Nickel on charcoal

Another way toward more cost-efficient and environmentally friendly catalysts is their immobilization on a solid phase as could be realized with nickel on charcoal . ... 

B. H. Lipshutz, Development of Nickel-on-Charcoal as a, Dirt-Cheap Heterogeneous Catalyst A Personal Account, Adv Synth. Catal. 2001, 343, 313-326. 

Lipshutz BH, Tasler S, Chrisman W, SpUethoff B, Tesche B (2003) On the nature of the heterogeneous catalyst nickel-on-charcoal. J Org Chem 68 1177... 

Cross-coupling reactions catalysed by heterogeneous nickel-on-charcoal... 

CROSS-COUPLING REACTIONS CATALYSED BY HETEROGENEOUS NICKEL-ON-CHARCOAL... 

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. 

Other catalysts have been used to effect Suzuki coupling reactions. A mixture of Pd2(dba)3 and tn-tert-butylphosphine has proven to be very effective.2 5 Nickel on charcoal,276 rhodium catalysts,277 and silver oxide mediated palladium catalysts278 have also been used. The latter catalyst was effective for the preparation of 4-substituted 2(5//)-furanones.279... 

Lipshutz has developed an original method using nickel on charcoal [44], This valuable catalyst was prepared by -BuLi-reduction of nickel(II) nitrate adsorbed on the activated charcoal with high surface area in the presence of triphenylphosphine. Thus the Negishi reaction of 3-tolylzinc chloride (155) with 2-chlorobenzonitrile (114) afforded 2-(3-tolyl)benzonitrile (156) in 92% yield [44], respectively. Scheme 18. 

The SM-catalysts of the first generation are mainly consisted of simple palladium and nickel salts and complexes with the most common Pd(0)- and Ni(0)-stabilizing mono-, or bidentate phosphine ligands. In this group, the palladium and nickel on charcoal as heterogeneous catalysts were put, despite quite recent use of these catalysts. 

Among the nickel-based catalysts, beside the nickel on charcoal [43], mainly the various nickel(0)-phosphine complexes were employed [12,13,44,45]. Several common bidentate phosphine ligands such as dppf, dppe, dppp, dppb and tricyclohexylphosphine (PCys) are the most popular in the nickel-based SM crosscoupling reactions of less reactive aryl chlorides with arylboronic acids [44], While the nickel complexes of electron-rich trialkylphosphines react readily with aryl chlorides. 

Lipshutz has demonstrated heterogeneous nickel on charcoal as catalyst for Negishi couplings of aryl chlorides, utilizing highly functionaHzed zinc reagents (Equation 2.9) [18, 19]. 

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]. 

Lipshutz showed that nickel on charcoal ( Ni/C ) was found to be an efficient heterogeneous catalyst for mediating carbon-carbon bond constructions involving chloroarenes 28 and functionalized organozinc reagents to give 29 Importantly retention of nickel on the solid support offers control over such critical parameters as waste disposal and toxicity. 

Nickel salts are also excellent catalysts, however, the nature of the ligands attached to the nickel metal center is very important and often needs to be carefully chosen to achieve high reaction yields. Interestingly, nickel on charcoal... 

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