Dinuclear Pd complex

Finally, dinuclear Pd complexes can be prepared, which contain bridging cyclopentadienyl ligands (see Dinuclear Organometallic Cluster Complexes). WheuPdl/j -CsHsK ) -2-MeC3Hs) is reacted with two equivalents of phosphines or phosphites, dinuclear species Pd2(/r-C5H5)(/u,-2-MeC3H5)L2 are formed (equation 50). 

We list in Table 2 a few of the systems that have been reported in the recent literature to show metal complexes supported on amorphous, non-porous oxides. We also include a few recent reports on the decorating of mesoporous supports with metal complexes. Complexes have also been introduced into porous, crystalline oxides as well as placed on organic supports." We reported the use of metal complexes as templates for forming familiar crystalline solids and new crystalline materials, some of them adopting the chirality of the metal complex. " Preparations have appeared recently using dinuclear Pd(II) complexes [Pd2Me2Cl2(dppm)2] as the precursor and these were reacted with a silica surface to produce the grafted dinuclear Pd complex with the elimination of methane from the complex. ... 

Finally, dinuclear Pd complexes can be prepared, which contain bridging cyclopentadienyl ligands see Dinuclear Organometallic Cluster Complexes Pdljj -CsHsXjj ... 

Palladium(II) normally coordinates to the N3 atoms of the cytosine base forming a square planar geometry. " An unexpected isomerization from trans- to cA-coordination of ammine ligands about Pd" occurs when tr<2 x-[Pd (NH3)2(H20)2] is added to the mononuclear trans-Pd"(NH3)2(1-methyl cytosine)2(N03)2. The resulting bridged dinuclear Pd" complex has two cis-[Pd (NH3)2] units bridged by cytosines through their to both N3 and deprotonated N4... 

Fig. 30 The resting state of Pd-catalyzed chlorination of benzo[/i]qumolme (51) is succinate-bridged dinuclear Pd complex 53. Pd-Pd bond length in 53 2.8628(4) A...

Sanford proposed the product of oxidation during catalysis to be one of the two constitutional isomers of a high-valent dinuclear Pd complex shown in Fig. 34 and suggested that the second palladium center in either 60 or 61 functions as an auxiliary ligand to the metal center that mediates the C-C bond formation. 

Fig. 34 Formulations of the high-valent, dinuclear Pd complex proposed by Sanford in the arylation of 2-arylpyridine derivatives...

In 2010, we reported a study regarding the role of the dinuclear core during C-Cl reductive elimination from 62, an analog of the dinuclear Pd complexes that have been proposed in catalysis (Fig. 35) [96,119]. Experimental results established that reductive elimination from 62 proceeds without fragmentation of the dinuclear core C-Cl bond formation proceeds from a dinuclear complex. 

Pd(III), in both mono- and dinuclear complexes, may play a much more prominent role in catalysis than has previously been appreciated. We anticipate that the unique reactivity of both mono- and dinuclear Pd complexes will provide a foundation for the discovery of new reactions mediated by Pd(lll) in the future. 

By using microwave irradiation the reaction time was shortened to 10 min and the catalyst amount was decreased to 0.1 mol%of Pd [114]. Various simple species like Pd (PPh3)4, Pd(OAc)2, or PdCl2 may, in the presence of PPhs, be utilized as catalyst precursors. To study catalytic reactions in the molten-state systems a special NMR technique was developed [116]. Using this technique intermediate dinuclear Pd complexes with the same trans-/cis- isomers ratio were detected in solvent-free/melt systems after conventional and microwave heating [116]. 

Even under Pd catalysis, the C-H bond addition in cis manner was reported. Tsukada, Inoue, and coworkers [89] demonstrated that benzenes, pyrroles, and thiophenes react with alkynes in the presence of a dinuclear Pd complex catalyst to give cis-adducts (Scheme 18.87). 

Nevertheless, the group of Peris reported in 2009 that dinuclear Pd complexes with the Janus-type ditz ligand were quite effective in the sequential Sonogashira/hydroxyalkoxylation coupling leading to benzofurans (Fig. 17), with a catalytic efficiency comparable to that ofmono-NHC analogues. The reaction worked well with 2-iodobenzyl alcohol, whereas only moderate yields could be obtained with the bromo derivative and the chloro derivative was quite unreactive." ... 

The bis-phosphonium salt 56 in presence of Pd(OAc)2 leads to the formation of the neutral bis-ylide 57 which reacts with TICIO4 to give the dinuclear cationic complex 58 (Scheme 22) [89,90]. The bis-ylide part, which has potentially two carbons and one oxygen donor atoms, acts as a C,C-chelating ligand through its two soft ylidic carbons. 

Akita and coworkers established a dehydrative condensation procedure, starting from hydroxo metal precursors containing the hydrotris(3,5-diisopropylpyrazolyl) borato ligand, and they were able to obtain dinuclear (/r-peroxo)Pd complexes, as indicated in Scheme 4. With the same procedure peroxo and hydroperoxo species (for Pd and Rh) and alkyl peroxides (for Mn, Co, Ni and Pd) complexes may be obtained. 

Palladium forms with both silylenes 83 and 84 silylene-bridged dinuclear complexes. The dinuclear Pd(0) complex 110 (R = Ph) was found to be active in Suzuki and Stille cross-coupling reactions <2001CC2372, 2002JOM141>. NMR investigations indicate that also homoleptic silylene complexes of Pd(0) such as Pd(83)(, [Pd(83)2]2, and Pd(84)4 exist these complexes are, however, very labile <2002JOM141>. 

Using the 2-chloro-imidazole annulated Cp ligand, deprotonation of the Cp end and reaction with a suitable Cp Ru precursor forms the appropriate annulated ruthenocene that can in turn be reacted with a palladium(O) source to form the dinuclear Ru/Pd complex (see Figure 4.61). 

Vilar and coworkers reported the isolation of two new dinuclear Pd(I) dimers containing P(Bu-f)2Bph (Bph = biphenyl) (equation 48) as ligand168. The complexes were prepared by the same conproportionation used to prepare the palladium dimers with trialkylphosphines. The complexes contain a single phosphine, and both metals are coordinated to the terminal phenyl group of the biphenyl unit in a p2 — rf -iy fashion. These complexes were tested for the animation of aryl halides with arylamines. The reaction of 4-chlorotoluene with p-tolylamine catalyzed by 52a or 52b formed di-p-tolylamine in 78 to 81% yield within 3 h at room temperature, whereas the same reaction conducted with a mixture of Pd2(dba)3 and P(Bu-f)2Bph required 80 °C to obtain 90% yield. 

The compound trans-PdHCl[As(Bu-t)3]2 gives, at a slower rate, a mixture of cis and trans hydrido-bridged dinuclear Pd(II) complexes, [PdCH2C(Me)2As(Bu-t)2]2 (/ -H)2. 

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