SynopsisAbstraction of phosphine from the nickel(I1) P, 0-chelated complexes, Ni[Ph, PCH=C(Ph)O] (Ph)(PPh,), and related species converts them from olefin oligomerization to olefin polymerization catalysts. Phosphine acceptors such as Rh(acetylacetonate)(C2H4)2 or Ni(l,5-cyclooctadiene), are most effective. Alternatively, nickel complexes-in which the phosphine ligand is replaced with weakly coordinated pyridine can be prepared. These active, homogeneous catalysts can be tuned to give either low or high molecular weight, linear low or high density polyethylene. Depending on the diluent, the same catalytic complex can be used as heterogeneous or homogeneous catalyst. They are tolerant of oxygenated, hydroxylic, or polar molecules that would poison normal early transition metal-based Ziegler-Natta catalysts. In fact, the polymerizations can be run in solvents such as ethanol or acetone, but hydrocarbon solvents are preferred.

Reaction of ferric chloride in methanol with 3 equiv of sodium mercaptide followed by 1 equiv of a methanolic solution of sodium hydrosulfide and sodium methoxide affords the complexes [Fe4S4(SR)4]2~(R = alkyl, aryl), which may be precipitated and purified in the form of salts of quaternary cations. The crystal structure of a prototype member of the series, [Et4NMFe4S4(SCH2Ph)4], has been determined from 4084 independent reflections collected by counter methods. The red-black crystals are monoclinic, space group Cm5-P2i/c, with a = 11.922 (6), b = 34.523 (17), and c = 12.762 (5) Á and ß = 95.78 (2)°. The measured density of 1.43 (3) g cm-3 agrees with the density of 1.40 g cm-3, calculated for eight anions and four cations in the cell. The absorption corrected data gave a conventional R factor (on F) of 0.036 on least-squares refinement. The structure consists of discrete anions and cations; the geometry of the tetraethylammonium ion is unexceptional. The core (Fe4S4*) of the anion exhibits distortions from cubic symmetry which are those of the point group Did-A2m such that each face of the polyhedron is a nonplanar rhomb. The bonded Fe-S* distances occur as sets of four (2.239 (4) Á) and eight (2.310 (3) Á), giving an average of 2.286 Á. The Fe-Fe distances occur as four short (2.732 (3) Á) and two slightly longer (2.776 Á) separations and imply some direct metal-metal interactions. All four iron atoms are structurally indistinguishable. Comparisons of certain structural parameters of [Fe4S4(SCH2Ph)4pwith those of the active sites of the reduced high-potential iron protein from Chromatium and the oxidized ferredoxin from P. aerogenes show that the three structures are unmistakably closely similar. This information together with comparative spectroscopic and magnetic evidence presented elsewhere demonstrates that the synthetic complexes [Fe4S4(SR)4]2-are true analogs of the active sites of bacterial iron-sulfur proteins.ron-sulfur proteins constitute one of the classes of metalloproteins and metalloenzymes which have been particularly extensively investigated in the last decade. Their biological, structural, and electronic properties have been reviewed in detail recently.5-8The well characterized forms of these proteins contain one, two, four, and eight iron atoms; zero, two, four, and eight atoms of acid-labile or "inorganic" sulfur (S*); and a number of cysteinyl residues which equals or exceeds the number of iron atoms present. X-Ray structure determinations8-11 and physicochemical stud-ies7•8 have provided evidence for the minimal active site compositions as Fe(S-cys)4 (rubredoxins), (cys-S)2-FeS*2Fe(S-cys)2 (plant, mammalian, and certain bacterial proteins), and (cys-S)4Fe4S*4 [4-Fe ("high-potential" iron proteins or HP) and 8-Fe bacterial proel

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The compound (Et4N)2[Fe4S4(SCH2Ph)4J has been prepared and its structure determined by x-ray diffraction. The Fe4S4 core of the anion possesses a configuration of D2d symmetry that is closely related to the Fe4S4 active-site structures of the high-potential iron protein from Chromatium and the ferredoxin from Micrococcus aerogenes. Electronic properties of the tetrameric anion have been partially characterized by measurement of proton magnetic resonance, Mossbauer, photoelectron, and electronic spectra, and magnetic susceptibility.