Metal complexes hydrogen bonding

Compared to CMP, the mechanism of separation on a chiral stationary phase is easier to predict, due to a much simpler system. Because the ligand is immobilized to a matrix and is not constantly pumped through the system, the detection limits for the enantiomers are much lower. Depending on the ligand immobilized to the matrix, one can have different types of interactions between the selectand and selector metal complexes, hydrogen-bonding, inclusion, tt-tt interactions, and dipole interactions, as well as a combination thereof. 

Besides metal-complexation, hydrogen bonding can also be applied to fix a temporary shape and to create shape-memory materials [275-277]. 

Dendrimers can be constructed from chemical species other than purely organic monomers. For example, they can be built up from metal branching centres such as ruthenium or osmium with multidentate ligands. The resulting molecules are known as metallodendrimers. Such molecules can retain their structure by a variety of mechanisms, including complexation, hydrogen bonding and ionic interactions. 

Platinum-thiourea complexes have been extensively studied because of their biological activity [54], but few have been used in catalysis. Neutral thioureas are able to coordinate to metal centres through their sulfur atom (Scheme 9) [55,56] monomeric (I) and oligomeric (II) species are known for Rh [57], and an X-ray structure has also been determined for the chiral complex III [58]. In many complexes hydrogen bonding has been observed... 

In these compounds the transition state to rotation is more or less planar whereas the ground state is twisted, but in contrast to unbridged bipyridyl the transition state is the one in which the two nitrogen atoms will pass in front. Complexation by a metal or hydrogen bonding stabilizes the planar transition state. The lowering of the barrier for racemization is at least 33.5 kJ mol-1 with complexation with PdCl2 The results are summarized in Table XV. 

Hydrogen-bonding Domains in Metal Complexes and the Role of Metals in Hydrogen Bonding... 

Lignin metal and hydrogen-bonded complexes that contribute to the color of... 

Metal complexes can add components of bonds between carbon and some other elements via oxidative addition mechanism to produce derivatives, which contain both metal-carbon and metal-element bonds. Here the element is Si, S, P, etc. [74]. Analogously, metal complexes split bonds between two atoms of an element [75] and between element and hydrogen [76]. Examples of such reactions published in recent years [77] are depicted in Scheme IV.37. 

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