dioxotungsten(VI) complexes react with benzoin to yield oxotungsten(IV) complexes and benzil. The W(IV) complexes are then rapidly oxidised back to the initial dioxocompounds with DMSO to complete the catalytic cycle [4,5].
References [1] K.J. Ivin, J.C. Mol, Olefin Metathesis and Metathesis Polymerization, Academic Press, London, 1997. [2] H. Arzoumanian, Coord. Chem. Rev. 180 (1998) 191. [3] J.H. Enemark, J.J.A. Cooney, J.-J. Wang, R.H. Holm, Chem. Rev. 104 (2004) 1175.
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A. Lehtonen / Inorganic Chemistry Communications 8 (2005) 122–124
[4] (a) R. Dinda, P. Sengupta, S. Ghosh, W.S. Sheldrick, Eur. J. Inorg. Chem. (2003) 363; (b) N.R. Pramanik, S. Ghosh, T.K. Raychaudhuri, S. Ray, R.J. Butcher, S.S. Mandal, Polyhedron 23 (2004) 1595. [5] (a) Y.-L. Wong, J.-F. Ma, W.-F. Law, Y. Yan, W.-T. Wong, Z.-Y. Zhang, T.C.W. Mak, D.K.P. Ng, Eur. J. Inorg. Chem. (1999) 313; (b) Y.-L. Wong, Y. Yan, E.S.H. Chan, Q. Yang, T.C.W. Mak, D.K.P. Ng, J. Chem. Soc., Dalton Trans. (1998) 3057. [6] F.E. Ku¨hn, W.-M. Xue, A. Al-Aijlouni, A.M. Santos, S. Zang, C.C. Roma˜o, G. Eickerling, E. Herdtweck, Inorg. Chem. 41 (2002) 4468, and references therein.
[7] W.A. Herrmann, J. Fridgen, G.M. Lobmaier, M. Spiegler, New J. Chem. (1999) 5. [8] K. Dreisch, C. Andersson, C. Sta˚lhandske, Polyhedron 10 (1991) 2417. [9] S. Yu, R.H. Holm, Inorg. Chem. 28 (1989) 4385. [10] F.A. Schro¨der, J. Scherle, Z. Naturfor. 28b (1973) 46. [11] For example: A. Lehtonen, R. Sillanpa¨a¨, Polyhedron 22 (2003) 2755. [12] A. Lehtonen, R. Sillanpa¨a¨, Inorg. Chem. 43 (2004) 6501. [13] A. Lehtonen, R. Sillanpa¨a¨, Polyhedron, accepted. [14] M. McCann, D. McDonnell, J. Chem. Soc., Chem. Commun. (1993) 1718.
Dioxotungsten(VI) complexes with tetradentate [O,N,N,O] ligands: syntheses, spectral characterisation and catalytic applications Ari Lehtonen
*
Department of Chemistry, University of Turku, Vatselantie, FIN-20014 Turku, Finland Received 10 November 2004; accepted 19 November 2004
Abstract Two new tungsten(VI) complexes of the type WO2(ONNOR) (ONNOR = tetradentate diaminobis(phenolate) ligand) were prepared by the reaction of trisdiolatetungsten(VI) complex W(eg)3 (eg = 1,2-ethanediolate) and diaminobis(phenol)s in the presence of water. Studied complexes catalysed ROMP of norbornene when activated by Et2AlCl. They also catalysed oxotransfer reaction between DMSO and benzoin. Ó 2004 Elsevier B.V. All rights reserved. Keywords: Alkoxide complexes; Oxo complexes; Phenolate ligands; Tungsten; Catalysis
High-valent molybdenum and tungsten complexes with oxo ligands have attracted considerable interest due to their applications in organometallic and catalytic chemistry. In particular, these complexes are known to catalyse olefin metathesis reaction [1] and are also used in various industrial and biological oxidation processes [2,3]. Numerous dioxomolybdenum(VI) complexes with a variety of supporting ligands have been prepared and studied as catalyst model compounds [4,5], whereas the chemistry of analogous tungsten complexes is still inadequately studied [5–7]. One reason for the relatively little number of known dioxotungsten(VI) complexes is the poor availability of suitable starting materials, since typical synthetic routes start from soluble derivatives of
*
Tel.: +358 2 3336733; fax: +358 2 3336700. E-mail address: ari.lehtonen@utu.fi.
1387-7003/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2004.11.021
WO2Cl2, i.e., WO2Cl2(dme) [8] and WO2(acac)2 [9]. Trisdiolatotungsten(VI) complex W(eg)3 (1) (eg = ethylene glycolate) [10] is a straightforwardly available, stable and moderately soluble compound, which can be easily converted to different tungsten(VI) alkoxide and phenoxide complexes [11]. We have earlier found that 1 can react with tridentate aminobis(phenol)s (H2ONOR; R = Me, tert-Bu) to produce mixed ligand oxotungsten(VI) complexes [WO(eg)(ONOR)] [12]. The current paper presents reactions of 1 with tetradentate diaminobis(phenol)s. Syntheses and spectral characterization of two new dioxotungsten(VI) complexes with [O,N,N,O] donor ligands have been reported. Trisdiolato complex 1 was treated with tetradentate ligands, N,N 0 -bis(2-hydroxy-3,5-dimethylbenzyl)-N,N 0 dimethylethane-1,2-diamine (H2ONNOMe) and N,N 0 bis(2-hydroxy-3,5-di-tert-butylbenzyl)-N,N 0 -dimethylethane-1,2-diamine (H2ONNOtBu), in watery methanol and the reaction mixtures were stirred under reflux.
A. Lehtonen / Inorganic Chemistry Communications 8 (2005) 122–124
Scheme 1. Formation of complexes [WO2(ONNOR)].
The reaction yielded monomeric complexes [WO2(ON NOMe)] (2) and [WO2(ONNOtBu)] (3), respectively (see Scheme 1). 1 Presumably, the mechanism for the formation of these complexes includes ligand displacement in association with hydrolytic cleavage of two diolato groups. Complex 2 deposited as pale yellow microcrystals upon cooling to the room temperature, whereas complex 3 was obtained as white crystalline solid. Both compounds were characterised by spectral methods and ele-
1 1.00 mmol (364 mg) of 1 and equivalent amount of ligand precursor H2ONNOMe (356) or H2ONNOtBu (525 mg) were suspended in 20 ml of moist MeOH. The reaction mixtures were stirred under reflux for 6 h to obtain pale yellow solutions. Complexes 2 and 3 crystallised upon cooling to the room temperature. Crystalline products were washed with cold methanol and dried under ambient atmosphere. [WO2(ONNOMe)] (2): Pale yellow crystalline solid. Yield 310 mg (54%). IR: 1316(m), 1271(s), 1252(vs), 1231(vs), 1163(vs), 1144(m), 1061(s), 995(s), 959(m), 934(vs), 899 (vs), 868(m), 843(vs), 808(m), 774(m), 739(w), 688(m), 617(m), 588(m), 554(m). NMR: dC 153.88, 131.49, 129.95, 127.98, 127.31, 121.21, 64.01, 62.89, 53.09, 52.24, 48.71, 47.75, 20.41, 16.30. dH 6.98 (2H, ArH), 6.66 (2H, ArH), 5.08 (d, J = 14 Hz, 2H, NCH2), 3.51 (d, J = 14 Hz, 2H, NCH2), 3.18 (d, J = 13 Hz, 2H, NCH2), 2.74 (s, 6H, NCH3), 2.24 (s, 6H, ArCH3), 2.22 (d, J = 10 Hz, 2H, NCH2), 2.09 (s, 6H, ArCH3). Found: C, 40.29; H, 5.32; N, 4.71. C22H30N2O4W requires: C, 46.33; H, 5.30; N, 4.91. [WO2(ONNOtBu)] (3): White crystalline solid. Yield 275 mg (37%). IR: 1304(s, br), 1263(vs), 1253(vs), 1238(vs), 1204(s), 1171(s), 1132(s), 1063(m), 1015(m), 993(m), 937(s), 901(vs), 876(s), 855(s), 812(m), 785(m), 756(s), 692(w), 617(m), 557(s), 475(m). NMR: dC 155.56, 142.75, 138.80, 124.29, 123.83, 121.35, 65.64, 53.59, 49.49, 35.15, 34.24, 31.58, 30.63. dH 7.36 (d, J = 3 Hz, 2H, ArH), 6.86 (d, J = 3 Hz, 2H, ArH), 4.94 (d, J = 14 Hz, 2H, NCH2), 3.62 (d, J = 14 Hz, 2H, NCH2), 3.29 (d, J = 10 Hz, 2H, NCH2), 2.81 (s, 6H, NCH3), 2.40 (d, J = 10 Hz, 2H, NCH2), 1.45 (s, 18H, C(CH3)3), 1.29 (s, 18H, C(CH3)3). Found: C, 55.13; H, 7.29; N, 3.69. C34H54WN2O4 requires: C, 55.29; H, 7.37; N, 3.79.
123
mental analyses. IR and NMR data of these complexes were practically identical with those recorded earlier for their molybdenum analogues [13]. Both studied compounds show two characteristic cis-WO2 vibrational bands at around 900 and 935 cm1 in their IR spectra. The latter bands occur at 20 cm1 higher frequencies than those for the molybdenum congeners [13]. 1H and 13 C NMR spectra in CDCl3 show expected resonances for octahedral complexes with C2 rotation axis. Catalytic activities of complexes 2 and 3 were investigated using ROMP of norbornene as a test reaction. Sixcoordinated tungsten complexes (10 lmol) were dissolved in 6 ml of CH2Cl2/norbornene (2 mmol of cycloalkene monomer) mixture to form colourless solutions, which were treated with 1.8 M toluene solution of Et2AlCl. As a result, the solutions changed rapidly to an orange colour and simultaneous gel-formation started leading quickly to the completeness of reactions, which produced mainly insoluble, rubber-like polymers in high yields. However, polymerisations were difficult to control, whereas product outcome seems to depend predominately on the amount of used cocatalyst. The activation mechanism is not known, but the colour change of catalyst precursors upon addition of Et2AlCl is probably related to the reduction of W(VI) centres. Similar activation by reducing aluminium compounds has earlier been used in heterogeneous polymerisation of norbornene, which was catalysed by single crystals of (Bu4N)2[W6O19] [14]. The utility of studied dioxotungsten(VI) complexes to catalyse oxo-transfer reactions was investigated using DMSO as the oxygen donor and benzoin as the reductant. In a typical test reaction, 0.10 mmol of benzoin was dissolved in 0.7 ml of DMSO in a NMR tube and subsequently treated with 0.01 mmol of catalyst. The reaction mixture was kept at 100 °C for 48 h. Both complexes catalysed these oxidation reactions, since detected yields of oxidised products (benzil) were 50–60%, whereas in control experiments without catalysts no reactions between substrates and DMSO were observed. On the grounds of comparable molybdenum and tungsten based catalyst systems, it is supposed that the dioxotungsten(VI) complexes react with benzoin to yield oxotungsten(IV) complexes and benzil. The W(IV) complexes are then rapidly oxidised back to the initial dioxocompounds with DMSO to complete the catalytic cycle [4,5].
References [1] K.J. Ivin, J.C. Mol, Olefin Metathesis and Metathesis Polymerization, Academic Press, London, 1997. [2] H. Arzoumanian, Coord. Chem. Rev. 180 (1998) 191. [3] J.H. Enemark, J.J.A. Cooney, J.-J. Wang, R.H. Holm, Chem. Rev. 104 (2004) 1175.
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A. Lehtonen / Inorganic Chemistry Communications 8 (2005) 122–124
[4] (a) R. Dinda, P. Sengupta, S. Ghosh, W.S. Sheldrick, Eur. J. Inorg. Chem. (2003) 363; (b) N.R. Pramanik, S. Ghosh, T.K. Raychaudhuri, S. Ray, R.J. Butcher, S.S. Mandal, Polyhedron 23 (2004) 1595. [5] (a) Y.-L. Wong, J.-F. Ma, W.-F. Law, Y. Yan, W.-T. Wong, Z.-Y. Zhang, T.C.W. Mak, D.K.P. Ng, Eur. J. Inorg. Chem. (1999) 313; (b) Y.-L. Wong, Y. Yan, E.S.H. Chan, Q. Yang, T.C.W. Mak, D.K.P. Ng, J. Chem. Soc., Dalton Trans. (1998) 3057. [6] F.E. Ku¨hn, W.-M. Xue, A. Al-Aijlouni, A.M. Santos, S. Zang, C.C. Roma˜o, G. Eickerling, E. Herdtweck, Inorg. Chem. 41 (2002) 4468, and references therein.
[7] W.A. Herrmann, J. Fridgen, G.M. Lobmaier, M. Spiegler, New J. Chem. (1999) 5. [8] K. Dreisch, C. Andersson, C. Sta˚lhandske, Polyhedron 10 (1991) 2417. [9] S. Yu, R.H. Holm, Inorg. Chem. 28 (1989) 4385. [10] F.A. Schro¨der, J. Scherle, Z. Naturfor. 28b (1973) 46. [11] For example: A. Lehtonen, R. Sillanpa¨a¨, Polyhedron 22 (2003) 2755. [12] A. Lehtonen, R. Sillanpa¨a¨, Inorg. Chem. 43 (2004) 6501. [13] A. Lehtonen, R. Sillanpa¨a¨, Polyhedron, accepted. [14] M. McCann, D. McDonnell, J. Chem. Soc., Chem. Commun. (1993) 1718.