LIGAND EXCHANGE REACTION BETWEEN NiMe2L2 (L = 1/2 bpy, PEt3) AND DITERTIARY PHOSPHINES Ph2P(CH2)nPPh2 (n = 1-4) AND EFFECT OF LIGAND ON EASE OF REDUCTIVE ELIMINATION OF C2H6 FROM NiMe2(Ph2P(CH2)nPPh2)

Article abstract of DOI:10.1016/S0022-328X(00)94431-0

Reactions of the dimethylnickel(II) complexes NiMe2L2 (L = 1/2 bpy, PEt3 (bpy=2,2'-bipyridine)) with diphosphines Ph2P(CH2)nPPh2 (n = 1-4) give NiMe2(Ph2P(CH2)nPPh2) (n = 2, 3) or produce ethane and Ni⁰-diphosphine complexes (n = 1, 4), depending on the chain length of (CH2)n of the diphosphine ligand employed.The ligand exchange reaction between NiMe2(bpy) and Ph2P(CH2)3PPh2 (dpp) proceeds through an S_N2 process with the activation parameters ΔH^<*> = 8.3 kcal/mol and ΔS^<*> = -35 e.u.A mechanism involving coordination of dpp via one phosphorus atom and ensuing chelation of dpp accompanied by dissociation of bpy is proposed for the ligand exchange reaction.Kinetic studies on the thermal decomposition of NiMe2(Ph2P(CH2)nPPh2) (n = 2, 3) show that the reductive elimination of C2H6 from NiMe2(Ph2P(CH2)nPPh2) (n = 2, 3) proceeds by a unimolecular process with the activation parameters ΔH^<*> = 26.8 kcal/mol and ΔS^<*> = 1.9 e.u. for NiMe2(Ph2P(CH2)2PPh2) and ΔH^<*> = 25.1 kcal/mol and ΔS^<*> = 4.8 e.u. for NiMe2(Ph2P(CH2)3PPh2).The rate of reductive elimination of NiMe2(Ph2P(CH2)3PPh2) is 46 times faster than that of NiMe2(Ph2P(CH2)2PPh2) at 64.3 deg C.