[36421-86-0] · Cl12NiP4 · Tetrakis(trichlorophosphine)nickel(0) · (MW 607.97)
(source of nickel(0) useful for the cyclotetramerization of alkynes2)
Physical Data: thermochromic crystalline solid that is pale yellow at rt and white at temperatures below -30 °C; mp 120 °C (dec).
Solubility: readily sol benzene, cyclohexane, chloroform, CCl4, pentane
Preparative Methods: the original preparation involved addition of excess Phosphorus(III) Chloride to Tetracarbonylnickel (caution: extremely toxic, volatile), whereupon CO was immediately evolved. The reaction was completed by heating the pale-yellow solution to reflux. Distillation removed most of the remaining PCl3. The pot residue was dissolved in pentane at rt and the resulting solution cooled to -60 °C to crystallize the product as fine crystals, which were dried on a porous plate. Two recrystallizations were sufficient to remove all PCl3 and gave an 80% yield of Ni(PCl3)4. All manipulations were carried out under inert atmosphere.5 The complex may also be prepared by reaction of PCl3 with Ni(allyl)2.6
Handling, Storage, and Precautions: the flammable crystalline solid is stable in air but highly oxygen sensitive in solution. Special inert-atmosphere techniques must be used.7 Should be stored at 0 °C.
The methyl and ethyl esters of propiolic acid can be cyclotetramerized in the presence of catalytic Ni(PCl3)4 to form cyclooctatetraenes (1) (eq 1).2 For the methyl ester, the remaining product (17%) is the trimerization product (2). For the ethyl ester, the selectivity favoring cyclotetramerization reverses, and trimerization accounts for 72% of the product. Attempts to cyclotetramerize a wide variety of other alkynes were unsuccessful. Although the scope of this reaction is extremely limited, Ni(PCl3)4 is one of only very few compounds that are able to catalyze the cyclotetramerization of substituted alkynes.8 The order of reactivity of several such catalysts is Ni(PCl3)4 > Ni(PF3)4 >> Ni(PBr3)4 &AApprox; Ni(PhPCl2)4.
The polymerization of butadiene has been described using a three-component system made up of Ni(PCl3)4, Titanium(IV) Chloride and Aluminum Chloride.9
Paul A. Wender & Thomas E. Smith
Stanford University, CA, USA