Nitro compounds catalysts, palladium complexes

Secondary amines can be added to certain nonactivated alkenes if palladium(II) complexes are used as catalysts The complexation lowers the electron density of the double bond, facilitating nucleophilic attack. Markovnikov orientation is observed and the addition is anti An intramolecular addition to an alkyne unit in the presence of a palladium compound, generated a tetrahydropyridine, and a related addition to an allene is known.Amines add to allenes in the presence of a catalytic amount of CuBr " or palladium compounds.Molybdenum complexes have also been used in the addition of aniline to alkenes. Reduction of nitro compounds in the presence of rhodium catalysts, in the presence of alkenes, CO and H2, leads to an amine unit adding to the alkene moiety. An intramolecular addition of an amine unit to an alkene to form a pyrrolidine was reported using a lanthanide reagent. 

Asymmetric synthesis of tricyclic nitro ergoline synthon (up to 70% ee) is accomplished by intramolecular cyclization of nitro compound Pd(0)-catalyzed complexes with classical C2 symmetry diphosphanes.94 Palladium complexes of 4,5-dihydrooxazoles are better chiral ligands to promote asymmetric allylic alkylation than classical catalysts. For example, allylic substitution with nitromethane gives enantioselectivity exceeding 99% ee (Eq. 5.62).95 Phosphi-noxazolines can induce very high enatioselectivity in other transition metal-catalyzed reactions.96 Diastereo- and enantioselective allylation of substituted nitroalkanes has also been reported.9513... 

The carbonylation of nitro arenes can lead to amines, isocyanates, carbamates, azo compounds, or ureas.80 Iron, ruthenium, rhodium, or palladium complexes have been used as catalysts. The carbonylation to give isocyanates, for example, involves the steps... 

Reductions. Acenaphthoquinonediimine ligated palladium complexes and a polymer-bound palladaisoindoline have found use as catalysts for semihydrogenation of alkynes and reduction of several common unsaturated compounds (including the nitro group), respectively. 

The conversion o f the nitro compound with R=R =Me to the isocyanate using a variety o-f palladium halide complexes has also been studied. In a comparative study o-f the rhodiumwith Lewis acids as co-catalysts, the activity and selectivity have been -found to -follow the order (Bu N) fPdCl33-U or VO chlorides > [Rh Rh... 

The palladium catalysed reaction -follows a rate law which is independent on the substrate concentration, but dependent on the CO pressure. In a later work, a AS =-233 J mol " "K, instead o-f -414, has been reported -for this react i on [1843, tor which it has been confirmed a zero order in substrate and first order in each metallic component and in CO pressure. The carbonyl ation of an intermediate complex forming the isocyanate is considered the rate determinin step in the palladium-catalysed reaction. In this work[183j, the oxidative addition of the nitro compound to the catalyst was considered a more likely rate determining step in the case of the rhodium-catalysed reaction. 

A deoxygenation reaction o-f the nitro compound by the metal is also probably involved when tetraphenylporphyrinate and phtalocyaninate derivatives o-f metals such as palladium or rhodium are used as catalysts [169,170]jpossibly -forming dimeric complexes having oxo and imido groups as bridging ligands. 

In the reduction of nitro compounds, the addition of a nitrogen-donor ligand is necessary, and bidentate ligands are far superior to monodentate ligands. The conversion of nitrobenzene within two h rose from 14.5 to 72 % by changing 2,2 -bipyridine to 1,10-phenanthroline. The anion of palladium catalysts also plays an important role. With the [Pd(bidentate ligand)2][PF6]2 complexes as a catalyst... 

For nitromesitylene in dichlorobenzene at 120 °C and 1 atm, k = 1.3 10, AH = 18 kcal mol and AS = - 30 cal K. Large substituents in the or//io position of the nitro compound accelerate the reaction, a situation already described in the case of some palladium and ruthenium systems [26, 38,43] (see paragraph 6.3.1. for a discussion of this effect). If other rhodium complexes were used as catalyst precursors, [Rh(CO)2(Cl)]2 was anyway formed by ligand exchange with the molybdenum chloride [207]. 

---