Bis(N-methylsalicylaldimine)nickel1

[14322-02-2]  · C16H16N2NiO2  · Bis(N-methylsalicylaldimine)nickel  · (MW 327.00)

(used in conjunction with triisobutylaluminum for alkyne coupling,2 allene synthesis,3 and conjugate reduction of a,b-enones5)

Alternate Name: Ni(mesal)2.

Physical Data: mp 195-198 °C, d 1.45 g cm-3, lmax 354 nm (solid).

Solubility: sol alcohol, ether, benzene, CHCl3; slightly sol hexane.

Form Supplied in: olive-green solid, not commercially available.

Preparative Method: easily prepared from a 2:2:1 mixture of salicylaldehyde, methylamine, and nickel acetate in alcohol solution at 60 °C for 1 h. The green solid can be recrystallized from alcohol or from chloroform/petroleum ether.1

Handling, Storage, and Precautions: stable, nonhygroscopic; nickel compounds are cancer suspect agents.

Triisobutylaluminum-Bis(N-methylsalicylaldimine)nickel.

Ni(mesal)2 modifies reactions of Triisobutylaluminum, allowing for greater selectivity in reactions of alkynes. The two reagents are premixed, typically in a 50:1 Al:Ni molar ratio, in the reaction vessel before addition of substrates, but no isolation of the combined reagent is necessary. Note that most reactions are carried out in the absence of solvent.2 Caution: triisobutylaluminum is pyrophoric and moisture sensitive.

Alkyne Coupling.

By itself, (i-Bu)3Al promotes the coupling of 1-alkynes to give a complex mixture of i-butylalkenes, 1,3-dienes, and trisubstituted benzenes (eq 1). Catalytic amounts of Ni(mesal)2 accelerate the reaction and show a preference for formation of head-to-tail dimers and benzene products (eq 2).2 Nickel metallacyclopentadienes are proposed intermediates.

Allene Synthesis.

Ni(mesal)2 catalyzes the cross-coupling reaction of allenic bromides with trialkylaluminum or Grignard reagents (eq 3).3 The method is fairly general. Triisobutylaluminum was used in two-fold molar excess to the allene and 1 mol % Ni(mesal)2 catalyst was added. When an enantiomerically enriched sample of the bromoallene was used as substrate, the reaction was found to occur with predominant retention of configuration in the allenyl moiety.4

Reduction of a,b-Unsaturated Ketones.

Triisobutylaluminum alone leads to both 1,2-reduction products and 1,2-addition products on reaction with a,b-unsaturated ketones. In contrast, the same reaction catalyzed by 3 mol % Ni(mesal)2 leads predominantly to reduction of the C-C double bond (eq 4).5 The reaction is carried out in pentane at rt using a 1:1 molar ratio of enone and i-Bu3Al.


1. Sacconi, L.; Paoletti, P.; Del Re, G. JACS 1957, 79, 4062.
2. Giacomelli, G.; Caporusso, A. M.; Lardicci, L. JOC 1979, 44, 231.
3. Caporusso, A. M.; Da Settimo, F.; Lardicci, L. TL 1985, 26, 5101.
4. Caporusso, A. M.; Lardicci, L.; Da Settimo, F. TL 1986, 27, 1067.
5. Caporusso, A. M.; Giacomelli, G.; Lardicci, L. JOC 1982, 47, 4640.

Cynthia J. Burrows & Shiow-Jyi Wey

State University of New York at Stony Brook, NY, USA



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