Bis species

This mechanism is supported by identical dissociation and racemization rate constants. This further implies either that the bis species M(AA)2 is racemic as formed, or that it may racemize (by a cis-trans change, or by a dissociative or intramolecular path) more rapidly than it re-forms iris in the dynamic equilibrium (7.23). Identical activation parameters for the dissociation (to the bis species) and racemization in aqueous acid (Table 7.5) and other solvents of Nifphen) " and Ni(bpy)3 indicate that these ions racemize by an intermolecular mechanism. This is the only such example for an M(phen)"+ or M(bpy) + species (see Table 7.5) although recently it has been observed that Fe(bps)3 (bps is the disulfonated phenanthroline ligand shown in 13, Chap. 1) but not Fe(phen)3+ also racemizes predominantly by a dissociative mechanism in water. For the other tr/s-phenanthroline complexes (and for Fe(bps)3 in MeOH rich, MeOH/HjO mixtures ) an intramolecular mechanism pertains since the racemization rate constant is larger than that for complete dissociation of one ligand, Table 7.5. 

Figure 9.5 E-pH diagram for Bi species. Soluble species concentrations (except H+) = 10 ° M. Soluble species and most solids are hydrated. No agents producing complexes or insoluble compounds are present other than HOH and OH. ...

Similar to the zinc insertion methodology for the preparation of fluorinated vinylzinc reagents (Section II.C), zinc reacts quantitatively with bromo- and iodopentafluorobenzene in coordinating solvents such as THF, Et20, DME, DG (diglyme), DMF, DMAC and DMSO to give bis(pentafluorophenyl)zinc (equation 72)68. These workers also obtained equilibrium constants for the Schlenk equilibrium between the mono/bis species via 19F NMR spectra. 

The preparation of the trinuclear nickel (II) complex by solubilization of the uncharged bis species with nickel (II) ion has been generalized by the use of... 

Species like M(Hdo)2X and M(Hdo)2X2, obtained by the oxidation of M(Hdo)2 (where M = Ni, Pd and Pt and H2do is vic-dioxime) with bromine and iodine, were initially believed to involve metal atoms in higher oxidation states. However, later work has shown that the halogen molecules may be held in these either by charge-transfer interactions or in the form of species like X ions.51 On the other hand, there are various reports that species like K2[Ni(DMG)3] can be synthesized by the oxidation of the bis species in alkaline medium with an excess of two-electron oxidant (hypo-iodide).52... 

The white n = 1 compounds are known only for MnF2 and MnC204, and they are the stable species at ambient conditions for both. They can be prepared either by direct reaction or by loss of N2H4 from the bis species. The structure is unknown, but is undoubtedly polymeric and probably consists of both bridging hydrazine and anions. A similar compound has been described for 1,2-dimethylhydrazine, and with 4-nitrophenylhydrazine. 

The solid pyridine compounds are summarized in Table 10. Unlike the amines, tetrakis compounds are quite common, and hexakis species are less usual. This is probably related to the steric requirements of the a-hydrogens of pyridine. The room-temperature-stable combination of MnX2 and py is usually a bis species. 

Substituted pyridines (/ or y) generally give compounds of the same type as pyridine, although no hexakis compounds have yet been described. We especially notice, however, the compound Mn(NCS)2(3-Br-py)2, which is freely soluble in the common organic solvents , unlike the other bis species. A tetrahedral [MnN4] has been proposed, although small oligomers, such as a five-coordinate dimer, are also possible. 

Reaction (16a) is very slow and is included in the model only to prevent complete blockage of the surface by the Bi species. This model also predicts oscillations and in addition was analyzed for spatial effects. On sufficiently long surfaces, Sheintuch found the existence of symmetry breaking that would in turn result in spatial structures. 

Moc and Morokuma have recently undertaken the first comparative calculations of the series of the tetravalent MH and MF (M = P, As, Sb and Bi) species in an attempt to provide theoretical insight into the periodic trends in the structures and stability in these species, only AsH " was the subject of previous theoretical work , except for the lighter PH and PF " . The lowest energy forms were caleulated to be the pseudo-trigonal-bipyramidal structures (14) of symmetry for both MH and MF and all... 

These results suggest that part of the promoting element initially present in the catalyst is not essential to allow the reaction to proceed and that the useless Bi is removed from the catalyst surface during the first experiments. However, the dissolution process involving a small quantity of the initial Bi might be critical to control the performances of these catalysts by setting a chemical equilibrium between reduced and oxidised Bi species at the catalyst surface. 

No intermediate formation of (Et3P)2Au" is seen in the reaction of dmp with auranofin-treated red cells, perhaps another indication that little TATG is displaced inside the cells under these conditions although it is possible that the bis species is shorter-lived. After ca. 2.5 hr in the presence of one equivalent of dmp about half of the coordinated Et3P has been converted to Et3P0, Figure 7. 

Oxalate forms red [MnOxj] and green cis) or yellow trans-[MnOx2(H20)2] which have been known since Usually, preparations of the bis species give the cis isomer, but it is the trans... 

In view of the strong colours of many of the biguanide complexes, these have been used as colorimetric reagents, e.g. the use of phenylbiguanide for spectrophotometric determination of Fe and CN ions. A polarographic study" of a bis(biguanide)copper(II) complex gives a kinetically controlled wave prior to a two-electron transfer, followed by a diffusion controlled second wave due to the reduction of bis species in solution. 

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