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Lanthanide complexes as oxidation catalysts for alcohols and alkenes
Polyhedron Vol. 15, No. 20, pp. 3493-3500, 1996
~
Pergamon S0277-5387(96)00088-5
Copyright 9 1996 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0277-5387/96 $15.00+0.00
L A N T H A N I D E C O M P L E X E S AS OXIDATION CATALYSTS FOR A L C O H O L S A N D ALKENES WILLIAM P. GRIFFITH,* RUKSANA G. H. MOREEA and HELENA I. S. NOGUEIRA Department of Chemistry, Imperial College of Science, Technology and Medicine, London SW7 2AY, U.K. (Received 8 January 1996 ; accepted 2 February 1996)
Abstract--Studies on the use of lanthanide species and lanthanopolyoxotungstates [LnW~0036]9- and [Ln{PW11039}2]11 as catalysts for the oxidation of alcohols and the expoxidation of alkenes are reported. In a number of such oxidations reported in the literature it appears that the lanthanide centre plays little or no catalytic role. The effectiveness of the cerium(IV)-bromate catalytic system for the oxidation of alcohols is, however confirmed and its use extended. Copyright 9 1996 Elsevier Science Ltd
Lanthanide species have been used to effect a number of organic transformations, generally as stoichiometric reagents but in some cases as catalysts ; there are, however, relatively few applications of lanthanides as catalysts for organic oxidations.1 We have for some time been interested in the application of oxoruthenates as catalysts for a number of organic oxidations,z3 and also in the use of isopolyperoxo and heteropolyperoxo-tungstates and molybdates for catalytic oxidations of alkenes, alcohols and tertiary amines. 4'5 In this paper we report the results of our attempts to repeat some of the work reported on lanthanide-catalysed oxidations of alcohols and alkenes, and report for the first time the attempted use of lanthanophosphopolyoxotungstates, [LnnI {PW11039} 2]I1-- as oxidation catalysts in the presence of hydrogen peroxide.
RESULTS AND DISCUSSION Lanthanide salts as oxidation catalysts
It was reported in 1993 that "simple" lanthanide salts M(NO3)3" nH20 (M = Yb, Tb, Ho, Lu) would oxidize primary alcohols to aldehydes and secondary alcohols to ketones using iodosylbenzene as
* Author to whom correspondence should be addressed.
co-oxidant in dichloroethane at 80~ most of the reported oxidations involved ytterbium nitrate. 6 These results seem surprising since ytterbium, holmium and lutetium are not thought to exhibit oxidation states higher than III, so we studied the oxidation of typical primary and secondary alcohols by ytterbium and terbium nitrates and also cerium(Ill) nitrate, since cerium has a well-authenticated tetravalent chemistry. The results are summarized in Table 1. The products of alcohol oxidation (benzaldehyde from benzyl alcohol, anisaldehyde from anisyl alcohol, menthone from menthol and 2-decanone from 2decanol) were quantified by gas chromatography. It is clear that the co-oxidant itself has a significant effect; no "blank" experiments using iodosylbenzene in the absence of lanthanide catalyst had been reported by Yokoo et al. 6 It seems that there may be a minor catalytic effect from the lanthanide salts for secondary alcohols and none at all for primary alcohols. We conclude that this is not a useful method for the oxidation of alcohols.
Lanthanopolyoxotungstate complexes
It has been reported by Shiozaki et al. 7 that complexes of the type [CelVW10036]8- and [LnIn W10036]9 (Ln = Nd, Sm) will catalytically oxidize cyclohexanol to cyclohexanone in a t-butanol/ aqueous hydrogen peroxide mixture, the H202
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W. P. GRIFFITH et al. Table 1. Oxidations of alcohols catalysed by lanthanide nitrates with iodosylbenzenea Yield (%) (turnover) b Substrate
Catalyst
T (~
(a)
(b)
Benzyl alcohol
Yb(NO3)3- 5H20 Tb(NO3)3' 5H20
80
96 (10)
99
80
68 (14)
p-Anisyl alcohol Menthol
Yb(NO3)s' 5H20 Yb(NO3)3" 5H20
2-Decanol
Yb(NO3)3 "5H20 Ce(NO3)3 96H20
80 80 70 60 50 80 80
72
>99 (10) 45 (4) 32 (3) 27 (2) 24 (2) > 99 (8) > 99 (8)
>99 32 23 20 23 43 43
aOxidations carried out for 3 h, in 1,2-dichloroethane, using PhlO as cooxidant. Products analysed by gas chromatography. bTurnover (moles of product/moles catalyst). (a) In the presence of lanthanide. (b) In the absence of lanthanide.
functioning as co-oxidant. No yields or turnovers were reported and cyclohexanol was the only substrate studied. In a subsequent brief communication, the use of cetylpyridinium salts of [Lnlnwt003619- (Ln --- Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb) as catalysts with H202 as cooxidant, in a biphasic chloroform/water mixture, was studied; benzyl alcohol was oxidized to benzaldehyde over 30 min and 2-octanol to 2octanone over 6 h, with yields varying from 5 to 60%. 8 We have repeated these oxidation experiments using a number of lanthanopolyoxotungstate complexes (Table 2), studying the oxidation of benzyl alcohol to benzaldehyde, cyclohexanol to cyclohexanone and the epoxidation of cyclooctene, all with H202 as co-oxidant using the conditions reported in the literature, 7 viz. in a t-butanol/aqueous 30% H202 system at 92~ We also used a biphasic benzene/aqueous 30% H202 system in the presence of tetra-n-hexylammonium chloride as phase-transfer catalyst, since such a system has been shown 4"5'9to be effective for alkene epoxidations and alcohol oxidations catalysed by [PO4{WO(O2)2}4] 3- and related species. If, however, the procedure for making [LnInWloO36]9- is followed 1~ (reaction of [WO4]2- with the lanthanide salt at pH 7.2) in the absence of lanthanide, essentially the same yields and turnovers are obtained ("blank" in Table 2). The species in such lanthanide-free solutions are likely to be l~ [W7024] 6- and [H2W12042]10-. It is clear that the lanthanide has little effect--in fact, in some cases it seems to exert an inhibitory effect on the oxidations.
We also carried out experiments on oxidation of benzyl alcohol and 2-octanol in a biphasic chloroform/aqueous 30% H202 mixture at 60~ over 30 rain (benzyl alcohol) and 6 h (2-octanol) using the procedure of Shiozaki et al. 8 Our yields and turnovers using the cetylpyridinium salt of [SmW10036] 9- were broadly similar to those reported (we obtained yields of 74% of benzaldehyde and 45% of 2-octanone, compared with 23 and 48% by Shiozaki et al.8). However, the use of tungstate at pH 7.2 under the same conditions gave 40% of benzaldehyde and 52% of 2-octanone, again suggesting that the presence of the lanthanide is not essential for catalysis. It was suggested by Shiozaki et al. 7 that the H202 causes some decomposition of the lanthanopolyoxotungstates, and this indeed appears to be the case. We find that the profiles of the Raman spectra of Na9[SmW10036]" 30H20 in the solid state and in aqueous solution are very similar (Fig. 1), suggesting retention of the solid state structure in solution. These spectra are consistent with the known structures 12 of the [LnlIIW10036]9anions: in these, the lanthanide links two W5018 units in each of which the tungsten atoms, linked as WO6 octahedra, form square-based pyramids. The four basal oxygen atoms of the vertices of the basal WO6 octahedra coordinate to the lanthanide such that the resulting LnO8 unit has Archimedean antiprismatic geometry with approximately Dad symmetry. 12 When H202 is added to these [Lnm W10036] 9- complexes new bands appear. Some of the extra bands are likely to arise from [W203(O2)4(H20)2]2-, for which the Raman spec-
Lanthanide complexes as oxidation catalysts for alcohols and alkenes
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Table 2. Oxidations of alcohols and alkenes catalysed by lanthanopolyoxotungstates Yield (%) (turnover) Catalyst
Benzaldehyde Cyclohexanone (a) 83 (996) 78 (936) 72 (864) 45 (540)
(a) 77 (924) 73 (876) 24 (288) 36 (432)
86 (1032) 83 (996) 84 (1008)
80 (960) 77 (924) 81 (972)
86 (1032)
77 (924)
85 (1020)
88 (1056)
K,, [La {PW, iO30}21935H20
87(1044)
89(1068)
KII [Pr {PWl 1039}21"20H~O K,, [Sm{PWI ~O39}2]' 20H,O K,, [Tb {PW,,O39}21' 12H20 (NMe4)sK2[PWl iO39] 97H20 H3[PWI2040]" xH20
94 (1128) 77 (924) 26(312)
89 (1068) 74 (888) 4(48)
(NMe4)3Na6[YW~oO,6] - 12H~_O (NMe4)Na7[LaWtoO36] ' 10H~_O Nag[CemWloO3o] 943H20 (NMe4)4Na4 [CeWWioO36] ' 10H20 Nag[PrWloO36] 928H20 Nag[SmW,oO36] 930H20 (NMe4)2Na7 [TbWloO36] 910H20 (NMe4)2Na7 [YbWloO36]" 10H20 Blank in absence of lanthanide
Cyclooctene oxide (a)
(b)
26 (203) 13 (101) 45 (351)
61 (476)
55 (429)
44 (429)
48 (374)
87 (679) 86 (671) 18(140)
81 (810) 79 (790) 81 (810) 72 (720) 90 (936) 90 (900)
(a) Oxidations carried out at 92"C (reflux) for 3 h, in a t-butanol/aqueous 30% H202 system. (b) Oxidations carried out at 71:~C (reflux) for 3 h, in a biphasic benzene/aqueous 30% H202 system. Products analysed by gas chromatography.
trum has been assigned, ~3 e.g. those at 962 (v(W--O)), 852 (frO--O)) and 556 cm -~ (vas(MO2)). Although Raman studies have been reported on Na6Hz[CeW10036] 930H20 in aqueous and H20 2 solutions, no comparison with the spectrum of the complex in the solid state was given.~4 Such decomposition of heteropolyoxolmetallates by H20: has been reported before: thus [PWlzO40] 3- gives, amongst other products, [W203(O2)4(H20)2] 2- with H202 .5"15 It appears that in lanthanopolyoxotungstates the lanthanide does not exert a significant catalytic effect ; such catalysis as is observed probably arises from the formation of isopolyperoxo- or heteropolyperoxo-tungstates, known 4'5'9'13'15'16 to be active in such oxidations. The significantly lower efficiencies of [CelllW10036] 9- and [CelVW10036]8in such systems may result from the fact ~~that these are more stable in solution than the other lanthanopolyoxotungstate species. Lanthanophosphopolyoxotunystates
The unstable red-brown complex [Tb w {PWI iO39}2]~0- can be made from the oxidation of
[Tbm{PWuO39}_~]u - with aqueous persulfate. ~7 Since we have shown that persulfate is an excellent co-oxidant for trans-[Ru(OH)203] 2- in catalytic oxidations of the latter for alcohol and alkyl halide oxidations, z it was thought that the terbium(IV) complex might act as an oxidation catalyst with persulphate. However, on addition of benzyl alcohol to [TblV{PWuO39}2]l~ in excess persulfate with an H202/t-butanol mixture the brown colour of the complex was discharged but the oxidative efficiency of the system was no greater than that observed for [TbIn{PWuO39}2]u- in a similar solvent. In view, however, of the known ability 4'5'9'~5'~6 of phosphopolyoxotungstates to function as catalysts for alkene epoxidations and alcohol oxidations with H202 as co-oxidant, we studied a number of lanthanophosphopolyoxotungstates as possible catalysts for alcohol oxidations and alkene epoxidations using an aqueous 30% HzO2/t-butanol mixture under the conditions used by Shiozaki et al. 7 for oxidations by [LnW10036] n- (Table 2). We also used a biphasic 30% aqueous H2Oz/benzene mixture with tetrahexylammonium chloride as phase-transfer reagent under the conditions used 4.5.9.15.16for oxidations cat-
W. P. GRIFFITH et al.
3496
J ~
a
e.
e. e', t~
E
260
460
660 860 Wavenumber (cm -I)
~-
b
lobo
L 1200
l
Fig. 1. Raman spectra of Na9[SmW~0036]'30H20: (a) solid, (b) 0.2 M in aqueous solution, (c) 0.1 M in 15% H202 solution.
alysed by [PO4{WO(O2)2}4] 3- ("Venturello's compound" ;9 Table 2). The lanthanophosphopolyoxotungstates were prepared by the method of Haraguchi et al.18 and were characterized both analytically and by the positions ~9 of their 31p N M R shifts in aqueous solution. It will be seen from Table 2 that, although these are good catalysts, there is relatively little difference between yields and turnovers effected by [PWllO39] 7-, [PW~204o]3- or [Ln{PWnO39}2] 11(Ln = La, Pr, Sm, Tb). It is likely that the [Ln{PWllO39}2] 11- species are decomposed by H202, probably initially to give the known 2~ [PWIIO39] 7-. The latter will then react, as [PW12040] 3- is known to do, 15A6 to give a mixture of species, probably [W203(O2)4(H20)2] 2- ,
[PO4{WO(O2)2}4] a-, [PO3(OH){WO(O2)2}2{WO (O2)2(H20)}] 2- and [PO4{WO(O2)2}213-, all of which will catalyse the epoxidation of alkenes and the oxidation of alcohols. 4'5'9"~5'~6 Although the structure of Na2[N(CH3)4]4 H[PWHO39] "7H20 has been reported, z~ few oxidation reactions with it are known, but it is clear from Table 2 that with H202 it is in general as effective an oxidation catalyst as [PW12040] 3-, and a much better one in t-butanol (perhaps due to the more open 2~ structure of the anion). It is apparent from Table 2 that [PWuO39] 7- and [Ln{PWHO39}2] H- show similar properties as catalysts for oxidation by H202 of benzyl alcohol to benzaldehyde, cyclohexanol to cyclohexanone and cyclooctene to its epoxide in t-butanol. It is clear,
Lanthanide complexes as oxidation catalysts for alcohols and alkenes
3497
however, that, as with [LnW10036]" species, the presence of a lanthanide confers no special extra reactivity. Studies on the 31p N M R and Raman spectra of [Ln{PWllO39}2] ll a r e i n progress.
CeHIO6"4H2 O27 does oxidize benzyl alcohol to benzaldehyde in dichloromethane with tetrabutylammonium periodate as co-oxidant, but the yield is only 45%, and periodate alone under the same conditions gives 23% of benzaldehyde.
Use o f ceric ammonium nitrate-bromate and related systems as catalytic oxidants for alcohols
CONCLUSIONS
Organic oxidations by ceric ammonium nitrate, (NH4)2[Ce(NO3)6] ("CAN"), have been reviewed. ~'21 Its use as a stoichiometric oxidant for alcohols has been noted, 22 but a more useful application would seem to be the CAN-bromate catalytic system described by Ho 23 and Kanemoto et al. 24 involving the use of CAN and excess sodium bromate in a 7:3 acetonitrile/water solvent. We have confirmed that it is an effective oxidant under these conditions (Table 3) and find also that primary alcohols are oxidized to aldehydes in addition to the reported 23"24oxidation of secondary alcohol to ketones by the reagent. Nevertheless, it is apparent that simpler and cheaper systems such as those offered by ruthenium-based catalysts 2'3 are probably much more convenient and specific. Firouzabadi et al. have reported that "Ce(OH)3 (OOH)", made from CeC13"7H20 with H20225 and "[Ce(NO3)313(H2IO6)", made from CAN and KIO4, 26 will stoichiometrically oxidize alcohols in dry benzene. We have repeated these procedures and attempted to make them catalytic by using biphasic benzene/aqueous H 2 0 2 and benzene/aqueous NaIO4 solutions. However, neither Ce(OH)3(OOH) nor [Ce(NO3)313(H2IO6) give any significant oxidation of p-anisyl alcohol, benzyl alcohol or cyclohexanol. The recently reported
We conclude that "simple" lanthanide salts with iodosylbenzene as co-oxidant are not effective oxidants for alcohols. The lanthanotungstates [Ln m W10036] 9- (Ln = Y, La, Ce, Pr, Sm, Tb, Yb) and [CelVW10036]8- with H 2 0 2 as co-oxidant will catalyse the oxidation of primary and secondary alcohols to aldehydes and ketones and the epoxidation of alkenes, but it is likely that the active catalyst is [W203(O2)4(H20)2] 2-. Similar catalysis by the lanthanophosphopolyoxotungstates [Ln nl {PWI~ 039}2]9- (Ln = La, Pr, Sin, Tb) probably arises from [PWllO39] 7- and subsequent formation of polyperoxotungstate species. The ceric ammonium nitrate-bromate reagent is, however, an effective catalytic system for the oxidation of primary alcohols to aldehydes and of secondary alcohols to ketones. EXPERIMENTAL
Lanthanide salts were obtained from Aldrich and used without further purification, as was H3[PWI2040]'xH20. Hydrogen peroxide was obtained from BDH as a 30% w/v aqueous solution and was used as supplied, as was Na2WO4" 2H20. Raman spectra were recorded on a Spex Ramalog 5 instrument, with a Datamate data acquisition unit, using excitation at 514.5 nm from a Coherent
Table 3. Oxidation of alcohols by ceric ammonium nitrate Substrate
Product
Yield (%) (turnover)
Benzyl alcohol 2-Methylbenzyl alcohol 4-Methylbenzyl alcohol Piperonyl alcohol Geraniol
Benzaldehyde 2-Methyl benzaldehyde 4-Methyl benzaldehyde Piperonyl aldehyde Citral 1-Octanal Menthone ~-Tetralone Cyclohexanone Cyclododecanone 2-Decanone
91 (91) 96 (96) 90 (90) 8 9 0 73 (73) > 99 (> 99) 96 (96) > 99 ( > 99) > 99 ( > 99)
1-Octanol
Menthol c~-Tetralol Cyclohexanol Cyclododecanol 2-Decanol
Oxidations carried out at 80"C (reflux) for 3 h, in acetonitrile/H20 (7/3 v/v), using sodium bromate as co-catalyst. Products analysed by gas chromatography.
3498
W. P. GRIFFITH et al.
Radiation Innova 70 argon-ion laser. The GC data were obtained on a Perkin-Elmer Autosystem instrument using a Perki~Elmer stainless steel column (2 m) packed with 15% Carbowax 20M. Microanalysis were carried out by the Microanalytical Laboratories at Imperial College. ICPAES analysis were recorded on an A R L instrument by Mr B. Coles of the Geology Department, Imperial College.
Anal. for (NMe4)2Na7[YbW10036] ~10H20. Found C, 3.2; H, 1.4; N, 0.9. Calc. for CsH44N2046Na7WIoYb : C, 3.1 ; H, 1.4; N, 0.9%. K ll [Ln {PW,,O39 } 21" nH:O
Lanthanophosphopolytungstates of general formula [Ln{PWuO39}2] u - , where Ln = La nI, Pr III, Sm III and Tb lI1, were synthesized using the method of Haraguchi et al. TM Phosphotungstic acid hydrate (4.3 g, 1.5 mmol) was dissolved in hot (NMe4)xNa)[LnWloO36] 9nH20 water (5 cm3). An aqueous solution of a salt of the Lanthanopolyoxotungstates of general formula lanthanide (LaC1397H20, Pr(NO3)3 96H20, [LnWloO36]n , where Ln = La ul, Ce III, Ce iv, Pr hi, Sm(NO3)3" 6H20 or Tb(NO3)3" 5H:O ; 0.75 mmol, Sm m, Tb m, Yb uI and ym, were synthesized using 2 cm 3 of water) was added to the hot solution in a the general method of Peacock and Weakley. ~~ molar proportion (H3PW1204o : Ln) of 2 : 1. Then To an aqueous solution of sodium tungstate concentrated potassium acetate solution (5.0 g, 50 (5.0 g, 15.2 mmol, 10 cm 3 of water) was ad- mmol, 2 cm 3 of water ; pH adjusted to 7 with acetic ded glacial acetic acid until pH ~ 7. A warm aque- acid) was added dropwise with vigorous stirring. ous solution of a salt of the lanthanide The reaction mixture was filtered and the filtrate (LaC13" 7H20, Ce(NO3)3" 6H20, Pr(NO3)3" 6H20, refrigerated. The precipitate obtained was filtered, Sm(NO3)3 96H20, Tb(NO3)3 95H20 and recrystallized from water and dried in a desiccator Yb(NO3)3"5H20) or YC13"6H20 (1.5 mmol in 2 over silica gel. cm 3 of water) was added dropwise to the hot, stirred Anal. for KlI[Pr{PWuO39}2 ] "20H20. Found P, tungstate solution (90~ A transient precipitate 0.9; K, 6.9; Pr, 2.0; W, 64.2. Calc. for appeared after each drop, but dissolved with further H4oO98PzKuPrWz2: P, 1.0; K, 6.8; Pr, 2.2; W, stirring. For the tetramethylammonium salts an 64.4%. aqueous solution of tetramethylammonium chlorAnal. for Ku[Sm{PWuO39}2] "20H20. Found P, ide (0.99 g, 9.0 mmol, 2 cm 3 of water) was added to 0.9; K, 6.8; Sm, 2.5; W, 64.1. Calc. for the resultant solution. The solution was filtered and H4oO98P2KllSmW22: P, 1.0; K, 6.8; Sm, 2.4; W, refrigerated for several days until a precipitate was 64.3%. formed; for the Ce w compound a precipitate Anal. for Ku[Tb{PWuO39}2 ] 9 12H20. Found P, was obtained immediately. The solid obtained was 0.9; K, 6.9; Tb, 2.5; W, 66.4. Calc. for filtered, washed with water and dried in a desiccator H24090P2KIITbW22: P, 1.0; K, 7.0; Tb, 2.6; W, over silica gel. For preparation of (NMe4)4 65.7%. Na4[CelvWloO36]'10H20, (NH4)2[Ce(NO3)6] was used in place of the (NH4)2[Ce(SO4)3] used by Pea- (Me4N)sK2[PWllO39] "7H20 cock and Weakley. l~ The preparation is based on that by Maksimov Anal. for (NMen)3Na6[YWloO36] 9 12H20. Found C, 4.6; H, 1.9; N, 1.3. Calc. for C12H6oN3048 et al. 28 Phosphotungstic acid hydrate (2.9 g, 1.0 mmol) was dissolved in water (5 cm 3) and phosNa6WloY : C, 4.7; H, 2.0; N, 1.4%. Anal. for (NMea)zNa7[LaW~oO36] 9 10H20. phoric acid (0.09 mmol) added. The pH of the Found C, 3.4; H, 1.6; N, 0.9. Calc. for solution was adjusted to 4 with aqueous NaOH 1M. Then an aqueous solution of tetraCsHaaN2046Na7LaWI0 : C, 3.2 ; H, 1.5 ; N, 0.9%. Anal. for Na9[CeWmO36]'43H20. Found Ce, methylammonium chloride (1.5 g, 14.0 mmol) was 3.8; Na, 5.8; W, 51.1. Calc. for H86079CeNa9W10 : added with formation of a white solid. The precipitate obtained was filtered, washed with ethanol Ce, 4.0; Na, 5.9; W, 52.0% . Anal. for (NMe4)aNa4[CelvWloO36] 9 10H20. and dried in a desiccator over silica gel. Found C, 6.2; H, 1.9; N, 2.5. Calc. for C16H68 Anal. for (NMe4)sK2[PWuO39] 97H20. Found C, NaOa6CeNa4Wlo : C, 6.2; H, 2.2; N, 1.8%. 7.6; H, 1.9; N, 2.1. Calc. for C2oH74Oa6PK2WH : C, Anal. for Na9[PrWmO36]'28H20. Found Na, 7.4 ; H, 2.3 ; N, 2.2%. 7.0; Pr, 3.4; W, 55.9. Calc. for H56064Na9PrWxo: Na, 6.3; Pr, 4.3; W, 56.3% . Oxidations of alcohols by lanthanide salts Anal. for Nag[SmWloO36 ] ' 3 0 H 2 0 . Found Na, 7.0 ; Sm, 4.8 ; W, 54.0. Calc. for H60066Na9SmWlo : Oxidations of benzvl alcohol and cyclohexanol Na, 6.3; Sin, 4.5; W, 55.5% . by lanthanopolyoxotungstates and lanthano-
Lanthanide complexes as oxidation catalysts for alcohols and alkenes polyoxophosphotungstates. An adaptation of the method of Shiozaki et al. 7 was used for alcohol oxidations in an aqueous 30% H202/t-butanol mixture. To a solution of the alcohol (24 mmol) in tbutanol (10 cm 3) was added an aqueous solution of the catalyst (0.02 mmol, 2 cm 3 of water) and aqueous 30% H_~O2 (4 cm 3, 32 mmol). The resultant solution was refluxed (temperature of 92cC) for 3 h with continuous stirring. The final solution was analysed by gas chromatography. Epoxidation of cyclooctene by lanthanopolyoxotungstates and lanthanopolyoxophosphotungstates. Two main methods were used. (a) In an aqueous 30% H202/t-butanol mixture. To a solution of cyclooctene (1.1 g, 10 mmol) in tbutanol (10 cm 3) was added an aqueous solution of the catalyst (0.02 mmol, 2 cm 3 of water) and aqueous 30% H20 2 (2.5 cm 3, 20 mmol). The resultant solution was refluxed (temperature of 92~C) for 3 h with continuous stirring. The final solution was analysed by gas chromatography. (b) In a biphasic aqueous 30% HzO2-benzene mixture. The procedure is based on a method used with ["C6(HI3)4N]3[PO4{WO(02)2}4] as catalyst. 4 To a solution of cyclooctene (1.1 g, 10 mmol) and tetrahexylammonium chloride (23 mg, 6 retool) in benzene (10 cm 3) was added an aqueous solution of the catalyst (0.02 mmol, 2 cm 3 of water) and aqueous 30% H,O2 (2.5 cm 3, 25 mmol). The resultant mixture was refluxed at 71 ~C for 3 h with continuous stirring. The final organic layer was analysed by gas chromatography. Oxidations o f alcohols' by Ln(NO3)3"nH20 (Ln = Yb, Tb, Ce). The method of Y o k o o et al. 6 was used. Ln(NO3)3"nH20 (0.1 mmol) was added to a suspension of iodosylbenzene (0.33 g, 1.5 mmol) and the alcohol (1.0 mmol) in 1,2-dichloroethane (10 ml). The resultant suspension was refluxed at 80~C for 3 h with continuous stirring. The final solution was analysed by gas chromatography. Oxidations o f alcohols by ceric ammonium nitrate. An adaptation of the method of Ho 23 was used. A stirred mixture of the alcohol (2 mmol), sodium bromate (0.45 g, 3 mmol) and ceric ammonium nitrate (11 rag, 0.02 mmol) in aqueous acetonitrile (7 : 3 v/v, 10 ml) was refluxed at 8OC for 3 h. The final solution was analysed by gas chromatography. Acknowledgements--We thank the Calouste Gulbenkian Foundation (HISN) for a postgraduate grant, and the ULIRS for the Raman spectrometer.
REFERENCES 1. G. A. Molander, Chem. Rev. 1992, 92, 29; H. B. Kagan and J. C. Namy, Tetrahedron 1986, 42, 6573.
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2. A. J. Bailey, W. P. Griffith, A. J. P. White and D. J. Williams, J. Chem. Soc., Chem. Commun. 1994, 1833; A. J. Bailey, W. P. Griffith, S. I. Mostafa and P. A. Sherwood, Inor9. Chem. 1993, 32, 268. 3. W. P. Griffith, Chem. Soc. Rev. 1992, 21, 179 and references therein. 4. A. C. Dengel, W. P. Griffith and B. C. Parkin, J. Chem. Soc., Dalton Trans. 1993, 2683. 5. W. P. Griffith, B. C. Parkin, A. J. P. White and D. J. Williams, J. Chem. Soc., Dalton Trans. 1995, 3131 ; A. J. Bailey, W. P. Griffith and B. C. Parkin, J. Chem. Soc., Dalton Trans. 1995, 1833. 6. T. Yokoo, K. Matsumoto, K. Oshima and K. Utimoto, Chem. Lett. 1993, 571. 7. R. Shiozaki, H. Goto and Y. Kera, Bull. Chem. Soe. Jpn 1993, 66, 2790. 8. R. Shiozaki, A. Inagaki, A. Nishino, H. Kominami and Y. Kera, Kidorui 1995, 26, 274. 9. C. Venturello, R. D'Aloisio, J. C. J. Bart and M. Ricci, J. Mol. Cat. 1985, 32, 107. 10. R. D. Peacock and T. J. R. Weakley, J. Chem. Soc. (A) 1971, 1836. 11. J. J. Hastings and O. W. Howarth, J. Chem. Soc., Dalton Trans. 1992, 209. 12. T. Yamase, T. Ozeki and M. Tosaka, Acta Crvst. 1994, C50, 1849 and references therein; J. Iball, J. N. Low and T. J. R. Weakley, J. Chem. Soc., Dalton Trans. 1974, 2021. 13. N. C. Campbell, A. C. Dengel, C. J. Edwards and W. P. Griffith, J. Chem. Soc., Dalton Trans. 1992, 209. 14. R. Shiozaki, M. Morimoto, E. Nishio and Y. Kera, Chem. Express 1993, 8, 361. 15. L. Salles, C. Aubry, R. Thouvenot, F. Robert, C. Dor6mieux-Morim G. Chottard, H. Ledon, V. Jeannin and J.-M. Br6geault, Inorg. Chem. 1994, 33, 871. 16. D. C. Duncan, R. C. Chambers, E. Hecht and C. L. Hill, J. Am. Chem. Soc. 1995, 117, 681. 17. W. S. You and Y. P. Gu, Chin. Chem. Lett. 1993, 4, 369 ; A. S. Saprykin, V. P. Shilov, V. I. Spitsyn and N. N. Krot, Proc. Acad. Sci. USSR (Doklady Chem.) 1976, 226, 114; A. S. Saprykin, V. I. Spitsyn and N. N. Krot, Doklady Phys. Chem. 1976, 231, 1038. 18. N. Haraguchi, Y. Okaue, T. Isobe and Y. Matsuda, Inor9. Chem. 1994, 33, 1015. 19. M.A. Fedotov, B. Z. Pertsikov and D. K. Danovich, Polyhedron 1990, 9 (10), 1249. 20. J. Fuchs, A. Thiele and R. Palm, Z. NaturJbrsch. 1981, 36b, 544. 21. T. L. Ho in Organic Syntheses by Oxidation with Metal Complexes (edited by W. J. Mijs and C. R. H. I. de Jonge), p. 569: Plenum, New York (1986); T. L. Ho, Synthesis 1973, 347. 22. W. S. Trahanovsky, L. B. Young and G. I. Brown, J. Or9. Chem. 1967, 32, 3865; W. S. Trahanovsky and C. B. Young, J. Chem. Soc. 1965, 5777. 23. T. L. Ho, Synthesis 1978, 936. 24. S. Kanemoto, H. Tomioka, K. Oshima and H. Nozaki, Bull. Chem. Soc. Jpn. 1986, 59, 105; H. Tomioka, K. Oshima and H. Nozaki, Tetrahedron Lett. 1982, 23, 539.
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25. H. Firouzabadi and N. Iranpoor, Synth. Commun. 1984, 14, 875. 26. H. Firouzabadi, N. Iranpoor, G. Hajipour and J. Toofan, Synth. Commun. 1984, 14, 1033.
27. W. Levason and R. D. Oldroyd, Polyhedron 1996, 15, 409. 28. G. M. Maksimov, G. N. Kustova, K. I. Matveev and T. P. Lazarenko, Soviet J. Coord. Chem. 1990, 472.
~
Pergamon S0277-5387(96)00088-5
Copyright 9 1996 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0277-5387/96 $15.00+0.00
L A N T H A N I D E C O M P L E X E S AS OXIDATION CATALYSTS FOR A L C O H O L S A N D ALKENES WILLIAM P. GRIFFITH,* RUKSANA G. H. MOREEA and HELENA I. S. NOGUEIRA Department of Chemistry, Imperial College of Science, Technology and Medicine, London SW7 2AY, U.K. (Received 8 January 1996 ; accepted 2 February 1996)
Abstract--Studies on the use of lanthanide species and lanthanopolyoxotungstates [LnW~0036]9- and [Ln{PW11039}2]11 as catalysts for the oxidation of alcohols and the expoxidation of alkenes are reported. In a number of such oxidations reported in the literature it appears that the lanthanide centre plays little or no catalytic role. The effectiveness of the cerium(IV)-bromate catalytic system for the oxidation of alcohols is, however confirmed and its use extended. Copyright 9 1996 Elsevier Science Ltd
Lanthanide species have been used to effect a number of organic transformations, generally as stoichiometric reagents but in some cases as catalysts ; there are, however, relatively few applications of lanthanides as catalysts for organic oxidations.1 We have for some time been interested in the application of oxoruthenates as catalysts for a number of organic oxidations,z3 and also in the use of isopolyperoxo and heteropolyperoxo-tungstates and molybdates for catalytic oxidations of alkenes, alcohols and tertiary amines. 4'5 In this paper we report the results of our attempts to repeat some of the work reported on lanthanide-catalysed oxidations of alcohols and alkenes, and report for the first time the attempted use of lanthanophosphopolyoxotungstates, [LnnI {PW11039} 2]I1-- as oxidation catalysts in the presence of hydrogen peroxide.
RESULTS AND DISCUSSION Lanthanide salts as oxidation catalysts
It was reported in 1993 that "simple" lanthanide salts M(NO3)3" nH20 (M = Yb, Tb, Ho, Lu) would oxidize primary alcohols to aldehydes and secondary alcohols to ketones using iodosylbenzene as
* Author to whom correspondence should be addressed.
co-oxidant in dichloroethane at 80~ most of the reported oxidations involved ytterbium nitrate. 6 These results seem surprising since ytterbium, holmium and lutetium are not thought to exhibit oxidation states higher than III, so we studied the oxidation of typical primary and secondary alcohols by ytterbium and terbium nitrates and also cerium(Ill) nitrate, since cerium has a well-authenticated tetravalent chemistry. The results are summarized in Table 1. The products of alcohol oxidation (benzaldehyde from benzyl alcohol, anisaldehyde from anisyl alcohol, menthone from menthol and 2-decanone from 2decanol) were quantified by gas chromatography. It is clear that the co-oxidant itself has a significant effect; no "blank" experiments using iodosylbenzene in the absence of lanthanide catalyst had been reported by Yokoo et al. 6 It seems that there may be a minor catalytic effect from the lanthanide salts for secondary alcohols and none at all for primary alcohols. We conclude that this is not a useful method for the oxidation of alcohols.
Lanthanopolyoxotungstate complexes
It has been reported by Shiozaki et al. 7 that complexes of the type [CelVW10036]8- and [LnIn W10036]9 (Ln = Nd, Sm) will catalytically oxidize cyclohexanol to cyclohexanone in a t-butanol/ aqueous hydrogen peroxide mixture, the H202
3493
3494
W. P. GRIFFITH et al. Table 1. Oxidations of alcohols catalysed by lanthanide nitrates with iodosylbenzenea Yield (%) (turnover) b Substrate
Catalyst
T (~
(a)
(b)
Benzyl alcohol
Yb(NO3)3- 5H20 Tb(NO3)3' 5H20
80
96 (10)
99
80
68 (14)
p-Anisyl alcohol Menthol
Yb(NO3)s' 5H20 Yb(NO3)3" 5H20
2-Decanol
Yb(NO3)3 "5H20 Ce(NO3)3 96H20
80 80 70 60 50 80 80
72
>99 (10) 45 (4) 32 (3) 27 (2) 24 (2) > 99 (8) > 99 (8)
>99 32 23 20 23 43 43
aOxidations carried out for 3 h, in 1,2-dichloroethane, using PhlO as cooxidant. Products analysed by gas chromatography. bTurnover (moles of product/moles catalyst). (a) In the presence of lanthanide. (b) In the absence of lanthanide.
functioning as co-oxidant. No yields or turnovers were reported and cyclohexanol was the only substrate studied. In a subsequent brief communication, the use of cetylpyridinium salts of [Lnlnwt003619- (Ln --- Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb) as catalysts with H202 as cooxidant, in a biphasic chloroform/water mixture, was studied; benzyl alcohol was oxidized to benzaldehyde over 30 min and 2-octanol to 2octanone over 6 h, with yields varying from 5 to 60%. 8 We have repeated these oxidation experiments using a number of lanthanopolyoxotungstate complexes (Table 2), studying the oxidation of benzyl alcohol to benzaldehyde, cyclohexanol to cyclohexanone and the epoxidation of cyclooctene, all with H202 as co-oxidant using the conditions reported in the literature, 7 viz. in a t-butanol/aqueous 30% H202 system at 92~ We also used a biphasic benzene/aqueous 30% H202 system in the presence of tetra-n-hexylammonium chloride as phase-transfer catalyst, since such a system has been shown 4"5'9to be effective for alkene epoxidations and alcohol oxidations catalysed by [PO4{WO(O2)2}4] 3- and related species. If, however, the procedure for making [LnInWloO36]9- is followed 1~ (reaction of [WO4]2- with the lanthanide salt at pH 7.2) in the absence of lanthanide, essentially the same yields and turnovers are obtained ("blank" in Table 2). The species in such lanthanide-free solutions are likely to be l~ [W7024] 6- and [H2W12042]10-. It is clear that the lanthanide has little effect--in fact, in some cases it seems to exert an inhibitory effect on the oxidations.
We also carried out experiments on oxidation of benzyl alcohol and 2-octanol in a biphasic chloroform/aqueous 30% H202 mixture at 60~ over 30 rain (benzyl alcohol) and 6 h (2-octanol) using the procedure of Shiozaki et al. 8 Our yields and turnovers using the cetylpyridinium salt of [SmW10036] 9- were broadly similar to those reported (we obtained yields of 74% of benzaldehyde and 45% of 2-octanone, compared with 23 and 48% by Shiozaki et al.8). However, the use of tungstate at pH 7.2 under the same conditions gave 40% of benzaldehyde and 52% of 2-octanone, again suggesting that the presence of the lanthanide is not essential for catalysis. It was suggested by Shiozaki et al. 7 that the H202 causes some decomposition of the lanthanopolyoxotungstates, and this indeed appears to be the case. We find that the profiles of the Raman spectra of Na9[SmW10036]" 30H20 in the solid state and in aqueous solution are very similar (Fig. 1), suggesting retention of the solid state structure in solution. These spectra are consistent with the known structures 12 of the [LnlIIW10036]9anions: in these, the lanthanide links two W5018 units in each of which the tungsten atoms, linked as WO6 octahedra, form square-based pyramids. The four basal oxygen atoms of the vertices of the basal WO6 octahedra coordinate to the lanthanide such that the resulting LnO8 unit has Archimedean antiprismatic geometry with approximately Dad symmetry. 12 When H202 is added to these [Lnm W10036] 9- complexes new bands appear. Some of the extra bands are likely to arise from [W203(O2)4(H20)2]2-, for which the Raman spec-
Lanthanide complexes as oxidation catalysts for alcohols and alkenes
3495
Table 2. Oxidations of alcohols and alkenes catalysed by lanthanopolyoxotungstates Yield (%) (turnover) Catalyst
Benzaldehyde Cyclohexanone (a) 83 (996) 78 (936) 72 (864) 45 (540)
(a) 77 (924) 73 (876) 24 (288) 36 (432)
86 (1032) 83 (996) 84 (1008)
80 (960) 77 (924) 81 (972)
86 (1032)
77 (924)
85 (1020)
88 (1056)
K,, [La {PW, iO30}21935H20
87(1044)
89(1068)
KII [Pr {PWl 1039}21"20H~O K,, [Sm{PWI ~O39}2]' 20H,O K,, [Tb {PW,,O39}21' 12H20 (NMe4)sK2[PWl iO39] 97H20 H3[PWI2040]" xH20
94 (1128) 77 (924) 26(312)
89 (1068) 74 (888) 4(48)
(NMe4)3Na6[YW~oO,6] - 12H~_O (NMe4)Na7[LaWtoO36] ' 10H~_O Nag[CemWloO3o] 943H20 (NMe4)4Na4 [CeWWioO36] ' 10H20 Nag[PrWloO36] 928H20 Nag[SmW,oO36] 930H20 (NMe4)2Na7 [TbWloO36] 910H20 (NMe4)2Na7 [YbWloO36]" 10H20 Blank in absence of lanthanide
Cyclooctene oxide (a)
(b)
26 (203) 13 (101) 45 (351)
61 (476)
55 (429)
44 (429)
48 (374)
87 (679) 86 (671) 18(140)
81 (810) 79 (790) 81 (810) 72 (720) 90 (936) 90 (900)
(a) Oxidations carried out at 92"C (reflux) for 3 h, in a t-butanol/aqueous 30% H202 system. (b) Oxidations carried out at 71:~C (reflux) for 3 h, in a biphasic benzene/aqueous 30% H202 system. Products analysed by gas chromatography.
trum has been assigned, ~3 e.g. those at 962 (v(W--O)), 852 (frO--O)) and 556 cm -~ (vas(MO2)). Although Raman studies have been reported on Na6Hz[CeW10036] 930H20 in aqueous and H20 2 solutions, no comparison with the spectrum of the complex in the solid state was given.~4 Such decomposition of heteropolyoxolmetallates by H20: has been reported before: thus [PWlzO40] 3- gives, amongst other products, [W203(O2)4(H20)2] 2- with H202 .5"15 It appears that in lanthanopolyoxotungstates the lanthanide does not exert a significant catalytic effect ; such catalysis as is observed probably arises from the formation of isopolyperoxo- or heteropolyperoxo-tungstates, known 4'5'9'13'15'16 to be active in such oxidations. The significantly lower efficiencies of [CelllW10036] 9- and [CelVW10036]8in such systems may result from the fact ~~that these are more stable in solution than the other lanthanopolyoxotungstate species. Lanthanophosphopolyoxotunystates
The unstable red-brown complex [Tb w {PWI iO39}2]~0- can be made from the oxidation of
[Tbm{PWuO39}_~]u - with aqueous persulfate. ~7 Since we have shown that persulfate is an excellent co-oxidant for trans-[Ru(OH)203] 2- in catalytic oxidations of the latter for alcohol and alkyl halide oxidations, z it was thought that the terbium(IV) complex might act as an oxidation catalyst with persulphate. However, on addition of benzyl alcohol to [TblV{PWuO39}2]l~ in excess persulfate with an H202/t-butanol mixture the brown colour of the complex was discharged but the oxidative efficiency of the system was no greater than that observed for [TbIn{PWuO39}2]u- in a similar solvent. In view, however, of the known ability 4'5'9'~5'~6 of phosphopolyoxotungstates to function as catalysts for alkene epoxidations and alcohol oxidations with H202 as co-oxidant, we studied a number of lanthanophosphopolyoxotungstates as possible catalysts for alcohol oxidations and alkene epoxidations using an aqueous 30% HzO2/t-butanol mixture under the conditions used by Shiozaki et al. 7 for oxidations by [LnW10036] n- (Table 2). We also used a biphasic 30% aqueous H2Oz/benzene mixture with tetrahexylammonium chloride as phase-transfer reagent under the conditions used 4.5.9.15.16for oxidations cat-
W. P. GRIFFITH et al.
3496
J ~
a
e.
e. e', t~
E
260
460
660 860 Wavenumber (cm -I)
~-
b
lobo
L 1200
l
Fig. 1. Raman spectra of Na9[SmW~0036]'30H20: (a) solid, (b) 0.2 M in aqueous solution, (c) 0.1 M in 15% H202 solution.
alysed by [PO4{WO(O2)2}4] 3- ("Venturello's compound" ;9 Table 2). The lanthanophosphopolyoxotungstates were prepared by the method of Haraguchi et al.18 and were characterized both analytically and by the positions ~9 of their 31p N M R shifts in aqueous solution. It will be seen from Table 2 that, although these are good catalysts, there is relatively little difference between yields and turnovers effected by [PWllO39] 7-, [PW~204o]3- or [Ln{PWnO39}2] 11(Ln = La, Pr, Sm, Tb). It is likely that the [Ln{PWllO39}2] 11- species are decomposed by H202, probably initially to give the known 2~ [PWIIO39] 7-. The latter will then react, as [PW12040] 3- is known to do, 15A6 to give a mixture of species, probably [W203(O2)4(H20)2] 2- ,
[PO4{WO(O2)2}4] a-, [PO3(OH){WO(O2)2}2{WO (O2)2(H20)}] 2- and [PO4{WO(O2)2}213-, all of which will catalyse the epoxidation of alkenes and the oxidation of alcohols. 4'5'9"~5'~6 Although the structure of Na2[N(CH3)4]4 H[PWHO39] "7H20 has been reported, z~ few oxidation reactions with it are known, but it is clear from Table 2 that with H202 it is in general as effective an oxidation catalyst as [PW12040] 3-, and a much better one in t-butanol (perhaps due to the more open 2~ structure of the anion). It is apparent from Table 2 that [PWuO39] 7- and [Ln{PWHO39}2] H- show similar properties as catalysts for oxidation by H202 of benzyl alcohol to benzaldehyde, cyclohexanol to cyclohexanone and cyclooctene to its epoxide in t-butanol. It is clear,
Lanthanide complexes as oxidation catalysts for alcohols and alkenes
3497
however, that, as with [LnW10036]" species, the presence of a lanthanide confers no special extra reactivity. Studies on the 31p N M R and Raman spectra of [Ln{PWllO39}2] ll a r e i n progress.
CeHIO6"4H2 O27 does oxidize benzyl alcohol to benzaldehyde in dichloromethane with tetrabutylammonium periodate as co-oxidant, but the yield is only 45%, and periodate alone under the same conditions gives 23% of benzaldehyde.
Use o f ceric ammonium nitrate-bromate and related systems as catalytic oxidants for alcohols
CONCLUSIONS
Organic oxidations by ceric ammonium nitrate, (NH4)2[Ce(NO3)6] ("CAN"), have been reviewed. ~'21 Its use as a stoichiometric oxidant for alcohols has been noted, 22 but a more useful application would seem to be the CAN-bromate catalytic system described by Ho 23 and Kanemoto et al. 24 involving the use of CAN and excess sodium bromate in a 7:3 acetonitrile/water solvent. We have confirmed that it is an effective oxidant under these conditions (Table 3) and find also that primary alcohols are oxidized to aldehydes in addition to the reported 23"24oxidation of secondary alcohol to ketones by the reagent. Nevertheless, it is apparent that simpler and cheaper systems such as those offered by ruthenium-based catalysts 2'3 are probably much more convenient and specific. Firouzabadi et al. have reported that "Ce(OH)3 (OOH)", made from CeC13"7H20 with H20225 and "[Ce(NO3)313(H2IO6)", made from CAN and KIO4, 26 will stoichiometrically oxidize alcohols in dry benzene. We have repeated these procedures and attempted to make them catalytic by using biphasic benzene/aqueous H 2 0 2 and benzene/aqueous NaIO4 solutions. However, neither Ce(OH)3(OOH) nor [Ce(NO3)313(H2IO6) give any significant oxidation of p-anisyl alcohol, benzyl alcohol or cyclohexanol. The recently reported
We conclude that "simple" lanthanide salts with iodosylbenzene as co-oxidant are not effective oxidants for alcohols. The lanthanotungstates [Ln m W10036] 9- (Ln = Y, La, Ce, Pr, Sm, Tb, Yb) and [CelVW10036]8- with H 2 0 2 as co-oxidant will catalyse the oxidation of primary and secondary alcohols to aldehydes and ketones and the epoxidation of alkenes, but it is likely that the active catalyst is [W203(O2)4(H20)2] 2-. Similar catalysis by the lanthanophosphopolyoxotungstates [Ln nl {PWI~ 039}2]9- (Ln = La, Pr, Sin, Tb) probably arises from [PWllO39] 7- and subsequent formation of polyperoxotungstate species. The ceric ammonium nitrate-bromate reagent is, however, an effective catalytic system for the oxidation of primary alcohols to aldehydes and of secondary alcohols to ketones. EXPERIMENTAL
Lanthanide salts were obtained from Aldrich and used without further purification, as was H3[PWI2040]'xH20. Hydrogen peroxide was obtained from BDH as a 30% w/v aqueous solution and was used as supplied, as was Na2WO4" 2H20. Raman spectra were recorded on a Spex Ramalog 5 instrument, with a Datamate data acquisition unit, using excitation at 514.5 nm from a Coherent
Table 3. Oxidation of alcohols by ceric ammonium nitrate Substrate
Product
Yield (%) (turnover)
Benzyl alcohol 2-Methylbenzyl alcohol 4-Methylbenzyl alcohol Piperonyl alcohol Geraniol
Benzaldehyde 2-Methyl benzaldehyde 4-Methyl benzaldehyde Piperonyl aldehyde Citral 1-Octanal Menthone ~-Tetralone Cyclohexanone Cyclododecanone 2-Decanone
91 (91) 96 (96) 90 (90) 8 9 0 73 (73) > 99 (> 99) 96 (96) > 99 ( > 99) > 99 ( > 99)
1-Octanol
Menthol c~-Tetralol Cyclohexanol Cyclododecanol 2-Decanol
Oxidations carried out at 80"C (reflux) for 3 h, in acetonitrile/H20 (7/3 v/v), using sodium bromate as co-catalyst. Products analysed by gas chromatography.
3498
W. P. GRIFFITH et al.
Radiation Innova 70 argon-ion laser. The GC data were obtained on a Perkin-Elmer Autosystem instrument using a Perki~Elmer stainless steel column (2 m) packed with 15% Carbowax 20M. Microanalysis were carried out by the Microanalytical Laboratories at Imperial College. ICPAES analysis were recorded on an A R L instrument by Mr B. Coles of the Geology Department, Imperial College.
Anal. for (NMe4)2Na7[YbW10036] ~10H20. Found C, 3.2; H, 1.4; N, 0.9. Calc. for CsH44N2046Na7WIoYb : C, 3.1 ; H, 1.4; N, 0.9%. K ll [Ln {PW,,O39 } 21" nH:O
Lanthanophosphopolytungstates of general formula [Ln{PWuO39}2] u - , where Ln = La nI, Pr III, Sm III and Tb lI1, were synthesized using the method of Haraguchi et al. TM Phosphotungstic acid hydrate (4.3 g, 1.5 mmol) was dissolved in hot (NMe4)xNa)[LnWloO36] 9nH20 water (5 cm3). An aqueous solution of a salt of the Lanthanopolyoxotungstates of general formula lanthanide (LaC1397H20, Pr(NO3)3 96H20, [LnWloO36]n , where Ln = La ul, Ce III, Ce iv, Pr hi, Sm(NO3)3" 6H20 or Tb(NO3)3" 5H:O ; 0.75 mmol, Sm m, Tb m, Yb uI and ym, were synthesized using 2 cm 3 of water) was added to the hot solution in a the general method of Peacock and Weakley. ~~ molar proportion (H3PW1204o : Ln) of 2 : 1. Then To an aqueous solution of sodium tungstate concentrated potassium acetate solution (5.0 g, 50 (5.0 g, 15.2 mmol, 10 cm 3 of water) was ad- mmol, 2 cm 3 of water ; pH adjusted to 7 with acetic ded glacial acetic acid until pH ~ 7. A warm aque- acid) was added dropwise with vigorous stirring. ous solution of a salt of the lanthanide The reaction mixture was filtered and the filtrate (LaC13" 7H20, Ce(NO3)3" 6H20, Pr(NO3)3" 6H20, refrigerated. The precipitate obtained was filtered, Sm(NO3)3 96H20, Tb(NO3)3 95H20 and recrystallized from water and dried in a desiccator Yb(NO3)3"5H20) or YC13"6H20 (1.5 mmol in 2 over silica gel. cm 3 of water) was added dropwise to the hot, stirred Anal. for KlI[Pr{PWuO39}2 ] "20H20. Found P, tungstate solution (90~ A transient precipitate 0.9; K, 6.9; Pr, 2.0; W, 64.2. Calc. for appeared after each drop, but dissolved with further H4oO98PzKuPrWz2: P, 1.0; K, 6.8; Pr, 2.2; W, stirring. For the tetramethylammonium salts an 64.4%. aqueous solution of tetramethylammonium chlorAnal. for Ku[Sm{PWuO39}2] "20H20. Found P, ide (0.99 g, 9.0 mmol, 2 cm 3 of water) was added to 0.9; K, 6.8; Sm, 2.5; W, 64.1. Calc. for the resultant solution. The solution was filtered and H4oO98P2KllSmW22: P, 1.0; K, 6.8; Sm, 2.4; W, refrigerated for several days until a precipitate was 64.3%. formed; for the Ce w compound a precipitate Anal. for Ku[Tb{PWuO39}2 ] 9 12H20. Found P, was obtained immediately. The solid obtained was 0.9; K, 6.9; Tb, 2.5; W, 66.4. Calc. for filtered, washed with water and dried in a desiccator H24090P2KIITbW22: P, 1.0; K, 7.0; Tb, 2.6; W, over silica gel. For preparation of (NMe4)4 65.7%. Na4[CelvWloO36]'10H20, (NH4)2[Ce(NO3)6] was used in place of the (NH4)2[Ce(SO4)3] used by Pea- (Me4N)sK2[PWllO39] "7H20 cock and Weakley. l~ The preparation is based on that by Maksimov Anal. for (NMen)3Na6[YWloO36] 9 12H20. Found C, 4.6; H, 1.9; N, 1.3. Calc. for C12H6oN3048 et al. 28 Phosphotungstic acid hydrate (2.9 g, 1.0 mmol) was dissolved in water (5 cm 3) and phosNa6WloY : C, 4.7; H, 2.0; N, 1.4%. Anal. for (NMea)zNa7[LaW~oO36] 9 10H20. phoric acid (0.09 mmol) added. The pH of the Found C, 3.4; H, 1.6; N, 0.9. Calc. for solution was adjusted to 4 with aqueous NaOH 1M. Then an aqueous solution of tetraCsHaaN2046Na7LaWI0 : C, 3.2 ; H, 1.5 ; N, 0.9%. Anal. for Na9[CeWmO36]'43H20. Found Ce, methylammonium chloride (1.5 g, 14.0 mmol) was 3.8; Na, 5.8; W, 51.1. Calc. for H86079CeNa9W10 : added with formation of a white solid. The precipitate obtained was filtered, washed with ethanol Ce, 4.0; Na, 5.9; W, 52.0% . Anal. for (NMe4)aNa4[CelvWloO36] 9 10H20. and dried in a desiccator over silica gel. Found C, 6.2; H, 1.9; N, 2.5. Calc. for C16H68 Anal. for (NMe4)sK2[PWuO39] 97H20. Found C, NaOa6CeNa4Wlo : C, 6.2; H, 2.2; N, 1.8%. 7.6; H, 1.9; N, 2.1. Calc. for C2oH74Oa6PK2WH : C, Anal. for Na9[PrWmO36]'28H20. Found Na, 7.4 ; H, 2.3 ; N, 2.2%. 7.0; Pr, 3.4; W, 55.9. Calc. for H56064Na9PrWxo: Na, 6.3; Pr, 4.3; W, 56.3% . Oxidations of alcohols by lanthanide salts Anal. for Nag[SmWloO36 ] ' 3 0 H 2 0 . Found Na, 7.0 ; Sm, 4.8 ; W, 54.0. Calc. for H60066Na9SmWlo : Oxidations of benzvl alcohol and cyclohexanol Na, 6.3; Sin, 4.5; W, 55.5% . by lanthanopolyoxotungstates and lanthano-
Lanthanide complexes as oxidation catalysts for alcohols and alkenes polyoxophosphotungstates. An adaptation of the method of Shiozaki et al. 7 was used for alcohol oxidations in an aqueous 30% H202/t-butanol mixture. To a solution of the alcohol (24 mmol) in tbutanol (10 cm 3) was added an aqueous solution of the catalyst (0.02 mmol, 2 cm 3 of water) and aqueous 30% H_~O2 (4 cm 3, 32 mmol). The resultant solution was refluxed (temperature of 92cC) for 3 h with continuous stirring. The final solution was analysed by gas chromatography. Epoxidation of cyclooctene by lanthanopolyoxotungstates and lanthanopolyoxophosphotungstates. Two main methods were used. (a) In an aqueous 30% H202/t-butanol mixture. To a solution of cyclooctene (1.1 g, 10 mmol) in tbutanol (10 cm 3) was added an aqueous solution of the catalyst (0.02 mmol, 2 cm 3 of water) and aqueous 30% H20 2 (2.5 cm 3, 20 mmol). The resultant solution was refluxed (temperature of 92~C) for 3 h with continuous stirring. The final solution was analysed by gas chromatography. (b) In a biphasic aqueous 30% HzO2-benzene mixture. The procedure is based on a method used with ["C6(HI3)4N]3[PO4{WO(02)2}4] as catalyst. 4 To a solution of cyclooctene (1.1 g, 10 mmol) and tetrahexylammonium chloride (23 mg, 6 retool) in benzene (10 cm 3) was added an aqueous solution of the catalyst (0.02 mmol, 2 cm 3 of water) and aqueous 30% H,O2 (2.5 cm 3, 25 mmol). The resultant mixture was refluxed at 71 ~C for 3 h with continuous stirring. The final organic layer was analysed by gas chromatography. Oxidations o f alcohols' by Ln(NO3)3"nH20 (Ln = Yb, Tb, Ce). The method of Y o k o o et al. 6 was used. Ln(NO3)3"nH20 (0.1 mmol) was added to a suspension of iodosylbenzene (0.33 g, 1.5 mmol) and the alcohol (1.0 mmol) in 1,2-dichloroethane (10 ml). The resultant suspension was refluxed at 80~C for 3 h with continuous stirring. The final solution was analysed by gas chromatography. Oxidations o f alcohols by ceric ammonium nitrate. An adaptation of the method of Ho 23 was used. A stirred mixture of the alcohol (2 mmol), sodium bromate (0.45 g, 3 mmol) and ceric ammonium nitrate (11 rag, 0.02 mmol) in aqueous acetonitrile (7 : 3 v/v, 10 ml) was refluxed at 8OC for 3 h. The final solution was analysed by gas chromatography. Acknowledgements--We thank the Calouste Gulbenkian Foundation (HISN) for a postgraduate grant, and the ULIRS for the Raman spectrometer.
REFERENCES 1. G. A. Molander, Chem. Rev. 1992, 92, 29; H. B. Kagan and J. C. Namy, Tetrahedron 1986, 42, 6573.
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2. A. J. Bailey, W. P. Griffith, A. J. P. White and D. J. Williams, J. Chem. Soc., Chem. Commun. 1994, 1833; A. J. Bailey, W. P. Griffith, S. I. Mostafa and P. A. Sherwood, Inor9. Chem. 1993, 32, 268. 3. W. P. Griffith, Chem. Soc. Rev. 1992, 21, 179 and references therein. 4. A. C. Dengel, W. P. Griffith and B. C. Parkin, J. Chem. Soc., Dalton Trans. 1993, 2683. 5. W. P. Griffith, B. C. Parkin, A. J. P. White and D. J. Williams, J. Chem. Soc., Dalton Trans. 1995, 3131 ; A. J. Bailey, W. P. Griffith and B. C. Parkin, J. Chem. Soc., Dalton Trans. 1995, 1833. 6. T. Yokoo, K. Matsumoto, K. Oshima and K. Utimoto, Chem. Lett. 1993, 571. 7. R. Shiozaki, H. Goto and Y. Kera, Bull. Chem. Soe. Jpn 1993, 66, 2790. 8. R. Shiozaki, A. Inagaki, A. Nishino, H. Kominami and Y. Kera, Kidorui 1995, 26, 274. 9. C. Venturello, R. D'Aloisio, J. C. J. Bart and M. Ricci, J. Mol. Cat. 1985, 32, 107. 10. R. D. Peacock and T. J. R. Weakley, J. Chem. Soc. (A) 1971, 1836. 11. J. J. Hastings and O. W. Howarth, J. Chem. Soc., Dalton Trans. 1992, 209. 12. T. Yamase, T. Ozeki and M. Tosaka, Acta Crvst. 1994, C50, 1849 and references therein; J. Iball, J. N. Low and T. J. R. Weakley, J. Chem. Soc., Dalton Trans. 1974, 2021. 13. N. C. Campbell, A. C. Dengel, C. J. Edwards and W. P. Griffith, J. Chem. Soc., Dalton Trans. 1992, 209. 14. R. Shiozaki, M. Morimoto, E. Nishio and Y. Kera, Chem. Express 1993, 8, 361. 15. L. Salles, C. Aubry, R. Thouvenot, F. Robert, C. Dor6mieux-Morim G. Chottard, H. Ledon, V. Jeannin and J.-M. Br6geault, Inorg. Chem. 1994, 33, 871. 16. D. C. Duncan, R. C. Chambers, E. Hecht and C. L. Hill, J. Am. Chem. Soc. 1995, 117, 681. 17. W. S. You and Y. P. Gu, Chin. Chem. Lett. 1993, 4, 369 ; A. S. Saprykin, V. P. Shilov, V. I. Spitsyn and N. N. Krot, Proc. Acad. Sci. USSR (Doklady Chem.) 1976, 226, 114; A. S. Saprykin, V. I. Spitsyn and N. N. Krot, Doklady Phys. Chem. 1976, 231, 1038. 18. N. Haraguchi, Y. Okaue, T. Isobe and Y. Matsuda, Inor9. Chem. 1994, 33, 1015. 19. M.A. Fedotov, B. Z. Pertsikov and D. K. Danovich, Polyhedron 1990, 9 (10), 1249. 20. J. Fuchs, A. Thiele and R. Palm, Z. NaturJbrsch. 1981, 36b, 544. 21. T. L. Ho in Organic Syntheses by Oxidation with Metal Complexes (edited by W. J. Mijs and C. R. H. I. de Jonge), p. 569: Plenum, New York (1986); T. L. Ho, Synthesis 1973, 347. 22. W. S. Trahanovsky, L. B. Young and G. I. Brown, J. Or9. Chem. 1967, 32, 3865; W. S. Trahanovsky and C. B. Young, J. Chem. Soc. 1965, 5777. 23. T. L. Ho, Synthesis 1978, 936. 24. S. Kanemoto, H. Tomioka, K. Oshima and H. Nozaki, Bull. Chem. Soc. Jpn. 1986, 59, 105; H. Tomioka, K. Oshima and H. Nozaki, Tetrahedron Lett. 1982, 23, 539.
3500
W. P. G R I F F I T H et al.
25. H. Firouzabadi and N. Iranpoor, Synth. Commun. 1984, 14, 875. 26. H. Firouzabadi, N. Iranpoor, G. Hajipour and J. Toofan, Synth. Commun. 1984, 14, 1033.
27. W. Levason and R. D. Oldroyd, Polyhedron 1996, 15, 409. 28. G. M. Maksimov, G. N. Kustova, K. I. Matveev and T. P. Lazarenko, Soviet J. Coord. Chem. 1990, 472.