Palladium® complexes pyridine ligands

The flexibility of the pincer carbene ligand system can be seen from the crystal structures of their palladium complexes. The ligand without linker units features the central pyridine ring and the flanking NHC units strictly coplanar [431] whereas the linker unit introduces twisting of these three ring systems [490]. The flanking NHC units are now... 

Hydrosilylation of dienes accompanied by cyclization is emerging as a potential route to the synthesis of functionalized carbocycles. However, the utility of cycliza-tion/hydrosilylation has been Umited because of the absence of an asymmetric protocol. One example of asymmetric cycUzation/hydrosilylation has been reported very recently using a chiral pyridine-oxazoUne ligand instead of 1,10-phenanthroline of the cationic palladium complex (53) [60]. As shown in Scheme 3-21, the pyridine-oxazoUne Ugand is more effective than the bisoxazoUne ligand in this asymmetric cyclization/hydrosilylation of a 1,6-diene. 

A helical homobimetallic mercury(II) complex with a bridging bis(NHC) ligand serves as a starting point for a supramolecular assembly. Also tetrameric cyclic palladium(II) complexes have been obtained with bridging NHC-pyridine ligands. 

The asymmetric Baeyer-Villiger oxidation using a palladium complex of 2-(phosphinophenyl)pyridine ligand provides a useful procedure for the synthesis... 

Nitrogen nucleophiles, in a similar manner to oxygen- and sulfur-based functionality, undergo transition metal-catalyzed cross-coupling with halopyridines. The use of palladium(O) catalysts is most effective in combination with chelating bis-(phosphine) ligands such as BINAP that prevent the formation of pyridine-palladium complexes that... 

Better catalytic behavior was observed in the copolymerization of CO and norbornadiene with palladium complexes containing a hemilabile pyridyl-carbene ligand [23]. The choice of a pyridine-functionalized carbene can be explained by the fact that the hemilabile arm in such a ligand is capable of reversible dissociation from the metal center, leading to vacant coordination sites for the complexation of the substrates while the strong donor moiety remains bound to the metal. 

Pyridine ligands containing one or two carboxylic acids have also attracted recent attention. The palladium nicotinic and isonicotinic acid complexes trans-[PdCl2(n-NC5H4C02H)2] (n=3 or 4) form the anticipated one-dimensional tapes... 

Two new expanded porphyrins, that would perhaps best be classified as vinylogous porphyrins, have also been reported in the last several months. Corriu et al. have developed a facile synthesis of new tetrapyrrolic macrocyclic derivatives [241]. A notable difference between these new vinylogous porphyrins and those described above (Section 11) is the incorporation of pyridine, in one case, as part of the macrocycle. While these new expanded porphyrins are not aromatic, they may have great potential as ligands. Indeed, the formation of a bimetallic palladium complex was described. 

If a palladium(II) allyl complex is used as the palladium precursor, there is no electronic need for the pyridine ligand to coordinate to the metal [29]. It therefore remains pendant and the pyridyl functionalised NHC ligand coordinates in monodentate fashion with its carbene... 

The zero-valent palladium complex Pd(nbd)(ma), nbd = norbomadiene, ma = maleic anhydride, is a useful precursor to novel Pd° complexes with nitrogen a-donor ligands. In THF, pyridine, diethyl amine, aniline, and even NH3 displaced the nbd ligand to form E2Pd(ma) complexes. ... 

Melaimi, M., Thoumazet, C., Ricard, L., Floch, P. L. Syntheses of a 2,6-bis-(methylphospholyl)pyridine ligand and its cationic Pd(ll) and Ni(ll) complexes - application in the palladium-catalyzed synthesis of aryiboronic esters. J. Organomet. Chem. 2004, 689, 2988-2994. 

In 1998, Kempe and coworkers [34] reported the first aminopyridinato rare-earth metal complexes. 4-Methyl-2-[(trimethylsilyl)amino]pyridine(HLl) was utilized in this complex. The reaction of lithiated LI and YCI3 in ether and pyridine led to the ate complex [Y(Ll)4(LiPy)] (Py = pyridine) (1). The complex 1 catalytically mediated a ligand transfer reaction to form [Pd(Ll)2] and [Y(Ll)3(py)] (2) from [Pd(cod)Cl2] (cod = cyclooctadiene). The LI ligand transfer from yttrium to palladium and the regeneration of 1 are significant in the efficient synthesis of the very strained amido palladium complexes (Scheme 2). Lithiated LI underwent a salt metathesis reaction with ScCb, at low temperature in THF, to yield the homoleptic complex [Sc(L1)3] (3) (Scheme 2). 3 is the first reported scandium aminopyridinato complex [35]. 

The PflN ligands 10a,b as well as the corresponding palladium complexes were synthesized as depicted in Fig. 2.14. Treatment of 2-(chloromethyl)pyridine with one equivalent of bis(2-methylphenyl)phosphane in the presence of potassium tert-butylate yielded ligand 10 a which was directly converted into the palladium diiodide complex 11b. Purification of 11b was achieved by column chromatography on sihca. 

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