Darryl R. Fahey

The coordination-catalyzed ortho-halogenation of azobenzene

Abstract Azobenzene is halogenated by chlorine and bromine selectively ortho to theazo group when its solutions are treated with the respective halogen in the presence of a palladium(II) catalyst. All possible ortho-chlorinated products are obtained, and 2,6,2′,6′-tetrachloroazobenzene is obtained as the major product upon exhaustive chlorination. The specificity for ortho-halogenation is derived from the interaction of the halogen with a carbon-metal σ-bonded intermediate, di-μ-halobis[2-(phenylazo)phenyl]dipalladium(II) (I). Intermediates such as (I) were isolated from reaction mixtures and characterized by their far-IR spectra and their reactions with chlorine and triphenylphosphine.

A very low-field aromatic proton resonance in the PMR spectrum of a conformationally constrained arylnickel complex

The 1H NMR spectrum of 2,2′-bis[chlorobis(triethylphosphine)nickel]biphenyl, (I), exhibits the H6 and H6, resonance at δ 12.00 ppm in CDCl3 (12.27 in C6D6), 4.4 ppm downfield from the resonance of the corresponding protons in biphenyl. The large downfield shift is attributed to static very-short distances of H6 and H6, to nickel atoms in (I) that are enforced by its sterically-fixed conformation.

Photodegradation and photostabilization of poly(p-phenylene sulfide). Part 2. UV induced physicochemical changes

Abstract The photodegradation of PPS as a result of UV irradiation manifests itself not only in yellowing and color-darkening, but also surface oxidation (conversion of S to S(O) x ), IR and UV-visible spectral changes, and partial loss of solubility (in hot 1-chloronaphthalene). The formation of insoluble fractions and the size exclusion chromatography (SEC) analysis of soluble fractions strongly suggest that crosslinking, rather than chain scission, is a major outcome of the photolysis. The effects of various factors on photocoloration have been examined; these include resin purity, morphology, molecular weight, nature of end group, presence of oligomers, oxygen vs inert atmosphere, and spectral region of excitation. While the presence of extractable oligomers in PPS does not affect the magnitude of its photocoloration, oxygen in the ambient atmosphere accelerates the process considerably. The color changes of crystalline translucent films are generally higher than those of transparent amorphous films. The estimated short lifetime of the PPS singlet excited state suggests that the degradation arising from it would not be easily controllable by quenchers. Attempts at photostabilization of PPS based on a screening mechanism should focus on maximum spectral overlap between the screener and the polymer in the near-UV region (300–380 nm).

Photostabilization of poly (p-phenylene sulfide)

Abstract Various additives have been studied for effectiveness in rendering PPS colorfast against UV light. Only UV-absorber (screener) type stabilizers are found to work satisfactorily for PPS. Color changes (Δ E ) ≤ 2 after 50 h irradiation in a weather-Ometer have been obtained by bulk-adding a phenylsulfonyl derivative of a hydroxyphenylbenzotriazole at 8–10 wt% loading. Quencher-type photostabilizers, antioxidants and hindered amine light stabilizers (HALS) are generally ineffective; some of these photostabilizers (e.g. metalloorganics) are unacceptable because they cause drastic changes in color or moldability of the resin, Aromatics in general sensitize photodegradation of the polymer.

Study of NickelCarbon bonding by x-ray photoelectron spectroscopy[1]

Abstract X-ray photoelectron spectroscopy (XPS) nickel 2p 3 2 binding have been measured for a series of trans square-planar Ni(X)(Y)(PEt3)2 complexes and correlated with a calculated ‘charge parameter’ for the nickel atoms. A reasonbly good correlation exists when X or Y is chloro, alkyl, vinyl, acyl, or phenyl, but not when both X and Y are acetylide. The deviation of ther diacetylide complex from the correlation is attributed to a substantial π character in the nickelcarbon bonds. The agreement of the aryl, vinyl, and acyl complexes with the correlartion indicates that any π character in these nickelcarbon bonds is small.

Reactions of 2-chlorophenyl acrylate with nickel(0) complexes. A metal- promoted cyclization reaction

Abstract At elevated temperatures, 2-chlorophenyl acrylate is converted to coumarin, 3,4-dihydrocoumarin, and several other products by the action of certain nickel(0) complexes. At 10 °C, a bis(triphenylphosphine)(2-chlorophenyl acrylate)nickel(0) complex can be isolated which produces the same organic products upon thermolysis. In one case, a nickel(I) complex was isolated from the thermolysis. 2-Iodophenyl acrylate yields a polymer and NiI(PPh3)3 when treated with Ni(PPh3)2(1,5-cyclooctadiene).

Absence of nickelcarbon π-bonding in nickel aryls

Abstract When nickel core electron binding energies in trans -Ni(X)(Y)(PEt 3 ) 2 complexes (X, Y = alkyl, alkenyl, alkynyl, aryl, halide) are compared with calculated nickel charges, nickelaryl π-bonding is concluded to be unimportant.

Synthesis, characterization and polymerization properties of isopropylidene(η5-3-neomenthylcyclopentadienyl)(η5-fluorenyl)zirconium dichloride

Abstract The reaction of neomenthylcyclopentadiene with acetone solution led to 6,6-dimethyl-3-neomenthylfulvene (6). The bridged 3-neomenthylcyclopentadienyl-2-fluorenylpropane (7) has been isolated after reaction of 6 with fluorenyllithium salt. The reaction of ZrCl4 with the dilithium salt of 7 in diethyl ether yields the complex isopropylidene(η5-3-neomenthylCp)-(η5-9-fluorenyl)ZrCl2 (4) as a 60:40 mixture of diastereomers. The complex was fully characterized by single-crystal X-ray diffraction and NMR methods. Complex 4 is an active catalyst for the homogeneous polymerization of propylene when activated by methylaluminoxane (MAO). The polypropylene polymer produced with 4 has lower molecular weight and a lower degree of syndiotactic or hemiisotactic stereoregularity, but a higher degree of isotactic character (mm triad of 63%) than the polymer produced with the syndiospecific catalyst isopropylidene(Cp)(Flu)ZrCl2 (1a) under these conditions.