Cyclopalladated binuclear complexes of schiff bases

PolyhedronVoI. 15, No. 22, pp. 3979 3986, 1996

~

Copyright :~ 1996 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0277 5387/96 $15.00+0.00

Pergamon S0277-5387(96)00139-8

CYCLOPALLADATED BINUCLEAR COMPLEXES OF SCHIFF BASES

K. SELVAKUMAR and S. VANCHEESAN* Department of Chemistry, Indian Institute of Technology, Madras 600 036, India

(Received 24 January 1996 ; accepted 28 February 1996) Abstract--Refluxing palladium acetate with Schiff bases C 6 H 5 C H : N M e (1), C 6 H s C H : N Bu n (2), 4-MeC6H4CH:NBu n (3), 4-OCH3C6H4CH=NBu n (4), 3,4-(OMe)zC6H3CH=N Bu n (5) and 2,4-(OMe)2C6H3CH=NBu n (6) in acetic acid followed by metathesis with LiC1 on methanol gave chloro-bridged cyclopalladated complexes l a ~ a . The reactions of these chloro-bridged complexes with binucleating ligands such as 4,4'-bipyridine, 1,1,2,2-tetraacetyl ethane,N,N'-bis(2-hydroxybenzylidene)-l,4-diaminobutane, N,N'-bis(2-hydroxy-3t-butyl-5-methylbenzylidene)-1,4-diaminobutane, N,N'-bis(2-hydroxy-5-methyl-c~-phenylbenzylidene)-l,4-diaminobutane and 2-hydroxybenzalazine gave binuclear cyclopalladated complexes. All the complexes were analysed by means of IR, 1H and 13C N M R and H H COSY N M R spectroscopic techniques. Copyright 9 1996 Elsevier Science Ltd

The synthesis of cyclometalled complexes has received considerable interest over the past two decades. 1 Complexes with palladocycles are of unique importance, since they are used as versatile starting materials for regio- and stereo-selective organic synthesis2 and also for applications in diverse areas such as photochemistry, 3 liquid crystal, 4 homogeneous catalysis, 5 optical resolution 6 and antitumour reagents. 7 Synthesis of cyclopalladated binuclear complexes is of current interest. Vila et al. first synthesised complexes of this type from chloro-bridged cyclopalladated Schiff base complexes using bis(diphenylphosphino)alkane and -alkene. s We have recently demonstrated the synthesis ofcyclopalladated binuclear complexes using 2,2'-polymethylenebipyridine from cyclopalladated Schiff bases and benzylamines. 9 As a continuation of our earlier work 1~in this area we report the results of synthesis of cyclopalladated binuclear complexes from cyclopalladated Schiff base complexes using binucleating ligands such as 4,4'-bipyridine, 1,1,2,2-tetraacetylethane, N,N'his(2 - hydroxybenzylidene) - 1,4 - diaminobutane, N,N' - bis(2 - hydroxy - 3 - t - butyl - 5 - methylbenzylidene)- 1,4-diaminobutane, N,N'-bis(2-hy-

* Author to whom correspondence should be addressed.

droxy - 5 - methyl - c~- phenylbenzylidene) - 1,4 - diaminobutane and 2-hydroxybenzalazine.

EXPERIMENTAL Solvents were purified using standard methods. H Palladium acetate was prepared from palladium sponge. 12 1 , 1 , 2 , 2 - T e t r a a c e t y l e t h a n e , 132-hydroxy-3t-butyl-5-methylbenzaldehyde~4 and 2-hydroxy-5methylbenzophenone 15 were prepared by literature methods. Commercial samples of 4,4'-bipyridine, salicylaldehyde and 1,4-diaminobutane were used as such. The Schiff bases ( 1 ~ ) were prepared by refluxing 1 equiv, of amine with 1 equiv, of aldehyde in methanol for 1 h. The chloro-bridged cyclopalladated complexes of Schiff bases l a ~ a were prepared by refluxing palladium acetate with Schiff base in acetic acid followed by metathesis with LiC1 in methanol.16 The binucleating ligands N,N'-bis(2hydroxybenzylidene)- 1,4-diaminobutane (hbd) and N,N'-bis(2-hydroxy-3-t-butyl-5-methylbenzylidene)- 1,4-diaminobutane (hbbd) were prepared by refluxing 1 equiv, of 1,4-diaminobutane with 2 equiv, of corresponding aldehyde in methanol for 1 h. N,N'-Bis(2-hydroxy-5-methyl-c~-phenylbenzylidene)-1,4-diaminobutane (hmpbd) was prepared by refluxing 1 equiv, of 1,4-diaminobutane

3979

K. SELVAKUMAR and S. VANCHEESAN

3980

with 2 equiv, of 2-hydroxy-5-methylbenzophenone in ethanol for 5 h. 2-Hydroxybenzalazine (hba) was prepared by refluxing 1 equiv, of hydrazine with 2 equiv, of salicylaldehyde in methanol for 1 h. Elemental analyses were carried out in a Heraeus CHN-O rapid elemental analyser. IR spectra in the range 4000-400 cm -1 were recorded using a Shimadzu IR-470 spectrophotometer. IR spectra in the range 400-180 cm -1 were recorded as polyethylene discs using a Perkin-Elmer 983G spectrophotometer, tH and t3C NMR, and H - H COSY N M R spectra were taken in CDC13 solution with TMS as internal standard using a JEOL-JNM-GSX 400 spectrometer.

i

[{iM(4,6-(OMe)zC6HzCH=I~--Bu") (2-O-3-C(CH3)3-5-CH3C6HaCH--N--(CHa)2--)}21

Synthesis of (re)

The chloro-bridged dimer 6a (72.4 mg, 0.1 mmol) was added to a refluxing methanol solution (20 cm 3) of N,N'-bis (2-hydroxy-3-t-butyl-5-methylbenzylidene)-l,4-diaminobutane (43.6 mg, 0.1 mmol) and sodium hydroxide (8 mg, 0.2 mmol). The solution was stirred for 10 h at room temperature. The yellow complex tle formed was filtered, washed with methanol, dried and finally recrystallized from CH2C12/MeOH (96 mg, 88%). Complexes le, 2e and 5e were also synthesized by the same procedure.

i

Synthesis of [{Pd(4,6-(OMe)2C6HaCH=N--Bun)C1 (CsH4N) }2] (611) The chloro-bridged complex 6a (72.4 mg, 0.1 mmol) was stirred with 4,4'-bipyridine dihydrate (19.2 mg, 0.1 mmol) in CH2C12 (5 cm 3) for 2 h at room temperature. The resulting clear solution was filtered and concentrated. The complex 6b obtained was recrystallized from CH2Clz/MeOH (85 mg, 96%). Similarly complexes 2b-Sb were synthesized.

Synthesis of [{iM(4,6-(OMe)aC6H2CH=I~--Bu n) (CH3CO)2--C--}z] (6e) The chloro-bridged dimer 6a (72.4 rag, 0.1 mmol) was added to a clear solution of 1,1,2,2-tetraacetylethane (19.8 mg, 0.1 mmol) and sodium hydroxide (8 rag, 0.2 mmol) in methanol (10 cm 3) and stirred for 10 h at room temperature. The volume of the solvent was reduced to 3 cm 3and filtered. The complex 6e obtained was washed with a small volume of methanol and recrystallized from CHzC12/MeOH (73 mg, 86%). Similarly complexes le, 3c and 5c were prepared.

Synthesis of [{i~d(4,6-(OMe)2CrH2CH=I~--Bu n) (2-O--C6H4CH=N--(CH2)2--) }z] (6d) The chloro-bridged dimer 6a (72.4 mg, 0.1 mmol) was added to a well stirred clear methanol (15 cm 3) solution of N,N'-bis(2-hydroxybenzylidene)-l,4diaminobutane (29.6 mg, 0.1 mmol) and sodium hydroxide (8 mg, 0.2 mmol). Stirring was continued for 10 h at room temperature. The product 6d formed was filtered, washed with methanol and recrystallized from CH2C12/MeOH (91 mg, 96%). Similarly complexes ld-5d were prepared.

I

1

Synthesis of [{Pd(C6H4CH--N--Bu")(2-O-5-CH3 C6H3C(C6Hs)--N

(CH2)2--))2] (2t)

This complex was prepared by the above procedure for 6e using N,N'-bis(2-hydroxy-5-methyl~-phenylbenzylidene)- 1,4-diaminobutane (47.6 mg, 0.1 mmol) and the chloro-bridged dimer 2a (60.4 mg, 0.1 mmol).

Synthesis of [{i3d(C6H4CH--N--Bu")(2-O-C6H4 CH--N--)}2] (2g) The chloro-bridged dimer 2a (60.4 mg, 0.1 mmol) was added to a clear methanol (10 cm 3) solution of 2-hydroxybenzalazine (24 mg, 0.1 mmol) and sodium hydroxide (8 mg, 0.2 mmol). Stirring was continued for 6 h at room temperature. The yellow complex 2g formed was filtered, washed with methanol and recrystallized from CH2C12/MeOH (70 mg, 91%). RESULTS AND DISCUSSION

The Schiff bases 1 4 upon refluxing with palladium acetate in acetic acid under nitrogen gave acetato-bridged complexes. The corresponding chloro-bridged complexes laqla were prepared from acetato-bridged complexes by a metathesis reaction using LiC1 in methanol. 16The far-IR spectra of these complexes exhibit two strong bands at ca 300 and 260 cm -1, suggesting a dimer 17 (Fig. 1). The asymmetric stretching frequency of the C - - N bond is shifted to a lower wave number in complexes labia compared with free ligands, suggesting that the nitrogen atom is coordinated to palladium. 16,18 The bridge-splitting reaction of the chlorobridged complexes l a - r a was carried out with

Cyclopalladated binuclear complexes of Schiff bases R7 R1

2

~R3

R2

Fig. 1. la : R ~= CH3, R 2 = R 3 = R 4 = H ; 2a : R ~= Bu n, R 2 = R 3 = R 4 = H; 3a: R l = Bu n, R2 = CH3, R 3 = R 4 = H ; 4a : R 1 = B u n, R 2 = O C H 3 , R 3 = R 4 = H ; 5a : R ~= Bu ~, R 2 = R 3 = O C H 3 , R 4 = H ; 6a : R ~= Bu", R 2 = R 4 = O C H 3 , R 3 = H.

bidentate binucleating ligand such as 4,4'-bipyridine. The reaction of l a with 4,4'-bipyridine gave lb, which was insoluble in c o m m o n organic solvents, 9 whereas the chloro-bridged complexes 2a~ia gave soluble complexes 2bqlb with 4,4'bipyridine under similar conditions (Fig. 2). The v(Pd--C1) of these complexes is in the range 300~ 280 c m - 1 reported for a series of cyclopalladated complexes in which chlorine is t r a n s to the palladated carbon atom 17 (Table 1). The asymmetric stretching frequency of the C - - N bond of these complexes is shifted to a lower wave number to the extent of 40 cm 1, suggesting coordination of nitrogen to the metal. ~8 The ~H N M R spectrum of complex 6b shows that the proton adjacent to the metallated carbon a t o m (H 3) is shielded and resonates at 5.33 ppm. This high-field shift is due to the diamagnetic anisotropy of the coordinated pyridine ring of 4,4'-bipyridine. A similar type of high field shift was already noticed in several cyclopalladated complexes. ~~ The ~H N M R spectrum of 6b also suggests that the methoxy group (C a) resonates at 3.62 ppm, whereas in the free ligand it resonates at 3.79 ppm. The other methoxy group (C 6) remains intact after complexation and resonates at 3.81

I

H'~7~ N

\

/

C[

!, Fig. 2. lb : R I = CH3, R 2 = R 3 = R 4 = H ; 2b : R ~= Bu n, R2 = R3 = R 4 = H ; 3b : R ~ = B H n, R 2 = CH3, R 3 ---- R 4 = H ; 4b : R t = Bu n, R 2 = OCH3, R 3 = R 4 = H ; 5b : R 1 = B u n, R 2 = R 3 = O C H 3 , R 4 = H ; 6b : R ~ = Bu n, R 2 = R 4 = O C H 3 , R 3 = H.

3981

ppm. This high-field shift of methoxy protons is also due to diamagnetic shielding of 4,4'-bipyridine. A similar effect on OCH3 protons was also noticed in monomeric triphenylphosphine derivatives of cyclopalladated complexes, z~ The reaction of chloro-bridged complexes was also studied with bis(/%diketone) ligands such as 1,1,2,2-tetraacetylethane (tae). The reaction of the dimeric complex l a gave the binuclear cyclometallated complex le with tae in the presence of sodium hydroxide. Similarly the binuclear complexes 3e-6e were synthesized from the respective dimeric complexes 3 a 4 a (Fig. 3). The I R spectra of these binuclear complexes exhibit three bands at c a 1560, 1410 and 1360 cm -~, which are characteristic for the chelated acetyl acetanato moiety, l~ The asymmetric stretching frequency of the C - - N bond of these complexes is shifted to a lower wave number, suggesting that the C - - N chelation with the metal atom is intact. ~8It is inferred from the ~H N M R spectrum of complex 6e that both the methyl groups of the acetylacetanato moiety of the ligand tae are not magnetically equivalent. This is due to the high t r a n s influence of the carbon atom that lengthens the P d - - O bond t r a n s to the metallated carbon atom. We have extended our studies on the synthesis of binuclear complexes from l a 4 a using various salen-based tetradentate binucleating ligands such as N,N'-bis(2-hydroxybenzylidene)- 1,4-diaminobutane (hbd), N,N'-bis(2-bydroxy-3-t-butyl-5methylbenzylidene)-1,4-diaminobutane (hbbd), N , N ' - bis(2 - hydroxy - 5 - methyl - c~- phenylbenzyl idene)-l,4-diaminobutane (hmpbd) and 2-hydroxybenzalazine (hba). The bridge-splitting reaction of hbd with l a in the presence of sodium hydroxide in a 1:1 ratio gave the yellow complex ld. The IR spectrum of this complex exhibited a strong band at 1609 c m - 1, which corresponds to the asymmetric stretching frequency of both C z N groups. The asymmetric stretching frequency of the C - - N bond of the free metallated ligand 1 and the coordinated ligand hbd are, respectively, 1651 and 1640 c m - ~. The shift of the C ~ N bond stretching frequency to the lower wave number suggests that both nitrogen atoms are coordinated to the central metal a t o m ] 8 Similarly the yellow complexes 2d~id were synthesized from the corresponding dimeric complexes 2a~ia (Fig. 4). The I R spectra of the complexes 2 d ~ d exhibit only one strong band for the asymmetric stretching frequency of both the C z N bonds. The asymmetric stretching frequency of the C ~ N bond of free and coordinated ligands are summarized in Table 1. The ~H N M R spectra of complexes 2d and 6d suggest that the imine proton of both the metallated and

K. SELVAKUMAR and S. VANCHEESAN

3982

Table 1. Elemental and IR spectral data of the complexes

Complex

Colour

C

Analytical data (%)a H

N

IR spectral data (cm-1) v(C--N) b Others

2b

Yellow

1609

325 c

4b

Yellow

1603

31 lC

5b

Yellow

1600

300 c

6b

Yellow

1606

28Y

le

Pale yellow

7.5 (7.4) 7.2 (7.1) 6.8 (6.8) 6.4 (6.4) 6.4 (6.4) 4.4 (4.3)

313 c

Yellow

4.7 (4.8) 5.1 (5.1) 5.0 (4.9) 5.1 (5.0) 5.1 (5.0) 4.4 (4.4)

1609

3b

50.4 (50.6) 51.8 (51.8) 49.7 (49.8) 49.2 (49.1) 49.2 (49.1) 48.5 (48.4)

1612

3e

Pale yellow

53.9 (53.9)

5.9 (5.9)

3.7 (3.7)

1603

4c

Pale yellow

51.7 (51.7)

5.7 (5.6)

3.6 (3.6)

1606

5e

Pale yellow

50.8 (50.9)

5.8 (5.7)

3.3 (3.3)

1606

6e

Pale yellow

50.8 (50.9)

5.8 (5.7)

3.4 (3.3)

1600

1564 1408 1360 1558 1404 1360 1561 1408 1360 1564 1411 1369 1561 1408 1363

ld

Yellow Yellow

3d

Yellow

4d

Yellow

5d

Yellow

6d

Yellow

le

Yellow

2e

Yellow

5e

Yellow

6e

Yellow

2f

Yellow

2g

Yellowish orange

4.7 (4.6) 5.7 (5.6) 6.0 (5.9) 5.7 (5.7) 5.8 (5.7) 5.8 (5.7) 6.2 (6.2) 6.9 (6.9) 6.9 (6.9) 6.8 (6.9) 5.9 (5.8) 4.9 (5.0)

7.6 (7.5) 6.8 (6.8) 6.5 (6.6) 6.3 (6.3) 5.9 (5.9) 6.0 (5.9) 6.3 (6.3) 5.9 (5.8) 5.1 (5.2) 5.3 (5.2) 5.5 (5.6) 7.3 (7.3)

1609

2d

54.9 (54.9) 58.2 (58.1) 58.9 (59.0) 57.0 (56.8) 55.8 (55.8) 55.8 (55.8) 59.9 (59.8) 62.0 (62.0) 59.7 (59.6) 59.7 (59.6) 64.4 (64.4) 56.1 (56.0)

1611 1609 1610 1609 1610 1619 1610 1613 1609 1606 1610 1580 1604 1595

aCalculated values are given in parenthesies. b v ( ~ N ) of the free ligands; 1 = 1651; 2 = 1644; 3 = 165l; 4 = 1649; 5 = 1645; 6 = 1648; h b d = 1640; hbbd = 1632; hmpbd = 1611 ; hba = 1625 cm -1 CTerminal Pd--C1 stretching frequency.

Cyclopalladated binuclear complexes of Schiff bases R2

H 7 N

01 0

\

~2 Fig. 3. lc : R2 = CH3, R 3 =

R 2 = R 3 = R 4 = H ; 3e : R l = Bu", H ; 4c : R I = Bu n, R 2 = O C H 3 , R 4 = H ; 5c : R 1 = B u n, R 2 = R 3 = OCH3, R 4 = H ; 6c: R l = Bu n, R a = R 4 = O C H 3 , R 3 = H. R l =

R 3 =

C H 3,

R 4 =

R2

4 F~

H 7 i1

19~N211//H

Fig. 4. ld : R 1 = CH3, R 2 = R 3 = R 4 = H ; 2d : R 1 = B u n, R 2 = R 3 = R 4 = H; 3d: R' = Bu n, R: = C H 3 , R 3 = R 4 = H ; 4d : R ~ = Bu n, R 2 = O C H 3 , R 3 = R4 = H ; 5d : R 1 = B u n, R 2 = R 3 = O C H 3 , R 4 -- H ; 6d : R 1 = B u n, R 2 = R 4 = O C H 3 , R 3 = H.

coordinated ligands are shifted to high field after complexation.18 The extent of the high-field shift of the imine proton of the metallated ligand is c a 0.4 ppm, whereas that of the coordinated ligand hbd is c a 0.7 p p m (Table 2). The reaction of the other salen ligand, hbbd, in the presence of sodium hydroxide with the dimeric complexes la, 2a, 5a and 6a was carried out. The resulting yellow cyclopalladated binuclear complexes le, 2e, 5e and 6e were thoroughly analysed. The I R spectrum of the complex le exhibits two strong bands at 1619 and 1610 cm ~corresponding to the asymmetric stretching frequency of both C - - N bonds, respectively, for the metallated ligand 1 and the coordinated ligand hbbd. Complexes 2e, 5e and 6e exhibit only one strong band corresponding to the asymmetric stretching frequency of C - - N bonds of both metallated and coordinated ligands. The asymmetric stretching frequency of the C ~ - N bond of all these complexes is shifted to lower

3983

wave number compared with that of free metallated and coordinated ligands, suggesting the coordination of nitrogen to palladium (Fig. 5). The ~H N M R spectra of complexes 2e and 6e suggest that the imine proton resonance of both metallated ligands 2 and 6 and the coordinating ligand hbbd were shifted to high field] 8 The extent of the highfield shift of the imine proton of metallated ligand is c a 0.35 ppm, whereas that of the coordinated ligand is c a 0.75 p p m (Table 2). A similar type of bridge-splitting reaction was also investigated with the ligand hmpbd. The reaction of 2a with h m p b d gave the yellow complex 2f. The I R spectrum of this complex exhibited two strong bands at 1604 and 1580 cm -1, corresponding to the asymmetric stretching frequency of the C = N bond of the metallated ligand 2 and hmpbd, respectively. The ~H N M R spectrum of this complex shows that the imine proton of metallated ligand 2 was shifted to 7.75 p p m from 8.24 ppm. The shielding of the imine proton and the shift of the C = N bond stretching frequency to a lower wave number suggest that both the nitrogen atoms are coordinated to a palladium atom. is It is noticed from the H - H COSY N M R spectrum of complex 2f that the resonance peak of the proton ( H 16) is shifted to high-field (Fig. 6). This shift is due to the diamagnetic shielding of the e-phenyl group of the ligand h m p b d (Fig. 7). The investigation of the bridge-splitting reaction of 2a was extended with 2-hydroxybenzalazine (hbd) in the presence of sodium hydroxide. The resulting complex 2g was found to be cyclopalladated binuclear (Fig. 8). This complex exhibited two strong bands in the I R spectrum at 1604 and 1595 c m - l , corresponding to the asymmetric C = N stretching frequency of the metallated ligand 2 and coordinated ligand hba, respectively. The ~H N M R spectrum of this complex shows that the imine proton resonance of metallated ligand 2 was shielded compared with the free ligand, whereas the imine proton of the coordinated ligand hba was deshielded and appeared at 9.10 ppm. The imine proton of the free ligand hba resonates at 8.69 ppm. This deshielding could be due to the paramagnetic anisotropy of the metal atom on the imine proton. 21 It is noticeable that only one set of signals was observed for both the cyclopalladated moieties of each complex in their 1H and 13C N M R spectra. This suggests that the cyclopalladated binuclear complexes are symmetrical. The ~3C N M R values of all the complexes are summarised in Table 2, which confirms the proposed structure of the complexes. The resonance peak of the metallated carbon atom is greatly shifted down field in relation to the normal range of 6' values to aromatic carbons.

3984

K. SELVAKUMAR and S. VANCHEESAN

Table 2. IH and ~3C NMR spectral data of the complexes 6b

1H NMR: 6 0.97 (t, 3H, HH), 1.39 (m, 2H, H~~ 1.87 (m, 2H, H9), 3.62 (s, 3H, OHC4), 3.72 (t, 2H, H8), 3.81 (s, 3H, OCH3~), 5.33 (s, 1H, Ha), 6.09 (s, 1H, H~), 7.70 (d, 2H, H~a), 8.05 (s, 1H, HT), 9.05 (d, 2H, H~). 13C NMR: 6 13.87 (q, CII), 19.89 (t, Cl~ 32.80 (t, C9), 55.18 (q, OCHa), 55.33 (q, OCH3), 60.09 (t, C8), 92.94 (d, CS), 110.78 (d, C3), 122.72 (d, C~3), 127.43 (s, C~), 145.29 (s, Ca4), 153.92 (d, ClZ), 158.88 (s, C), 161.03 (s, C'), 162.39 (s, C6), 170.63 (d, C7).

6c

~H N M R : 6 0.95 (t, 3H, HH), 1.39 (m, 2H, W~

1.79 (m, 2H, Hg), 1.95 (s, 3H, H~2), 2.04 (s, 3H, H~6), 3.55 (t, 2H, Hs), 3.78 (s, 3H, OCH3) , 3.88 (s, 3H, OCH3), 6.05 (d, 1H, Hs), 6.72 (d, 1H, H3), 8.05 (s, 1H, HT). ~3C N M R : 6 13.84 (q, Cll), 20.91 (t, C~~ 28.28 (q, C12Ai-C16),32.39 (t, C9), 55.12 (q, OCH3), 55.37 (q, OCH3), 57.85 (t, C8), 94.55 (d, C5), 106.98 (d, C3), 113.11 (s, C~4), 127.28 (s, C~), 158.38 (s, C2), 161.85 (s, C4), 162.07 (s, C6), 169.22 (d, C7), 186.81 (s, Cl3), 189.42 (s, ClS).

(xl

~H NMR: 6 0.90 (t, 3H, Hit), 1.39 (m, 2H, H~~ 1.74 (m, 2H, Hg), 1.98 (s, 3H, H2~ 3.55 (t, 2H, Hs), 3.72 (s, 3H, OCH3), 3.76 (s, 3H, OCH3), 4.00 (s, 2H, H19), 6.02 (d, 1H, Hs), 6.36 (d, 1H, Ha), 6.44 (t, 1H, HIS), 6.75 (d, 1H, Hi3), 7.02 (dd, 1H, H16), 7.19 (dt, 1H, H~4), 7.67 (s, 1H, HIS), 8.09 (s, 1H, H7).

13C NMR: ~ 13.90 (q, CH), 20.17 (t, C~~ 30.13 (t, C9), 32.77 (t, C2~ 55.12 (q, OCH3), 55.25 (q, OCH3), 57.07 (t, C8), 62.43 (t, Clg), 93.29 (d, C5), 111.97 (d, C3), 113.51 (d, C~5), 121.74 (d, C~3), 122.65 (s, C~7), 128.29 (s, C~), 133.88 (d, C~6), 134.44 (d, C~4), 158.61 (s, C~2), 161.54 (s, C4), 161.96 (s, C6), 164.64 (d, Cl8), 167.89 (s, C2), 169.20 (d, C7). 2e

1H NMR: 6 0.95 (t, 3H, Hll), 1.40 (S, llH, H~~ 1.90 (m, 2H, H9), 1.95 (s, 2H, H2~ 2.19 (s, 3H, H2~), 3.85 (s, 2H, Hs), 4.00 (s, 2H, H19), 6.64 (s, 1H, HI4), 7.00 (s, 2H, HS+H4), 7.08 (s, 1H, n3), 7.23 (m, 2H, H6+H16), 7.55 (s, 1H, HIS), 7.90 (s, IH, HT).

13C NMR: 6 13.97 (q, CH), 19.92 (t, C~~ 20.37 (q, C2Z), 29.48 (q, C22), 30.69 (t, C9), 32.38 (t, C2~ 35.16 (s, C23), 57.33 (t, C8), 62.98 (t, CI9), 120.69 (s, C~5), 121.27 (s, ClT), 123.53 (d, C6), 126.78 (d, C5), 129.63 (d, C'), 132.13 (d, Ca), 132.89 (d, Ct6), 134.41 (d, Cl4), 140.16 (s, C~3), 147.46 (s, C1), 158.33 (s, C~2), 164.98 (s, C2), 165.45 (d, ClS), 173.35 (d, C7). 2f

~H NMR: 6 0.92 (t, 3H, Hll), 1.35 (m, 2H, HI~ 1.72 (m, 2H, H9), 1.94 (s, 3H, H25), 2.00 (s, 2H, H24), 3.53 (t, 2H, H8), 3.69 (s, 2H, H23), 6.19 (d, 1H, H~6), 6.66 (d, IH, Wa), 6.87 (dd, 1H, W4), 6.98 (dt, 1H, Hs), 7.02 (m, 3H, H'+H2~ 7.08 (d, 1H, H3), 7.15 (dd, 1H, H6), 7.32 (t, 2H, H:~), 7.38 (t, 1H, HZ2). laC NMR: 6 13.84 (q, Cll), 20.10 (t, C~~ 20.19 (q, C25), 30.22 (t, C9), 32.03 (t, C24), 57.68 (t, C8), 57.76 (t, C23), 121.29 (d, Cl3), 121.42 (s, C15), 123.62 (d, C6), 126.50 (d, C5), t28.37 (d, C21), 128.54 (d, C2~ 128.98 (d, C4), 129.01 (s, C17), 129.60 (d, C22), 133.38 (d, C3), 133.80 (d, C~4), 134.68 (d, C~6), 137.70 (s, Clg), 147.25 (s, C~), 157.82 (s, C~2), 167.30 (s, C2), 173.15 (d, C7), 173.33 (s, C~8).

2g

~H NMR: 6 1.05 (t, 3H, HN), 1.50 (m, 2H, W~ 1.95 (bs, 2H, Hg), 3.90 (bs, 2H, Hs), 6.38 (t, 1H, Ws), 6.83 (d, 1H, HI6), 6.90 (M, 3H, H4+HS+H3), 7.23 (m, 2H, Hxa-+'H6), 7.63 (m, 1H, Ha), 8.00 (s, 1H, Hv), 9.10 (s, 1H, W 8) 13C NMR: ~ 13.90 (q, C"), 20.31 (t, Cl~ 32.77 (t, C9), 57.27 (t, C8), 114.25 (d, C~5), 117.77 (s, C17), 122.09 (d, C6), 123.79 (d, C13), 126.75 (d, C5), 130.45 (d, C4), 135.17 (d, C16), 135.59 (d, C~4), 136.87 (d, C3), 147.04 (s, C~2), 157.92 (s, C~), 165.35 (d, C~8), 168.58 (s, C2), 174.71 (d, C7).

Chemical shifts in ppm (6) with respect to internal TMS. See the structures for the numbering sequence. Chemical shifts due to C H i N of the free ligands 1 = 8.23; 2 = 8.25; 3 = 8.16; 4 = 8.12; 5 = 8.04; 6 = 8.53; hbd = 8.36; hbbd = 8.31,9 hba = 8.69. The numbering sequence of the n-butyl group 1S " CH 3~ --CH270--CH2--CH2--. 9 8

C y c l o p a l l a d a t e d b i n u c l e a r c o m p l e x e s o f Schiff bases

3985 R2

~ ,~

,

R4

N/

~N~H

R1

19/20 H

I

\ ,8/

H - N ~4 R~

h

\ Pd

/19 ~u 17k....~ 16

~

13 14 R': Fig. 7. C o m p l e x 2f.

Fig. 5. l e : R ~ = CH3, R 2 = R 3 = R 4 = H ; 2e : R L = Bu n, R 2 = R 3 = R 4 = H ; 5e: R ] = Bu n, R 2 = R 3 = O C H 3 , R 4 = H ; 6e : R l = B u n, R 2 = R 4 = O C H 3 , R 3 = H.

"I

6

5

4

3

2

1

0

~

oDO 0 9 o

9

o

Q

J

OO.

.~.-]

-tO

o.

O

.cO

e 9

Fig. 6. H - H C O S Y N M R s p e c t r u m o f c o m p l e x 2f. See Table 2 for a s s i g n m e n t o f peaks.

O

K. SELVAKUMAR and S. VANCHEESAN

3986

R2

~--o~

R~

.'----~/=:7 / P d ., \, r ~A,' ' " I H l',,.l ','

.

V('-')~2 ~o~,, R2

7.

8.

9. 10.

Fig. 8. Complex 2g. 11.

Acknowledgements--We thank the Catalysis Division, Department of Chemistry and Regional Sophisticated Instrumentation Centre, I.I.T., Madras, for instrumental analyses. One of the authors (KS) thanks I.I.T., Madras, for financial assistance and a research fellowship.

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12.

13. 14.

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1862. 15. E. H. Cox, J. Am. Chem. Soc. 1927, 49, 1028. 16. H. Onoue and I. Moritani, J. Or#anomet. Chem. 1972, 43, 431. 17. B. Crociani, T. Boschi, R. Pietropaolo and U. Belluco, J. Chem. Soc. A 1970, 531. 18. (a) H. Onoue, K. Minami and K~ Nakagawa, Bull. Chem. Soc., Jpn 1970, 43, 3480; (b) J. Albert, J. Granell and J. Sales, J. Organomet. Chem. 1984, 273, 393; (c) J. M. Vila, A. Suarez, M. T. Pereira, E. Gayoso and M. Gayoso, Polyhedron 1987, 6, 1003. 19. S. Chakladar, P. Paul, A. K. Mukherjee, S. K. Dutta, K. K. Nanda, D. Podder and K. Nag, J. Chem. Soc., Dalton Trans. 1992, 3119. 20. J. M. Vila, M. T. Pereira, E. Gayoso and M. Gayoso, Trans. Met. Chem. 1984, 11,342. 21. (a) J. Granell, J. Sales, J. Vilarrasa, J. P. Declercq, G. Germain, C. Miravitlles and X. Solans, J. Chem. Soc., Dalton Trans. 1983, 2441 ; (b) R. M. Ceder, J. Sales, X. Solans and M. Font-Altaba, J. Chem. Soc., Dalton Trans. 1986, 1351.