The initiation of vinyl polymerization by tetrakis (trialkyl-phosphite) nickel (o) derivatives

The study of the polymerization of vinyl monomers initiated by zero-valent nickel phosphite derivatives in the presence of organic halides has been extended to tetrakis (triethylphosphite) nickel (o) and tetrakis (tri 2-chloroethylphosphite) nickel (o). A kinetic study with methyl methacrylate and carbon tetrachloride shows that the polymerization proceeds by a free radical process and that the mechanism of initiation resembles that previously reported for the corresponding triphenylphosphite and carbonyl derivatives. The primary process which becomes rate determining at sufficiently high carbon tetrachloride concentration is the nonreversible S_N1 scission of an alkylphosphite ligand. These alkylphosphite initiators are considerably more active than the corresponding carbonyl derivatives, but are less active than the corresponding triphenyl-phosphite derivative. The difference in activities between the aryl and alkylphosphite derivatives has been accounted for by differences in steric over-crowding of these molecules.     

Heterobimetallic complexes of cis-1,2-bis(diphenylphosphine)ethene containing tin and nickel,palladium or platinum

Summary New heterobimetallic complexes of nickel, palladium or platinum and the ligand cis-1,2-bis(diphenylphosphine)-ethene, dppen, and tin were prepared. The transition metal is bonded either directly or via chlorine bridges to the tin atom. The compounds were obtained from precursor complexes of the general formula [M(dppen)Cl₂] (M = Ni, Pd or Pt) by reaction with Ph₃SnH or SnCl₂.     

Photochromism of cis(z)-1,2-bispyrryl-substituted ethene derivatives

Photochromism of two bispyrryl-substituted ethenes, 2, 3-bis-(1-p-methoxyphenyl-5-phenyl-2-methyl-3-pyrryl)-2-butene (BPE1) and 2,3-bis(1-p-bromophenyl-4-phenyl-2-methyl-3-pyrryl)-2-butene (BPE2), was studied by laser flash photolysis technique. The results indicate that photocyclization of these compounds proceeds mainly via the excited triplet state, and the cis-trans isomerization proceeds mainly via the excited singlet state. After UV laser pulse irradiation, both photocylization and cis-trans isomerization of BPEl occur, but photocydization is the main reaction. On the other hand, laser photolysis of BPE2 leads mainly to photocydization. The effects of the substituents on the photochromic mechanism are also discussed.     

Electron transfer reactions of nickel(III) and nickel(IV) complexes

This review narrates the electron transfer reactions of various nickel(III) and nickel(IV) complexes reported during the period 1981 until today. The reactions have been categorized mainly with respect to the type of nickel complexes. The reactivity of nickel(III) complexes of macrocycles, 2,2′-bipyridyl and 1,10-phenanthroline, peptides and oxime–imine, and of nickel(IV) complexes derived from oxime–imine, oxime and miscellaneous ligands with various organic and inorganic electron donors have been included. Kinetic and mechanistic features associated with such interactions have been duly analyzed. The relevance of Marcus cross-relation equations in the delineation of the electron transfer paths has also been critically discussed.