Mirror image complexes

Where unidentate ligands are present, the ability to effect the resolution of an octahedral complex (i.e. to separate 2 optical isomers) is proof that the 2 ligands are cis to each other. Resolution of [PtCl2(en)2] therefore shows it to be cis while of the 2 known geometrical isomers of [CrCl2en(NH3)2] the one which can be resolved must have the cis-cis structure since the trans form would give a superimposable, and therefore identical, mirror image ... 

A chiral complex is one that is not identical to its mirror image. Thus, all optical isomers are chiral. The cis isomers of [CoCl2(en)2 + are chiral, and a chiral complex and its mirror image form a pair of enantiomers. The trans isomer is superimposable on its mirror image complexes with this property are called achiral. Enantiomers differ in one physical property chiral molecules display... 

FIGURE 16.22 Optical isomers. The two complexes are each other s mirror image no matter how we rotate them, one complex cannot be superimposed on the other. 

SOLUTION The mirror image of each complex is shown on the right of each pair. 

When the mirror image of (c) is rotated by 90° around the vertical B-D axis, it becomes the complex (d). 

It is now possible to see why, as mentioned on page 126, enantiomers react at different rates with other chiral molecules but at the same rate with achiral molecules. In the latter case, the activated complex formed from the (/ ) enantiomer and the other molecule is the mirror image of the activated complex formed from the (S) enantiomer and the other molecule. Since the two activated complexes are... 

The composite vector is seen to spiral around the z-axis and in projection moves anti-clockwise in a circle around the z-axis. The other component which is the mirror image of the first, performs a clockwise circular motion in projection along z. The decomposition into circularly polarized components can also be formulated in complex notation, Er = E0e t6. 

Figure 4.32 Mirror-image atomic charge variations AQ = Q(R) — Q(oo) for Os (circles) and nitrogen (squares) atoms of the ctosN dative bond (Req = 2.087 A) of the OsH2NH3 coordination complex (see Fig. 3.34).

In addition to a fluorescence perturbation, the Cd(II)-5d combination also uniquely yields aperturbation in the ultraviolet (UV) spectrum. A difference spectrum obtained by subtracting a fractional amount of an uncomplexed 5d spectrum from the perturbed spectrum is the mirror image of a fluorescence difference spectrum obtained by similar means. Moreover, excitation at 400 nm (where 1-4 are weakly absorbing but where moderate absorption is seen in the difference spectrum) gives rise to an emission spectrum with identical shape and Amax (456 nm) to that of the fluorescence difference spectrum. Thus, evidence points to the existence of two equilibrating ground state species as the physical basis for the chelatoselective emission. Bouas-Laurent has reported a related observation in methanol where a red-shifted CHEF was observed for a T1(I) 7r-complex.(14)... 

The formal view. The fluorenyl-cyclopentadienyl complex contains a mirror plane. The two sites are therefore mirror images. One site co-ordinates to the re-face of propene, the other site to the si-face of propene. One site will therefore be enantiospecific for making R configured carbon atoms and the other site for S configured carbon atoms. This alternation of configuration leads to a syndiotactic polymer. 

Another issue is validated by the presented X-ray structures This is related to the pseudoenantiomeric character of the tert-butylcarbamates of quinine and quinidine (Figure 1.19a,b). Except for the vinyl on the backside of the quinuclidine ring, both the complexes that are actually diastereomeric to each other actually look like mirror images with regard to conformations and intermolecular interactions as well so that the pseudoenantiomeric experimental chromatographic behavior for DNB-Leu can be rationalized also on the basis of their X-ray crystal structures. 

Optical Nonsuperiraposable mirror images. In R, S tetrahedral and A A octahedral complexes chiral centers in coordinated ligands. 

The starfish provides a more complex example of symmetry in a living organism. If we approximate a starfish by a regular five-pointed star, we can recognize that there are five lines or planes through the organism that divide it into mirror images ... 

Chiral dirhodium(II) carboxamidates are preferred for intramolecular cyclopropanation of allylic and homoallylic diazoacetates (Eq. 2). The catalyst of choice is Rh2(MEPY)4 when R " and R are H, but Rh2(MPPIM)4 gives the highest selectivities when these substituents are alkyl or aryl. Representative examples of the applications of these catalysts are listed in Scheme 15.1 according to the cyclopropane synthesized. Use of the catalyst with mirror image chirality produces the enantiomeric cyclopropane with the same enantiomeric excess [33]. Enantioselectivities fall off to a level of 40-70% ee when n is increased beyond 2 and up to 8 (Eq. 2) [32], and in these cases the use of the chiral bisoxazoline-copper complexes is advantageous. 

---