Palladium complexes dinuclear

Dimethyl-1,2,4-triazolium iodide with palladium acetate yields the carbene adduct 182 (97JOM(530)259). Under water it undergoes cis-trans isomerization to 183. Some other derivatives were reported in 1981 (81BCSJ800). 1,1 -Methylenebis(4-alkyl-l,2,4-triazolium)diiodides (alkyl = /-Pr, n-Bu, octyl) with palladium(II) acetate give the mononuclear complexes [L Pdl ] (99EJIC1965), where L2= l,l -methylenebis(4-R-l,2,4-triazol-2-ylidene) (R = /-Pr, n-Bu, octyl). Thermolysis of the products in THF gives the rran -dinuclear complexes 184... 

A limited chemistry of the +1 oxidation state of palladium and platinum has developed since the 1970s, mainly involving metal-metal bonded dinuclear complexes [61]. 

Benzy 1-6-chloropurine reacts with tetrakis(triphenylphosphine)palladium in DCE to give, not only the 6-purinylpalladium(Il) complex 102, but a dinuclear complex 103. Using Stille coupling (RSnBus) only the 6-substituted purine is obtained <96ACS462>. 

Sources of catalytically active palladium(O) typically arise from ligand dissociation from coord-inatively more saturated Pd° complexes871-880 or from reduction of a Pd11 species.353,881 Another route to catalytically active (P—P)Pd fragments is the dissociation of the dinuclear complexes [(//-P—P)Pd]2.882 Complexes [(/r-dcpm)Pd]2 and [(/r-dtbpm)Pd]2 were obtained from the reductive elimination of ethane from dimethylpalladium(II) complexes (dippm = bis(diisopropylphosphino)methane dcpm = bis(dicyclohexylphosphino)methane dcpm = bis(di-t-butylphosphino)methane).883... 

An efficient synthesis of the dinuclear palladium(O) complexes has been devised.169... 

Quadruply Bridged Dinuclear Complexes of Platinum, Palladium, and Nickel Keisuke Umakoshi and Yoichi Sasaki... 

Tanase, T., Ukaji, H. and Yamamoto, Y. (1995) Dinuclear palladium(l) complexes with isocyanide and N-donor bidentate ligands. /. Chem. Soc., Dalton Trans., 3059-54. 

Ferrocenoylamino acids have been converted into 2-ferrocenyl-5(477)-oxazo-lones 348 and 350 that act as N donors in palladium, platinum, and iridium complexes. Reaction of 348 with chloro-bridged palladium(II) and platinum(II) complexes affords a series of N-coordinated oxazolone complexes 349. Reaction of the unsubstituted 2-ferrocenyl-5(477)-oxazolone 350 with the chloro-bridged iridium(III) complex [(ri -C5Me5)IrCl2]2 produces a dinuclear complex 351, analogous to that obtained from 2-phenyl-5(477)-oxazolone (Scheme 7.113)." ° ... 

Another example is the palladium-catalyzed oxidation of ethylene to acetaldehyde in the presence of oxygen and cupric salts, the so-called Wacker reaction. This catalytic cycle combines two stoichiometric processes, which involve first the reduction of Pd11 to Pd°, followed by reoxidation with Cu11. The understanding of the first step of this process came from the earlier work of Kharasch et al., who showed that the stoichiometric dinuclear complex shown in Figure 2.14 decomposed in the presence of water to acetaldehyde (ethanal), Pd° and HC1 [38]. 

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>. 

Chiral N-arylated imidazolinylidene ligands have been employed in the palladium(II) catalyzed aerobic oxidation of secondary alcohols to the corresponding ketones [55]. The chiral variant of this reaction, which does not generate a new element of chirality, is again based on the kinetic resolution of racemic mixtures. The active catalyst is formed in situ by a combination of two precursors, a dinuclear NHC-palladium(II) complex and an achiral (acetate) or chiral base ((-)-sparteine) (Scheme 18). 

Diaryl ditellurium compounds and tetrakis[triphenylphosphane]palladium reacted in benzene to form the dinuclear complex bis[/r-arenetellurolato]bis[arenetellurolato]bis[tri-phenylphosphane]dipalladium3. 

Bildstein et al. have previously shown that Fc functionalised NHC (annulated and nonan-nulated) can be successfully employed to synthesise a broad range of transition metal complexes [166]. These include palladium, tungsten and mercury. Interestingly, two different species of mercury NHC complexes could be synthesised and structurally characterised (see Figure 4.49), with the dinuclear complex being the precursor for the mononuclear one. 

Pyridyldiphenylphosphine forms a number of homo-and heteronuclear palladium dinuclear clusters with short Pd-M bonds (about 260 pm). They are usually made by comproportionation of a Pd(II) complex and a second complex in a low oxidation state, for example, Pd(0), Rh(I), Ru(0). For these derivatives, head-to-head and head-to-tail isomers are possible, but the latter seems to be preferred (Figure 2). The metal-metal bonds in these derivatives are not as reactive as in the corresponding dppm complexes and insertion reactions do not occur. Some single-bridged complexes, such as [Cp(CNR)Rh(/u.-PPh2Py)Pd(CNR)Cl]+ (Pd-Rh distance 263.1 pm) are also known. 

QUADRUPLY BRIDGED DINUCLEAR COMPLEXES OF PLATINUM. PALLADIUM, AND NICKEL... 

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