Oxad reaction

This type of reaction involves both oxidation and addition of groups, so it is known as an oxad reaction. Alkyl derivatives of PC13 can be prepared by the reactions with Grignard reagents and metal alkyls illustrated in the following equations ... 

Chlorine is a strong oxidizing agent that converts S02 into sulfuryl chloride, S02C12. In the reaction, sulfur is oxidized as chlorine is added, so the process is an oxad reaction. 

Oxidation-addition (oxad) reactions of this type also occur with other compounds as shown in the following examples ... 

This oxad reaction is first order in both complex and CH3I, and the entropy of activation is large and negative. It is believed that the reaction goes through an ionic transition state in which CH3 adds to a pair of electrons on Ir followed by the attachment of I- in the trans position. 

The nature of the oxad reaction requires that the following conditions generally apply ... 

Much of Chapter 20 was devoted to the description of mechanisms of reactions of coordination compounds with emphasis on substitution reactions. Because there are numerous aspects of oxad reactions that are different from those involving substitution, we will address some of the mechanistic aspects of oxad reactions briefly in this section. 

The bonding of H2 in metal complexes was described in Chapter 16. In connection with the oxad reaction in which the bonding is not static, it can be presumed that the o orbital on the hydrogen molecule functions as an electron pair donor to an orbital on the metal atom. Simultaneously, the o orbital on the H2 molecule receives electron density from the populated d orbitals on the metal atom as a result of back donation. The result is that two M-H bonds form as the H-H bond is broken in a process that is accompanied by a very low activation energy. 

Kinetic data are available for the oxad reaction of CH3I with a series of complexes that are derivatives of Vaska s compound, rans-IrCl(CO)L2 where L = P3, PHt( >2, PEt2[Pg.786]

In another study (see Atwood, 1985, p. 168), a series of oxad reactions was carried out at 30°C with methyl iodide and trans-[IrCl(CO)(P(p-C6H4Y)3)2]. The identities of the groups in the para position of the phosphine ligands, Y, are shown in Figure 22.4, which is a graph of the values for the enthalpy and entropy of activation for reactions. 

An oxidative addition reaction occurs when there is an increase in oxidation state of a metal that is accompanied by a simultaneous increase in its coordination number. Numerous examples of oxidative addition (sometimes referred to as oxad) reactions have already been presented for nonmetallic elements including the following ... 

Each of these reactions involves an increase in the oxidation state of the central atom and the formation of additional bonds to that atom. In this chapter, the discussion of such oxad reactions will be limited to those involving transition metals in complexes. An interesting reaction of this type involving hydrogen is the following ... 

In this reaction, Ir is oxidized from the +1 oxidation state to +3 during the addition of a hydrogen molecule. When coordinated to the metal, hydrogen is considered to be coordinated as hydride ions, FT. Thus, hydrogen has been added by increasing the coordination number of Ir to 6, and the metal has been oxidized to +3. A general oxad reaction can be represented as... 

The addition of oxygen in the following oxad reaction is slightly different because when an oxygen molecule adds to the complex, the atoms do not become separated ... 

Draw the structure of the product obtained when m-[Pt(NH3)2Cl2] undergoes an oxad reaction with Cl2. 

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