Palladium complexes imino

In reactions closely related to the carbonylation processes described above, the dimeric azoarene palladium complexes (78) can be transformed efficiently in two steps into 3-imino-2-phenylindazolines (Scheme 95).162... 

Addition of disilanes to isocyanides is catalyzed by palladium complexes, giving A-substituted bis(silyl)imino-methanes (Equation (53)).132 A wide range of isocyanides including aryl isocyanides and alkyl isocyanides can take part in the reaction. However, it is important to note that tert-alkyl isocyanides hardly undergo the bis-silylation reaction. This low reactivity of / r/-alkyl isocyanides allows their use as spectator ligands in the catalytic bis-silylations. 

Chiral palladium complexes have been employed as enantio- and diastereo-selective catalysts of a Mannich-type addition of /3-kclo esters to aldimines and imino esters, q. in a strategy which activates both reactants 28 anti-Selective direct enantioselective Mannich reactions use a BINAP-derived axi- ally chiral aminosulfonamide as organocatalyst.29... 

Figure 3.42 Cationic palladium complexes with a chelating imino functionalised NHC ligand.

Not only palladium, but many more non-metallocene late (and early) transition metal catalysts for the coordination polymerization of ethene and 1-olefins were reported [11]. Among the most significant findings in this area are the disclosures of novel highly active and versatile catalysts based on (i) bidentate diimine [N,N] nickel and palladium complexes [12], (ii) tridentate 2,6-bis(imino)pyridyl [N,N,N] iron and cobalt complexes [13], and (iii) bidentate salicyl imine [N,O] nickel complexes [14]. 

Multiple, successive insertion of isonitriles into the palladium-carbon o--bond has also been found with organopalladium(II)bis(phosphine) complexes. However, unlike the Ni- catalyzed polymerization, only single, double, and triple insertion reactions of isonitriles have been reported for Pd-mediated reactions. For instance, reaction of methylpalladium(II) complex 2 with cyclohexyl isonitrile in ratios of 1 1, 1 2, and 1 3 afforded selectively single (3), double (4), and triple (5) insertion products, respectively (Scheme 3). However, no further insertion of cyclohexyl isonitrile to 5 took place. No reactivity of the triple insertion complex 5 was explained by the intramolecular coordination of the nitrogen atom of the third imino group, which formed a stable five-mem-bered chelating palladium complex. 

The synthesis of arylglycine derivatives, which are fundamental building blocks for many important pharmacological active molecules, could be performed through the arylation of Al-aryl imino esters [37], as was reported by Dai and Lu in 2007. They used the commercial achiral Pd-bypyridyl complex [35]. In 2012, the group of Zeng [38] developed a cationic palladium-complex-catalyzed... 

Aldol reactions of silyl enolates are promoted by a catalytic amount of transition metals through transmetallation generating transition metal enolates. In 1995, Shibasaki and Sodeoka reported an enantioselective aldol reaction of enol silyl ethers to aldehydes using a Pd-BINAP complex in wet DMF. Later, this finding was extended to a catalytic enantioselective Mannich-type reaction to a-imino esters by Sodeoka s group [Eq. (13.21)]. Detailed mechanistic studies revealed that the binuclear p-hydroxo complex 34 is the active catalyst, and the reaction proceeds through a palladium enolate. The transmetallation step would be facilitated by the hydroxo ligand transfer onto the silicon atom of enol silyl ethers ... 

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. 

Figure 3.39 Synthesis of palladium(ll) complexes of imino functionalised NffC.

Although the main emphasis with imino functionalised carbene hgands is on their silver complexes, as carbene transfer agents, and on late transition metal complexes - palladium. 

Oxazolidines (53) are readily formed from aldehydes or ketones and ethanolamines they can be hydrolyzed with ease and show reactions that might be expected of the imino alcohol intermediate (54). Among these are the addition of Grignard reagentsand catalytic hydrogenolysis of the C—O Ixjnd (equation 28).This reaction is exothermic over Adam s catalyst in methanol but slower in acetic acid. Nickel and copper chromite are also effective but at higher temperatures and pressures,as is the case with palladium. The same cleavage occurs with LAH (unassisted)and with the borane-THF complex. ... 

The search for a catalyst suitable to promote addition of the less reactive silyl enol ethers of ketones has identified a novel class of cationic transition metal complexes in two independent laboratories. The use of a chiral palladium(II) di-aquo complex in the catalytic asymmetric addition of silyl enol ethers to aldehydes (first demonstrated by Shibasaki, Sodeoka et al. [52a, 52b]) provided a clear precedent for their subsequent use with a-imino esters [53] (Scheme 27). Initial experiments focused on the reaction of various a-imino esters 82a-c with silyl enol ether 83 (1.5equiv) in the presence of the Pd diaquo complex 80a (10 mol %) in DMF. Extensive experimentation led to the formation of 84c in 67% ee, and also underscored the importance of suppressing the generation of tetrafluoroboric acid during the course of the reaction. 

An a,p-di(methoxycarbonyl)-P-iminophosphorane was prepared and used in complexation with Pd(ii) and Pt(n) precursors as shown in Scheme 104/1. The heteroatoms of the P-imino and oxo-functions took part in the complexation. Interaction with Pd(OAc)2 led to a dimeric cyclic complex. It is noteworthy that the phenyl ring was covalently bound to the central palladium atom. The dimer was cleaved by triphenylphosphine reactant (Scheme 104/2). ... 

Several examples of imino-functionalized carbene complexes of palladium have been described. " The imidazolium salt 97 was prepared and coordinated to Pd by an Ag-transfer reaction. Tautomerization of the carbene-imine bond occurs during the transfer reaction to give the the enamine complex 98. Neutral and cationic Pd complexes of a second closely related chelating iminocarbene ligand, 99, were also prepared via an Ag-transfer route. " In this case, no tautomerization was reported. However, evidence of solvent-dependent hemilability was observed. 

Closely related to some of the complexes in Scheme 11 are the structures of Pd(dtbpx)( 7 -qn), [Pd(PPh3>2-(77 -qn)] 2H2qn, Pd2( 7, 77 -qn)2(PPh3)2, Pd(bipy)( 7 -qn), and Pd l,2-bis(A-(4-methylphenyl)imino)acenaphtene -Also closely related is complex II, involving a cyclohexenone, which was prepared by two methods in the course of a mechanistic study of the palladium-catalyzed intramolecular cyclization of alkadienyl-substituted 1,3-dike-tones (Scheme 12). ... 

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