Palladium® complexes imine ligands

Currently, a significant body of work deals with the use of chiral cationic palladium complexes bearing ligands of the BINAP type or related bisphosphine ligands such as SEGPHOS (Fig. 3). These are based on the pioneering work from Sodeoka on the direct formation of chiral palladium enolate complexes from the palladium precursors and 1,3-dicarbonyl compounds [10, 23]. Within this context, the combination of cationic BINAP-Pd complexes and N-fluoro-bis(phenylsulfonyl)imine (NFSI) was introduced by Sodeoka for the realization of an extremely efficient a-fluorination of 3-keto esters (Scheme 5). 

The reaction of the palladium complex with diacetyl is rather more interesting and yields the palladium(n) complex of a novel tetraphospha macrocyclic ligand. Note that the phosphorus analogue of an aminol rather than an imine is once again obtained, representing the general instability of P=C bonds in the absence of sterically hindering substituents (Fig. 5-52). 

A nickel-based catalyst system, which produces, in the absence of comonomers, highly short-chain branched polyethene was developed by Brookhart et al. [23]. Independently, the groups of Brookhart [24, 25, 26] and Gibson [27, 28, 29, 30] developed efficient iron- and cobalt-based catalyst systems. Nickel or palladium is typically sandwiched between two a-di-imine ligands, while iron and cobalt are tridentate complexed with imino and pyridyl ligands. 

It is very well known that jr-allyl palladium complex 1, which is a key intermediate for the Tsuji-Trost type allylation, has an electrophilic character and reacts with nucleophiles to afford the corresponding allylation products. We discovered that bis 7r-allyl palladium complex 2 is nucleophilic and reacts with electophiles such as aldehydes [27] and imines [28-32] (Scheme 2, Structure 2). We have also shown that bis 7r-allyl palladium complex 2 can act as an amphiphilic catalytic allylating agent it reacts with both nucleophilic and electrophilic carbons at once to produce double allylation products [33]. These complexes incorporate two allyl moieties that can bind with different hapticity to palladium (Scheme 3). The different complexes may interconvert by ligand coordination. The complexes 2a, 2b and 2c are called as r]3,r]3-bisallypalladium complex (also called bis-jr-allylpalladium complex), r)l,r)3-bis(allyl)palladium complex, -bis(allyl)palladium complex, respectively. Bis zr-allyl palladium complex 2 can easily be generated by reaction of mono-allylpalladium complex 1 and allylmetal species 3 (Scheme 4) [33-36]. Because of the unique catalytic activities of the bis zr-allyl palladium complex 2, a number of interesting cascade reactions appeared in the literature. The subject of the present chapter is to review some recent synthetic and mechanistic aspects of the interesting palladium catalyzed cascade reactions which in-... 

Amino sulfides 13 were inactive, but transformation of the amino function into an imine produced ligands that made good chiral catalysts with palladium, since amine ligands afford palladium complexes of low reactivity compared to ligands containing rr-accepting donor groups. 

The chloro-bridged palladium complex was prepared by reacting the imine ligand with palladium acetate, followed by treatment with HCl, and the other complexes by ion-exchange reactions with KBr, KI, and KSCN. The flat, dinuclear halogeno- and thiocyanato-bridged complexes ((77) M = Pd X = Cl, Br, I, SCN R = CgHia) exhibited a monotropic phase, whereas the acetato-... 

Coupling reactions between allyltins and allyl chlorides are assumed to proceed via bis(7T-allyl)palladium intermediates Yamamoto [9] has shown that in the presence of aldehydes or imines, it is possible to control the chemoselectivity of the reaction so that either the allyl halide or the aldehyde/imine is allylated by the organotin. The key element is coordination of a ligand, such as triphenylphosphine, which is suggested to form a trigonal palladium complex with an and an /jCallyl... 

The origin of enantioselectivity which accompanies the allylic acetate substitution reaction of l,3-diphenylprop-2-enyl acetate with dimethyl malonate, catalysed by palladium complexes having chiral imine-sulfide chelate ligands, has been explored. 

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