It is possible to synthesize Ni(COD)2 from a mixture of anhydrous nickel dichloride, cyclooctadiene, pyridine, and sodium in tetrahydrofuran. The crude product is recrystallized from toluene at -80 °C.

You will find the complete procedure in this article:

Synthesis, structure, and properties of π-cyclo-octenyl-π-cyclo-octa-1,5-dienecobalt

S. Otsuka and M. Rossi

J. Chem. Soc. A, 1968, 2630-2633

DOI: 10.1039/J19680002630

The synthesis of the nickel complex is written on the last page of the article.

Please be careful when you work with sodium, it is dangerous!

Good luck. Sincerely Yours,

Uwe Boehme.

Thank you Uwe for your valuable information.

As Uwe had mentioned, it is possible to prepare Ni(COD)2 from NiCl2. But the best option is to prepare from Ni(acac)2 which is commercially available or can be prepared in almost quantitative yield by following Inorg. Synth. procedure.

Procedure is  not that tedious but involves

Ni(acac)2 + 2.5  Bu2AlH + 2 COD  in THF ( -78 to zero deg C) gives in 65-70% of Ni(COD)2.

Previously Et3Al was used in the place of Bu2AlH. Please look into the JOC article by Peter B. Mackenzie published in 1990.

Balakrishna