Markku Ahlgrén

The oxidative addition of diphenyl diselenide and ditelluride to tetrakis(triphenylphosphine)palladium

Abstract The oxidative addition of diphenyl diselenide to [Pd(PPh3)4] in dichloromethane results in the formation of a dinuclear complex [Pd2(SePh)4(PPh3)2] (1) and a mononuclear complex [PdCl(SePh)(PPh3)2] (2) that have been identified and characterized structurally by X-ray crystallography and 31P-NMR spectroscopy. The analogous reaction involving diphenyl ditelluride leads to a mixture of products. [Pd6Cl2Te4(TePh)2(PPh3)6]·1/2CH2Cl2 (3) can be isolated and its X-ray structure determined. While the oxidative addition of Ph2Se2 mainly involves the clevage of the Se–Se bond, that of Ph2Te2 indicates the rupture of both Te–Te and C–Te. Cumulative evidence shows that the choice of the central atom and the solvent also plays an important role in the oxidative addition. The final polynuclear complexes can be conceived to be formed from the mononuclear addition products by sequential condensation steps.

The NMR spectroscopic and X-ray crystallographic study of the oxidative addition of bis(2-thienyl) diselenide to zerovalent palladium and platinum centers

Abstract The pathway of the reaction of dithienyl diselenide with tetrakis(triphenylphosphine)palladium(0) and -platinum(0) has been explored by the use of NMR spectroscopy and X-ray diffraction. The oxidative addition of dithienyl diselenide to [Pd(PPh 3 ) 4 ] mainly results in the formation of two isomers of dinuclear [Pd 2 (SeTh) 4 (PPh 3 ) 2 ] (Th=2-thienyl, C 4 H 3 S) complex. The workup of the solution produced X-ray-quality crystals of trans -[Pd 2 (SeTh) 4 (PPh 3 ) 2 ]. The corresponding reaction with [Pt(PPh 3 ) 4 ], however, affords isomers of mononuclear [Pt(SeTh) 2 (PPh 3 ) 2 ]. Upon recrystallization from dichloromethane a small amount of crystals of dinuclear [Pt 2 (SeTh) 4 (PPh 3 ) 2 ] is obtained together with those of trans -[Pt(SeTh) 2 (PPh 3 ) 2 ]. While the products from both reactions imply that the oxidative addition takes place with the cleavage of the SeSe bond, a small amount of trans -[PdCl(Th)(PPh 3 ) 2 ] is formed in the reaction of [Pd(PPh 3 ) 4 ] and Th 2 Se 2 in dichloromethane indicating that CSe cleavage may also take place during the oxidative addition.

Zirconium-loaded activated charcoal as an adsorbent for arsenic, selenium and mercury

The adsorption of arsenic, selenium and mercury from aqueous solutions onto zirconium-loaded activated charcoal was studied as a function of adsorption time, amount of adsorbent, pH, concentration of adsorbates, sample volume and the oxidation states of the adsorbates. The cross-interference of the analytes was also investigated. Loaded filters were measured by energy-dispersive X-ray fluorescence spectrometry (EDXRF) and the amount of the unadsorbed analytes were determined by vapour generation atomic absorption spectrometry (VGAAS).

The X-ray crystallographic study of the reaction of bis(2-thienyl)ditelluride with tetrakis(triphenylphosphine)platinum or -palladium

Abstract The oxidative addition of dithienyl ditelluride to [Pt(PPh3)4] in dichloromethane results in the formation of a trinuclear complex [Pt3Te2(Th)(PPh3)5]Cl (Th=2-thienyl, C4H3S) (1) as well as a mononuclear complex [PtCl(Th)(PPh3)2] that have been identified and structurally characterized by X-ray crystallography and 31P-NMR spectroscopy. The analogous reaction involving [Pd(PPh3)4] forms a mixture of several products. In dichloromethane [Pd6Cl2Te4(TeTh)2(PPh3)6] (2) can be isolated and its X-ray structure determined. In toluene [Pd6Te4(TeTh)4(PPh3)6] (3) is formed. Both 2 and 3 have a similar hexanuclear framework which has previously been reported for [Pd6Te6(PEt3)8] in the literature. These products indicate that the cleavage of both TeTe and CTe bonds as well as the choice of the solvent play an important role in the oxidative addition. The trinuclear and hexanuclear complexes can be considered to be formed from an initial mononuclear addition product. The reaction pathways are compared to those involved in the reaction of Th2Se2 and [M(PPh3)4] (M=Pt, Pd).

Determination of trace elements in heavy oil samples by graphite furnace and cold vapour atomic absorption spectrometry after acid digestion

A procedure was developed to determine the concentrations of trace elements (As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb and V) in heavy oil samples. The wet digestion (HNO3-H2SO4) method developed for the sample preparation was both repeatable and quantitative and allowed element determinations by graphite furnace atomic absorption spectrometry (GFAAS) or cold vapour atomic absorption spectrometry (CVAAS) from the same sample solution. The detection limits were low, and low concentrations of analyte could be determined accurately. V and Ni were determined also by inductively coupled plasma atomic emission spectrometry (ICP-AES), in samples merely diluted with xylene (1:10), the 1CP-AES results were in good agreement with the GFAAS results.

Optimized arsenic, selenium and mercury determinations in aqueous solutions by energy dispersive x-ray fluorescence after preconcentration onto zirconium-loaded activated charcoal

Abstract Adsorption onto zirconium-loaded activated charcoal (ZrC ∗) allows the efficient collection of arsenic, selenium and mercury from aqueous solutions in a thin layer, and at the same time removes or minimizes elemental interferences. When this preconcentration method is combined with energy dispersive x-ray fluorescence, the resulting analysis is accurate and precise. The method is simple and rapid and almost free from contamination because only a small amount of sodium hydroxide or nitric acid is required for pH adjustment, in addition to ZrC ∗ adsorbent. Spectral interferences from other elements are negligible because the ZrC ∗ adsorbent is highly selective. The procedure is also suitable for the determination of organometallic compounds of arsenic, selenium and mercury.

Separation of microgram quantities of Cr(III) and Cr(VI) in aqueous solutions and determination by energy dispersive X-ray fluorescence spectrometry

Abstract A procedure was developed for the separation and independent determination of microgram quantities of Cr(VI) and Cr(III) in aqueous solution. Cr(VI) was adsorbed onto zirconium-loaded activated charcoal (ZrC ∗), and Cr(III) was collected by Fe(OH) 3 precipitation and the precipitate bound to activated charcoal. Chromium in the activated charcoal was measured by energy dispersive X-ray fluorescence spectrometry. The detection limits for both chromium species were better than 0.05 mg/l. The procedure was tested with the Ground Water and Waste Water Pollution Control Check Standard WP-15 spiked with Cr(VI) and several samples from the plating industry.

Chiral palladium(II) and platinum(II) complexes of diaminocyclohexane: X-ray structures of (1R,2R)-(−)-1,2-diaminocyclohexane dihydrochloride and its corresponding oxalato platinum(II) complex

Abstract The nucleophilic substitution reaction of the enantiomerically pure ligand, (1R,2R)-(−)-1,2-diaminocyclohexane [DACH] (1) with cis-bis(benzonitrile)palladium(II) dichloride [(PhCN)2PdCl2] leads to the formation of the complex [(DACH)PdCl2] (2) in a high yield. The reaction of the corresponding platinum(II) complex [(PhCN)2PtCl2] with DACH, under the same reaction conditions, surprisingly, took a different course, in which nucleophilic addition to the benzonitrile ligand occurred forming an enantiomerically pure amidine complex [(PhCNHNH(C6H10)NH2)Pt(NCPh)Cl]Cl (3), where the nitrogen ligand form a seven-membered chelate around the central atom. The aqua and oxalato derivatives of complex 2, [(DACH)Pd(H2O)2](NO3)2 (4) and [(DACH)Pd(C2O4)] (5) have also been prepared and characterized. The platinum analogue complex to 5, [(DACH)Pt(C2O4)] (6), was prepared starting from the enantiomerically pure isomer (1) and the platinum salt K2PtX4 (X=Cl, I). According to X-ray structural analysis carried out on the complex, the product does not consist of just the desired isomer, but a mixture of both the trans-l (trans-(−)-1R,2R) and trans-d (trans-(+)-1S,2S) isomers. No retention of optical isomerism was observed. The single crystal structural analysis was also carried out on the ligand N,N′-(1R,2R)-(−)-diaminocyclohexane dihydrochloride (DACH·2HCl)] (1a). The result indicates, however, that only the R,R-isomer exists in the free ligand.

Trends in the structure and bonding of [MCl2{(C4H3S)ECH3}2] (M=Pd, Pt; E=Te, Se)

Abstract The complex formation of (C 4 H 3 E)E′Me (E=S, O; E′=Te, Se) ( 1 – 4 ) with palladium and platinum has been explored by use of NMR spectroscopy and X-ray diffraction. Whereas the 125 Te-NMR spectra of [PdCl 2 {(C 4 H 3 E)TeMe} 2 ] [E=S ( 5 ), E=O ( 6 )] show the existence of both cis - and trans -isomers in solution the spectroscopic information of [MCl 2 {(C 4 H 3 E)SeMe} 2 ] (M=Pd, Pt, E=S, O; 8 – 10 ) indicates the presence of only one isomer. The crystal structure determinations have shown that 5 and 6 are isomorphous and crystallize as cis -isomers forming dimers with close chalcogen–halogen contacts. In contrast, 8 and 10 have turned out to be trans -isomers and form skewed stacks that are bound together in a helical arrangement by weak hydrogen bonds. The structural data indicate that back donation may weakly contribute to the palladium–tellurium bonding in 5 and 6 . In 8 and 10 the effects of the back bonding are negligible.

An experimental and theoretical study of the isomerization of mononuclear bis(arylselenolato)bis(triphenylphosphine)platinum complexes [Pt(SeR)2(PPh3)2]

Mononuclear bis(thienylselenolato)bis(triphenylphosphine)platinum [Pt(SeTh) 2 (PPh 3 ) 2 ] (Th=2-thienyl, C 4 H 3 S) has been prepared by the treatment of cis -[PtCl 2 (PPh 3 ) 2 ] with NaSeTh. The 31 P-NMR spectroscopic information indicates that cis -[Pt(SeTh) 2 (PPh 3 ) 2 ] is initially formed in the reaction. Upon prolonged standing in solution it isomerizes to trans -[Pt(SeTh) 2 (PPh 3 ) 2 ] . The reaction of cis -[PtCl 2 (PPh 3 ) 2 ] with LiSeFu (Fu=2-furyl, C 4 H 3 O) affords immediately a mixture of cis - and trans -isomers of [Pt(SeFu) 2 (PPh 3 ) 2 ] with the relative amount of the trans -isomer increasing with time. The recrystallization of the two reaction mixtures yielded cis , anti - and trans , syn -isomers of [Pt(SeTh) 2 (PPh 3 ) 2 ] as well as cis,syn - and trans , anti -isomers of [Pt(SeFu) 2 (PPh 3 ) 2 ]. Their structures were compared with those of cis , anti - and trans , anti -isomers of [Pt(SePh) 2 (PPh 3 ) 2 ]. The geometries and relative stabilities of all isomers of [Pt(SeTh) 2 (PH 3 ) 2 ], [Pt(SeFu) 2 (PH 3 ) 2 ] and [Pt(SePh) 2 (PH 3 ) 2 ] were studied by the use of ab initio molecular orbital techniques in order to model the structures and isomerization of the observed mononuclear selenolato complexes.