Diphosphines palladium complexes

In 1998, Strukul and coworkers presented a diphosphine-palladium complex, with which the Baeyer-Villiger oxidation of cyclic and for the first time also acyclic ketones could be catalyzed in the presence of various peroxidic oxidants (H2O2, TBHP, KHSO5, carbamide peroxide) (Scheme 158)4 . pj-om these oxidants H2O2 turned out to be the most efficient one, whereas almost no conversion was obtained (<1% after several days) with TBHP. The authors could show that an increase in the bite angle of the diphosphine caused... 

The increase of the catalyst turnover numbers is indeed one other major area where further improvements could be expected. Such improvements have recently been achieved for the standard Heck reaction by the use of high pressure conditions [86], the use of preformed palladacycles as catalysts [87], or by using a macrocyclic tetraphole as hgand [88].Dendritic diphosphine-palladium complexes as catalysts for Heck reactions have also been reported to possess superior stabihty compared to the monomeric parent compounds [89]. Transferring such iimovations to the AHR remains an important goal. 

Studies of Configuration.— The separation of diastereomeric bisphosphonium salts was monitored by n.m.r. N.m.r. was also able to detect <3% of a minor isomer of the diphosphine palladium complex (26). Mercury-199 n.m.r. spectra showed extra splitting due to bound diastereomeric phosphorus groups. The threo- and erythro- forms of the phosphine (27) gave well separated signals (8p—17 and —27). Diastereomeric anisochronocity of various -aminophos-phonates (28) has also been reported. ... 

Reaction of the diphosphines Ph2P(CH2) PPh2 (n = 1-3) with MCl2(PhCN)2 affords 1 1 m-complexes (Figure 3.46) [102]. (Note the use of the labile PhCN adducts if the MCl salts are used, Magnus type compounds M(P-P)2+MCl4- are formed.) Similar complexes are formed with other halides for the thiocyanates see section 3.8.6. The structures of the palladium complexes have been determined (Table 3.10) with square coordination only achieved for n = 3 with the formation of a six-membered metal-chelate ring. 

B(3,5-(CF3)2C6H3)4-.512 Palladium complexes with a hemilabile terdentate carbene ligand, 1,3-bis(pyl)imidazol-2-ylidene, were active toward the catalytic polymerization of CO/norbornylene.513 Palladium complexes of cz s-bidentate C4-bridged diphosphines cis- and trans- 1,2-bis [(diphenylphosphino)methyl]cyclohexane, e fl o,e fl o-2,3-bis[(diphenylphosphino)methyl] norbornane,... 

Similarly, a double functionalization can be reached when an activating group is present in close vicinity to the triple bond. Tsuji et al. have discovered that with a diphosphine palladium(O) complex, a carbonate function in the a-position of the alkyne provides by decarboxylation a palladium methoxy species on which the alkyne moiety can be isomerized into an al-lenyl a -bonded group. CO insertion in the Pd - C bond, reductive elimination with the methoxy group and further cyclization with incorporation of a second CO molecule give rise to the corresponding cyclopentenone as shown in Scheme 21 [127]. 

The water-soluble palladium complex prepared from [Pd(MeCN)4](Bp4)2 and tetrasulfonated DPPP (34, n=3, m=0) catalyzed the copolymerization of CO and ethene in neutral aqueous solutions with much lower activity [21 g copolymer (g Pd) h ] [53] than the organosoluble analogue in methanol. Addition of strong Brpnsted acids with weakly coordinating anions substantially accelerated the reaction, and with a catalyst obtained from the same ligand and from [Pd(OTs)2(MeCN)2] but in the presence of p-toluenesulfonic acid (TsOH) 4 kg copolymer was produced per g Pd in one hour [54-56] (Scheme 7.16). Other tetrasulfonated diphosphines (34, n=2, 4 or 5, m=0) were also tried in place of the DPPP derivative, but only the sulfonated DPPB (n=4) gave a catalyst with considerably higher activity [56], Albeit with lower productivity, these Pd-complexes also catalyze the CO/ethene/propene terpolymerization. 

Better results were obtained by using in situ prepared palladium complexes of a G4 dendrimer (calculated molecular weight 20 564 Da for 100% palladium loading of the 32 diphosphines). After 100 residence times, the conversion had decreased from 100% to approximately 75% (Fig. 3). A small amount of palladium was leached from the catalyst during this experiment (0.14% per residence time), which only partly explains the decrease in conversion. The formation of inactive PdCl2 was proposed to account for the additional drop in activity. A sound conclusion about the effect of this dendritic catalyst requires more experiments. 

Mizugaki et al. 74) have recently utilized thermomorphic properties of Pd(0)-complexed phosphinated dendrimers for dendritic catalyst recycling. Using the method developed by Reetz 16), they prepared dendritic ligands containing, respectively, 2, 8, 16, and 32 chelating diphosphines. Palladium dichloride was com-plexed to the dendrimers, and a reduction in the presence of triphenylphosphine gave the Pd(0)-complexed dendrimers (80—83). The dendritic complexes were active... 

Legros and Fiaud also developed enantioselective benzyiic alkylation of 1-naphthylethyl esters with dimethyl sodiomalonate and dimethyl sodiomethylmalonate in the presence of a catalytic amount of a palladium complex and a chiral diphosphine such as BINAP 113, Chiraphos 114, or DIOP 115 (Equation (45)). Use of BDPP 116 as a chiral... 

Larsen, J., Rasmussen, B.S., Hazell, R.G. and Skrydstrup, T, (2004) Preparation of a novel diphosphine-palladium macrocyclic complex possessing a molecular recognition site. Oxidative addition studies. Chem, Commun., 202-203 Braunstein, P., Clerc, G. and Morise, X. (2003) Cyclopropanation and Diels-Alder reactions catalyzed by the first heterobimetallic complexes with bridging phosphinooxazoline ligands. New J. Chem., 27,68-72 Braunstein, P., Clerc, G., Morise, X., Welter, R. and Mantovani, G. (2003) Phosphinooxazolines as assembling ligands in heterometallic complexes. Dalton Trans., 1601-1605. 

Recently, we [53] and others [54] simultaneously reported an example of a complex in which the transition metal dictates the coordination mode, viz. urea-functionalized phosphine 20, which forms a trans palladium complex, complemented by hydrogen bonding ofthe urea fragments (Figure 10.6). Bear in mind that any monophosphine, and even wide bite angle diphosphines, give trans complexes with a hydrocarbyl palladium halide. More interestingly, the urea moieties can function as a host for another halide ion. 

The current high level of interest in binuclear metal complexes arises from the expectation that the metal centers in these complexes will exhibit reactivity patterns that differ from the well-established modes of reactivity of mononuclear metal complexes. The diphosphine, bis(diphenylphosphino)methane (dpm), has proved to be a versatile ligand for linking two metals while allowing for considerable flexibility in the distance between the two metal ions involved (1). This chapter presents an overview of the reaction chemistry and structural parameters of some palladium complexes of dpm that display the unique properties found in some binuclear complexes. Palladium complexes of dpm are known for three different oxidation states. Palladium(O) is present in Pd2(dpm)3 (2). Although the structure of this molecule is unknown, it exhibits a single P-31 NMR reso-... 

Figure 5-52. The reaction of the palladium diphosphine complex with diacetyl gives a palladium complex of a macrocyclic P4 donor ligand.

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