Comments on TM-Based Catalysts

despite its 18e count, the activity of this complex is wide-ranging. It arises because two of the electrons on the Fe O moiety are not paired, and the 0-center acts as a radical. Thus, it can abstract H atoms and perform other reactions that radicals initiate. As this is due to QM effects, we make some comments about it in the Retouches (see Section 9.R.3). Another aspect of catalysts is that they act like nanomachines using a cycle of reactions that turns over many times and performs the same final reaction such that the product of the reaction is produced with great efficiency. This aspect is also discussed in the Retouches (see Section 9.R.4). 

You recall from Lecture 7 that the VSEPR (valence shell electron pair repulsion) rules predict the shapes of main-element molecules with nice compact reasoning, by simply counting the number of electron pairs, bond pairs and lone pairs around the central atom. In transition metal (TM) complexes, the lone pairs on the TM do not occupy space in the same manner as they do in the case of the main group elements, so what matters for the 3D shape is only the number of bond pairs the TM maintains with the ligands. This number is also known as the coordination number (cn) by the historical referral of Werner to these complexes as coordination complexes. 

Of course it may be very bothersome for some of you that there are exceptions to the rule, but recall that this is the nature of all rules. .. Rules are needed because they paint 

FIGURE 9.6 Common geometries and 3D shapes of transition metal (TM) complexes as a function of the number of bond pairs around the TM. This number is also called the coordination niunber (cn), which is shown within parentheses near each complex. 

6 BRIDGING TRANSITION METAL AND ORGANIC MOLECULES BONDING CAPABILITIES OF FRAGMENTS OF TRANSITION METAL COMPLEXES 

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