The Complexes Shown Below Are Catalysts For The

Question

The complexes shown below are catalysts for the water splitting process. It has been found that t…

The complexes shown below are catalysts for the water splitting process. It has been found that the carbonyl stretching frequency is a useful parameter to gauge the effect of ligand environment on the key step in the reaction. Describe the bonding characteristics of the N2P-ligand and the structures of the complexes, and predict how the electronic property (donating or withdrawing) of the substituent X is reflected by the carbonyl stretching frequency (Suresh et al. Inorg. Chem. 2015, 54, 11150). Et2NRuP(tBu)2 H CO

Solutions

Expert Solution

Covalent strength of the bond can be studied using IR
spectroscopy. In the molecular orbital diagram of CO, we can find
HOMO or highest occupied molecular orbital is a bonding molecular
orbital and LUMO or lowest unoccupied molecular orbital is an
antibonding molecular orbital. So the addition of electron density
to the molecular orbital of CO makes the CO bond order less. Thus
stretching frequency of CO decreases.

Usually, ligands of type PR3 are π- acceptor
type. So metal to CO back-donation will be less and thus CO
stretching frequency increases because of more CO bond order. It is
because, as PR3 pulls electrons from metal and metal
become electron deficient to donate to the molecular orbital of CO.
Likewise NR3 ligands also. So as X is electron donating,
then CO stretching frequency decreases because ligand
N2P accepts less
electron density from metal. but X is electron withdrawing then CO
stretching frequency increases because N2P ligand
accepts more electron density from metal. Electron donating X group
makes ligand environment more electron rich and thus less

π acceptance fro metal orbital. This makes metal to CO
back donation high and thus decrease in CO stretching
frequency. Likewise, if X is electron withdrawing then the ligand
environment become electron deficient and thus accept more electron
density from metal. This makes the metal more electron deficient
and less viable to back donate electron density to CO orbital. So
CO stretching frequency increases.


Submit Your Answer

[contact-form-7 id=”5″ html_class=”cf7_custom_style_1″ title=”Answer Question”]