Palladium dithiocarbamate complexes

Considerably less is known about the chemistry of palladium and platinum 1,1-dithio complexes. Of late, there has been only one report that dealt with the synthesis of a large number of palladium dithiocar-bamates 392). Twenty-five yellow palladium dithiocarbamate complexes were obtained by reaction of PdCla with NaR2dtc in methanol solution. Several other reports have appeared in which a few dithiocarbamate complexes of palladium were synthesized. Thus, the novel [Pd (OH)2dtc 2], which is soluble in water, was isolated 393). The synthesis of optically active palladium(II) complexes of AT-alkyl-a-phen-ethyldithiocarbamates, similar to (XXIV), via the reaction between the optically active amine, CS2, and PdCl2, has been described. From ORD and CD spectra, it has been established that the vicinal contribution of a remote, asymmetric carbon center could give rise to optical activity of the d—d transitions of palladium 394). Carbon disulfide has been shown to insert into the Pt-F bond of [PtF(PPh3)3]HF2, and X-ray studies indicated the structure (XXIX). 

The mechanism of 1 1 complex formation between palladium(II) and catechol and 4-methylcatechol has been studied in acidic media, and the rate of 1 1 (and 1 2) complex formation between silver(II) and several diols is an order of magnitude higher in basic solution than in acidic. The kinetics of formation and dissociation of the complex between cop-per(II) and cryptand (2,2,1) in aqueous DMSO have been measured and the dissociation rate constant, in particular, found to be strongly dependent upon water concentration. The kinetics of the formation of the zinc(II) and mercury(II) complexes of 2-methyl-2-(2-pyridyl)thiazolidine have been measured, as they have for the metal exchange reaction between Cu " and the nitrilotriacetate complexes of cobalt(II) and lead(II). Two pathways are observed for ligand transfer between Ni(II), Cu(II), Zn(II), Cd(II), Pb(II) and Hg(II) and their dithiocarbamate complexes in DMSO the first involves dissociation of the ligand from the complex followed by substitution at the metal ion, while the second involves direct electrophilic attack by the metal ion on the dithiocarbamate complex. As expected, the relative importance of the pathways depends on the stability of the complex and the lability and electrophilic character of the metal ion. 

Restricted carbon-nitrogen bond rotation has also been studied in unsymme-trical palladium bis(dithiocarbamate) complexes by HPLC (Fig. 54). At high temperature, there is rapid rotation and a single peak is observed, however, at lower temperatures two peaks can be separated. For [Pd(S2CNHCH2CH2Ph)2], AH was found to be 83 5 kJ mol (372). 

Figure 54. Rotomers of asymmetric palladium bis(dithiocarbamate) complexes being inteicon-verted via rotation about the backbone carbon-nitrogen bonds.

Both Bruce (1485) and Hoshino-Miyajima (1486) and co-workers prepared bis(dithiocarbamate) complexes with long-chain substituents as potential liquid crystals. Most are derived from four-substituted piperazines with flexible alkoxy tails (345), and are mesomorphic, showing smectic phases Sc and crystal B mesophases (1485). Palladium, copper, and zinc bis(dithiocarbamate) complexes of the same ligands showed similar behavior, but nickel piperazine complexes with 4-phenyl, alkyl, and 3-alkoxy tails are non-mesomorphic (1485). 

Palladium and platinum dithiocarbamate complexes are known for the - -2 and +A oxidation states, although the former is by far the more prevalent. Stable complexes are not known in either the +1 or +3 oxidation states, although some evidence has been found for the generation of both in electrochemical experiments (231,1561,1578). 

Monodentate phosphine complexes have also been reported. Dithiocarbimato complexes [M(PR3)2(S2CNR)] of palladium and platinum have been prepared from [MCl2(PR3)2], primary amines, and carbon disulfide and can be reversibly protonated to give dithiocarbamate complexes [M(PR3)2(S2CNHR)] (Eq. 155) (1520). 

Palladium bis(dithiocarbamate) complexes derived from 4-(4 -alkyloxyphe-nylethyl)piperidines (434) display mesomorphic liquid-crystalline properties (1485), while in contrast, related complexes lacking the alkyl chains such as [Pd(S2CNC4HgNPh)2] and [Pd S2C N(CH2) Me 2 2] ( = 6,8) (1486) showed no mesomorphism as the chain length was not sufficiently long to depress the melting point enough (1486). 

The alleged preparation of the supposed cobalt(II) complex Na[Co(Et2dtc)3] described by D Ascenzo and Wendlandt (305) has been repeated by Holah and Murphy (306), who identified the product as [Co(Et2dtc)3]. Complexes of cobalt(III), nickel(II), and palladium(II) salts with cationic, dithiocarbamate ligands have been synthesized (307). Reaction of the secondary amine (Et2N(CH2)2)2NH with CS2 produces... 

Pt(S2CNMe(Hex))2] and [Pd(S2CNMe(Hex))2] have been synthesized and used as precursors to grow the first TOPO-capped PtS and PdS nanoparticles and thin films of PtS and PdS by the metallo-organic chemical vapor deposition (MOCVD) method [204]. Platinum and palladium chalcogenides find applications in catalysis [205-210] and materials science [211,212]. The synthesis of thiocarbamato complexes of platinum and palladium from reaction of an aqueous solution of ammonium dithiocarbamate with the platinum or palladium salt has been reported by Nakamoto et al. [213]. However... 

Carbon-based sorbents are relatively new materials for the analysis of noble metal samples of different origin [78-84]. The separation and enrichment of palladium from water, fly ash, and road dust samples on oxidized carbon nanotubes (preconcentration factor of 165) [83] palladium from road dust samples on dithiocarbamate-coated fullerene Cso (sorption efficiency of 99.2 %) [78], and rhodium on multiwalled carbon nanotubes modified with polyacrylonitrile (preconcentration factor of 120) [80] are examples of the application of various carbon-based sorbents for extraction of noble metals from environmental samples. Sorption of Au(III) and Pd(ll) on hybrid material of multiwalled carbon nanotubes grafted with polypropylene amine dendrimers prior to their determination in food and environmental samples has recently been described [84]. Recent application of ion-imprinted polymers using various chelate complexes for SPE of noble metals such as Pt [85] and Pd [86] from environmental samples can be mentioned. Hydrophobic noble metal complexes undergo separation by extraction under cloud point extraction systems, for example, extraction of Pt, Pd, and Au with N, A-dihexyl-A -benzylthiourea-Triton X-114 from sea water and dust samples [87]. 

Temperature-dependent luminescence spectra for a series of palla-dium(ii) and platinum(ii) complexes with thiocyanate, halide, and dithiocarbamate ligands have been investigated. The results show that the luminescence band maxima of palladium(ii) and platinum(ii) complexes have opposite shifts with increasing temperature. The palladium complexes exhibit a negative shift of at least 1 cm /K, while the platinum(ii) ones have a positive shift of -1-1.6 cm /K. ... 

A number of synthetic approaches involve the cleavage of a sulfur-element bond in order to generate the dithiocarbamate. Faraglia and co-workers (206, 207) developed a route to certain palladium and platinum dithiocarbamate from the thermolysis of dithiocarbamic ester complexes, upon loss of methyl halide (Eq. 27). 

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