Dipalladium I Compounds

Compounds with Unsupported Pd(l)-Pd(l) Bond - Corner-Sharing Geometry This type of Pd(I)-Pd(I) compound has a long history and is fundamentally important in understanding the nature of the Pd(I)-Pd(I) bond, in homogeneous catalytic reactions, and as model complex for cluster and for metallic surfaces [57]. The two four-coordinate square planar Pd(l) centers are connected by an unsupported Pd(l)-Pd(I) bond, with the bond length usually less than 2.6 A, 

Hydroformylation, known as an oxo process, which converts alkene, H, and CO into higher 

A series of Pd(I)-Pd(I) compounds (105-111) bearing bidentate P, P- or P, N-donor ligand were synthesized and characterized recently, ofwhich the Pd(I) -Pd(I) bondlength and references arelisted 

5cheme 10.56 Synthesis of an arene-bridged dipalladium(l) compound 113 with two kinds of Pd(l)-arene interactions. 

Dipalladium(l) Compounds with Other Ligand In 2009, two NPN-tridentate ligands with oxazoline pendant arms were reported to react with [Pd2(MeCN)g] [BF ] j) to afford dipalladium(I) compounds 

---

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. 

Triazenido ligands (R-NH-N=N-R ) are isoelectronic with the widespread amidinate [92]. In 2007, a series of novel triazenido ligand were synthesized and used to support paddlewheel dipal-ladium(I) compounds (Scheme 10.52) [66]. The synthesis started from a Pd(n) precursor with satisfactory yields (50-80%). The resultant dipalladium(I) compounds 99-101 were reported to be diamagnetic, and to have very short Pd(I)-Pd(I) bonds (2.41-2.43 A) (Entries 9-11, Table 10.7). 

In 2010, an indolyl-phosphine ligand was used in the synthesis of a dipalladium(I) compound with Pd(I)-Pd(I) bond. The reaction between [Pd(OAc)2] and a ligand precursor in acetonitrile afforded dipalladium(I) compound 103 as product with low yield (30%) (Scheme 10.53) [68]. If the reaction... 

A tridentate ligand based on 1,8-naphthyridine (NP), which bears a ferroceneyl amide pendant arm, was synthesized and used to support dipalladium(I) and diruthenium(I) compounds [69]. The synthesis of the dipalladium(I) compound 104 started with a Pd(II) precursor, but the detail of the redox reaction was not discussed in the original article (Scheme 10.54). Complex 104 is diamagnetic and the Pd(I)-Pd(I) bond is short at 2.3952(8) A (Entry 14, Table 10.7). Compound 104 was proven to be an active catalyst for Suzuki and Heck coupling, and a bimetallic-synergy mechanism was proposed for the pivotal oxidative addition/reductive elimination steps. 

Examples of dipalladium(I) compounds with jc-coordinated bridging neutral naphthalene, pyrrole, and indole were reported very recently [80]. These syntheses started with [PdjfMeClSOejiXjj (X = BF or PFg) and naphthalene, pyrrole, or indole, while 116-118 were obtained as products (Scheme 10.59). 

A series of dipalladium(I) compound with bridging anionic allylic ligands were synthesized as intermediates or catalysts for pivotal organic transformations, for example, allylic substitution (122) (Figure 10.7) [94], or functionalization of CO (123-124) (Scheme 10.61) [83]. 

As it has been discussed in Section 10.2.2.2.4), a dipalladium(I) precursor [Pd2(MeCN)g][BF4]2l can react with neutral arene to produce a dipalladium(I) compound with Pd(I)-Pd(I) bond bridged by a neutral arene ligand [80a]. A systematic study revealed that the outcome of the reaction was dependent on the arene/conjugated 2ilkene involved small arenes (benzene, anthracene) afford the Pd(I)-Pd(I) compound, while cyclophane gives the oxidative addition of Pd(I)-Pd(I) toward... 

The stepwise growth of a Pd chain of up to four metals has been achieved within the sandwich polyene framework. Dipalladium(I) compound sandwiched by 1,4-diphenyl-1,3-butadiene (dpbd) is obtained from the reaction of... 

Two diphosphane bridging diplatinum(I) compounds 180, 181 (Figure 10.18) were synthesized tilong with their dipalladium(I) counterpart (107, Section 10.2.2.2) [72]. They were demonstrated to exist as polymers or oligomers in the solid state, and the luminescence properties of these compounds were studied [72],... 

Dipalladium(ii) complexes (8), and their platinum(ii) analogues, react rapidly with five-co-ordinate rhodium(i) compounds [RhCl2H(PR%)2] to give di-/ -chloro-species... 

Solvent effects on, and products from, reaction of styrene with ethylene in the presence of di-)ti-chloro-dichlorobis(styrene)dipalladium(n), [Pd-(Ph CH—CH2)Cl2]2, indicate a mechanism similar to (i)->(iv) above, with the addition of a preliminary equilibrium between the dimer and solvated monomers. The mechanism of reaction of styrene with vinyl compounds, catalysed by the same chloride-bridged dipalladium complex, has been studied using isotopic tracer (H, D) experiments. Palladium-acetate-catalysed reaction of styrene with benzene, also investigated using deuterium tracer experiments, involves no hydride shift, in contrast to the rather closely related Wacker process. The importance of intermediates with palladium-carbon n-bonds in palladium(ii)-catalysed alkylation and arylation of alkenes has been demonstrated. 

---