Palladium complexes porphyrins

Porphyrin, octaethyl-, palladium complex cyclic voltammetry, 4, 399 <73JA5140)... 

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. 

The low trans selectivity and increased propensity for 1,4-m addition is thought to arise from a direct interaction with the metal-porphyrin peroxo complex similar to that suggested for the 2,5-dimethoxyphenyl derivatives shown in Scheme 8-13. It was demonstrated that the 2,5-dimethoxyphenyl derivatives worked in the aerobic oxidation, even without p-benzoquinone being present [64], Interestingly, in this case the 1,4-cis addition product predominates. It was proposed that the (jr-allyl)palladium complex is activated as shown in Scheme 8-13. 

A, N -dimethyl-palladium complex, 21 133 N4C20H14, Porphyrin actinide and lanthanide complexes,... 

The rich coordination chemistry of palladium provides a plethora of more or less readily available complexes, almost all applicable in type 1 or type 2 Mizoroki-Heck reactions. Only a limited series of truly robust and almost indefinitely stable ( dead ) palladium complexes, such as palladium porphyrinate or phthalocyanine complexes, as well as salen-type chelates with Schiff bases, are known not to release palladium even under the harshest conditions used in Mizoroki-Heck reactions. Results from the investigation of reactivity of... 

Kostas, I.D., Coutsolelos, A.G., Charalambidis, G. and Skondra, A. (2007) The first use of porphyrins as catalysts in cross-couphng reactions a water-soluble palladium complex with a porphyrin ligand as an efficient catalyst precursor for the Suzuki-Miyaura reaction in aqueous media under aerobic conditions. Tetrahedron Lett., 48, 6688-91. 

There has been a summary of computational and experimental studies of the use of palladium complexes with A -heterocyclic carbenes (NHCs) in the asymmetric coupling of -hybridized carbon-hydrogen bonds with aryl halides. It has been shown that the electronic and catalytic properties of NHCs fused to porphyrins may be modified by varying the inner metal in the porphyrin. A DPT study of the use of palladium-NHC complexes in the asymmetric intramolecular a-arylation of 2-bromoaryl amides to give 3,3-disubstituted oxindoles (101) has been reported. The likely pathway involves insertion of the palladium into the arene-bromine bond to form a palladacycle which deprotonates to give an (9-enolate. Conversion into the C-enolate followed by reductive elimination gives the product. The intramolecular reaction of 0 a cyclopropane carbon-hydrogen bond in a 2-bromoanilide derivative has been used to form cyclopropyloxindoles, (102), in a palladium-catalysed, silver-mediated reaction. 

With their preference for square planar coordination, palladium(II) and platinum(II) are well suited to binding to porphyrins and related N4 donor macrocycles. Therefore, Pd(octaethylporphyrin) is readily synthesized starting from the labile PhCN complex (like the platinum analogue) [92]... 

Organometallic porphyrin complexes containing the late transition elements (from the nickel, copper, or zinc triads) are exceedingly few. In all of the known examples, either the porphyrin has been modified in some way or the metal is coordinated to fewer than four of the pyrrole nitrogens. For nickel, copper, and zinc the 4-2 oxidation state predominates, and the simple M"(Por) complexes are stable and resist oxidation or modification, thus on valence grounds alone it is easy to understand why there are few organometallic examples. The exceptions, which exist for nickel, palladium, and possibly zinc, are outlined below. Little evidence has been reported for stable organometallic porphyrin complexes of the other late transision elements. 

Fullerenes are spontaneously attracted to porphyrins and metalloporphyrins. The palladium-linked m-pyridyl dimer (shown in Figure 42) has a high binding constant in solution. Addition of C60 or C70 to solutions of these palladium-linked bis-porphyrins gave complexes that were chromatographically distinct from their individual components. This indication of tight binding was also seen in MALDI mass spectra.517... 

Like the palladium(II) complexes, the platinum(II) porphyrins show appreciable phosphorescence even in aqueous media at room temperature in one study,169 singlet oxygen quantum yields ranged from 0.1 to 0.9 and were strongly influenced by dimerization/aggregation. Platinum(II) 5,10,15,20-tetrakis(/>-carboxyphenyl)porphyrin and platinum(II)coproporphyrin-I ((36) for Pd read Pt) have been studied as phosphorescent labels of antibodies for use in time-resolved microscopy.189... 

Equations 1 to 3 show some of fixation reactions of carbon dioxide. Equations la and lb present coupling reactions of CO2 with diene, triene, and alkyne affording lactone and similar molecules [2], in a process catalyzed by low valent transition metal compounds such as nickel(O) and palladium(O) complexes. Another interesting CO2 fixation reaction is copolymerization of CO2 and epoxide yielding polycarbonate (equation 2). This reaction is catalyzed by aluminum porphyrin and zinc diphenoxide [3],... 

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