Ortho-coordination

Figure 4. (a) Trimeric copper(I) thiolate complexes with intramolecular ortho-coordination. (b) The Cu,S, heterocyele. 

Sartori, G., Casnati, G., Bigi, R, and Predieri, G. 1990. Ortho-coordinated acylation on phenol systems. /. Org. Chem. 55 4371-4377. 

A hydroxyl group is situated ortho to a carboxyl group which as a bidentate ligand is terminally metallized on the fiber when aftertreated with dichromate. An example is Alizarine Yellow GG [584-42-9] (50) (Cl Mordant Yellow 1 Cl 14025). Cr(III) has a coordination number of six, and therefore normally two dye molecules of the sahcyhc type are chelated to the metal ion. 

This boronate was developed to confer added stability toward hydrolysis. It was shown to be substantially more stable to hydrolysis than the simple phenyl boronate because of coordination of the the ortho acetamide to the boronate. ... 

One important difference between the present and the previous case should be noted. For the hydroquinone clathrates, where the wall of a cavity consists of 12 OH groups, 6 adjacent carbon atoms, and 6 CH groups in ortho position to the OH groups, it seemed best to consider the product z qjk) as one unknown. For hydrates one may not do this the walls of both types of cavities consist exclusively of tetrahedrally-coordinated water molecules. Hence, one should use the same value of (,eg/k) —characteristic for a water molecule in a hydrate lattice—for both types of cavities and multi-... 

When a heteroatom, such as N, O, or a halogen, is present in a molecule containing an aromatic ring or a double bond, lithiation is usually quite regio-selective. The lithium usually bonds with the sp carbon closest to the hetero atom, probably because the attacking species coordinates with the hetero atom. Such reactions with compounds such as anisole are often called directed metala-tions. In the case of aromatic rings, this means attack at the ortho position.Two examples are... 

Lateral monofluorination of the p-alkoxyphenyl isocyanide system [XAu (CNC6H40C H2 +i)] (X = C1, Br, I), in ortho-(3-F) (6a) and meta-(2-F) (6b) positions relative to the alkoxy chain was also studied [18]. None of the free fluorinated ligands is a LC, but their gold complexes display mesomorphic properties. This is a typical case of a promesogenic ligand which yields a mesogen upon coordination to a metal. 

Sterically bulky 3,3 substituents reduced the enantioselectivity, while coordination between La and O atoms of ortho-substituents improved ees. 6,6 -diphenyl-BI-NOL gave the best results (69% ee for para-tolualdehyde) it was proposed that the phenyl substituents affected the Lewis acidity of the catalyst via electronic effects. With this catalyst, ee and yield depended strongly on solvent, THE being the most... 

A Hammett plot for para-substituted benzaldehydes showed that electron-rich aldehydes gave higher ees (r = -0.4). As in Shibuya s related results (Section 5.3.3.1 above), this indicates that aldehyde coordination is important in enantiodifferentia-tion, but the lower rvalue (compared to Shibuya s r = -1.30) suggests a weaker electronic influence, probably due to the relative Lewis acidities of A1 and La. For ortho-substituted aldehydes, lower ees were observed, presumably due to steric effects. Although Al-Cl and Al-triflate complexes 29-30a-b did not catalyze the reaction, they... 

Entry 8 uses a to-trifluoromethanesulfonamido chelate of methylaluminum as the catalyst. As in Entry 6, the use of a 3,5-dimethylphenyl group in place of phenyl improved enantioselectivity. The ortho-methylphenyl substituent on the maleimide dienophile restricts the potential coordination sites at the metal center. NMR characterization of the reactant-catalyst complex suggests that reaction occurs through the TS shown below. 

Compounds such as phenylacetate esters and phenylethyl ethers, which have oxygen substituents that can serve as directing groups, show high ortho. para ratios under these conditions.12 These reactions are believed to involve coordination of the N02+ at the substituent oxygen, followed by intramolecular transfer. 

Fig. 14. The molecular structure of l,3-bis(diphenylhydroxysilyl)-2,2-dimethyl-4,4-diphenylcyclodisilazane, showing the orientation of the ortho -CH groups of one of the aromatic rings with respect to the SiO groups. Other hydrogen atoms have been omitted for clarity. Drawn using coordinates taken from the Cambridge Crystallographic Database.

Bied-Charreton (63) showed by XH NMR spectroscopy that a zinc porphyrin bearing a primary amino group attached via a flexible spacer to the meta position of a /neso-phenyl ring spontaneously dimerizes in solution via NH Zn coordination. The corresponding ortho derivative shows an equilibrium between the dimeric form and the intramolecu-larly coordinated monomer. ESR spectroscopy was used to demonstrate the same behavior in the corresponding cobalt porphyrin (64). 

In a similar approach, double deprotonation of r 6-coordinated ortho- and para-cresols, 30 and 31, with t-BuOK led to formation of stable r 4-coordinated p- and o-quinone methide complexes of manganese, 32 and 33 (Scheme 3.19).37... 

The X-ray structure of the dibromine complex with toluene (measured at 123 K) is more complicated, and shows multiple crystallographically independent donor/acceptor moieties [68]. Most important, however, is the fact that in all cases the acceptor shows an over-the-rim location that is similar to that in the benzene complex. In both systems, the acceptor is shifted by 1.4 A from the main symmetry axis, the shortest Br C distances of 3.1 A being significantly less than the sum of the van der Waals radii of 3.55 A [20]. Furthermore, the calculated hapticity in the benzene/Br2 complex (x] = 1.52) is midway between the over-atom (rj = 1.0) and over-bond (rj = 2.0) coordination. In the toluene complex, the latter varies from rj = 1.70 to 1.86 (in four non-equivalent coordination modes) and thus lies closer to the over-bond coordination model. Moreover, the over-bond bromine is remarkably shifted toward the ortho- and para-carbons that correspond to the positions of highest electron density (and lead to the transition states for electrophilic aromatic bromination [12]). Such an experimental location of bromine is in good agreement with the results of high level theoretical... 

---