Uncharged complexes

Even if it is assumed that the reaction is ionic, Occam s Razor would lead to the conclusion that the system is too complex and that the effort to keep it ionic is too great. It is difficult to undersand why step 8c is slow and why a simple uncharged complex would not be equally reasonable. We prefer a mechanism in which the carbon monoxide molecule is adsorbed parallel to the surface and in which the oxygen orbitals as well as the carbon orbitals of C=0 bond electrons interact with the metal. It seems reasonable that hydrogenolysis occurs exclusively only because the oxygen is held in some way while the two bonds are broken and it finally desorbs as water. The most attractive picture would be (a) adsorption of CO and H2 with both atoms on the surface... 

The kinetics of base hydrolysis of several complexes of the type [Co(NH3)3L3] have been examined in order to see whether the mechanism for these uncharged complexes is the same as that operating for base hydrolysis of the standard cationic complexes (75). A comparison of kinetic parameters - a small selection is given in Table II (76,77) - suggests that all cobalt(III)-nitro-amine complexes, charged and uncharged, undergo base hydrolysis by the SnICB (Dch) mechanism. 

Equation (4.41) is valid only when the complexes MA ° can be neglected in the aqueous phase. Comparing Eqs. (4.37b) and (4.41c), it is seen that no horizontal asymptote is obtained even at high concentrations of AT or HA and H. Thus, for very large distribution constant of the uncharged complex (i.e., >1000) a straight line with slope -z is experimentally observed, as in the case for the Cu(II)-thenoyltrifluoroacetone (HTTA) system (Appendix D 5g). 

The distribution constant of the neutral complex MA, T dc, has been referred to several times. In favorable cases, when both the organic and the aqueous phases are dominated by the same uncharged complex over a larger concentration region, Adc can be directly measured, as is the case for most of the data in Table 4.10 [22-23b]. Otherwise A"dc can be estimated or calculated from data combined with (3 , K, and A dr [see Eqs. (4.8) and (4.46)]. 

In the reaction below a metal ion reacts with n ligand anions h to form an uncharged complex ML. If the ions dissolve only in the aqueous phase, and the metal complex and undissociated acid HL dissolve only in the organic phase, lUPAC allows the reaction to be written in four different ways ... 

Charley and Saltman studied the migration of radioactive Ca2ffi in the presence and absence of lactose in aqueous solution at pH 7.0. The solutions were buffered with sodium hydrogen carbonate. The inability of calcium to migrate in the presence of lactose indicated that Ca2ffi had reacted with the sugar to form a soluble, uncharged complex. 

Isolation, once the reaction is over, usually utilizes solubility properties. Uncharged complexes are frequently insoluble in water. Rarely are coordination compounds soluble in diethylether or hydrocarbons. Thus, the addition of water, ether, or hydrocarbons (if miscible with the reaction medium) precipitates the product and many other components of the solution. 

It is extremely useful to have available a technique for rapidly monitoring reaction progress or assessing sample purity. An ideal technique for these purposes is thin layer chromatography (TLC). The method is fast, very sensitive, readily set up, and inexpensive. Uncharged complexes can generally be developed on silica gel plates with a variety of solvents recently we have had good success with ethylacetate. 

Simple complexes. Many transition and B-subgroup metals form complex ions with pyridines in aqueous solution, e.g., Ni2+ Ni(CsHsN)42+ Ag+ Ag(GsHsN)2+ if certain anions are also present, uncharged complexes can result, e.g., Cu2+ + 20CN + 2C5H5N Cu(OCN)2n(CsHsN)2, soluble in both H20 and CHC13 Ni2+, Cd2 and Zn2+ react similarly. 

In fact there are a series of complex cations and anions formed (see Section III.22, reaction 11). The (uncharged) complex can be extracted by shaking with ether. The red colour is discharged by fluorides, mercury(II) ions, and oxalates when colourless, more stable complexes are formed ... 

For the moment we neglect the lower complexes and assume that the uncharged complex species ML is formed in one step ... 

Water solubility and ability to pass through cell membranes (uncharged complexes)... 

The [Ir(C6H6)2]+ ion, analogous to the [00(05115)2] + and [Rh(05115)2]+ ions, also has been obtained and investigated as was expected, it showed similar properties. The uncharged complex Ir (05115)2, like Rh(C6H6)2, has not yet been prepared. For palladium and platinum only simple olefin complexes are, as yet, known. Among these there is also a complex of platinous chloride with cyclopentadiene, but physical evidence excludes the possibility of a sandwich structure in this compound (29). 

Although attempts made so far to prepare complexes of the type Mn (aromatic)2 or [Mn(aromatic) 2] + have been unsuccessful, it has been possible to isolate a bright yellow tetraphenylborate of the [Re(C6He)2] + ion (as fine needles) and a red-brown reineckate of the [Re(sj/TO-(CHs)3 CeHs) 2] ion by the aluminum chloride method. The free bases are stable, but attempts at reduction to the uncharged complex of the element were unsuccessful (5S). 

A key assumption about the ability of small complexes to cross membranes passively relates to their overall charge uncharged complexes cross membranes more easily than do highly charged complexes. Thus much effort has been directed toward determining the structures of AP+-citrate complexes and their corresponding stability constants. 

Tridentate nitrogen ligands form 1 1 uncharged complexes with copper, in contrast to bidentate ligands that form tetrahedral ionic complexes.81 Well-controlled polymers of styrene and MA are obtained with a substituted terpyridine (L-18), whereas the unsubstituted derivative induced a heterogeneous and uncontrolled polymerization.111 A similar controlled polymerization of styrene was reported for a substituted terpyridine-based complex of Cu(II) (Cu-5) coupled with Al(O i-Pr)3.112 A tridentate ligand with two pyridines and one amine (L-19) gave narrow MWDs for styrene, MA, and MMA (MJMn = 1.1 —... 

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