Vaska-type iridium compound

Vaska-type iridium compounds Ir(CO)Cl(PR3)2 bind readily and reversibly to fullerenes via the iridium atom. Flexible, aromatic substituents on both phosphorus atoms then may accommodate interactions with the convex exterior of Ceo- As a result linear fullerene chains precipitate as black crystallites (Figure 5.37). 

Wickman and Silverthom [276] have investigated bond properties in molecular adducts of the planar Vaska type compound frans-h s(triphenyl-phosphine)iridium carbonyl chloride, IrCl(CO) ((C6H5)3P)2, with small molecules such as H2, O2, CI2, I2, CH3I, and HCl. They essentially observed a decrease of the isomer shift in the following series of adduct molecules XY H2 > HCl > CH3J > O2 > I2 > CI2,... 

One of the first detailed studies of OA was performed by L. Vaska57 on 16-electron square planar iridium complexes, the most notable of which is currently known as Vaska s compound, the central compound in Scheme 7,3. The reactions portrayed in Scheme 7.3 indicate that several different kinds of molecules react with the iridium complex. Mechanistic pathways leading to the products shown and to products resulting from other metal complexes are many and varied. We will consider a few of these mechanistic types, trying to point out as we go along similarities to other reactions from the realm of organic chemistry. 

The equilibrium constant (K) for the addition of benzoic acid to Vaska s type compounds depends on the electron density at iridium. Thus electron attracting ligands lower the basicity and electron donating ones raise it (Order of K where X = I > Br > Cl L = Me, > Me,PPh > MePPh, > PPh,). 

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