Ultrasound assisted synthesis of metal-1,3-diketonates

Inorganic Chemistry Communications 11 (2008) 733–736

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Ultrasound assisted synthesis of metal-1,3-diketonates Nitin S. Nandurkar a, Dinkar S. Patil b, Bhalchandra M. Bhanage a,* a b

Department of Chemistry, Institute of Chemical Technology, N. Parekh Marg, Matunga, Mumbai 400019, India Laser and Plasma Technology Division, Bhabha Atomic Research Centre, Mumbai 400085, India

a r t i c l e

i n f o

Article history: Received 21 February 2008 Accepted 12 March 2008 Available online 15 March 2008 Keywords: Ultrasound Diketonate Complex Organometallic Chemical vapour deposition Structure

a b s t r a c t A simple and convenient methodology for complex formation of wide variety of transition metals/alkaline earth metals with 1,3-diketones under sonication have been reported. The present method showed a significant rate enhancement for metal complex formation in the presence of ultrasound as compared to their silent counterpart, thereby providing higher yields. The role of ultrasound and solvent were also discussed. Moreover, the metal-1,3-diketonates were characterized by various techniques like FT-IR, 1 H NMR, mass spectrometry and magnetic susceptibility. Ó 2008 Elsevier B.V. All rights reserved.

Metal-1,3-diketonates are extensively studied as MOCVD precursors for the deposition of metal-oxide films [1]. Thin films of this metal-oxide are used as insulating layers in microelectronics [2], as a protective or optical coatings [3,4], in tunnel junctions [4], fuel cells [3b,5], and in gas sensors [3a,3b–5]. They are also used as catalyst in organic transformations [6]. Owing to such an enormous industrial applications the synthesis of metal-1,3-diketontes has gained considerable interest in recent years. Traditionally the metal-1,3-diketonates are synthesized either by metathesis reaction from the halides in basic conditions or by ligand exchange reactions. There are several reports in the literature for the synthesis of metal 1,3-diketonates such as Cr(thd)3 [thd = 2,2, 6,6-tetramethyl-3,5-heptanedionate]/24 h, 80 °C [7], Zr(thd)4 [8], Hf(tod)4/Zr(tod)4/Y(tod)3 (tod = 2,7,7-trimethyl-3,5-octanedionate)/ 5–24 h [9], Hf(thd)2Cl2/16 h, 110 °C [10], Ru(thd)3/Pd(thd)2/Pt(thd)2 [11], Hf(tbob)4 (tbob = terbutylacetoacetate)/24 h [12], Hf(tmnd)4/ Zr(tmnd)4 (tmnd = 2,2,8,8-tetramethyl-3,5-nonanedionate)/5–24 h [13]. These methods have drawbacks like requirement of higher temperature, longer reaction time and use of additives. Thus, there is a need to develop an efficient and simple protocol, which could facilitate the formation of wide variety of complexes at a faster rate under mild reaction conditions. In recent years, the application of ultrasound in synthetic methodologies has gained considerable interest as it can enhance the rate, yield and selectivity of such reactions [14]. It can also facilitate reactions at ambient conditions eliminating requirement of drastic conditions such as temperature, pressure and concentra* Corresponding author. Tel.: +91 22 24145616; fax: +91 22 24145614. E-mail address: [email protected] (B.M. Bhanage). 1387-7003/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2008.03.014

tion. In continuation of our work on ultrasound assisted reactions [15]. We herein report for the first time the complex formation of wide variety of transition metals and alkaline earth metals with 1,3-diketones under sonication. The present methodology showed a significant rate enhancement for metal complex formation under sonication as compared to the reactions performed under silent conditions. The main objective of this study was to study the effect of ultrasound on the synthesis of these metal-complexes and their steric and electronic properties. Moreover, the metal-1,3-diketonates were characterized by various techniques like FT-IR, 1 H NMR, mass spectrometry and magnetic susceptibility. Various metal-1,3-diketonates were synthesized by reacting metal nitrates/halides with the corresponding 1,3-diketone ligands under ultrasound and the results were compared with those obtained without ultrasound (Scheme 1) (Table 1) [16,17]. It has been observed that the synthesis of yttrium-1,3-diketonate by reacting Y(NO3)3  6H2O with 2,2,6,6-tetramethyl-3,5-heptanedione under silent conditions required 6 h and it gave 80% yield. The same reaction under sonication showed a significant rate enhancement and got completed within 30 min providing 89% yield. Similar trend was also observed for complex formation of metal halide like ZrCl4 with 2,2,6,6-tetramethyl-3,5-heptanedione. It took about 12 h for complex formation without ultrasound, while the same reaction under sonication got completed within 45 min providing 95% yield. To show the generality of the system, several other transition metals and alkaline earth metals were coupled with 1,3-diketones, which gave excellent yields within a shorter reaction time under sonication. The probable reason for the significant rate enhancement observed under sonication, may be due to the well known cavitational effect generated due to

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N.S. Nandurkar et al. / Inorganic Chemistry Communications 11 (2008) 733–736

Table 1 (continued)

1

R H O

+

))))))))

M(X)n

b

11

M

Methanol

R1

R

Entry

O

O

Metal

Condition

MnCl2  4H2O

Product

((((((

O O

R, R1 = alkyl.

Mn R

O

n

X = Cl, NO3 etc

Scheme 1. Synthesis of metal-1,3-diketonates. 12

Sr(NO3)2

((((((

O Sr

O

Table 1 Synthesis of metal-1,3-diketonatesa Entry

Metal

Condition

1

Y(NO3)3  6H2O

Silent

Product

Bu

O Y

O

t

But

c

Time

Yield (%)

6h

80

O 13

3b

4b

Y(NO3)3  6H2O

ZrCl4

ZrCl4

((((((

Silent

((((((

O

But

O

O Zr

O

O 5

Cr(NO3)3

((((((

Cr

6

7

8

9

NiCl2  6H2O

La(NO3)3

Zn(NO3)2  6H2O

Co(NO3)2  6H2O

((((((

((((((

((((((

((((((

Ni

O

O La

15

But 12 h

But

But

O

O Co

O

O 10

Ba(NO3)2

((((((

Ba

30 min

87

45 min

83

30 min

92

O

3

t

Bu

Bu

t

2

But 30 min

But

Bu

30 min

94

30 min

85

2

t

But

2

85

30 min

93

30 min

93

30 min

94

But

But

2

But

But

2

But

O

t

2

Ce(NO3)3  6H2O

((((((

O Ce

O

But

But

3 NaOH

Entry

Solvent

Condition

Time

Yieldb (%)

1 2 3 4 5 6 7 8 9 10 11 12

Methanol THF EDC 1,4-Dioxane Toluene DMF Methanol THF EDC 1,4-Dioxane Toluene DMF

(((((( (((((( (((((( (((((( (((((( (((((( Silent Silent Silent Silent Silent Silent

30 min 30 min 30 min 30 min 30 min 30 min 6h 6h 6h 6h 6h 6h

89 80 69 72 67 40 80 36 38 50 21 30

92

2

But

30 min

2

a Reaction conditions: Y(NO3)3  6H2O (10 mmol); thd (30 mmol); NaOH (36 mmol); solvent (30 ml). b Isolated yield.

3

But

85

Table 2 Effect of solvent on complexation using ultrasounda

Me

t

45 min

95

4

But

Yieldc (%)

a Reaction conditions: M(NO3)n (10 mmol); thd (10 mmol  n); (n  10 mmol  1.2); methanol (30 ml). b M(Cl)n (10 mmol); thd (10 mmol  n); methanol (40 ml). c Isolated yield.

4

45 min

Bu

Cu

90

But

O

O Zn

((((((

Time

89

O

O

O

O

3

Me b

Fe

But

Bu 30 min

O Zr

Cu(NO3)2  3H2O

But

O Y

((((((

3 14

2

Fe(NO3)2  9H2O

Bu

t

ultrasound [14]. The cavitation effect, which is predominant in methanol, plays an important role of solublization of reactants thereby enhancing the interaction between the metal salt and 1,3-diketone which results in a complex formation. While in the absence of ultrasound the extent of interaction between the metal salt and 1,3-diketone was so slight that no physical evidence of the reaction was apparent within the expected time. The selection of solvent for a sonochemical reaction is a crucial factor as the cavitational intensity changes with the solvent and depends on the nature of solvent [14] (Table 2). In the present case, six different solvents like methanol (bp 64.7 °C), tetrahydrofuran (bp 65–67 °C), 1,2-dichloroethane (bp 83 °C), 1,4-dioxane (bp 100 °C) toluene (bp 110 °C) and N,N-dimethylformamide (bp 153 °C) have

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N.S. Nandurkar et al. / Inorganic Chemistry Communications 11 (2008) 733–736 Table 3 Properties of the metal-1,3-diketonates Product

IR spectra (cm1) vC@O, vC@C, vM–O

1

H NMR (ppm, CDCl3) CH, But

Mass spectra

Y(thd)3 Zr(thd)4 Cr(acac)3 Ni(thd)2 La(thd)3 Zn(thd)2 Co(thd)2 Ba(thd)2 Mn(thd)2 Sr(thd)2 Fe(thd)2 Cu(thd)2 Ce(thd)3

1588, 1558, 1561, 1566, 1596, 1591, 1593, 1574, 1588, 1550, 1593, 1602, 1595,

5.74 5.67 – 5.78 5.63 5.84 5.74 5.77 5.88 5.65 5.74 5.64 5.69

m/z = 638.7(M+), m/z = 824.3(M+), m/z = 349.9(M+), m/z = 425.1(M+), m/z = 689.0(M+), m/z = 431.9(M+), m/z = 426.1(M+), m/z = 503.9(M+), m/z = 422.0(M+), m/z = 455.0(M+), m/z = 422(M+) m/z = 430.0(M+), m/z = 689.9(M+),

1515, 1519, 1522, 1535, 1577, 1569, 1580, 1533, 1563, 1530, 1540, 1558, 1523,

496, 480, 463 562, 493, 458 592, 543, 458 1504, 518, 486, 455 1525, 502, 466 1533, 469, 487, 576 1531, 502, 466, 455 1502, 565, 496, 478 1522, 503, 474 578, 491, 477 1504, 529, 480, 463 1525, 536, 482, 458 535, 479

(3H), 1.18 (27H) (4H), 1.18 (36H) (2H), (3H), (3H), (2H), (2H), (2H), (2H), (2H), (2H), (3H),

2.04 (18H) 1.19 (27H) 1.17(18H) 1.20 (18H) 1.16 (18H) 1.15 (18H) 1.17 (18H) 1.19 (18H) 1.18 (18H) 1.19 (27H)

Table 4 Elemental analysis of Y, Zr and Cu-1,3-diketonates Compound

Y(thd)3 Zr(thd)4 Cu(thd)2

Experiment (%)

Calculation (%)

C

H

C

H

62.08 64.08 61.51

9.03 9.31 8.93

62.06 64.12 61.48

9.00 9.29 8.91

Magnetic susceptibility 455.6, 641.0, 249.9 305.1, 505.9, 247.0, 368.0, 320.9, 238.2, 422.0,

320.4 457 213.0, 207.0 379.0, 363.0 207.0 241.9 207.0 207.0 320.0 270.9

229.9, 207.0 506.6, 323.3

Diamagnetic Diamagnetic paramagnetic Diamagnetic Diamagnetic Diamagnetic Diamagnetic Diamagnetic Paramagnetic Diamagnetic Diamagnetic Paramagnetic Diamagnetic

In conclusion, application of ultrasound in promoting complex formation of wide variety of transition metal and alkaline earth metal with 1,3-diketones is reported for the first time. Ultrasound plays an important role of enhancing the reaction rate of complex formation as compared to the reaction performed under silent conditions. Further work is in progress to test these precursors for MOCVD applications. Acknowledgement

been selected for complex formation of Y(NO3)3  6H2O with thd both with and without sonication. It has been observed that under sonication as the boiling point of the solvent increases the reaction yield was found to decrease, while no such trend was observed under silent conditions. The probable reason may be that solvents with lower boiling point have high vapour pressure. For liquids with high vapour pressure, the ease of cavity generation is higher, possibly resulting in higher number of cavities for the given power input in the system resulting in higher yield under sonication. Moreover, the metal-1,3-diketonates were characterized by using different techniques like FT-IR, 1H NMR, mass spectrometry and magnetic susceptibility (Table 3). FT-IR spectra of the complexes shows shifts of the absorption band’s of the carbonyl’s in the range of 1600–1500 cm1 depending on the structural variation. Shift of the absorption bands of the carbonyl’s in these region as well as the appearance of the metal-oxygen band’s in the range of 450–600 cm1 confirms the formation of metal-1,3-diketonates. While, hydrated metal-1,3-diketonates showed an additional absorption band in the range of 3190–3200 cm1 due to the presence of water molecules in the metal coordination sphere. The 1 H NMR of 1,3-diketonates was also studied. It showed typical peaks at around 5.63–5.88 ppm (CH) and at around 1.15– 2.03 ppm (But) indicating that the complexes exist predominantly in the enol form. The mass spectra showed only a limited number of fragments in which major peak corresponds to the loss of diketonate radical. Other fragments resulted from the loss of diketonate moieties such as (CðMeÞ3 , Me) were also detected. The hydrated metal complex losses water molecule under high vacuum conditions of the mass spectra and the MðthdÞþ 3 ion was observed instead of [M(thd)3 (H2O)]+. The magnetic susceptibility of 1,3diketonates was studied. It is well known in the literature that most of the metal-1,3-diketonates are diamagnetic in nature. Similar trend was observed in the present case, all the metal-1,3-diketonates were found to be dimagnetic, except Cr, Mn and Cu complexes which were paramagnetic in nature. The representative elemental analysis of Y(thd)3, Zr(thd)4 and Cu(thd)2 was studied and compared with theoretical calculations listed in Table 4 and it indicates the success of synthesis of these compounds with high purity.

The financial assistance from Department of Atomic Energy/ Board of Research in Nuclear Science (DAE/BRNS) is kindly acknowledged. References [1] L.G. Hubert-Pfalzgraf, Inorg. Chem. Commun. 6 (2003) 102. [2] E.P. Gusev, E. Cartier, D.A. Buchanan, M. Gribelyuk, M. Copel, H. OkornSchmidt, C. D’Emic, Microelectron. Eng. 59 (2001) 341. [3] (a) P.A. Williams, J.L. Roberts, A.C. Jones, P.A. Chalker, N.L. Tobin, J.F. Bickley, H.O. Davies, L.M. Smith, T.J. Leedham, Chem. Vapor Depos. 8 (2002) 163. and refs. therein; (b) M.A. Cameron, S.M. George, Thin Solid Films 348 (1999) 90. [4] K. Kukli, M. Ritala, T. Sajavaara, J. Keinonen, M. Leskela, Chem. Vapor Depos. 8 (2002) 199. and refs. therein. [5] G. Garcia, J. Casado, J. Llibre, A. Figueras, J. Cryst. Growth 156 (1995) 426. [6] (a) N.S. Nandurkar, M.J. Bhaushali, M.D. Bhor, B.M. Bhanage, Tetrahedron Lett. 48 (2007) 6573; (b) N.S. Nandurkar, M.J. Bhaushali, M.D. Bhor, B.M. Bhanage, Tetrahedron Lett. 49 (2008) 1045; (c) N.S. Nandurkar, B.M. Bhanage, Tetrahedron 64 (2008) 3655. [7] D. Stille, J.R. Doyle, in: J.M. Shreeve (Ed.), Inorganic Synthesis, vol. 24, Wiley Interscience Publication, New York, 1986, p. 183. [8] N.B. Morozova, I.K. Igumenov, V.N. Mit’kin, K.V. Kradenov, O.G. Potapova, V.B. Lazarev, Ya.Kh. Grinberg, Zh. Neorg. Khim. 34 (1989) 1193. [9] S.V. Pasko, L.G. Hubert-Pfalzgraf, A. Abrutis, P. Richard, A. Bartasyte, V. Kazlauskiene, J. Mater. Chem. 14 (2004) 1245. [10] L.G. Hubert-Pfalzgraf, N. Touati, S.V. Pasko, J. Vaissermann, A. Abrutis, Polyhedron 24 (2005) 3066. [11] M. Lashdaf, T. Hatanpää, M. Tiitta, J. Therm. Anal. Calorim. 64 (2001) 1171. [12] S.V. Pasko, L.G. Hubert-Pfalzgraf, A. Abrutis, Mater. Lett. 59 (2005) 1836. [13] S.V. Pasko, A. Abrutis, L.G. Hubert-Pfalzgraf, Mater. Lett. 59 (2005) 261. [14] (a) J.L. Luche, Synthetic Organic Sonochemistry, Plenum Press, New York, 1998; (b) T.J. Mason, Advances in Sonochemistry, JAI Press, London and Greenwich, CT, 1990. [15] (a) N.S. Nandurkar, M.J. Bhaushali, S.R. Jagtap, B.M. Bhanage, Ultrason. Sonochem. 14 (2007) 41; (b) N.S. Nandurkar, M.D. Bhor, S.D. Samant, B.M. Bhanage, Ind. Eng. Chem. Res. 46 (2007) 8590. [16] Typical procedure for complexation using metal nitrates under sonication (Table 1 entry 2): NaOH (1.44 g, 36 mmol) in methanol (15 ml) was added to 100 ml round-bottom flask, then thd (5.52 g, 30 mmol) was added under sonication. To the mixture, Y(NO3)3  6 H2O (3.83 g, 10 mmol) in methanol (15 ml) was added dropwise. The reaction was conducted for 20 min under sonication (temp. 25–28 °C). The frequency of the ultrasonic bath was 33 kHz with an HF

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outpower of 120 W. The crystals precipitated were filtered off and dried. To the filtrate water (40 ml) was added dropwise and sonicated for further 10 min. The resulting crystals were filtered and dried (5.68 g, 89%). [17] Typical Procedure for complexation using metal halides under sonication (Table 1 entry 4): ZrCl4 (2.33 g, 10 mmol) in methanol (20 ml) was added dropwise to a

suspension of thd (7.37 g, 40 mmol) in methanol (20 ml) under sonication. The reaction was conducted for 45 min under sonication (temp. 25–28 °C). The frequency of the ultrasonic bath was 33 kHz with an HF outpower of 120 W. After completion the solution was adjusted to pH 6 with a 20% NaOH solution. The resulting crystals precipitated were filtered off and dried (7.83 g, 95%).