The reaction of Ni(PPh3)(4) with acetic and trifluoroacetic acids is studie
d by ESR. When Ni(PPh3)(4) reacts with protonic acids, oxidative addition o
f the acid to the Ni(0) occurs along with contradisproportionation of the f
ormed Ni(II) complexes with the Ni(0) complex. As a result, stable Ni(I) ca
rboxylate complexes (PPh3)(3)Ni-OOCR are formed, where R = CH3, CF3. The am
ounts of the formed Ni(I) carboxylate complexes and of the evolved hydrogen
were found to depend on the rate of acid addition to the Ni(0) complex.