Industrial Roles for Ligands and Coordination Complexes

Coordination chemistry offers many examples of applications in industry beyond those addressed above. Recent developments in chemistry promise greater applications in the future. Here, a limited number of examples from two fields are presented to give a sense of opportunities for coordination complexes in commercial roles. 

The chemical industry as we currently know it would be markedly different without transition metal catalysts, as these play roles in a wide range of processes. The key task of a catalyst is to accelerate a reaction by effectively lowering the activation barrier for the reaction. Apart from acceleration, a catalyst may also be able to induce optical activity in an organic product if it includes a chiral ligand. The success of an asymmetric catalyst is defined by the enantiomeric excess, which is the difference in percentage yields of the major and minor enantiomers of the product. If 90% of one optical isomer forms and 10% of the other, the enantiomer excess is 80% obviously, the closer that this value is to 100% (which means stereospecificity is achieved) the better. Asymmetric synthesis in industry depends fully upon transition metals as the active site of the catalysis. 

The above example is of a homogeneous catalyst, which is one that is dissolved in solution for the reaction. One of the best understood and long established coordination complexes 

Chiral epoxidation with Jacobsen s catalyst. Chiral centres in the ligand and product are marked ( ). 

There are a number of others in common industrial use, such as those used for polymerization of alkenes. One example of an organometallic homogeneous catalyst is the Zr(IV) complex [Zr(CH3)(T 5-Cp)2X], which operates by binding alkene monomers to the metal prior to addition to a growing carbon chain. A similar coordination of substrate is involved in the use of [Co(CO)4H] as catalyst in the hydroformylation of alkenes to aldehydes. Likewise, the [Rh(CO)2l2] ion, formed in situ, catalyses the carbonylation of methanol to acetic acid. 

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