Dipalladium O Compounds

The d -d Pd(0)-Pd(0) bond within dipalladium(0) compounds is expected to have no o-bonding interaction, although some short Pd(0)-Pd(0) distances were reported (2.7-3.0A) [48, 49). The bonding interaction was caUed closed-shell attraction and has been discussed in fuU theoretical detaU [50]. 

As it was demonstrated earlier in the section for the Ni(0)—Ni(0) compounds, monovalent group 13 ligands can also stabUize dipaUadium(0) compounds with Pd(0)-Pd(0) bond. 

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A steric bulky Ga(l) ligand [GaCp ] (Cp = C5Me4Ph) was found to react with the Pd(0) precursor [Pd2(dvds)3] (dvds = tetramethyldivinyldisiloxane) to produce tripaUadium(0) cluster 83, which can further react with the [GaCp ] to afford dipalladium(O) compound 84-Cp (Scheme 10.38)... 

DipaUadium(O) compounds with p-P, P -coordinated diphosphane ligands [R2P(CH2) PR2] have been known for long time [49a] and have been studied for their potential to activate organic halides and hydrosilanes [49,56]. Recently, another example of this type of compound was reported from the reduction of Pd(II) dichloride with"BuLi (Scheme 10.41). The dipalladium(O) compound 88 features a Pd(0) - Pd(0) bond (2.8560(6) A) (Entry 7, Table 10.6), and can react with dichloromethane to produce dipaUadium(II) compound [55]. 

Scheme 10.39 Synthesis of dipalladium(O) compounds (85, 86) with bridging Al(l) ligand.

Scheme 10.38 Synthesis of tripalladium(O) (83) and dipalladium(O) (84) compounds that are supported by...

A corner sharing dipalladium(I) compound with PNP-pincer ligand (93) was synthesized by Ozerov and coworkers from photolysis of a Pd(II) tilkyl precursor (Scheme 10.44), in which the Pd(l)-Pd(l) bond length was reported as 2.5758(4) A (Entry 3, Table 10.7) and was validated as a Pd(I)-Pd(I) single o-bond [60]. The Pd(I)-Pd(I) bond in the compound was proven to have versatile reactivity toward organic smtJl molecules. A reactivity study revealed that C-X, H-H, and H-E (E = 0, N) bonds can add across the Pd(I)-Pd(I) bond to afford the corresponding Pd(II) compounds, which represents a new pathway of activation of Hj, H2O, and NH3. 

The concept and methodology was extended to C-H bond hydroxylation with O, using dipaUa-dium(II) compound 146 as catalyst [110]. A dipalladium(III) compound 152 was individually prepared and suggested by UV-vis spectroscopy as a possible model for the Pd(III) intermediate of the catalysis (Scheme 10.70). 

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