Nickel catalysts microwave irradiation

Aldehydes and ketones react with aniline derivatives in the presence of hydrogen and a catalyst to yield N-alkylanilines (Fache et al., 1996 Freifelder, 1971). N-Alkylation of aliphatic amines under microwave irradiation is a well-documented process (Caddick, 1995 Loupy et al., 1998 Varma, 1999 Lidstrom et al., 2001 Wathey et al., 2002). Jiang et al. (1996) reported the N-alkylation of anilines with alcohols over Raney nickel under microwave irradiation. More recently, Khadilkar and Jaizinghani (1999) carried out the direct monobenzylation of aniline with ben-zylchloride on alumina supported potassium carbonate. They reported a fast and efficient metal-free method for the N-alkylation of anilines under microwave irradiation. Romera et al. (2004) reported potassium iodide catalyzed monoalkylation of anilines, where they obtained 54-98% yield. 

Microwave-induced, catalytic gas-phase reactions have primary been pursued by Wan [63, 64], Wan et al. [65] have used pulsed-microwave radiation (millisecond high-energy pulses) to study the reaction of methane in the absence of oxygen. The reaction was performed by use of a series of nickel catalysts. The structure of the products seemed to be function of both the catalyst and the power and frequency of microwave pulses. A Ni/Si02 catalyst has been reported to produce 93% ethyne, whereas under the same irradiation conditions a Ni powder catalyst produced 83% ethene and 8.5 % ethane, but no ethyne. 

Unsymmetrical binaphthyls were synthesized by photochemically stimulated reaction of naphthyl iodides with naphthoxide ions in an SrnI reaction. " Methyl chloroacetate coupled with aryl iodides under electrolysis conditions, using a nickel catalyst. " " Unsymmetrical biaryls were prepared from two aryl iodides using a Cul catalyst and microwave irradiation. " ... 

Different conditions (including additives and solvent) for the reaction have been reported,often focusing on the palladium catalyst itself," or the ligand." Catalysts have been developed for deactivated aryl chlorides," and nickel catalysts have been used." Modifications to the basic procedure include tethering the aryl triflate or the boronic acid to a polymer, allowing a polymer-supported Suzuki reaction. Polymer-bound palladium complexes have also been used." " The reaction has been done neat on alumina," and on alumina with microwave irradiation." Suzuki coupling has also been done in ionic liquids," in supercritical... 

Nickel-on-charcoal can be made in multi-gram quantities via a straightforward and reproducible procedure using readily available and inexpensive materials. The initially formed Ni(II)/C is smoothly reduced by rc-BuLi to active Ni(0)/C, a catalyst that mediates many types of coupling reactions. It can be easily removed from reaction mixtures and recycled with little loss of catalytic activity and with similar isolated yields.[le,fl Reaction rates involving this catalyst may be increased significantly when these couplings are performed under microwave irradiation. 

Kappe and Stadler have developed an MW procedure for rapid production of triaryl phosphines by coupling diphenylphospine with aryl halides and triflates [134]. Taking into account the importance of phosphine ligands in a variety of transition metal-catalyzed reactions, convenient procedures for their production is valuable. Both homogeneous Pd-Ni and heterogeneous Pd catalysts were explored and the more unusual substrate phenyl triflate could also be coupled swiftly by use of nickel catalysis (Scheme 15.68). Couplings with other aryl halides proceeded in 26-85% yield after 3-30 min microwave irradiation at 180-200 °C. 

This reaction was modified by the replacement of CuCN with cheaper NaCN in the presence of palladium or nickel catalyst, as exemplified by the 5% Pd(PPh3)4/10% Cul catalyzed reaction and the Ni(CN)2 or NaCN/NiBr2 based reaction under microwave irradiation for aryl bromide. The latter condition is also used for the cyanation of aryl chloride with NaCN and NiBr2. In addition, this reaction has also been extended to the preparation of some Qf,)0-unsaturated nitriles. Further modifications include the copper-catalyzed domino halogen exchange-cyanation and the application of ionic liquid as reaction media. ... 

Lipshutz recently reported a Negishi coupling of a highly substituted aryl tosylate utilizing heterogeneous nickel on charcoal as catalyst with PPhs as ligand under microwave irradiation (Equation 2.81) [130]. 

Besides the mentioned catalysts, the other transition metals were also appUed in carbonylation of nitro compounds by various groups [71-79]. Such as nickel, osmium, iron, cobalt, and molybdenum. All the expected products were produced by the carbonylation of nitro compounds. Interestingly, anilines were produced from nitroarenes in the presence of Mo(CO)e and DBU under microwave irradiation in moderate to excellent yields (Scheme 9.7). 

Polyhydroquinoline derivatives have been prepared efficiently in a one-pot synthesis via Hantzsch condensation using nano-sized Nickel (Ni) as a heterogeneous catalyst under microwave irradiation by Shingare et al. [87] (Scheme 5.36). 

It was observed that the most efficient oxidant was KMnO absorbed on a fourfold molar amount of CUSO4.5H2O (100% yield), but attempts were made to oxidize 2-heptanol, under solvent-free conditions, by KMnO alone (i.e., in the absence of the support of an inorganic salt hydrate) were absolutely unsuccessful. Various inorganic salts were tried and yielded varied amounts of the product. The better supports include nickel sulfate (90%), zinc sulfate (74%), and cobalt sulfate (41%) while other supports were not that interesting like magnesium sulfate (12%), calcium sulfate (11%) and barium chloride (3%). Zeolite HZSM-5 was used as a catalyst for the oxidation of alcohols to the corresponding carbonyl compound with chromium trioxide under solvent-free conditions and microwave irradiation (Heravi et al., 1999). 

A number of low-grade transition metal ores (for example, minerals containing nickel oxides) can be used as catalysts. Smuda has demonstrated that microwave or radiofrequency irradiation of a mixture of such ores with a carbon source initiates reduction of the oxide to metal. With this approach, poisoning the active sites of the catalyst will not be critical for the process since there will be a constant supply and generation of active catalyst with the feed material. In addition to well-known catalytic properties of nickel in organic reactions, it was also shown that Ni on carbon and other supports, catalyzes hydrodechlorination and dehydrochlorination of chlorinated organic waste streams [22-24],... 

---