Palladium complexes reaction with amines

Palladium isocyanide complexes react with amines and alcohols to give palladium Carbene Complexes (equation 15) in a reaction that is a nucleophihc attack on the isonitrile carbon. These complexes easily lose a halide if it is trans to the carbene hgand, since the carbene carbon has a high trans influence. The structures of these compounds have the carbene carbon and its two heteroatom groups in one plane, which is perpendicular to the coordination plane of the Pd. 

A drug discovery program targeting 7-azabicyclo[2.2.1]heptane systems found utihty in bis(imidazol-2-ylidine)palladium complexes in conducting amination reactions [151]. The ligand Dilmes-HCl 426 was determined to be optimal in the Buchwald-Hartwig reaction of 427 with 19 to produce 428. 

In a generahzed and simpHfied mechanism, the reaction usually follows the standard catalytic cycle of metal-catalyzed cross-coupling reactions oxidative addition of the C(sp ) -X bond to paUadium(O), followed by coordination of the amine to the resulting palladium complex, occurring with extrusion of HX that is captured by the base. Finally, reductive elimination yields the couphng product, regenerating the catalyticaUy active paUadium(O) species. 

Careful mechanistic studies on the carbonylation process have been reported by Yamamoto, including studies with isolated model compounds. - These studies have revealed several reaction pathways, and the particular pathway depends on whether the electrophile is an aryl or benzyl halide and whether the nucleophile is an amine or an alkoxide. The existing experimental data suggest that the latter pathway b in Scheme 17.29 involving insertion of CO into the palladium-aryl bond to form a benzoylpalladium halide intermediate occurs. These complexes have been isolated with PMe and PPhj as ligand and have been shown to form the ester product upon reaction with an alcohol and amine base and to form the amide products upon reaction with amine alone. 

Oxadimethylenemethane and 77 -azadimethylenemethane palladium complexes have been synthesized. The azadimethylenemethane complexes were synthesized by the reaction of (T-allenylpalladium derivatives with amides (Scheme 75). The same reaction with amines, or the protonation of the azadimethylenemethene complexes, brings about the formation of 2-amino-substituted palladium allyls. ... 

The relative kinetic cis effects of halide ligands on substitution at palladium(ii) have been established by monitoring the reactions of trans-[Pd(4-Cl-py)2Xa] and of rra j-[Pd(py)2Xa], where X = Cl, Br, or I, with amines or with thioethers in 1,2-dimethoxyethane solution at 25 °C. The usual two-term rate law [equation (4)] applies to these reactions, but as the ky terms were all small, the c r-effect trends have been reported only for the k, terms. The cis effects on substrate discrimination are in the order I>Br> Cl for reaction with amines, and Cl>Br>I for reaction with thioethers. This pattern is the same as that established for platinum(n) complexes, ... 

Addition of several organomercury compounds (methyl, aryl, and benzyl) to conjugated dienes in the presence of Pd(II) salts generates the ir-allylpalladium complex 422, which is subjected to further transformations. A secondary amine reacts to give the tertiary allylic amine 423 in a modest yield along with diene 424 and reduced product 425[382,383]. Even the unconjugated diene 426 is converted into the 7r-allyllic palladium complex 427 by the reaction of PhHgCI via the elimination and reverse readdition of H—Pd—Cl[383]. 

Based on the above-mentioned stereochemistry of the allylation reactions, nucleophiles have been classified into Nu (overall retention group) and Nu (overall inversion group) by the following experiments with the cyclic exo- and ent/n-acetales 12 and 13[25], No Pd-catalyzed reaction takes place with the exo-allylic acetate 12, because attack of Pd(0) from the rear side to form Tr-allyl-palladium is sterically difficult. On the other hand, smooth 7r-allylpalladium complex formation should take place with the endo-sWyWc acetate 13. The Nu -type nucleophiles must attack the 7r-allylic ligand from the endo side 14, namely tram to the exo-oriented Pd, but this is difficult. On the other hand, the attack of the Nu -type nucleophiles is directed to the Pd. and subsequent reductive elimination affords the exo products 15. Thus the allylation reaction of 13 takes place with the Nu nucleophiles (PhZnCl, formate, indenide anion) and no reaction with Nu nucleophiles (malonate. secondary amines, LiP(S)Ph2, cyclopentadienide anion). 

The palladium-promoted conversion of 1,3-dienes to pyrroles proceeds via 4-acetoxy-2-alkenylpalladium complexes (Scheme 50g) (81CC59), and a similar pathway may be involved in the palladium mediated reaction of but-2-ene-l,4-diol with primary amines to give A-substituted pyrroles (74CC931). 

The alleged preparation of the supposed cobalt(II) complex Na[Co(Et2dtc)3] described by D Ascenzo and Wendlandt (305) has been repeated by Holah and Murphy (306), who identified the product as [Co(Et2dtc)3]. Complexes of cobalt(III), nickel(II), and palladium(II) salts with cationic, dithiocarbamate ligands have been synthesized (307). Reaction of the secondary amine (Et2N(CH2)2)2NH with CS2 produces... 

Palladium complexes also catalyze the carbonylation of halides. Aryl (see 13-13), vinylic, benzylic, and allylic halides (especially iodides) can be converted to carboxylic esters with CO, an alcohol or alkoxide, and a palladium complex. Similar reactivity was reported with vinyl triflates. Use of an amine instead of the alcohol or alkoxide leads to an amide. Reaction with an amine, AJBN, CO, and a tetraalkyltin catalyst also leads to an amide. Similar reaction with an alcohol, under Xe irradiation, leads to the ester. Benzylic and allylic halides were converted to carboxylic acids electrocatalytically, with CO and a cobalt imine complex. Vinylic halides were similarly converted with CO and nickel cyanide, under phase-transfer conditions. ... 

Fagnou and co-workers reported on the use of a palladium source in the presence of different phosphine ligands for the intramolecular direct arylation reaction of arenes with bromides [56]. Later, they discovered that new conditions employing palladium complex 27 promoted the direct arylation of a broad range of aryl chlorides to form six- and five-membered ring biaryls including different functionalities as ether, amine, amide and alkyl (Scheme 7.11) [57]. 

Helmchen and coworkers employed a,co-amino-1,3-dienes as substrates [51]. By using palladium complexes with chiral phosphino-oxazolines L as catalysts, an enantiomeric excess of up to 80 % was achieved. In a typical experiment, a suspension of Pd(OAc)2, the chiral ligand L, the aminodiene 6/1-90 and an aryltriflate in dimethylformamide (DMF) was heated at 100 °C for 10 days. Via the chiral palladium complex 6/1-91, the resulting cyclic amine derivative 6/1-92 was obtained in 47% yield and 80% ee (Scheme 6/1.23). Using aryliodides the reaction time is shorter, and the yield higher (61 %), but the enantiomeric excess is lower (67% ee). With BINAP as a chiral ligand for the Pd°-catalyzed transformation of 6/1-90 and aryliodide, an ee-value of only 12% was obtained. 

With the exception of intramolecular amination reactions, all of the early aryl halide aminations were catalyzed by palladium complexes containing the sterically hindered P(o-tol)3. In papers published back-to-back in 1996, amination chemistry catalyzed by palladium complexes of DPPF and BINAP was reported.36,37 These catalysts allowed for the coupling of aryl bromides and iodides with primary alkyl amines, cyclic secondary amines, and anilines. 

Activated aryl chlorides, which are close in reactivity to unactivated aryl bromides, underwent reaction with the original P(o-tol)3-ligated catalyst.58 Nickel complexes, which catalyze classic C—C bond-forming cross-couplings of aryl chlorides, 9-64 also catalyzed aminations of aryl chlorides under mild conditions.65,66 However, the nickel-catalyzed chemistry generally occurred with lower turnover numbers and with a narrower substrate scope than the most efficient palladium-catalyzed reactions. 

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