Effect of Substitution of [Pd(PPh 3 ) 4 ] by Related Compounds as Catalysts in Reactions of Organic Syntheses
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Catalysis Letters Vol. 109 Nos. 3–4, July 2006 (Ó 2006) DOI: 10.1007/s10562-006-0074-2
Effect of substitution of [Pd(PPh3)4] by related compounds as catalysts in reactions of organic syntheses Roberto S. Barbie´ri,a,b,* C.R. Bellato,c A.K.C. Dias,a and A.C. Massabnid a
Universidade Vale do Rio Verde - UNINCOR, Treˆs Corac¸o˜es, MG 36570–000, Brazil b Faculdade de Minas - FAMINAS, Muriae´, MG 36880–000, Brazil c Universidade Federal de Vic¸osa - UFV, Vic¸osa, MG 36570–000, Brazil d Universidade Estadual Paulista - UNESP, Araraquara, SP 14800–900, Brazil
Received 6 March 2004; accepted 4 March 2006
The effect of substitution of [Pd(PPh3)4], which is unstable in air, by complexes of the type½MCl2 L2 ðM ¼ Pd; Pt; L ¼ AsPh3 ; SbPh3 Þ; ½PdL4 ðL ¼ PPh3 ; AsPh3 ; SbPh3 Þ and [NiX2(PPh3)2] on the syntheses of thioethers, acetylenes and ketones is described. KEY WORDS: homogeneous catalysts; palladium complexes; platinum complexes; nickel complexes.
1. Introduction Nickel, palladium or platinum complexes with triphenylphosphine (PPh3) have been used as homogeneous catalysts in organic syntheses. The complex that seems to be the most used in laboratory scale is [Pd(PPh3)4] [1]. This zerovalent palladium compound decomposes immediately when exposed to air and requires the use of inert atmosphere techniques for its preparation and manipulation. In this work, we wish to describe the catalytic effect of some related compounds in organic syntheses. It is shown that it is possible to substitute [Pd(PPh3)4] by other compounds, more stable in air, which do not require special conditions for their syntheses and storage.
were carried out and the metal contents were determined by thermogravimetric analysis using a Perkin Elmer TGS-2 thermobalance. 2.3. Syntheses of the complexes The complexes [MCl2(EPh3)2] (M = Pd, Pt; E = P, As, Sb); [M(EPh3)4] (M = Pd, E = P, As, Sb; M = Pt, E = P, As); [Pt(SbPh3)3] and [NiX2(PPh3)2] (X=Cl), Br), I), NO3), NCS)) were prepared from Na2[PdCl4], H2[PtCl6] and NiX2 by methods described in the literature [2–8], and characterized by IR spectra and elemental analysis of carbon and hydrogen and thermogravimetric determination of the metals [9–11].
2. Experimental
2.4. Syntheses of thioethers
2.1. Materials
Method adapted from Migita et al. [12,13]: p-thiocresol (0.249 g, 2 mmol), iodobenzene (0.22 mL, 2 mmol), sodium t-butoxide (0.385 g, 4 mmol) and 2 mmol [PdCl2L2] or [PdL4] (L = PPh3, AsPh3, SbPh3) were added to EtOH (20 mL) and the reaction mixture was stirred thoroughly under reflux for 3 h. The solvent was removed by evaporation and the main product of the reaction phenyl-p-tolyl sulfide was extracted with npentane. The solution obtained was washed with water, n-pentane was evaporated and the residue, a brownish oil, was dried at 100 °C for 30 min. Using 2-mercaptobenzothiazole (0.335 g, 2 mmol), iodobenzene, butyl lithium (1.70 mL of a 15% m/v n-hexane solution, 4 mmol) and [PdCl2L2] or [PdL4], following the procedure described above, phenylbenzothiazole-2-sulfide was obtained.
Analytical grad
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