Synthesis and identification of N-[ ( 2-pyridyl ) methyliden ]-6-coumarin complex of Pt ( IV )

Coumarin derivatives have blood-thinning, anti-fungicidal, anti-tumor and anticoagulant activities. Photophysics and photochemistry of coumarin derivatives are also important. With reaction between 6-aminocoumarin and pyridine-2-carboxaldehyde, we synthesized N-[(2-pyridyl)methyliden]-6-coumarin(L). The ligand, L, reacts with hexachloroplatinic acid to synthesize a Pt(IV) complex of formulae, [Pt(L)2]Cl6 and [Pd(L)2]Cl2, respectively. On the other hand, all reactions in the attendance of pyrocatechol has isolated [Pt(L)(1,2-dihydroxybenzene)2]Cl6. This compound is characterized by FTIR, UV–Vis and 1H NMR spectroscopic data.


Introduction:
Coumarin is found in a variety of plants such as Tonka bean, lavender, sweet clover grass, licorice and also occurs in food plants such as strawberries, apricots, cherries, cinnamon.
Photophysics and photochemistry of coumarin derivatives are also important and have been used as dye lasers [4][5][6][7].Considerable effort has been given at present to functionalize coumarin so that metal-coumarin complexes may be synthesized and could display interesting excited state properties and be used in designing artificial photosynthetic systems, chemical sensors and molecular level devices [8].We are interested to anchor diimine (-N=C-C=N-) function to coumarin backbone so that the molecule may act as bidentate N,N-chelator.We have prepared coumarin based ligand, N-[(2-pyridyl) methyliden]-6-coumarin (L), which reacts with hexachloroplatinic acid to synthesize [M(L)2] + .All these compounds are characterized by spectroscopic methods.

Experimental:
Hexachloroplatinic acid and pyridine-2-carboxaldehyde were purchased from Aldrich Chemical Co.Coumarin was available from S.D. Fine Chem.Ltd.Solvents were purified by standard procedure [9].All other chemicals and solvents were of reagent grade and were used without further purification.

Step-1: synthesis of 6-nitrocoumarin
Coumarin was nitrated with mixed acid in an ice bath.Coumarin was dissolved in H2SO4 and then mixed acid (HNO3 and H2SO4) was added.The mixture was stirred keeping at room temperature.A white precipitate of 6-nitrocoumarin was obtained.It was then filtered and washed thoroughly with water and dried over CaCl2.Yield, 9.2 g (88%).m.p.Step-2: synthesis of 6-aminocoumarin Reduction of 6-nitrocoumarin was done with Fe-powder in water.6-Nitrocoumarin in water (150 cm 3 ) was treated with Fe-powder.The mixture was kept in water bath.A dark brown precipitate was obtained.After evaporation yielded a silky yellow precipitate of 6aminocoumarin (m.p. 158°C).It was then recrystallized from dil.HCl solution as 6aminocoumarin hydrochloride.Yield, 5.1 g (76%).m.p. >260 _C; 1

Results and discussion
N-[(2-pyridyl)methyliden]-6-coumarin (L) Nitration of coumarin and its subsequent reduction to 6-aminocoumarin has been carried out by Fe powder.The condensation of pyridine-2-carboxaldehyde with 6-aminocoumarin has isolated straw yellow crystalline compound (Scheme 1).Infrared spectra of 6-aminocoumarin shows two ʋ (NH2) bands at 3329 and 3409 cm -1 which is eliminated in the condensation product and a new band appears at 1582 cm -1 that is corresponding to ʋ (C=N) at 328 and 289 nm in acetonitrile.

Table 1 :
H NMR spectral data (Table1).1HNMR spectral data of the complex.
b Singlet c Multiple