Mechanism of Racemization of Complex Ions. I. Kinetics of the Dissociation and Racemization of Tris-(1,10-phenanthroline)-nickel(II) and Tris-(2,2'-dipyridyl)nickel (II) Complexes1
Abstract:Mechanism of Racemization of Complex Ions. I. Kinetics of the Dissociation and Racemization of Tris-(1,10-phenanthroline)-nickel(II) and Tris-(2,2 '-dipyridyl)nickel ( ) Complexes1
“…[25,26] Herein, it should be noted that the CD spectrum of the reaction solution was almost silent in the p-p* transition region, [19] indicative of the 1:1 formation of the D and L isomers of [NiA C H T U N G T R E N N U N G (phen) 3 ] 2+ in this reaction. When ethanol was added to the reaction solution, green crystals (4), the color of which is distinct from that of 3, were produced after storing it in a refrigerator for several days.…”
Chiral creation: A disproportionation reaction, in which achiral square‐planar NiII centers are converted into two kinds of chiral, octahedral NiII centers on treatment with an achiral diimine ligand, was discovered in a D‐penicillaminato AuINiII coordination system, presenting a unique method for generating and increasing chiral centers (see scheme).
“…[25,26] Herein, it should be noted that the CD spectrum of the reaction solution was almost silent in the p-p* transition region, [19] indicative of the 1:1 formation of the D and L isomers of [NiA C H T U N G T R E N N U N G (phen) 3 ] 2+ in this reaction. When ethanol was added to the reaction solution, green crystals (4), the color of which is distinct from that of 3, were produced after storing it in a refrigerator for several days.…”
Chiral creation: A disproportionation reaction, in which achiral square‐planar NiII centers are converted into two kinds of chiral, octahedral NiII centers on treatment with an achiral diimine ligand, was discovered in a D‐penicillaminato AuINiII coordination system, presenting a unique method for generating and increasing chiral centers (see scheme).
“…Davies and Dwyer (1) found that there was no change in the rate of racemization upon the addition of an excess of phen and hence postulated an intramolecular mechanism. However, Basolo and co-workers (2) showed that there was, within experimental error, no difference between the rates of dissociation of a phen ligand and racemization in acid solutions. They pointed out that if the dissociated product was either symmetrical or if it quickly racemized, then the rate of racemization should not be affected by the presence of an excess of phen and that it was therefore probable that a dissociative mechanism was correct.…”
SummaryCircular dichroism and electronic spectral measurements have established the existence of a covalent hydrate and a pseudobase arising from attack of H20 or HO-at the ligand in tris-(1,10-phenanthroline)nickel(ll). In anhydrous solvents and strongly acidic solution, the complex is largely unsolvated. Over a large pH range the dominant species present in aqueous solution is the covalent hydrate while at high pH, this is converted into the pseudo-base. The existence of these species, and the equilibria between them in aqueous solution elegantly explains the pH dependent dissociation and racemization of the parent molecule. It further explains the non-linear variation of these reactions in mixed solvents and indicates that more than one mechanism is responsible over the range of solvents studied here and previously.
“…Especially, Fe(II)-bipyridyl complex showed thermo-responsive property by thermal activation of the ligand exchange. 21,22 The obtained polymer hybrids by utilizing Fe(II)-bipyridyl complex are also expected to show thermo-responsive property.…”
mentioning
confidence: 99%
“…In this paper, four kinds of metal (M n+ = Ru 2+ , Fe 2+ , Co 2+ , Ni 2+ ) bipyridyl complexes [20][21][22] were used as cross-linking points to prepare organic gel. It was known that Ru(II)-bipyridyl and Fe(II)-bipyridyl complexes were thermodynamically inert, while Fe(II)-bipyridyl complex and Co(II)-bipyridyl complex were kinetically labile.…”
ABSTRACT:Organic-inorganic polymer hybrids having IPN (Interpenetrating Polymer Network) structure were synthesized utilizing an in-situ method, which was the simultaneous formation of organic gel through metal-bipyridyl complex and silica gel. Metal-bipyridyl complex was used as a cross-linking point to prepare the organic gel. The properties of the polymer hybrids, such as solvent-resistant and thermal properties, were different according to the kinds and the weight of the used metal ions. Especially, thermo-responsive polymer hybrids could be obtained using iron (II)-bipyridyl complex as a cross-linking point in the silica matrix.KEY WORDS Organic-Inorganic Polymer Hybrids / Sol-Gel Reaction / In-Situ Method / Interpenetrating Polymer Network (IPN) Structure / Solvent Resistant Property / Organic-inorganic polymer nanocomposite materials have received a great amount of scientific and technological interests. [1][2][3][4][5] Organic-inorganic polymer hybrids have not only the properties themselves of organic polymer and inorganic material but also the unique properties, which results from mixing of organic polymer and inorganic material at a nano-meter level. For instance, organic-inorganic polymer hybrids have high transparency, 6 excellent solvent-resistance, 7 gas-barrier property, flame retardance, gas-selective property, 8 and so on. The sol-gel reaction of alkoxysilane is one of the most efficient methods for the preparation of organicinorganic polymer hybrids. The method comprises initial hydrolysis of the alkoxysilane and subsequent condensation and removal of solvent, resulting in the silica gel. 9 One of the advantages of the sol-gel techniques to prepare composite materials is that the reactions can be performed under ambient condition, while conventional melt fusion technique for silica glass requires high temperature.Organic-inorganic polymer hybrids have been prepared by utilizing the formation of covalent bonds between organic polymers and inorganic phases. [10][11][12] In our group, a large variety of organic-inorganic polymer hybrids has been prepared through the sol-gel reaction of alkoxysilane. The most common method is utilizing physical interactions such as hydrogen bonding, 13-15 aromatic, 16 and ionic interactions 17 between organic polymer and silica gel. Another method is an in-situ method, in which the polymerization of vinyl monomer and the sol-gel reaction of silica gel are carried out simultaneously. By utilizing this method, trans- † To whom correspondence should be addressed. parent polymer hybrids can be prepared even if there is no covalent or physical interaction between organic polymer and silica gel. For example, transparent polymer hybrids can be prepared by the simultaneous occurrence of the polymerization of styrene monomer and the formation of silica gel. 18 Recently, we succeeded in the preparation of transparent polymer hybrids utilizing new in-situ method (Scheme 1). 19 In this method, the cross-linking reaction of bipyridyl-containing polymer was carried out together...
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