Oxidation nickel cyclam

This scheme suggests an overall pathway for nickel cyclam-catalyzed oxidation of olefins which uses PhIO stoichiometrically to produce a high valent nickel-oxo intermediate capable of three different types of reactions. One pathway is H atom... 

Macrocycle Vila readily forms the doubly deprotonated nickel complex upon addition of Ni(OAc)2. The methylene chloride soluble complex was unreactive under reaction conditions similar to those employed in the nickel cyclam/PhIO system. However, oxidation of - 8-methylstyrene occurred readily when the hypochlorite phase transfer conditions were used. Epoxidation represented about 50% of the reaction pathway with the remainder yielding a mixture of benzaldehyde and other over-oxidation products. 

It is well-established that electroreduced nickel(I) complexes of cyclam and a variety of substituted cyclams add oxidatively to alkyl halides to give alkylnickel(III) complexes in organic solvents,251,276 the lifetime of the carbon-nickel bond governing the overall behavior of the system. However, it was shown that [Ni (tmc)]+ (one-electron reduced form of complex (17) tmc= 1,4,8,11-teramethyl 1,4,8,11-tetraazacyclotetradecane) reacts with alkyl chlorides in aqueous alkaline solution in a one-electron process.277,278... 

As a catalyst Nin(cyclam)Br2 is employed which in a proposed cycle is reduced to Ni (cyclam)+ coordinated to C02. In the following, the catalyst undergoes an oxidative addition with the bromoaryl compound to form a Nini species which in a radical like reaction inserts into the double bond. It follows another le" reduction to give a Ni11 species which undergoes C02 uptake to form the nickel carboxyl-ate 171 as the final product. 

Ni(II) complexes of cyclam and oxocyclam derivatives catalyze the epoxidation of cyclohexene and various aryl-substituted alkenes with PhIO and NaOCl as oxidants, respectively. In the epoxidation catalyzed by the Ni(II) cyclam complex using PhIO as a terminal oxidant, the high-valent nickel- complexes (e.g., LNiin-0, LNi=0, LNiin-0-... 

The oxidation of nickel(II) complexes of cyclam and Me6cyclam by NO+ in acetonitrile solutions has been studied by Barefield and Busch.3049... 

Ni(II) complexes of cyclam and oxocyclam derivatives catalyze the epoxidation of cyclohexene and various aryl-substituted alkenes with PhIO and NaOCl as oxidants, respectively. In the epoxidation catalyzed by the Ni(II) cyclam complex using PhIO as a terminal oxidant, the high-valent nickel-oxo complexes (e.g., LNi -0, LNi=0, LNi -0-I-Ph, or LNi -0-Ni L) have been proposed as the active oxidant (92). In the reaction, E olefins are more reactive than the corresponding Z isomers, and a strong correlation was observed between the electron-donating effect of the para substituents in styrene and the initial reaction rate (91). Isotope labeling studies have shown that the epoxide oxygen is derived from PhIO. 

Concentrated nitric acid has been used to obtain nickel(III) complexes like [Ni L(N03)2]CI04 starting from [NPL](C104)2 (L = cyclam, Megcyclam) in aqueous solutions. Oxidation of the parent nickel(II) with nitric acid complexes also afforded the nickel(IV) species [Ni L] ( 104)2 where L is the amine-imine-oxime ligand (415) or... 

There is a brief discussion of kinetics of complex formation of nickel(III) complexes of tetraazamacrocyclic ligands such as cyclam with chloride, bromide, thiocyanate, and sulfate in a review of the synthesis and reactions of nickel(III) complexes.Such reactions are really rather fast—it is at nickel(IV) that slow substitution may be expected, if not obscured by rapid oxidation of ligands. 

While nickel(III) cyclam, [NiL(OH2)2], is known to form complexes with halide ions (Cl", Br"), the redox potential (0.96 V) is sufficiently high that iodide is oxidized quantitatively.The rate law, however, shows only a first-order dependence in the iodide concentration. Although not conclusive, the preferred mechanism for reaction is via an outer-sphere process when rates are compared with those for halide complex formation. 

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