Nickel, tris racemization

Nickel, tris(l, 10-phenanthroline) racemization, 1,24. 466 solid state, 1, 467 structure, 1,64 Nickel complexes, 5,1-300 acetylacetone alcoholysis, 2, 380 pyridine complexes, 2, 386 solvolysis, 2,379 structure, 2,388 amidines... 

The dissymmetry would thus be lost, and when the chelate ring reforms, it would have a 50-50 chance of producing either the A or A isomer (Chapter 12). Since the ratedetermining step in this mechanism is the dissociation of the ligand, the rate of racemization (k ) would have to equal the rate of dissociation (kj. For example, tris(phenanthroline)nickel(II) racemizes at the same rate = 1.5 x 10 s ) as it dissociates k = 1.6 x 10 s ), which implies dissociation is part of the racemization mechanism. If racemization takes place faster than dissociation [as it does, e.g., for tris(phenanthroline)iron II) k,. = 6.7 X 10 s and k = 0.70 x 10 s ], this mechanism can be eliminated. 

Nickel, tris( 1,10-phenanthroline)-racemization, 24,466 solid state, 467 structure, 64 Nickel(I) complexes magnetic properties, 274 Nickel(II) complexes, 470 allogonism, 207 equilibrium constants solvent effect, 516 isomerism, 184 liquid-liquid extraction, 544 magnetic properties, 274 5-mcrcaptoamine alkydation, 417 photoreactivity, 407... 

In one report, the enantiomers of the racemic compound 73, whose structure resembles ketone 2a, were separated by fractional recrystallization of the optically active mandelic acid salts [43]. Although we tried to optically resolve the optically active mandelic acid salts of the racemic ketone ( )-2a, no satisfying results were obtained. After several trials, the (+)- or (-)-di-p-toluoyl tartrate salt prepared from ketone ( )-2a was effectively fractionally recrystallized and finally provided the optically active ketones (+)-2a and (-)-2a [42]. The chiral ketone (-)-2a was converted to compound 73 via compound 72 by thioacetalization followed by desulfurization using Raney nickel... 

Later, a complete chromatographic resolution of Co(acac)3 and Cr(acac)3 on an optically active poly(triphenyhnethyl methacrylate) column was accomplished. The optical data of the pure enantiomers were obtained. Extensive use was made of columns composed of clay plus metal complex adducts. Thus, optical resolution was accomplished by LC on a column packed with an ion-exchange adduct of synthetic hectorite and optically active [Ni(II)](phen)3 and [Ru(II)](phen)3 . Using these systems, Co(acac)3, Cr(acac)3, Rh(acac)3 and [Co(acac)2(en)]+ (en = ethelenediamine) were resolved completely into enantiomers . Enantiomers of these four species were separated by LC on a column packed with ion-exchange adduct of synthetic hectorite and optically active metal complexes . One optically active metal complex used was tris(LlO-phenanthroline)-nickel(n), which was ion exchanged into synthetic hectorite. Racemic Co(acac)3, Cr(acac)3 and Ru(acac)3 were also enantiomerically separated via LC using poly(t-butylisocyanide) as stationary phase . ... 

Analogously, bis(i -l,2-diaminopropane)nickel(II) perchlorate reacts with acetone to give the RR-[Ni(L211)2] isomer, which is converted in pyridine exclusively into the / R-[Ni(L212)] + isomer [251]. Reaction of tris(propane-1,2-diamine) nickel(II) perchlorate prepared from racemic diamine with acetone affords C-rac and C-meso isomers of [Ni(L212)] + in approximately equal amounts [218, 251]. 

Kirschner and Ahmadhave applied the Pfeiffer effect to the resolution of complex inorganic compounds. These authors allowed a Pfeiffer effect to develop in the initially racemic nickel(II) tris(2,2 -dipyridyl) complex in levo-mahc acid, and then succeeded in freezing out the non-equimolar mixture of enantiomers from the system by means of precipitation of the enantiomers as the relatively insoluble perchlorates. These insoluble perchlorates were then redissolved by allowing an aqueous suspension of them to come in contact with Amberlite IRA-400 anion exchange resin in the chloride form, and the optical rotation of a solution of the soluble complexes (as chlorides) was then read on a photoelectric polarimeter. Table 2 shows the optical rotations of this complex, and Fig. 7 shows a comparison of the... 

Kirschner and Ahmadstudied the rate of racemization of the nickel-(II) tris(ort/io-phenanthroline) complex in (a) water (b) water containing levo-ma ic acid and (c) water containing dextro-ma ic acid. If Dwyer and Gyarfas postulate concerning the existence of an equilibrium which is shifted (in the presence of levo-mahc acid, for example) in the direction... 

In a study of racemisation of tris(bipy) and tris(phen) complexes of iron(II) and nickel(II) in the solid state, further evidence was obtained to support the assignment of an associative-type mechanism, with a transition state or intermediate of coordination number 7, for racemization at nickel(II), but of racem-ization via a trigonal prism intermediate for the iron(II) complexesA useful freeze-drying technique has been described for the isolation of optically active solids in preparations of halides of cations of this type/ Different kinetic patterns, and therefore the likelihood of different mechanisms, have been established for the racemization of [Fe(phen)3] and [Ni(phen)3] in water containing small amounts of nitrobenzene. The extent of association between the cations and the nitrobenzene was estimated from determination of the solubilities of nitrobenzene in aqueous solutions of [M(phen)3]Br2. Complementary determinations of the solubilities of [M(phen)3]Br2 in aqueous nitrobenzene might have permitted an initial-state-transition-state dissection to have been carried out. 

Intramolecular Rearrangement of Tris-chelate Complexes.— Rate data for the dissociation and racemization of [M(phen)3] + ions (M = Cr, Fe, Co, or Ni) are collected in Table 39. Only the nickel(ii) complex racemizes at a rate comparable to the ligand... 

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