Autoionization of Homogeneous Nickel(II) Diphosphane Hydrogenation Catalysts. An NMR Study and Crystal Structures of [Ni(o-MeO-dppe)I2] and [Ni(o-MeO-dppe)2](PF6)2
- 24 March 2001
- journal article
- research article
- Published by American Chemical Society (ACS) in Inorganic Chemistry
- Vol. 40 (9), 2073-2082
- https://doi.org/10.1021/ic0006955
Abstract
The synthesis of a number of nickel(II) complexes containing the didentate phosphane ligand 1,2-bis(di(o-methoxyphenyl)phosphino)ethane (o-MeO-dppe) is reported. Two types of complexes have been synthesized, i.e., the mono(chelate) complex (1) of the general formula [Ni(o-MeO-dppe)X2] (where X = Cl, Br or I) and the bis(chelate) complex (2) of the general formula [Ni(o-MeO-dppe)2]Y2 (where Y = PF6 or trifluoroacetate (TFA)). These complexes have been characterized using electronic absorption and NMR spectroscopy. The structures of the mono(chelate) complex [Ni(o-MeO-dppe)I2] (1c) and of the bis(chelate) complex [Ni(o-MeO-dppe)2](PF6)2 (2e) have been determined by X-ray crystallography. [Ni(o-MeO-dppe)I2] crystallizes in the monoclinic space group P21/c with Z = 4, a = 12.1309(1) Å, b = 16.5759(3) Å, c = 17.6474(2) Å, β = 119.3250(10)°. [Ni(o-MeO-dppe)2](PF6)2 crystallizes in the monoclinic space group C2/c with Z = 4, a = 22.5326(3) Å, b = 13.6794(2) Å, c = 21.7134(3) Å, β = 107.1745(7)°. In both structures the nickel ion is in a square-planar geometry with a NiP2I2 and NiP4 chromophore, respectively. Using 1H and 31P{1H} NMR spectroscopy the behavior of the complexes in various solvents has been studied. It appears that in solution these nickel complexes are involved in an autoionization equilibrium: 2[Ni(o-MeO-dppe)X2] ⇋ [Ni(o-MeO-dppe)2]2+ + [“NiX4”]2-. The ionized complex (3) consists of a cationic unit in which a nickel atom is surrounded by two didentate phosphane ligands, and an anionic unit that stoichiometrically consists of a nickel atom and four anions. The position of the autoionization equilibrium is highly dependent on the anion and the solvent used. In a polar solvent in combination with weakly coordinating anions only the ionized complex is observed, whereas in an apolar solvent in combination with coordinating anions only the mono(chelate) complex occurs. A comparison of the behavior of o-MeO-dppe with its unsubstituted analogue dppe in combination with nickel(II) acetate using 31P{1H} NMR spectroscopy shows that the latter is more readily oxidized.This publication has 16 references indexed in Scilit:
- Fast and selective homogeneous hydrogenation with nickel(II) phosphane catalystsChemical Communications, 1998
- Anion dependent deprotection of a thioether group in Schiff base NS2 ligands results in new mononuclear and dinuclear thiolato nickel complexesJ. Chem. Soc., Dalton Trans., 1998
- Rates and Mechanism of the Formation of Zerovalent Palladium Complexes from Mixtures of Pd(OAc)2 and Tertiary Phosphines and Their Reactivity in Oxidative AdditionsOrganometallics, 1995
- Dimorphs of [1,2-bis(diphenylphosphino)ethane]dichloronickel(II)J. Chem. Soc., Dalton Trans., 1993
- Nickel(II) bis(phosphine) complexesInorganic Chemistry, 1991
- Reductive cleavage of the carbon‐phosphorus bond with alkali metals. I. Cleavage of functionalised triphenylphosphines; formation of secondary and primary phosphinesRecueil des Travaux Chimiques des Pays-Bas, 1991
- .DELTA.R-ring contributions to phosphorus-31 NMR parameters of transition-metal-phosphorus chelate complexesChemical Reviews, 1981
- Hydrogenation and isomerization of oct-1-ene by (Ph3P)2MX2 and other complexesDiscussions of the Faraday Society, 1968
- Homogeneous Catalysis in the Reactions of Olefinic Substances.1a VII. Hydrogenation and Isomerization of Methyl Linoleate with Bis(triphenylphosphine)nickel Halides1bJournal of the American Chemical Society, 1967
- Die Herstellung kolloider, unedler Metalle durch Reduktion der Lösungen oder Suspensionen der Metallverbindungen bei‐erhöhter Temperatur in Gegenwart von Schutzkörpern. Über kolloides NickelEuropean Journal of Inorganic Chemistry, 1917