Palladium complexes exchange reactions

When the reaction is carried out with a racemic mixture of complexes, the product is a racemic mixture of the isotactic polymers. It was of interest to see what would happen if, after formation of a chiral block with one enantiomer of the bisoxazoline ligand, an equivalent of the other enantiomer was added. It was found that an excess of ligand changes the tacticity completely and the second block was syndiotactic In these diimine palladium complexes exchange of ligand is relatively fast and it can often be observed on the NMRtime scale as a broadening in the H NMR spectra. The process may well be associative. 

The mechanism of action of the cyanation reaction is considered to progress as follows an oxidative addition reaction occurs between the aryl halide and a palladium(O) species to form an arylpalladium halide complex which then undergoes a ligand exchange reaction with CuCN thus transforming to an arylpalladium cyanide. Reductive elimination of the arylpalladium cyanide then gives the aryl cyanide. 

The reaction of the stabilized yUde 46 (a-vinyl substituted) with the cycloocta-dienyl Pd(II) allows the synthesis of a novel complex, the (rj -allyl)palladium 47, in which the olefmic double bond participates in the coordination (Scheme 20) [83]. The coordination of the bis-yUde 48 with the same starting Cl2Pd(COD) leads to the formation of another new palladium complex 49 via COD exchange reactions. A C-coordination mode takes place between the carbanionic centers of the bis-ylide and the soft palladium and two stereogenic centers of the same configuration are thus created [83]. In contrast to the example described in Scheme 19, the Cl2M(COD) (M=Pd or Pt), in presence of a slightly different car-... 

The mercuration of phosphonium derivatives has also been observed. The methylene group of the dimeric palladium complex 63 substituted by a carbonyl and a phosphonium functionality is readily mercurated upon reaction with Hg(OAc)2 to afford complex 64 (Equation (22)).7 Further studies demonstrated that the presence of a triphenylphosphonium group alone is sufficient to promote proton-mercury exchange. For example, the reaction of... 

Further studies revealed that electron-deficient alkenes are capable of displacing O2 from a peroxopalladium(II) complex. The reaction of nitrostyrene derivatives with (bc)Pd(02) results in quantitative displacement of dioxygen and formation of the (bc)Pd(ns ) complex (i.e., the reverse reaction in Eq. 21) [138]. Moreover, preliminary results reveal that dioxygen and BQ undergo reversible exchange at a bathocuproine-coordinated Pd center (Eq. 22) (Popp BV, Stahl SS, unpublished results). This observation is the most direct experimental result to date that establishes the similar reactivity of dioxygen and BQ with palladium. 

With the objective of obtaining palladium chelates, the ligand-exchange reactions with the participation of nitrile complexes of Pd halides are widely used. Thus, coordination units PdN4 and PdN202 are formed as a result of the transformation (3.109) with participation of 2-tosylamino(hydroxy)phenylbenzazoles [282] ... 

Palladium complexes, e.g. Cl2Pd(dppf), have been shown to catalyse not only Zn-I exchange between alkyl iodides and dialkylzincs but also intramolecular carbozincation to produce cyclopentylmethylzincs.60 Once cyclopentyl-methylzincs are formed, they may be utilized in cross-coupling, conjugate addition, and other synthetically useful transformation reactions (Scheme 11.17). 

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