Alkoxycarbonyl complexes palladium

Under appropriate conditions, alcohols and amines can undergo an oxidative double carbonylation process, with formation of oxalate esters (Eq. 34), oxamate esters (Eq. 35) or oxamides (Eq. 36). These reactions are usually catalyzed by Pd(II) species and take place trough the intermediate formation of bis(alkoxycarbonyl)palladium, (alkoxycarbonyl)(carbamoyl)palladium or bis(carbamoyl)palladium complexes, as shown in Scheme 29 (NuH, Nu H = alcohol or amine) [227,231,267,293-300]. 

The alkoxide pathway occurs by initial insertion of CO into a palladium alkoxide, followed by insertion of the alkene into the bond between the metal and the alkoxycarbonyl group to form a paUadium-alkyl complex (Scheme 17.18). Protonation of this metal alkyl by alcohol would form the free organic product and regenerate the paUadium alkoxide. This mechanism has now been ruled out for the reactions of ethylene to form methyl propanoate. Although each of these steps has precedent, the absence of reduction products from the alkoxide argues against this pathway. Moreover, the alkyl generated from insertion of ethylene into the palladium-alkoxycarbonyl complex (Scheme 17.18) is chelated to the metal, and metha-nolysis of this species is slower than the steps of the alternative hydride mechanism. ... 

Most researchers currently agree that the hydrido mechanism is more common than the alkoxycarbonyl path in the alkoxycarbonylation of alkenes with palladium systems. However, carbalkoxy complexes are putative intermediates in carbonylation reactions giving succinates and polyketone diesters, with metals like Co, Rh, or Pd.137... 

Highly selective transformation of terminal acetylenes to either linear or branched carboxylic acids or esters may be achieved by appropriately selected catalyst systems. Branched esters are formed with high selectivity when the acetylenes are reacted with 1-butanol by the catalyst system Pd(dba)2/PPh3/TsOH (dba = dibenzylideneacetone) or palladium complexes containing PPh3. Pd(acac)2 in combination with various N- and O-containing phosphines and methanesulfonic acid is also an efficient catalyst for the alkoxycarbonylation of 1-alkynes to yield the branched product with almost complete selectivity.307,308... 

Catalytic systems to afford linear esters selectively are scant.306,309 A report in 1995 disclosed that palladium complexes based on l,l -bis(diphenylphosphine)fer-rocene showed excellent regioselectivity for the formation of linear a,p-unsaturated esters.309 The results with phenylacetylene are remarkable because this compound is known to exhibit a distinct preference for the formation of the branched products on palladium-catalyzed carboxylations. Mechanistic studies indicate that the alkoxycarbonylation of alkynes proceeds via the protonation of a Pd(0)-alkyne species to give a Pd-vinyl complex, followed by CO insertion and alcoholysis.310... 

A likely mechanism for this reaction involves the nucleophilic attack of alcohol on two molecules of coordinated CO, followed by the coupling of the two palladium-bonded alkoxycarbonyl moieties (equation 179).438,451 jn support of this mechanism, the reaction of the bis(methoxycarbonyl) complex (143) with CO and PPh3 produces dimethyl oxalate and the reduced palladium(O) complex.451... 

The palladium(II)-promoted hydrolysis of methyl glycylglycinate and isopropyl glycylglycinate has been investigated over a temperature range.80 Complexes of type (22) are formed in which the amino, deprotonated amide and alkoxycarbonyl groups act as donors. Hydrolysis by both H20 and OH ion is observed. Base hydrolysis of the coordinated peptide esters is ca. 105-fold faster than the unprotonated peptide esters. 

The key palladium intermediate is a carboalkoxypalladium complex formed through the nucleophilic attack by alcohol on carbonyl coordinated to palladium. The addition of a base with the appropriate pK, [sodium butyrate pK, = 4.82 (H20)] promotes the formation of die palladium carboxylate (22).93 The reaction is a general method for formation of inorganic alkoxycarbonyl derivatives. 

The cycle is started with the formation of a Pd-alkoxy complex that reacts with CO to an alkoxycarbonyl intermediate. In the next step, the approach of the olefin and insertion into the carbonyl palladium bond is predicted. In the last step, the starting complex is rebuilt by the addition of an alcohol and the cleavage of the hydroesterification product [59]. 

The most frequently used metallic catalysts for acyldiazo- and (alkoxycarbonyl)dia-zomethanes are complexes or salts of rhodium, palladium and copper. Alkenylboronic esters A-silylated allylamines and acetylenes are successfully cyclopropanat-ed with diazocarbonyl compounds under catalysis of one of those metal derivatives. Newly developed metallic catalysts for diazoacetic esters include polymer-bound, quantitatively recoverable Rh(II) carboxylate salts ", Cu(II) supported on NATION ion exchange poly-mer ruthenacarborane clusters, Rh2(NHCOCH3)4 which produces cyclopropanes with substantially enhanced trans (anti) selectivity as shown below and (rj -CsHs)... 

Palladium complexes bearing chiral monodentate phosphine ligands 592 (R = H, Ph) are effective catalysts for asymmetric alkoxycarbonylation of allyl phosphates <1997TL8227>. 

Carbonylphosphine complexes of zero-valent palladium are considerably less stable and more reactive than their Ni counterparts. Most common triphenyl-phosphine complexes of Pd are excellent catalysts for various carbonylation reactions of aryl iodides and bromides [15,129-131 ]. It is conceivable that the palladium-catalyzed alkoxycarbonylation of ArCl proceeds via a mechanism similar to that proposed for the analogous reactions of bromo- and iodoarenes (Scheme 5) [45,159,160,161]. 

The precise mechanism in the catalyhc oxalate synthesis has not been established, hut it is likely that the catalytic process proceeds as shown in Scheme 1.35. The catalyhc cycle is comprised of nucleophilic attack of RO on the CO coordinated to Pd(II) to give an alkoxycarhonylpalladium(II) species, which further undergoes the similar CO coordinahon followed by external RO attack to give bis(alkoxycarbonyl)palladium(ll) complex [105,106]. Reduchve eliminahon of the two alkoxycarbonyl ligands to generate a Pd(0) species and its re-oxidahon are... 

The participation of cationic diphosphine/diphosphane palladium complexes as catalysts for the co-polymerization of CO with alkenes and in the alkoxycarbonylation of alkenes has been studied extensively. Quite recently, delineation of the initiation, propagation, and termination steps of the cycle has been reported. The systems are very complex to permit readily detailed kinetics experiments. However, the mechanistic steps and reactivity of those steps have been established, by principally, NMR spectroscopic methods. 

Transition metal alkoxycarbonyl compounds are key intermediates in a number of metal-catalyzed processes involving alkanols and carbon monoxide. The square-planar palladium(ii) complex, [Pd(phen)(G02GH3)2] 63, was determined in this context.A compound isolated as a plausible intermediate in the catalytic reductive carbonylation of nitrobenzene (viz. PhN02 + 3GO PhNGO + 2GO2) using palladium-phen-based catalysts was established by... 

With esters of histidine (7.6) and cysteine which form complexes with pendant ester groups only small rate enhancements of 20-100 fold occur. For those esters where there is a direct interaction between the alkoxycarbonyl group and palladium(II), the ratios... 

Other attempts include the use of a combined bimetallic mthenium/paUadium catalyst [111], and heterogeneous palladium complexes were also carried out in order to develop more efficient and practicable catalysts for alkoxycarbonylations of aromatic iodides [112, 113]. Advantageously, the latter catalyst systems could be effectively removed from the reaction mixture by a simple filtration process and they were reused several times with only a minor loss of activity. 

The Carbonylative Heck Reaction is not the same as those that were traditionally called Heck carbonylations . Heck carbonylations normally include alkoxycarbonylation, aminocarbonylation and hydroxycarbonylation, while a carbonylative Heck reaction is more related to a Heck reaction. In the late 1960s, Richard Heck developed several coupling reactions of arylmercury compounds in the presence of either stoichiometric or catalytic amounts of palladium salts [1-7]. Based on this work in 1972, he described a protocol for the coupling of iodo-benzene with styrene, which today is known as the Heck reaction [8]. In contrast to this, the catalytic insertion of olefins into acylpalladium complexes is called a Carbonylative Heck reaction . Here the acylpalladium complexes can either by CO insertion or by the oxidative addition of benzoyl precursors [9, 10]. 

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