José M. Martí

Synthesis and reactivity of hydroxo-bridged binuclear platinum complexes. Crystal structure of [NBu4]2[{Pt(C6F5)2(µ-OH)}2]

The reaction of [NBu4]2[{Pt(C6X5)2(µ-Cl)}2] with NBu4OH(aq) in acetone leads to the formation of the hydroxo-complexes [NBu4]2[{Pt(C6X5)2(µ-OH)}2](X = F 1 or Cl 2). These react with weak protic acids such as acetylacetone (Hacac), benzoylacetone (Hbzac) and 8-hydroxyquinoline (Hquin) yielding the mononuclear complexes [NBu4][Pt(C6X5)2(L–L)](X = F, L–L = acac 3, bzac 4, or quin 5; X = Cl, L–L = acac 6, bzac 7, or quin 8). Treatment of complexes 1 and 2 with PhCN in the presence of HBF4 gives the mononuclear compounds cis-[Pt(C6X5)2(PhCN)2](X = F 9 or Cl 10). When the benzonitrile complexes are treated with aniline the corresponding cis-[Pt(C6X5)(NH2Ph)2](X = F 11 or Cl 12) are formed. The benzamido derivatives [NBu4][Pt(C6X5)2(HNOCPh)(H2O)](X = F 13 or Cl 14) are formed when complexes 9 and 10 are treated with NBu4OH(aq) in acetone, and thermal treatment of 13 yields [NBu4]2[{Pt(C6F5)2(µ-HNOCPh)}2]15. Complexes 9 and 10 react with methanol in the presence of NBu4OH to give the corresponding imido ester derivatives [Pt(C6X5)2{HNC(OMe)Ph}2](X = F 16 or Cl 17). Spectroscopic (IR, 1H and 19F) data have been used for structural assignments, and an X-ray structure determination carried out for [NBu4]2[{Pt(C6F5)2(µ-OH)}2] has established the centrosymmetric binuclear nature of the anion [(C6F5)2Pt(µ-OH)2Pt(C6F5)2]2–. The structure has been solved and refined up to R= 0.049 and R′= 0.056 based on 2278 observed reflections. The Pt atoms are four-co-ordinated and show slight deviations from a square-planar arrangement.

Synthesis and reactivity of the di-μ-hydroxo-bis[bis(pentachlorophenyl)palladate(II)] ion

Abstract The binuclear hydroxo-pentachlorophenyl palladium complex Q 2 [{Pd(C 6 Cl 5 ) 2 (μ-OH)} 2 ] (I) (Q = NBu 4 has been obtained by reaction between Q 2 [{Pd(C 6 Cl 5 ) 2 (μ-Cl)} 2 ] and QOH in acetone. Reaction of the hydroxo-complex I with protic electrophiles HL gives complexes of the types Q 2 [{Pd(C 6 Cl 5 ) 2 (μ-L)} 2 ] [L = pyrazolate (pz) (II), 3-methylpyrazolate (mpz) (III), indazolate (indz) (IV), or methoxo (V)], Q 2 [{Pd(C 6 Cl 5 ) 2 } 2 (μ-OH)(μ-dmpz)] (VI) (dmpz = 3,5-dimethylpyrazolate), or [Pd(C 6 Cl 5 ) 2 L] [L = acetylacetonate (acac) (VII), benzoylacetonate (bzac) (VIII), or 8-hydoxyquinolinate (oxin) (IX)]. However, complex VI is best prepared by reaction of the above chloro-complex with QOH and Hdmpz. The neutral mononuclear complex cis -[Pd(C 6 Cl 5 ) 2 (PhCN) 2 ] (X) has been obtained by treating complex I with benzonitrile in the presence of tetrafluoroboric acid. The lability of complex X is manifested by its reactivity towards aniline and 1,5-cyclooctadiene (cod), with which it gives the corresponding complexes cis -[Pd(C 6 Cl 5 ) 2 (PhNH 2 ) 2 ] (XI) and [Pd(C 6 Cl 5 ) 2 (cod)] (XII). The reaction between complex X and the chloro-complex [PdCl 2 (PEt 3 ) 2 ] yields the asymmetric binuclear complex [(C 6 Cl 5 ) 2 Pd(μ-Cl) 2 Pd(PEt 3 ) 2 ] (XIII).

Spectrophotometric methods for determining meloxicam in pharmaceuticals using batch and flow-injection procedures

Two sensitive and fast spectrophotometric methods using batch and flow-injection procedures for the determination of meloxicam (MX) are proposed. The methods are based on the formation of a green complex between this drug and Fe(III) [2MX/Fe(III)] in a methanolic medium. The calibration graphs resulting from measuring the absorbance at 570 nm are linear over the ranges 2.0-200 and 5.00-250 mg l(-1) with detection limits of 0.47 and 0.72 mg l(-1), respectively. Furthermore, a flow-injection spectrophotometric method involving measurement of the absorbance of the drug at 362 nm in 0.1 M NaOH is presented. The calibration graph is linear over the range 0.5-20 mg l(-1) with a detection limit of 0.04 mg l(-1). The methods are applied to the routine analysis of MX in pharmaceuticals.

Synthesis of palladium(II) and platinum(II) N,N-dialkyldithiocarbamates starting from hydroxo-halophenyl complexes

Abstract In dichloromethane, the hydroxo-complexes [NBu4]2[{M(C6X5)2(μ-OH)}2] [M = Pd (X = F or Cl) or Pt (X = F)] and [{Pd(C5X5)(PPh3)(μ-OH)}2] (X = F or Cl) react with amines in the presence of carbon disulfide to give the corresponding dithiocarbamate complexes [NBu4][M(C6X5)2(S2CNR2)] [M = Pd, X = F and R Me (I), Et (II), or C4H8 (III); M = Pd, X = Cl and R = Me (IV) or Et (V); M = Pt, X = F and R = Me (VI) or Et (VII)] and [Pd(C6X5)(PPh3)(S2CNR2)] [X = F and R = Me (VIII) or Et (IX); X = Cl and R = Me (X) or Et (XI)]. Conductance measurements and spectroscopic (IR, 1H and 19F NMR) methods have been used for structural assignments.

Synthesis and characterization of hydroxo, pyrazolato and carboxylato derivatives of the PdR(PPh3) moiety (R = C6F5 or C6Cl5)

Abstract The hydroxo-complexes [{PdR(PPh 3 )(μ-OH)} 2 ] (R  C 6 F 5 or C 6 Cl 5 ) have been obtained by reaction of the corresponding [{PdR(PPh 3 )(μ-Cl)}2] complexes with NBu 4 OH in acetone. In this solvent, the reaction of the hydroxo-bridged complexes with pyrazole (Hpz) and 3,5-dimethylpyrazole (Hdmpz) in 1:2 molar ratio leads to the formation of the new complexes [{Pd(C 5 F 5 )(PPh 3 )(μ-azolate)}2] and [{Pd(C 6 Cl 5 )(PPh 3 )} 2 (μ-OH)(μ-azolate)] (azolate = pz or dmpz). The reaction of the bis(μ-hydroxo) complexes with Hpz and Hdmpz in acetone in 1:1 molar ratio has also been studied, and the resulting product depends on the organic radical (C 6 F 5 or C 6 Cl 5 ) as well as the azolate (pz or dmpz). The identity of the isomer obtained has been established in every case by NMR ( 1 H, 19 F and 31 P) spectroscopy. The reaction of the bis(μ-hydroxo) complexes with oxalic (H 2 Ox) and acetic (HOAc) acids yields the binucle ar complexes [{PdR(PPh 3 )}2(μ-Ox)] (R  C 6 F 5 or C 6 Cl 5 ) and [{Pd(C 6 F 5 )(PPh 3 )(μ-OAc)}2], respectively. [{Pd(C 6 F 5 )(PPh 3 )(μ-OH)} 2 ] reacts with PPh 3 in acetone in 1:2 ratio giving the mononuclear complex trans -[Pd(C 6 F 5 ) (OH)(PPh 3 ) 2 ], whereas the pentachlorophenylhydroxo complex does not react with PPh 3 , even under forcing conditions.

New aryloxo allylpalladium complexes

Abstract Treatment of the di-μ-chloride allyl palladium complex [(η3-C4H7)Pd(μ-Cl)2Pd(η3-C4H7)] with [NBu4]OH (1:2 molar ratio) in methanol, followed by addition of phenol or para-substituted phenol ArOH (1:2 molar ratio), allows the preparation of dimeric aryloxo complexes of the type [(η3-C4H7)Pd(μ-OAr)2Pd(η3-C4H7)] (Ar=Ph 1, C6H4Me-p 2, C6H4Cl-p 3, C6H4Br-p 4). The addition of p-nitrophenol or pentafluorophenol to complex 1 results in quantitative substitution of the phenoxide anion to give the di-μ-aryloxo palladium complexes [(η3-C4H7)Pd(μ -OAr)2Pd(η3-C4H7)] (Ar=C6H4NO2-p 5 or C6F5 6). Complexes 1, 5 and 6 react with PPh3 to give the monomeric aryloxo complexes [(η3-C4H7)Pd(OAr)(PPh3)] (Ar=Ph 7, C6H4NO2-p 8, C6F5 9). The identity of these complexes has been established by partial elemental analyses and NMR (1H, 19F, 13C and 31P) spectroscopy.

Binuclear hydroxo-monopentahalophenyl complexes of palladium(II)

Abstract The novel binuclear hydroxo-bridged complexes trans -[R(PPh 3 )Pd(μ-OH) 2 Pd(PPh 3 )R] and cis -[R(PPh 3 )Pd(μ-OH)(μ-pz)Pd(PPh 3 )R] (R = C 6 F 5 or C 6 Cl 5 ; pz = pyrazolate) have been prepared, and their structures assigned on the basis of NMR data.