Aryl-nickel and acetylene-nickel(I) complexes

Reduction of various pentafluorophenylnickel(II) complexes in the presence of phosphines gives unstable nickel(I) compounds but Ni(C6F5)(CO)2(PPh3)2 is isolated in the presence of CO. Similar NiR(CO)2(PPh3)2 (R = C6F5,C6Cl5, 2,3,5,6-C6Cl4H) are obtained by reaction of the halogenonickel(I) complex with MgRBr or LiR. Reduction of NiX2L2 in the presence of acetylenes gives [NiXL2]2(μ-PhCCR) (R = H, X = Cl and R = Ph, X = Cl, Br) when L = P-n-Bu3 but only NiX(PPh3)3 are recovered when L = PPh3. No reaction with the alkyne is observed for [NiX(PPh3)2]n but [NiCl(PPh3)]n reacts with RCCR′ to give paramagnetic NiCl(PPh3)(CRCR′) (R = Ph, R′= H, COOEt), diamagnetic [NiCl(PPh3)]2(μ-PhCCPh) and cyclotrimerization when R = R′ = COOMe. Chemical and structural behaviour of the new nickel(I) complexes is described