4-Amino-2,6-dimethyl-5-oxo-3-thioxo-2,3,4,5-tetrahydro-1,2,4-triazine palladium(II) complexes

Transition Met. Chem., 16, 469-471 (1991)

Tetrahydrotriazine Pd n complexes

469

4-Amino-2,6-dimethyl-5-oxo-3-thioxo-2,3,4,5-tetrahydro1,2,4-triazine palladium(II) complexes Gregorio L6pez*, Gregorio S~inchez, Gabriel Gareia and Maria J. Viflal Departamento de Quimica lnorgdnica, Universidad de Murcia, 30071-Murcia, Spain Eduardo P~rez Departamento de Ingenieria Qulmica, E.U. Politdcnica de Cartagena, Cartagena (Murcia), Spain Summary The reaction of I-PdClz(PhCN)2 ] with 4-amino-2,6dimethyl-5-oxo-3-thioxo-2,3,4,5-tetrahydro- 1,2,4-triazine (L) yields [ {PdCIL(#-CI) }2] '2H20 and [PdCI2 L2] "4H20 complexes, which react with KBr in M%Co to give the corresponding bromo-complexes [{PdBrL(#-Br)}2] and [PdBrzL2]. When the chloro-complexes are treated with AgC10 4 in EtOH, [Pd(H20)zL](CIO4) 2 and [Pd(H20)2Le](C104) 2 are formed. I.r., visible, and ~H-n.m.r. spectra have been recorded and facilitate assignments.

Introduction Biologically active compounds containing the 1,2,4triazine ring are found in nature(i); 4-amino-l,2,4-triazin5-one complexes are widely used as herbicides (2). The complexes of nickel(II) and cobalt(II) with 4-amino6-methyl-5-oxo-3-phenylamino-4,5-dihydro-1,2,4-triazine (3) and 4-amino-6-methyl-5-oxo-3-thioxo-2,3,4,5-tetrahydro1,2,4-triazine (4'5), and of nickel(II) with 4-amino-2,6dimethyl-5-oxo-3-thioxo-2,3,4,5-tetrahydro-l,2,4-triazine (L)(6) have been reported previously. This ligand can act as monodentate N-donor or chelating bidentate N,Sdonor, the 4-amino and 3-thioxo groups being involved in bonding to the metal.

Me~N./N~Me "0 S'~""N"

NH2 (L)

In this paper we describe the preparation of some palladium(II) complexes with the above-mentioned ligand (L).

Experimental C, H, and N analyses were made with a Perkin-Elmer 240C microanalyzer. Spectra were recorded on PerkinElmer 1430 (i.r.), Hitachi U 2300 (visible), and Bruker AC 200E (1H-n.m.r.) instruments. Conductance measurements were performed with a Crison 525 conductimeter. The thermogravimetric curves were obtained using a Mettler TG-50 thermobalance operating under a dynamic N 2 atmosphere at a heating rate of 10~ M.p.'s were determined on a Reichert microscope.

* Author to whom all correspondence should be directed. 0340-4285/91 $03.00 + .12

The starting compound [PdClz(PhCN)z] (7~ and the triazine (L)(s) were prepared as described elsewhere; the triazine was recrystallized from EtOH before use.

Preparation of the new complexes [{PdCIL(#-C1)}2J.H20 (1) An EtOH (10cm 3) solution of the triazine (45mg; 0.261 mmol) was added to a solution of [PdCIz(PhCN)f] (100mg; 0.26tmmol) in the same solvent (10cm3), and one drop of (36~o) HC1 was added to the mixture. A yellow precipitate formed immediately. The suspension was stirred at room temperature for 1 h, then the solid was removed by filtration, washed with EtzO and dried in air.

[PdCI2L2]'4H20 (2) An EtOH (10era 3) solution of the triazine (90rag; 0.522mmol) and one drop of conc HC1 were added to an EtOH (10 cm 3) solution of [PdC12(PhCN)2] (100 rag; 0.261retool). After stirring at room temperature for 1 h, the small amount of complex (1) which precipitated was separated by filtration. The resulting solution was concentrated in vacuo to half the initial volume and was kept overnight in a refrigerator. Yellow crystals of complex (2) which formed were removed by filtration, washed with EtzO and air dried.

[ {PdBrL(#-Br) }2] (3) KBr (97.1 mg; 0.816 mmol) was added to a suspension of complex (2) (100rag; 0.168mmol) in Me2CO (10cm3), and the mixture was boiled under reflux for 4h. The resulting solid was filtered off, washed with H 2 0 and EtOH, and dried in air.

[PdL2Br2] (4) KBr (40.ling; 0.336mmol) was added to an Me2CO (10cm 3) solution of complex (2) (100mg; 0.168retool). The solution was then boiled under reflux for 2h and the precipitated KC1 was separated by filtration. Addition of Et20 resulted in the precipitation of a yellow solid which was filtered off, washed with Et20 ether and dried in air.

[Pd(H20)2L](CI04) 2 (5) AgC10r (122.6mg; 0.544mmot) was added to a suspension of complex ( I ) (100 rag; 0.136 mmol) in EtOH (10 cm3). This suspension was stirred at room temperature for 30rain and the resulting solid was removed by 9 1991 Chapman and Hall Ltd

470

G. L6pez et al.

Transition Met. Chem., 16, 469-471 (1991)

filtration, and then treated with MeCN to give an orange solution from which a precipitate of the same colour was formed on addition of Et20. This precipitate was washed with Et20, air dried, and recrystallized from M%CO.

Table 1. Analytical and physical data for the patladium(II) complexes.

[Pd(i-IzO)zL2](Cl04) 2 (6)

(1)

yellow

85

AgC104 (75.9mg; 0.336mmol) was added to a M e O H (10cm 3) solution of complex (2) (100mg; 0.168mmol), whereupon a precipitate was formed immediately. The suspension was stirred at room temperature for 30min and the solid was filtered off and treated with MeCN. The precipitated AgC1 was then separated by filtration and from the remaining yellow solution a solid of the same colour was precipitated by addition of EtzO, which was washed with the same solvent and dried in air.

(2)

yellow

78

(3)

yellow

84

(4)

orange

86

(5)

yellow

65

(6)

yellow

76

Results and discussion

aFrom the thermogravimetriccurves.

The results of our study are summarized in Scheme 1. Complexes (1) and (2) are formed by reacting the triazine and [PdC12(PhCN)2] in 1:1 and 2:1 molar ratios respectively, under the experimental conditions specified. Both (1) and (2) were used as precursors for complexes (3)-(6). Analytical data, colours, yields, and decomposition temperatures for all complexes are collected in Table 1. The i.r. data relevant to structural assignments are given in Table 2. The v ( N - - H ) stretching vibrations are observed at lower wavenumbers than in the free triazine, indicating that the 4-amino group is bonded to the palladium atom in every case. However, the C = O group is not involved in coordination to the metal because its stretching mode is located at higher energy (1730 1700cm -1 range) compared with that of the uncoordinated triazine. It is likely that the carbonyl oxygen in the free triazine is involved in hydrogen-bonding. On the other hand, the i.r. spectrum of free triazine exhibits two partly overlapping bands at 1400-1380 cm- 1, attributed to the thioamide band II and the methyl deformation mode (9-11). Complexes (1)-(4) and (6) exhibit a band at 1380cm-*, but a band at 1340cm -~

in complex (5) is attributed to additional coordination of the triazine through the 3-thioxo sulphur atom, i.e., the triazine acts here as a chelating bidentate ligand. A similar assignment was made for [Ni(H20)2L2](C104) > where a single-crystal x-ray diffraction study confirmed the chelating nature of L (6). The visible spectra of the palladium complexes show an absorption maximum located at 23300-29500 cm-1 (Table 3) in good agreement with the expected 1A~o--,1Azg electron transition in a square-planar field (12). The 1H-n.m.r. spectra of the CD3CN solutions of the complexes show resonance peaks due to the 2- and 6-methyl g r o u p s in the triazine ring, but no peak assignable to the 4-amino group is observed because of the proton-deuterium exchange. However, when acetonedo/trifluoroacetic acid is used as solvent, the expected N H 2 singlet is found at h 4.7-7.4 (Table 3). Three absorptions for complex (1) at 330, 310 and 300cm -~, are attributed to terminal and bridging Pd--C1 bonds (13~. The presence of lattice water in complex (I) is indicated by bands at 3460-3400 (v OH) and 1630 (h HOH) cm -1. The t.g. trace reveals that the

Complex Colour Yield Found (Calcd.)(%) Dec. temp. (%) C H N (~ 16.3 (16.3) 20.3 (20.2) 14.1 (13.7) 12.0 (11.7) 20.0 (19.7) 17.8 (17.5)

2.7 (2.7) 3.9 (4.1) 2.1 (1.8) 2.1 (2.3) 2.6 (2.6) 3.1 (2.9)

15.3 (15.2) 18.6 (18.9) 12.8 (12.8) 11.1 (10.9) 17.8 (18.3) 16.0 (16.3)

KBr - [ {PdBrL(/~-Br)}2]

(3) +L 9 [ {PdC1L(#-C1) } 2 ] . 2 H 2 0 - -

(1) AgC104 [Pd(H20)2L] (C104)2

(4) [PdC12(PhCN)2 ] - -

KBr ~, [PdBr2L2]

(5) + 2L ,'- [PdCI2L2].4H20

(2) AgC104 -~ [Pd(HzO)2L2](C104) 2

(6) Scheme 1. Preparation of the palladium complexes.

60a 55" 341 265 344 245

Transition Met. Chem., 16, 469-471 (1991)

Tetrahydrotriazine Pd II complexes

Table2. Relevant i.r. data (cm -1) for the palladium(II) complexes. Compound

v(NH)

v(C=O)

6(NHz)

v(C=S)

Free triazine (1) (2) (3) (4) (5) (6)

3320,3220 3170 3180 3120 3180 3100 3160

1670 1700 1730 1720 1715 1720 1720

1530 1595 1600 t600 1600 1600 1600

1380 1380 1380 1380 1340 1380 1380

Table3. Visible and XH-n.m.r. data for the palladium(II) complexes.

vl(1Alo~lA2g)

1H,

(cm- 1)

6/ppm (SiM%)a

(1)

Solid: 25500 MeCN: 25600

(2)

Solid: 29500 MeCN: 25700

(3)

Solid: 23300 MeCN: 22900

(4)

b

(5)

Solid: 29300 MeCN: 29000

(6)

b

2.34 (s, 3H, CH3--C ) 3.96 (s, 3H, CH3--N ) 7.36 (s, 2H, NHE--N ) 2.22 (s, 3H, CH3--C ) 3.89 (s, 3H, CH3--N ) 6.64 (s, 2H, NH~--N) 2.36 (s, 3H, CH3--C ) 3.99 (s, 3H, CH3--N ) 7.20 (s, 2H, NH2--N) 2.15 (S, 3H, CH3--C ) 3.53 (s, 3H, CH3--N ) 4.66 (s, 2H, NH2--N) 2.34 (s, 3H, CHa--C ) 3.96 (s, 3H, CH3--N) 5.72 (s, 2H, NH2--N) 2.42 (S, 3H, CH3--C ) 4.09 (s, 3H, CH3--N ) 6.83 (s, 2H, NH 2 N)

Complex

"In (CD3)2CO/CF3CO2H. bRegions masked by charge-transference bands.

two water molecules are released at 60-130~ (wt loss: Found 5.2; calcd.: 4.9~) to give an intermediate product which decomposes at 210 ~ C. However, this anhydrous intermediate could not be isolated. Only one band, at 360cm -1, observed in the i.r. spectrum of complex (2), is attributed to the terminal Pd--C1 bonds, and the thermogravimetric data is consistent with the presence of four water molecules (wt loss: Found 11.6; calcd.: 12.1~) which are liberated in the 55 85~ range. The absorption maximum, at 29500cm -1 in the visible spectrum (as Nujol mull), is shifted to 25 700 c m - i when the complex is dissolved in acetonitrile; this can be attributed to the dissociation

471

process represented by Equation 1. 2[PdC12LE] ---, [ {PdC1L(/~-C1)}a] + 2L

(1)

In fact, the tH-n.m.r, spectrum of the acetonitrile-d3 solution of complex (2) shows two peaks at/i 2.24 and 3.38 (methyl groups of coordinated triazine) together with two additional peaks at 3 2.32 and 3.93 (methyl groups of free triazine). As expected, the absorptions due to P d - - B r bonds are absent in the i.r. spectra of complexes (3) and (5), because they should lie below the lower limit (200 cm- i) of our apparatus. However, replacement of the chlorine atoms in complexes (1) and (2) by bromine atoms results in a visible absorption maxima shift to lower wavenumbers. The broad bands at 1100 and 625 cm -1 in the i.r. spectra of complexes (4) and (6) indicate the presence of free C10 4, and their conductances (in acetonitrile) indicate that they behave as 1:2 electrolytes (~4).

Acknowledgement The authors thank the Direcci6n Regional de Educaci6n y Universided (project PCT 88/17)), Murcia (Spain), for financial support.

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