J. J. Steggerda

Synthesis and structural characterisation of [Pt3Au(μ2-CO)3(PPh3)5]NO3

The compound [Pt3Au(μ2-CO)3(PPh3)5]NO3 was formed as the main product of the reaction of AuPPh3NO3 with Pt(PPh3)3 and CO. Its structure was determined by X-ray diffraction, using Cu-Kα radiation with a graphite crystal monochromator; λ 1.54184 A, AuC93H75NO6P5Pt3 · 12 C4H10O, Mr = 2276.80, triclinic, space group P1−, a 15.256(2), b 14.422(2), c 21.663(3) A, α 93.138(9), β 91.823(9), γ 68.654(9)°, V 4432(3) A3, Z = 2, Dc 1.678 Mg/m3, μ(Cu-Kα) 131.8 cm−1, F(000) = 21.94, T 290 K. Final conventional R factor = 0.063, Rw = 0.078 for 11193 unique reflections and 322 variables. The structure was solved by automated Patterson methods. The metal cluster is a strongly distorted tetrahedron with one short (2.700(1) A) and two longer (2.906(1) A) PtAu distances. This bonding asymmetry is discussed in a comparison with known structures of similar 54 and 56 valence electron Pt3Au clusters.

Interaction of Ph2PC(S)NHR and (R = Ph, Me) with [Rh(CO)2Cl]2. Mode of coordination of Ph2PC(S)NHR and [Ph2PC(S)NR]−

Abstract Upon reaction with [Rh(CO) 2 Cl] 2 , Ph 2 PC(S)NHR (R = Ph, Me) displaces one CO molecule and coordinates to the metal end-on (η 1 ) via P. All the complexes containing the protonated ligand rapidly eliminate HCl in the presence of a base. Generally, bidentate coordination via P and S is observed for the resulting deprotonated ligand. By loss of HCl coordinative unsaturation is generated. In some cases this results in the involvement of all three hereto atoms (P, S and N) in the coordination, as found in {Rh(CO)[Ph 2 C(S)NR]} 4 . The binuclear complex {Rh(μCl)H(CO)[Ph 2 PC(S)NHR]} {Rh(μCl)(CO)[PH 2 PC(S)NR]} occurs in the tautomeric form, in which both metal centres possess the formal oxidation state II and exhibit a metalmetal interaction. The rhodiumhydride complex RhH(CO)[Ph 2 PC(S)NPh] 2 , which results from intramolecular oxidative addition in RH(CO)[PH 2 PC(S)NHPh][Ph 2 PC(S)NPh] has been isolated. The nitrogen analogue Me 2 NC(S)NHPh only reacts with [RH(CO) 2 Cl] 2 under basic conditions to yield Rh(CO) 2 [Me 2 NC(S)NPh].

Synthesis and characterization of [Pt(CN)(AuCN)(AuPPh3)8](NO3) and Pt(CO)(AuPPh3)6(AuCN)2. Crystal structure of [Pt(CN)(AuCN)(AuPPh3)8] (NO3)

Abstract Pt(CN)(AuCN)(AuPPh3)8+ (1) can be prepared from Pt(AuPPh3)82+ (2) by an oxidative addition reaction with Au(CN)2−. The CO in Pt(CO)(Au- PPh3)82+ cannot be replaced with CN−, but in a slow process two PPh3 are replaced, forming Pt(CO)(Au- CN)2(AuPPh3)6 (3). The compounds are characterized by 31P, 13C and 195Pt NMR, FAB-MS and IR measurements. The structure of Pt(CN)(AuCN)- (AuPPh3)8(NO3) is determined by X-ray diffraction (monoclinic, space group P21/n, a = 17.269(20), b = 29.638(17), c = 27.88(3) A, β = 93.95(14)°, V = 14233 A3, Z = 4, the residuals are R = 0.063 and Rw = 0.090 for 5965 observed reflections and 467 variables Cu Kα radiation). In the metal cluster the central Pt atom is surrounded by eight Au atoms and one CN ligand in a spheroidal structure similar to that of Pt(CO)(AgNO3)(AuPPh3)82+.

A comparative electrochemical study of the iron-sulfur cluster series Fe4SxCp4 (x=4–6) in benzonitrile

Abstract The electrochemical redox behaviour of the compounds Fe 4 S x Cp 4 (x=4–6) has been investigated at a platinum electrode in benzonitrile solutions, using pulse polarographic and cyclic voltammetric techniques. In this solvent Fe 4 S 4 Cp 4 exhibits four reversible oxidation reactions, earlier noted in acetonitrile, and a thus far unknown irreversible reduction. Fe 4 S 5 Cp 4 shows two reductions one of which is reversible, and three reversible oxidations. Fe 4 S 6 Cp 4 shows a reversible reduction and two reversible oxidations, and also a third, previously undetected, irreversible one-electron oxidation. Thus far not reported detailed electrochemical data for these compounds (e.g. current functions and reversibility criteria) are measured under the same experimental conditions. In this way a detailed comparative study of the electrochemical properties of the Fe 4 S x Cp 4 compounds is possible. Some attention is paid to the nature of the decomposition products resulting from the irreversible transitions.

Gold clusters. Reactivity of [Au9(PPh3)8]3+ and [Au8(PPh3)7]2+ towards isopropyl isocyanide

Abstract Isopropyl isocyanide reacts with [Au 9 (PPh 3 ) 8 ] 3+ or [Au 8 (PPh 3 ) 7 ] 2+ in CH 2 Cl 2 to give the cluster complex [Au 9 (PPh 3 ) 6 (i-PrNC) 2 ]X 3 (X = NO 3 or PF 6 ), in which the peripheral Au atoms are bonded to PPh 3 or i-PrNC. The complex has been characterized by elemental analysis, molecular weight, NMR, IR and Mossbauer spectroscopy.

Hydride platinum gold clusters : synthesis and characterization

Abstract [Pt(H)(AuPPh3)8]+ and [Pt(H)(PPh3)(AuPPh3)6]+ were prepared from [Pt(AuPPh3)8]2+ and [Pt(PPh3)- (AuPPh3)6]2+, respectively, using an alkaline methanol solution as hydride forming reagent, while [Pt(H)(SnCl3)(AuPPh3)7]+ was prepared from [Pt(H)(PPh3)(AuPPh3)7]2+ and SnCl3-. The clusters were characterized by 31p, 195pt and 1H NMR, analysis and by the reaction with acid. The cluster growth of PtAux clusters is discussed. The newly prepared compounds did not show any catalytic activity for the hydrogenation and isomerization of hexenes at ambient temperature and atmospheric pressure.

Gold phosphine cluster compounds: Chemical and crystallographic difficulties

ConclusionsCompared with most routine structure determinations, analyses of gold cluster compounds are very measuring-time, computer-time, and man-time consuming, and give less accurate results. However, they are equally useful and relevant as far as chemical information is concerned, even when only the gold skeleton and its connectivity with the ligands have been determined. TheR value is a poor guide to the value of a structure determination of this kind. One may even question whether one should take all possible precautions (change X-ray tubes, measure crystal faces, measure high-order reflection intensities) and try to locate light atoms, or perform three or more incomplete analyses of different compounds; certainly the latter gives more chemical information. Of course, none of the difficulties summarized in this note are unique for gold cluster compounds; the conclusions given here are valid generally.

The electrochemical reactivity of [Pt(AuPPh3)8]2+ and [HPt(AuPPh3)8]+ under dihydrogen

Abstract [(H) 2 Pt(AuPPh 3 ) 8 ] 2+ is electrochemically reduced in a dihydrogen atmosphere at about −1.62 V in various solvents following a CEE reaction path. A chemical step (C), i.e. the fast dissociation into dihydrogen and [Pt(AuPPh 3 ) 8 ] 2+ , precedes the two closely spaced one-electron reduction steps (EE) shown by [Pt(AuPPh 3 ) 8 ] 2+ . Long-term experiments (controlled potential electrolysis) revealed that in a chemical follow-up reaction [HPt(AuPPh 3 ) 8 ] + is formed. The reduced cluster, [Pt(AuPPh 3 ) 8 ] O reacts as a base with the starting dihydride cluster as an acid. In a basic solvent like pyridine [HPt(AuPPh 3 ) 8 ] + undergoes a two-electron oxidation reaction. In chemical follow-up reactions the formed 3+ cluster reacts immediately with the solvent and dihydrogen and the starting material [HPt(AuPPh 3 ) 8 ] + is regenerated and C 5 H 5 NH + is formed. Thus an EC′ reaction mechanism is operative (C′ = catalytic reaction) in which dihydrogen is oxidised and whereby [HPt(AuPPh 3 ) 8 ] + acts as the catalyst.

An electrochemical study on the oxidation of tris(N,N-dimethyldithiocarbamato)ruthenium(III)

Abstract The electrochemical oxidation of Ru(Me 2 dtc) 3 (where Me 2 dtc= N , N -dimethyldithiocarbamate) in acetone or methylene chloride solution is a one- electron process followed by a dimerisation. This is concluded from cyclic voltammetric experiments at different scan rates, concentrations and temperatures with the use of Saveants diagnostic criteria. NMR spectra taken at different temperatures confirm this conclusion. This behaviour is in contrast with that in coordinating solvents like acetonitrile where the one-electron oxidation is followed by addition of a solvent molecule to the coordination sphere, yielding Ru(Me 2 dtc) 3 (CH 3 CN).