A series of nickel(II) hydride complexes supported by amido diphosphine ligands, including symmetrical [N(o-C6H4PR2)2]− ([R-PNP]−; R = Ph, i Pr, Cy) and unsymmetrical [N(o-C6H4PPh2)(o-C6H4P i Pr2)]− ([Ph-PNP- i Pr]−), have been prepared for the investigation of olefin insertion chemistry. The unsymmetrical ligand precursor H[Ph-PNP- i Pr] (1d) that features different substituents (phenyl and isopropyl) at the two phosphorus donors was prepared in 53% yield as colorless crystals. Treatment of Ni(COD)2 (COD = cycloocta-1,5-diene) with H[R-PNP] (R = Ph (1a), i Pr (1b), Cy (1c)) or 1d produced the corresponding four-coordinate nickel hydride complexes 2a−d. Attempts to isolate 2a led instead to the cyclooct-4-en-1-yl complex [Ph-PNP]Ni(η1-C8H13) (3a) as a consequence of COD insertion into the Ni−H bond of 2a. The reactions of 2a,d with ethylene, 1-hexene, and norbornene, respectively, generated cleanly the corresponding ethyl (4a,d), n-hexyl (5a,d), and 2-norbornyl (6a,d) complexes. The quantitative formation of 5a,d is indicative of exclusive 1,2-insertion of 1-hexene. In contrast, styrene inserts into the Ni−H bond of 2d in an exclusively 2,1-manner to afford [Ph-PNP- i Pr]NiCH(Me)Ph (7d) quantitatively. The selective 2,1-insertion products [Ph-PNP]NiCH(Me)CO2Me (8a), [ i Pr-PNP]NiCH(Me)CO2Me (8b), [Cy-PNP]NiCH(Me)CO2Me (8c), and [Ph-PNP- i Pr]NiCH(Me)CO2Me (8d) were also isolated from the reactions of methyl acrylate with the corresponding nickel hydride complexes 2a−d. The effects of the phosphorus and olefin substituents on the reactivity and regioselectivity of the olefin insertion reactions are discussed. In addition to solution NMR spectroscopic data for all new compounds, X-ray structures of 1d, 2b− d, 3a, and 5d− 7d are reported.

A series of five-coordinate aluminum complexes supported by o-phenylene-derived amido diphosphine ligands, [N(o-C(6)H(4)PR(2))(2)](-) ([R-PNP](-); R = Ph, (i)Pr) and [N(o-C(6)H(4)PPh(2))(o-C(6)H(4)P(i)Pr(2))](-) ([Ph-PNP-(i)Pr](-)), have been prepared and structurally characterized. Alkane elimination reactions of trialkylaluminum with H[Ph-PNP] (1a), H[(i)Pr-PNP] (1b), and H[Ph-PNP-(i)Pr] (1c) in toluene at -35 degrees C respectively produced the corresponding dialkyl complexes [Ph-PNP]AlR(2), [(i)Pr-PNP]AlR(2), and [Ph-PNP-(i)Pr]AlR(2) (R = Me (2a-c), Et (3a-c), (i)Bu (4a-c)) in high isolated yield. The dihydride complexes [Ph-PNP]AlH(2) (6a), [(i)Pr- PNP]AlH(2) (6b), and [Ph-PNP-(i)Pr]AlH(2) (6c) were prepared in one-pot reactions of in situ prepared dichloride precursors (5a-c) with LiAlH(4) in THF at room temperature. X-ray diffraction studies of 2a-c, 3b-c, 5b, and 6b revealed a distorted trigonal-bipyramidal structure for these molecules in which the two phosphorus donors are mutually trans. The solution structures of these organoaluminum complexes were all characterized by (1)H, (13)C, and (31)P NMR spectroscopy. The NMR data are indicative of solution C(2) symmetry for [Ph-PNP](-) and [(i)Pr-PNP](-) complexes, whereas they are indicative of C(1) for [Ph-PNP-(i)Pr](-) derivatives. The (1)H NMR spectra of 3a-c and 4a-c revealed diastereotopy for the alpha-hydrogen atoms in these molecules.

We report the synthesis of concave magnetic Mn(x)Fe(1-x)O nanoparticles with high-index facet structures by a thermal decomposition approach. The particle morphology varies from cubic shape under pure Ar, to star-like shapes with exposure to air during the reaction. The oxidative etching in the presence of air (O2) strongly affects the exposed facets on the surface. These concave nanoparticles are transferred from the organic phase to aqueous solution and show distinct catalytic activity toward the degradation of xylenol orange in aqueous solution.

This report describes the synthesis, structure, and reactivity of aluminum complexes containing tridentate biphenolate phosphine ligands of the type [RP(2-O-3,5-CHtBu)] (R = tBu (2a), Ph (2b)). Alkane elimination of AlMe with one equiv. of H[2a] or H[2b] in THF at 0 °C cleanly affords colorless crystalline [2a]AlMe(THF) (3a) and [2b]AlMe(THF) (3b), respectively. An X-ray diffraction study of 3a showed it to be a five-coordinate THF-bound species, whose coordination geometry is best described as trigonal bipyramidal, having the phosphorus donor and THF at axial positions. Treatment of either in situ prepared or isolated methyl complexes 3a,b with one equiv. of benzyl alcohol in toluene or THF generated their corresponding benzyloxides {[2a,b]Al(μ-OCHPh)} (4a,b). An X-ray diffraction study of 4a revealed a dimeric structure, in which the coordination geometry of aluminum is also distorted trigonal bipyramidal with the tridentate 2a ligand being facially bound. In the presence of one equiv. of benzyl alcohol, complex 3a is a competent catalyst precursor for the living ring-opening polymerization of ε-caprolactone (ε-CL) and rac-lactide (rac-LA), producing poly(ε-caprolactone) and poly(rac-lactide), respectively, in a controlled manner. As such, well-defined block copolymers of ε-CL with rac-LA can also be prepared by catalytic 3a. Kinetic studies revealed that 3a catalyzes the polymerization of rac-lactide at a rate 2-fold faster than that of 3b, indicating the significance of the P-substituent effect on this catalysis. Interestingly, the polymerization rate of rac-lactide by 3a is 16.5 times faster than that of l-lactide under otherwise identical conditions.

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