Nickel complexes neutral radical

The name dithiolenes was chosen to describe these compounds without prejudice towards one of the limiting structures. The equally descriptive name dithienes has been coined for the same reason, but it is now rarely used. The less fortunate description of dithiolenes as dithiolato complexes is found occasionally, but it does have a much more restricted meaning (see Section 16.5.2.4) and should be avoided for the neutral species. Nevertheless, Chemical Abstracts refers to dithiolenes as bis[l,2-ethenedithiolato(2—)] complexes of the respective central metal, for example the parent nickel complex (4) is listed as nickel, bis[l,2-ethenedithiolato(2—)-5,S ]- however, depending on the date of the CA issue, its tetraphenyl derivative will be found either under bis[a,a -stilbenedithiolato(2 — )]-nickel or as bis[ 1,2-diphenyl-1,2-ethenedithiolato(2 -)-S,S"]-nick-el. Even less appropriate are the CA names for the radical anions and dianions of the dithiolenes, which are referred to as metallates(—) and metallates(2 —) of the respective ligands the dianion of the parent nickel dithiolene thus is found as bis[l,2-ethenedithiolato(2—)]-nickelate(2—), a name which has little to do with the electronic structure of the compound. 

Ligand oxidation may be affected by molecular oxygen in the nickel complex of JV,iV-bis(2-mercaptoethyl)-2-methylthioethylamine) forming a sulfinato complex. " O2 has been detected by ESR in dry Nafion perfluorinated membranes neutralized by Ti " with the most likely source of the radical being electron transfer from The interaction of Pt(II) with creatinine generates a monomeric... 

As with iron(II), O Reilly et reported that nickel complexes with an a-diimine ligand (Ni-9), which is an analog of the precursor for a coordination polymerization catalyst, efficiently worked for controlling the radical polymerization of styrene. When coupled with 1-phenylethyl bromide as the initiator, the styrene polymerization with Ni-9 provided well-controlled molecular weights and MWDs (Mw/Mn= 1.15). Neutral Ni(II) acetylides (Ni-10 and Ni-11) were used for the polymerization of DMAEMA and MMA in conjunction with an organic halide as the initiator by Sun et Although judicious conditions, such as concentra-... 

Complexes with pyridine-2,6-diimine ligands, five-coordinate [NiX2(174)] (X = C1, Br) or six-coordinate [Ni(174)2]X2, were usually assumed to have innocent neutral ligands. The X-ray structure and spectroscopic characteristics of [Ni(174)2](PF6) confirm that the complex contains the neutral ligand ([174] ) and a divalent nickel ion.579 The cyclic voltamogram of this complex in CH2C12 shows three reversible one-electron-transfer processes at = 1.19 V, —1.30 V, and — 1.82V (vs. Fc+/Fc), of which the first is a one-electron oxidation, while the other two correspond to two successive one-electron reductions. The spectroscopic data allow one to assign these processes as follows ([174]1 is a one-electron reduced radical form of [174] ) [Nini(174)°2]3+ [NiII(174)02]21 - " [NiI(174)°2]+ = " [NiI(174)°(174)1 ]°. 

Scheme 6.27 considers other, formally confined, conformers of cycloocta-l,3,5,7-tetraene (COT) in complexes with metals. In the following text, M(l,5-COT) and M(l,3-COT) stand for the tube and chair structures, respectively. M(l,5-COT) is favored in neutral (18-electron) complexes with nickel, palladium, cobalt, or rhodium. One-electron reduction transforms these complexes into 19-electron forms, which we can identify as anion-radicals of metallocomplexes. Notably, the anion-radicals of the nickel and palladium complexes retain their M(l,5-COT) geometry in both the 18- and 19-electron forms. When the metal is cobalt or rhodium, transition in the 19-electron form causes quick conversion of M(l,5-COT) into M(l,3-COT) form (Shaw et al. 2004, reference therein). This difference should be connected with the manner of spin-charge distribution. The nickel and palladium complexes are essentially metal-based anion-radicals. In contrast, the SOMO is highly delocalized in the anion-radicals of cobalt and rhodium complexes, with at least half of the orbital residing in the COT ring. For this reason, cyclooctateraene flattens for a while and then acquires the conformation that is more favorable for the spatial structure of the whole complex, namely, M(l,3-COT) (see Schemes 6.1 and 6.27). 

The mechanism was proposed to involve reduction of the neutral nickel bis(dithiolene) complex by methyl viologen radical cation, followed by dimerization to form the active catalyst Ni(SS)212 2 - as shown in Eqs. 2-6 ... 

The redox noninnocence of the 2-mercapto-3,5-di-tert-butylaniline ligand has recently been investigated with nF ions. The spectroelectrochemistry of the complex displays a range of electron transfers where the monocation, the neutral species, and the mono- and dianions have been characterized. In a related manner, Wieghardt and coworkers have reported the first example of a stable N, O-coordinated o-iminobenzoquinone via air oxidation of the initial nF complex with 2-anilino-4,6-di-tert-butylphenol (94). The analogous o-iminobenzosemiquinonate 7r-radical complex was also isolated for this system and earlier for the bis-(o-immobenzosemiquinonate)nickel(II) complex. ... 

The polyethylene latexes obtained in the different emulsion polymerization procedures using the various aforementioned nickel(II) complexes display average particle diameters of 100 to 600 nm. A number of anionic surfactants or neutral stabilizers are suitable, i.e. compatible with the catalysts and capable of stabilizing the latex. Solids contents of up to 30% have been reported to date. A typical TEM image is shown in Fig. 7.2. By comparison to smooth, spherical latex particles of amorphous polystyrene as a well studied hydrocarbon polymer prepared by free-radical emulsion polymerization, the ruggedness of the particles shown can be rationalized by their high degree of crystallinity. 

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