Palladium . cyano complexes

Other works have shown that phosphonium yhdes a-stabilized by a cyano or keto group can behave as ambidentate hgands towards palladium complexes (Scheme 21) [85-89]. 

Yang described the Pd-induced cyclization of an aryl bromide onto a pendant cyano group leading to y-carbolines and related compounds [488], Genet studied the use of chiral palladium complexes in the construction of the C-ring of ergot alkaloids, a study that culminated in a synthesis of (-)-chanoclavine I [489-491]. For example, nitroindole 388 is cyclized to 389 in 57% yield and with enantioselectivities of up to 95% using Pd(OAc)2 and (S)-(-)-BINAP. 

The selective synthesis of the 2-allyltetrazoles 55 by the three-component coupling reaction of the cyano compounds 54, allyl methyl carbonate 5b, and trimethylsilyl azide 42 was accomplished in the presence of Pd2(dba)3.CHCl3 and P(2-furyl)3 (Scheme 19) [55,56]. Most probably, the formation of (r)3-allyl)( ]5-tetrazoyl)-palladium complex 56 took place through [3 + 2] dipolar cycloaddition of 7r-allylpalladium azide 44 with the nitrile 54. The complex 56 thus formed would undergo reductive elimination to form the products 55. 

Mechanistic studies on the reductive elimination of square-planar type aryl(j7 -allyl)palladium complexes demonstrated occurrence of bond formation between the aryl carbon and one of the allyl termini that are located cis to each other (Scheme 8.53) [91]. The allyl ligand remained 17 -coordinated during the coupling. Similar reductive elimination between 17 -allyl and cyano ligands may be a key step in the industrially important nickel catalyzed hydrocyanation of dienes (Scheme 8.54) [92]. 

Reaction of butadiene with aldehydes in the presence of palladium(o)-triphenylphosphine species leads to two products (80) and (81), whose formation can be explained by the mechanism outlined in Scheme 4. Whereas butadiene reacts with active-hydrogen-containing compounds such as a-cyano-esters or jS-diketones in the presence of palladium complexes of unidentate phosphines, in the presence of palladium complexes of bidentate phosphines addition of the butadiene to the active-hydrogen compound takes place. ... 

The catalytic enantiomeric fluorination of a-cyano acetates catalyzed by the chiral palladium complex was also reported leading to a-cyano-a-fluoro acetates with excellent enantiomeric excesses (up to 99% ee). °... 

Kim HR, Kim DY. Catalytic enantioselective fluorination of a-cyano acetates catalyzed by chiral palladium complexes. Tetrahedron Lett. 2005 46 3115-3117. 

Carbonyl-stabilized ylides and the cyano-stabiHzed ylides Ar3P=CHCN in spite of their low nucleophilicity are able to give stable complexes. By comparison, very few complexes involving the second category of ylides are known. However a new example has recently been described by reaction of the cyano-ylide 60 with palladium(II) to give the complex tra s-[PdCl2 CH(PTol3)CN 2] 61 (Scheme 24) [93]. 

The compound 70 has also been reported showing the ambident character (both C- and N-coordination) of the cyano-stabilized ylide as ligand. The authors have also transposed their work concerning the keto-bis-ylide and palladium, with the synthesis of the C-bonded complex 71 or the new cycloplatinated or-thometallated compound 72. The latter by various treatments allows one to obtain other ylidic cationic complexes of platinum such as 73. A C,C,C-terdentate coordination of the keto bis-ylide, already observed with the palladium is also obtained from the reaction of 73 with gold derivatives. 

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