Phosphine ligands, exchange

Thus, geometrical isomerization, phosphine ligand exchange and reductive elimination of H2 all proceed by independent kinetic processes. ... 

The phosphine ligands exchange at room temperature. Parameters are from spectra obtained at low temperature. c V(P—F) 7-2 Hz. 

Investigated tertiary phosphine catalysis of phosphine ligand exchange, and cis- trans isomerization. Results confirm consecutive displacement mechanism for isomerization via an ionic intermediate [PtXL3j X ... 

Adams ef al. also reported a number of interesting molecular dynamic processes for Ru-Pt clusters. The cluster [Ru5Pt(/i6-G)(PMe2Ph)(CO)i5] was shown to undergo facile intramolecular phosphine ligand exchange between a... 

Lithiation at C2 can also be the starting point for 2-arylatioii or vinylation. The lithiated indoles can be converted to stannanes or zinc reagents which can undergo Pd-catalysed coupling with aryl, vinyl, benzyl and allyl halides or sulfonates. The mechanism of the coupling reaction involves formation of a disubstituted palladium intermediate by a combination of ligand exchange and oxidative addition. Phosphine catalysts and salts are often important reaction components. 

It was recently found that the modification of neutral phosphine ligands with cationic phenylguanidinium groups represents a very powerful tool with which to immobilize Rh-complexes in ionic liquids such as [BMIM][PFg] [76]. The guani-dinium-modified triphenylphosphine ligand was prepared from the corresponding iodide salt by anion-exchange with [NH4][PFg] in aqueous solution, as shown in Scheme 5.2-15. The iodide can be prepared as previously described by Stelzer et al. [73]. 

More recently, Grubbs et al. obtained a refined mechanistic picture of the initiating step by conducting a 31P NMR spectroscopic study of the phosphine exchange in precatalysts 12-A. These investigations revealed that substitution of the phosphine proceeds via a dissociative-associative mechanism, i.e., a 14-electron species 12-B is involved that coordinates the alkene to give a 16-electron species 12-C (Scheme 12) [26a]. Increased initiation rates are observed if the substituents R and the phosphine ligands PR3 in precatalysts... 

Other dichloro(ditertiary phosphine)nickel(II) complexes (see Table VI) catalyze both hydrosilylation and H/Cl exchange, but analogous complexes containing monodentate phosphine ligands or bidentate amine groups are essentially inactive (173). 

Here, we have used this method for the synthesis of Au SG clusters. Undecagold clusters (Aun ) stabilized by triphenyl phosphine (TFF) were prepared according to the literature [6]. An aqueous solution of GSH was placed on top of a chloroform solution of Au TFF. The Au SG clusters were transferred to the aqueous phase as a result of ligand exchange reactions [19]. 

The phosphine ligands suffer from P-C-bond cleavage, which result in the corporation of the phosphine aryl groups into an unwanted side product. This is due to the facile exchange of Ph and Ph Y between the Pd" centres and co-ordinated phosphines on an intermediates of type tranj-Pd(PPh,i)2(aryl)X ... 

The study of rapid, intermolecular ligand exchange between square-planar complexes trans-Ir(CO)L2X (X = C1 or Me, L - PPh3, P(p-tolyl)3, or PMePh2) by variable-temperature 31P NMR spectroscopy indicates that the reaction proceeds through dissociation of phosphine from the metal center and a subsequent associative substitution with other complexes 559,560 Ligand exchange between square-planar Ir and Pt complexes is slow. 

---