Ligand points

As noted above, synthetically important prochiral centers are the carbonyl of a ketone or aldehyde and the double bond of an alkene. These functional groups do not contain a pro-R or pro-S group but it is clear that delivery of a fourth point ligand from one face or the other will lead to an (R) or (5) chiral center, as in conversion of 108 to 109 and/or 110. If the carbonyl is oriented as in ketone lllA, priorities can be assigned to the three atoms connected to the prochiral atom, based on the CIP rules. For lllA, the a b c priority is... 

Figure 7-3. Schematic representation of simple network stmetures (metal units as points, ligand units as small rods).

The two protons at C(l) are topologically nonequivalent, since substitution of one produces a product that is stereoisomerically distinct from that produced by substitution of the other. Ligands of this type are termed heterotopic, and, because the products of substitution are enantiomers, the definition can be made more precise.Ligands that on substitution produce enantiomers are enantiotopic. If a chiral assembly is generated when a point ligand is replaced by a new point ligand, the original assembly is prochiral Both C(l) and C(3) of 1,3-propanediol are prochiral centers. 

FIGURE 2.34 The symmetry and the charge points ligands prodiicing the crystal... 

Fig. 4. Typical AFM rupture experiment (top) Receptor molecules are fixed via linker molecules to a surface (left) in the same way, ligand molecules are connected to the AFM cantilever (right). When pulling the cantilever towards the right, the pulling force applied to the ligand can be measured. At the point of rupture of t he ligand-receptor complex the measured force abruptly drops to zero so that the rupture force can be measured.

Besides structure and substructure searches, Gmclin provides a special search strategy for coordiuation compouuds which is found in no other database the ligand search system, This superior search method gives access to coordination compounds from a completely different point of view it is possible to retrieve all coordination compounds with the same ligand environment, independently of the central atom or the empirical formula of the compound. 

The Fenske-Hall method is a modification of crystal held theory. This is done by using a population analysis scheme, then replacing orbital interactions with point charge interactions. This has been designed for the description of inorganic metal-ligand systems. There are both parameterized and unparameterized forms of this method. 

Lithiation at C2 can also be the starting point for 2-arylatioii or vinylation. The lithiated indoles can be converted to stannanes or zinc reagents which can undergo Pd-catalysed coupling with aryl, vinyl, benzyl and allyl halides or sulfonates. The mechanism of the coupling reaction involves formation of a disubstituted palladium intermediate by a combination of ligand exchange and oxidative addition. Phosphine catalysts and salts are often important reaction components. 

With an atomic number of 28 nickel has the electron conflguration [Ar]4s 3c (ten valence electrons) The 18 electron rule is satisfied by adding to these ten the eight elec Irons from four carbon monoxide ligands A useful point to remember about the 18 electron rule when we discuss some reactions of transition metal complexes is that if the number is less than 18 the metal is considered coordinatively unsaturated and can accept additional ligands... 

Table 7.10 groups 1 ELECTRONIC SPECTROSCOPY Classification of a ligand orbitals in various point... 

Table 7.10 shows how a ligand orbitals are elassified in various point groups with different ligand arrangements. It shows that, in oetahedral MLg, the six a ligand orbitals are split into aig,Sg and t-effeet of these on the e... 

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