Palladium bimetallic complexes

Behr A, Von Ilsemann G, Keim W, Kruger C, Tsay Y (1986) Octadienyl-bridged bimetallic complexes of palladium as intermediates in telomerization reactions of butadiene. Organometallics 5 514—518... 

The asymmetric allylic acetoxylation of cycloalkenes has also been reported. In this case, the catalyst is a bimetallic palladium(II) complex bearing a chiral bisox-azoline or a chiral diphosphine (DIOP). The reaction is performed in acetic acid/ sodium acetate under oxygen atmosphere at room temperature. Under these conditions, acetoxylation products of cyclohexene and cydopentene are obtained with 55 % and 78 % ee, respectively, albeit in low yields [39a]. 

No simple palladium tetrazadiene complexes have been isolated to date reactions between Pd(PPh3)4 and organic azides afford polymeric palladium phosphine complexes (232). The apparent instability of palladium tetrazadiene complexes has been tentatively attributed to the relatively low basicity of palladium, which does not permit sufficient n back donation to the tetrazadiene ligand (32). However, the bimetallic species Ni(p-tol-NNNN-tol-p)2PdL2 (L = Bu NC or PEtj) have been obtained from reactions between Pd(norbornene)3 and Ni(p-tol-NNNN-tol-p)2 in the presence of Bu NC or PEt3 at 0°C (170, 171). 

It is difficult to find direct bonding interaction between the ferrocene iron and the second transition metal in the hetero-bimetallic complexes. Only the mono-triphenylphosphine palladium and platinum compounds fc[E2M(PPh3)] (E = O, M = Pd (Scheme 5-14) [79] E = S, M = Pd [268, 269], and Pt [269]) appear to... 

While carefully isolating all products from a reaction of 2-bromopyridine 19 with palladium catalyst, bimetallic complex 148 was isolated and determined to be a pre-catalyst for the Suzuki reaction [52]. Upon examining the utility of this complex, it was found to be able to carry out Suzuki reactions, such as the conversion of 149 and 150 into 151. 

While, because of our interest in bimetallic species, most of the work discussed in this account has concentrated upon reactions which involve dppm, the synthetic procedure outlined clearly represents a novel and extremely simple approach to metal carbonyl phosphine complexes in general. Of particular significance, however, are the one-step reactions which lead to heterobimetallic or phosphido-bridged complexes and the ready access to palladium carbonyl complexes. Further research in this area is likely to be extremely productive. 

Palladium(II) complexes with heteropolyanions PWnOs and PW9034 , and originally synthesized bimetallic Pd(II)-Fe(III) complexes with PW9034 were used for the preparation of Si02 supported catalysts of hydrocarbons oxidation. The composition of the complexes in aqueous solution was characterized by P NMR and IR spectroscopy. 

Addition of a toluene solution of the cuprate, Cu2Li2(p-tolyl)4-2Et20 (1), to a solution of palladium(II) acetate in toluene leads to the in situ formation of a thermally unstable organocopper complex in which the lithium atom of 1 has been replaced by the more electronegative precious metal. Subsequent reductive elimination of the organic tolyl group from the unstable bimetallic complex in the presence of silica affords supported bimetallic particles, which without further treatment are an active catalytic system. (Equation 3)... 

An interesting class of cationic polyyne polymers 187 was prepared by reaction of the bimetallic complex, p-butadiynediyl-bis[/ra//i--chlorobis(tri-//-butylphosphine)palladium], with an equimolar amount of 4,4 -bipyridyl in... 

The complex [(OC)4Fe(//-PPh2)Pd( -Cl)]2 is a selective catalyst for the isomerization of 1-octene to 2-octene and the hydrogenation of 1-hexyne in the presence of 1-hexene. At 448 K, under 100 atm H2, 93% of a sample of 1-hexyne in benzene was reduced to hexene and only 3% to hexane. This is unexpected because palladium is usually an excellent catalyst for the hydrogenation of olefins. It also catalyzes the carbonylation of 1-octene under mild conditions (348 K, 50 atm). The total yield of esters was ten times greater than with [PdCl2(PPh3)2] as a catalyst. This bimetallic complex was also an effective catalyst for the carbonylation of 1,5-cyclooctadiene. ... 

An interesting class of cationic polyyne polymers (5.24) was prepared by reaction of the bimetallic complex /i-butadiynyl-bis[transmain chain (Eq. 5.13). Other analogous polyelectrolytes have been obtained similarly by the use of the appropriate dihalide complex and bipyridyl derivatives [37]. 

Abstract Square-planar palladium(II) and platinum(II) complexes with a high-lying filled d 2 orbital can act as metalloligands for Lewis-acidic metal centers such as d ° and s cations. This behavior is promoted by hard ligands such as a-bound hydrocarbyl ligands. A wide diversity of structural motifs based on this kind of donor-acceptor metal-metal bonds has been discovered in the last decades. This chapter reviews the coordination chemistry of metalloligands derived from alkyl, aryl, alkynyl, and carbene complexes of palladium(II) and platinum(II). The specific reactivity of the resulting bimetallic complexes is also addressed. 

There are two structurally characterized examples in which an arylpalladium(ll) coordinates to silver(l) in a type 11 fashion (Scheme 10). First, Kickham and Loeb [40] reported that an attempt to abstract the chloride ligand in a palladated thiacyclo-phane with two equivalents of silver(l) triflate unexpectedly resulted in the formation of a bimetallic complex in which the silver(l) ion is encapsulated by three oxygen atoms and an interaction with the Pd-C bond. Then, Braunstein et al. [41] synthesized a remarkable one-dimensional coordination polymer by reacting the phosphanyl immolate palladium complex depicted in Scheme 10 (bottom) with silver(l) triflate. 

In a study on the transmetallation of the bimetallic complex 40 with alkynylstan-nanes, a different precoordinated palladium intermediate 41 was observed, which evolved to the alkynyl-Pd(II) complex 42 (Scheme 1.26) [217, 218]. 

More recently, the asymmetric hydroxychlorination of alkenes has been achieved by Henry and co-woikers Given in Scheme 5 are representative examples in which the chiral catalyst used was either a bimetallic or a monomeric palladium(II) complex bearing... 

A number of bimetallic complexes which contain bridging alkylidene and vinylidene ligands semi-bonded to palladium are known, and as these also contain bridging carbonyl ligands, they are discussed in Section 8.04.1.8. In these dimers, the carbene ligand is more closely associated with the early transition metal, for which Schrock-type carbene complexes are well known. 

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