Abstract Reduction of various pentafluorophenylnickel (II) complexes in the presence of phosphines gives unstable nickel (I) compounds but Ni (C 6 F 5)(CO) 2 (PPh 3) 2 is isolated in the presence of CO. Similar NiR (CO) 2 (PPh 3) 2 (R= C 6 F 5, C 6 Cl 5, 2, 3, 5, 6-C 6 Cl 4 H) are obtained by reaction of the halogenonickel (I) complex with MgRBr or LiR. Reduction of NiX 2 L 2 in the presence of acetylenes gives [NiXL 2] 2 (μ-PhC CR)(R= H, X= Cl and ...