Pd n complex

Conjugate allylation reactions, characteristics, 9, 312 Conjugated alkenes, with Pd n-complexes, 8, 334 Conjugated dienes via Pd(IV) catalysts, 8, 306 polymerization, 4, 1084... 

The tridentate macrocyclic ligands 1,4,7-triazacyclo-nonane and 1,4,7-trithiacyclononane (39, E = NH, S, respectively), act as bidentate chelates toward Pd(II) to give square-planar complexes [Pd L2] + with two pendant E donor atoms (40). The complexes can be oxidized chemically or electrochemically to [Pd L2] + (41) (equation 15), which show tetragonaUy elongated octahedral coordination, as expected for a Jahn-Teller distorted d complex. Interestingly, electrochemical stndies on the Pd(n) complexes (30) and (31) (Section 6.5) show that only the second can be reversibly oxidized to Pd(III). 

The interactions of guanine, guanosine, and 5 -GMP with Pd(n) complexes have been studied by pH measurements and H NMR. In strongly acidic solution, where N -H is still protonated, only N-7 is coordinated to the metal ion, but as the pH increases to 3, H NMR shows that both N -only and N -only coordinated species come into existence. At pH 4-5, both N -only and N, N -bridged coordination to Pd(n) complexes are found. 

Pd(n) complexes tetracoordinated by a tridentate (pincer) Ugand and a monodentate ligand. 

The higher reactivity of square-planar 16e Rh(l) and Pd(n) complexes arises from the fact that there is an open axial 5 j-orbital that ligands can directly bind to forming five-coordinate 18e systems (Equation (2)). The coordination of a fifth ligand is, however, weakened by the presence of the filled orbital in these [Pg.120]

Palladium will form complexes with the great majority of organic compounds containing nitrogen donor atoms. Some representative Pd-N complexes containing mono- and bidentate nitrogen ligands are summarized in Table 5. 

Carbon Number Preparation Pd-N Complex Commercial Availability References for... 

Pd-N complexes are usually prepared similarly to Pd-P complexes from PdCl2, MiPdCLi (M = Li, Na, K), Cl2Pd(PhCN)2, Pd(OAc)2, or Pd(dba)2. They can also be conveniently generated in situ from Pd(OAc)2 or Pd(dba)2 " and the corresponding ligand. 

Although Pd-N complexes sometimes have catalytic activities that are comparable to that of the Pd-P complexes,they often lead to significantly different reactivity profiles as exemplified by the Pd-catalyzed regioselective carbonylation (Scheme 9) or the selective activation of a switchable bisnucleophile (Scheme 10). Other examples can be found in the catalytic hydrogenation of alkenes, or the carbacyclization of enynes, as well as in cross-coupling and allylic substitution reactions. ... 

It is well known that square-planar Pt(ii) and Pd(n) complexes with protruding filled d/ orbitals show a high tendency towards stacking through weak non-covalent metal-metal and/or n-n ligand-ligand... 

Fig. 33 The catalyst resting state for the Pd(OAc)2-catalyzed arylation of 3-methyl-2-phenylpyr-idine (56) is proposed to be mononuclear Pd(n) complex 59...

In 2011, Lautens and co-workers reported a palladium-catalyzed intramolecular carbon-carbon bond-forming reaction between atyl iodides and alkenes. This new cross-coupling reaction forms two new bonds and all of the atoms in the starting materials are incorporated into the product. The use of a palladium catalyst with bulky phosphine ligands was found to be crucial for reactivity as the bullty phosphine ligands favour the reductive elimination of Pd(n) complexes. Good to excellent 5delds of the desired products were isolated (Scheme 2.38a). In the same year, they found that aiyl... 

Scheme 2.99 Well-defined Pd(n) complex and thesis of indoles.

The 77 -allyiic fragment can act as a bridging iigand in paiiadium(l) derivatives supporting two palladium atoms linked by a metal-metal bond. The most common preparative route to these derivatives is the reaction of a palladium(ll) 77 -allylic complex with a Pd(0) derivative (Equation (42)). The reaction can be interpreted as a comproportiona-tion process but also as a nucleophilic attack of the Pd(0) center on the allylic fragment of the Pd(n) complex in a as- (or endo-) fashion, with retention of configuration. Mechanistically equivalent reactions lead to analogous allyl-phosphido and allyl-thiolato Pd(l) dimers. 

Non-conjugated dienes ate the source of many palladium enyl complexes. Nucleophilic attack at one of the double bonds of the coordinated diene has been used most, and many examples can be found in COMC (1982) and COMC (1995). The external attack of the nucleophile leads to an overall /rtf r-addition of Pd and the incoming species to the double bond. Oxidation followed by nucleophilic attack on COD affords <7,7 -enyl derivatives from Pd(l,5-COD)(benzoquinone). In the presence of acid, benzoquinone oxidizes Pd(0) to a Pd(n) diene complex with the concomitant formation of hydroquinone. If a suitable nucleophile is present, such as OAc when acetic acid is used, attack on the diene takes place, and a palladium complex is formed (Scheme 80). A weaker nucleophile like CH3S03 is not capable of adding to the double bond, and the reaction stops at the COD Pd(n) complex. The behavior of other quinones and acids was also studied. ... 

Several chiral PCN pincer Pd(n) complexes with aryl-based aminophosphine-imidazolines have been reported by Gong and co-workers. The complexes were prepared by a two step synthetic strategy, starting from the corresponding aminophenyl-imidazoline derivatives which upon reaction with disubstituted chlorophosphines, yielded the aminophosphines 45a-c. Further complexation with PdClz gave the Pd(n) pincer complexes 46a-c (Scheme 10), which were characterized by elemental analysis and H, C, and P 1H NMR. 

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