Nucleophilic Attack on Coordinated Double Bonds

The Pd(ll)- and Pt(ll)-promoted nucleophilic additions to olefins are important reactions in organic synthesis. Nucleophiles that have been shown to add to coordinated olefins include OH , RO , AcO , CP, amines, and amides, and with the possible exception of OH , nucleophilic attack takes place on the side of the double bond remote from the metal. The main difference between Pd(ll)- or Pt(Il)-promoted and Fe(II)-promoted addition is that nucleophilic attack on Pd(ll)- or Pt(II)-coordinated monoolefins results in reduction of the divalent metal to the zero valent state. In most cases, Pd(ll) salts promote nucleophilic attack on olefins more readily than Pt(II) salts (Hartley, 1973 Maitlis, 1971). Equations (97) (Stern and Spector, 1961), (98) (Baird, 1966), (99) (Kitching et al., 1966), (100) (Akermark et al., 1974), and (101) (Kohl and Van Helden, 1968 Henry, 1972) illustrate some typical Pd(ll)- and Pt(II)-promoted additions to olefins. 

Another possibility is that there is an initial (cis) transfer of a ligand such as Cl from the metal to the olefin and that this ligand then undergoes a metal-assisted Sn2 displacement by the attacking nucleophile to give the trans product ( ping-pong effect ). 

Some olefin oxidations related to the Wacker process are given in Eqs. (103) and (104) (Lloyd and Luberoff, 1969). 

Catalysts other then Pd(ll) and Pt(Il) have also been used in olefin oxidation reactions (Henry, 1974). For example (Dudley et al., 1974), hex-l-ene, hept-l-ene, and oct-l-ene are converted into the corresponding methyl ketones in yields of 70-80% at room temperature and pressure in benzene in the presence of oxygen and RhCl(PPh3)3 catalyst. There is evidence that oxidations catalyzed by Rh(l) are free-radical processes (Kurkov et al., 1968). 

C-X bond formation by nucleophilic attack on metal-stabilized allyl cations is analogous to C-C bond formation (Section II1,A,2) and is illustrated by Eqs. (105) and (106) (Whitesides et a ., 1973). 

---