[18750-53-3]  · C28H28Cl2NiP2  · Dichloro[1,4-bis(diphenylphosphino)butane]nickel(II)  · (MW 556.07)

(catalyst for allylic alkylation1 of stable enolates, dialkylation2 of dithioacetals and electrochemical carboxylation of terminal alkynes3)

Physical Data: light fawn-colored powder.

Solubility: sol benzene. Drying: the powder can be dried under vacuum.4

Preparative Method: prepared by adding a solution of NiCl2.6H2O in n-butanol to a solution of 1,4-bis(diphenylphosphino)butane (dppb) in n-butanol and refluxing until the complex drops out of solution as a light purple powder.

Handling, Storage, and Precautions: should be stored in dry, dark-colored bottles under an inert atmosphere.

Allylic Alkylation.

The title reagent has been used to catalyze alkylation of stabilized enolates with allylic acetates. The regioselectivity depends on the ligands present around nickel.1 For example, 1,4-diphenylphosphinobutane (dppb) shows better regioselectivity than 1,2-diphenylphosphinoethane (dppe) in the nickel-catalyzed alkylation of trans-2-buten-1-yl acetate with the anion of malonic ester even though the stereoselectivity is about the same (eq 1).5

Regioselective Alkylation of Allylic Dithioacetals.

NiCl2(dppb) shows higher regioselectivity than triphenylphosphine in the dialkylation of dithioacetal derivatives of a,b-unsaturated carbonyl compounds with Grignard reagents. The gem-dimethylation of cinnamaldehyde dithioacetal with MeMgI using NiCl2(dppb) as a catalyst occurs regiospecifically in 90% yield (eq 2).2 In contrast, Dichlorobis(triphenylphosphine)nickel(II) gives a 70/30 mixture of the gem-dimethyl adduct and 1-phenylbutadiene. Generally, the regioselectivity of all nickel catalysts decreases as the size of the 2-substituent on the allylic moiety increases.2

Electrochemical Carboxylation of Terminal Alkynes.

The product ratio in nickel-catalyzed electrochemical carboxylations of terminal alkynes depends strongly on the ligand.3 For example, 1-octyne has been electrochemically carboxylated with NiCl2(dppb) to give the diacid only (eq 3), whereas NiCl2(dppe) gives a mixture of alkynyl acid and trihexylbenzene (eq 4).3

1. Alvarez, E.; Cuvigny, T.; Julia, M. JOM 1988, 339, 199.
2. Yang, P.-F.; Ni, Z.-J.; Luh, T.-Y. JOC 1989, 54, 2261.
3. Labbé, E.; Duñach, E.; Périchon, J. JOM 1988, 353, C51.
4. Gray, L. R.; Higgins, S. J.; Levason, W.; Webster, M. JCS(D) 1984, 459.
5. Cuvigny, T.; Julia, M. JOM 1986, 317, 383.

Godson C. Nwokogu

Hampton University, VA, USA

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